ASSESSMENT OP ENVIRONMENTAL IMPACT
Of THE
MINERAL MINING INDUSTRY
by
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DISCLAIMER
This report has been reviewed by the Industrial Environ-
mental' Research Laboratory, 'tf,.s;. Environmental Protection Agency,
-and approved for publication.,'. JMention of trade names or, commer-
cial products does not constitute endorsement or recommendation
use.
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FOREWARD
When energy and material resources are extracted, processed,
converted, and used, the related pollution impacts on >our
environment and even on our health often require that, new and
increasingly more efficient pollution control methods be used.
The Industrial Environmental Research Laboratory - Cincinnati
(lERL-Ci) assists in developing and demonstrating new and im-
proved methodologies that will meet these needs both efficiently
and economically.
This report presents a multimedia (air, liquid, and solid
wastes) environmental assessment of the domestic mineral mining
industry. The primary objective of the study is to identify the
major pollution problems associated with the industry. A
secondary objective is to define research and development needs
for adequate control of air pollutants and liquid and solid
wastes connected with mineral mining. This study provides
lERL-Ci with 1) an initial data base on the type and quantity of
wastes generated and the treatment and disposal techniques now
applied for their control; 2) a data base for technical assis-
tance activities; and 3) the necessary background information to
implement research and development programs, to document effec-
tive pollution control techniques, and to fill gaps in the data
base.
For further information the Resource Extraction and Handling
Division can be contacted.
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EXECUTIVE SUMMARY
PROJECT OBJECTIVES
The overall objective of this multimedia environmental
,... assessment of the domestic mineral mining industry is to identify
-"potential problem areas. A secondary objective is to -define
'1 research and development needs for adequate control of air pollu-
- ..tants. and liquid and solid wastes connected with mineral mining.
cThis study provides lERL/Cincinnati with 1) an initial.data base
on ItJie type and quantity of wastes generated and the treatment
and"disposal techniques now applied for their control;-2) a data
base for technical assistance activities; and 3) the necessary
background information to implement research and development
programs, to document effective pollution control techniques, and
to fill gaps in the data base.
The minerals/metals of concern in this report are separated
into four main categories: 1) nonmetals, 2), nonferrous metals,
3) nonferrous metals that are by-products of the smelting and
refining of other metals, and 4) nonferrous metals that are
primarily imported. .-
Nonmetals; Nonmetals, or construction materials, are almost
- alwaysmined as the only recoverable constituent of an ore;
', however, some coproducts/by-products are associated with these
.v .minerals. Included in this category are ^ ; .
Dimension stone "
Crushed stone
Construction sand and gravel
Industrial sand -. ; , .<.
Gypsum
Asphaltic minerals -
Asbestos and wollastonite
Lightweight aggregate minerals ~
(perlite, pumice, and vermiculite)
.....!, Mica and sericite .. ,... , ,
,'. .Nohferrous Metals; The nonferrous metals " in this ~ category are
./usually mined as the primary or major constitutent of an ore, but
!', they can also be mined as a coproduct or. by-product "of other
minerals. Included in this category are
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Aluminum
Antimony
Beryllium
Copper
Gold
Lead and zinc
Magnesium
Mercury
Rare earth elements
Silver •"••
Titanium
Nonferrous Metals (Smelting and Refining By-products); 'These
nonferrbus metals are not mined for their own economic value"; but
are constituents of an ore mined for a more economically attrac-
tive metal such as .copper or zinc. These metals are not
separated1 from ores during beneficiation; they are recovered - as
by-products during the smelting and/or refining of other metals.
Included in this category are • • ;
Bismuth ' c -' ;
Cadmium :"
Gallium ki '•'•'
Germanium
Hafnium •
Indium
Selenium
Tellurium - • ~. -
Thallium • ;, .
Zirconium
Nonferrous Metals (Imports); These nonferrous metals are hot
recovered from domestic ores; they are either imported in a
finished or semifinished form or are produced from imported raw
ores. Included in this category are
Arsenic
Cesium
Platinum-group metals
Radium
Rubidium
Scandium
Tin
The scope of this project encompasses surface and under-
ground mining operations and related beneficiation operations
(e.g.screening, "crushing, storage) normally performed at -the
mine site. The scope does not cover operations such as smelting
"and refining, which are typically performed away from the mining
site. " '
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•Pollutants resulting from the various extraction and bene-
•ficiation operations are shown on process flow diagrams. When
possible, wastes are identified with specific sources (i.e., dust
from primary crushers or wastewater from scrubbing operations);
however, in certain instances it is necessary to report a waste
p stream as a composite of pollutants. Pollutants in these waste
•streams are identified and chemically and physically charac-
•"terized whenever possible, with special emphasis on potentially
hazardous contaminants. In this study, "potentially hazardous
•contaminants" is used to identify wastes that may pose a serious
- threat to the environment. This identification is based on the
: contractor's investigation and professional judgment and does not
necessarily concur specifically with the EPA hazardous waste
• 'listing under Section 3001 of the Resource Conservation and
Recovery Act 1976. Of necessity, the terminology is broadly
'• applied to widely differing types of waste streams.
.PROJECT APPROACH
Data base investigations not only provide the necessary
background information for a starting point, but also establish
opportunities and limitations for developing a realistic and
usable document. At the outset of this study it was found that
data were extremely limited relating directly to multimedia
wastes (air, water, solids) in the mineral mining industry;
therefore, much effort was expended to obtain and record as much
information as practical concerning mineral mining wastes, the
control of these wastes, and the need for research and develop-
ment (R&D). This was accomplished in three tasks.
The first task involved a literature search to gather,
review, and compile all available information (published and
unpublished) dealing with pertinent areas in the mineral mining
industry. Because it was evident from the start that data rela-
tive to certain subject areas would be scarce, sources closely
related to those areas were also explored. Two and a half months
were spent reviewing numerous references from a variety of
sources:, the Hamilton County Public Library and libraries
belonging to PEDCo Environmental, Inc., the "Colorado School of
Mines, and the University of Cincinnati; a National Technical
Information Services (NTIS) data base search performed at the
Science Information Retrieval Center at the University of
Cincinnati Chemistry Biology Library; and the files of various
local, state, and Federal agencies.
The second task involved contacting various EPA contractors
now working on projects dealing with any areas related to mineral
mining to identify, collect, and record the latest available
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information on mineral mining waste control technology and
corresponding R&D needs. Two such contractors were Calspan
Corporation and Monsanto Research Corporation.
The third and major task involved contacting several offices
of the Bureau of Mines (BM), industrial trade associations, 'and
specific mineral mining industries. Much valuable information
was acquired from these sources in the following manner: BM
offices and industrial trade associations were initially con-
tacted by telephone; meetings were held with the Directors and/or
environmental committees of the BM offices and trade associations
that had indicated they could provide useful information. -The
next step involved visits to facilities considered by the BM
and/or the associations to be representative of an industry. In
instances where needed information was not available from the BM
or from trade associations, visits were made to facilities
suggested by prominent corporations within an industry.
The following BM offices were contacted by phone and/or
letter:
U.S. Bureau of Mines, Mineral and Materials Research
Department, Washington, D.C.
0 Benjamin Petkof (beryllium)
0 Gertrude Greenspoon (arsenic)
0 Keith Harris (cesium, rubidium, tin)
0 Jim Jolly (rare earths, scandium)
U.S. Bureau of Mines Research Center
Spokane, Washington
0 Roy Soderberg
U.S. Bureau of Mines Research Center
Salt Lake City, Utah
0 Steve Wilson
0 Joe Bilbrey
.,....? •_ Parky Brooks . .
:° Don Seidel
U..S. Bureau of Mines, Liaison Office
0 Paul Fillo
: .U.S.: Bureau of Mines, Research Center
Reno, Nevada
0 R. E. Lindstrom
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Colorado Division of Mines, District Inspector
0 Bernie Javernick
The following BM offices were visited:
U.S. Bureau of Mines Research Center, Spokane,
Washington - Talked with the director of the center.
U.S. Bureau of Mines Research Center, Salt Lake City, Utah -
Talked with the director of the center:and with several of
the research metallurgists.
Colorado Division of Mines - Acquired information from the
District Inspector, who also accompanied PEDCo personnel on
several site visits.
In general, the Bureau Centers could provide little informa-
tion regarding the quantity of specific air, liquid, and solid
wastes associated with the extraction and processing of non-
ferrous and construction minerals. They did, however, provide
considerable information regarding process descriptions, major
waste problems by industry, control techniques, and R&D projects
now under way at the various centers.
Sixteen industrial trade associations were contacted by
phone and/or letter:
Northwest Mining Association
Colorado Mining Association
American Mining Congress
International Lead & Zinc Research Organization
Mining and Metal Society of America
The Indiana Limestone Institute of America
National Sand & Gravel Association
Gypsum Association
National Crushed Stone Association
Mica Industry Association
Vermiculite Association
Asbestos Textile Institute
Flexible Pavements, Inc.
Cultured Marble Institute
Building Stone Institute
Perlite Institute
Four trade associations were visited:
Northwest Mining Association (NWMA) - Talked with the
director of the association. Also, several PEDCo employees
attended the NWMA annual convention.
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Indiana Limestone Institute of America - Talked with the
Director of the Institute.
National Sand and Gravel Association (NSGA) - Talked with
the Director of Environmental Affairs. Also, several PEDCo
employees attended the meeting of the Environmental
Committee at NSGA's annual convention.
Gypsum Association - Acquired information from the Director,
who accompanied PEDCo personnel on several site visits.
Trade associations were generally unable to provide specific
quantitative or qualitative information regarding waste residuals
generated by mineral mining and processing. They did, however,
provide considerable input on process descriptions, the major
waste problems of specific industries, and current waste treat-
ment/control technologies. In some instances, they also fur-
nished information about planned R&D programs.
Selected associations were asked to suggest several facili-
ties representative of their industry, and conducted tours were
arranged. Visits were also made to several facilities suggested
by prominent corporations within an industry. For several in-
dustries, PEDCo's in-house experience and comprehensive infor-
mation acquired from other companies/agencies precluded the need
for visits to industry sites. The following is a list of those
plants that were visited.
Dimension Stone
0 Indiana Limestone Company, Bedford, Indiana
Gypsum
0 United States Gypsum Company, Shoals, Indiana
0 National Gypsum Company, Shoals, Indiana
0 National Gypsum Company, Sun City, Kansas
Perlite
0 Grefco, Inc., Antonito, Colorado
Beryllium
0 Brush Wellman, Salt Lake City, Utah
Lead-Zinc-Silver
0 Hecla Mining Company, Wallace, Idaho
0 Homestake Mining Company, Crede, Colorado
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Rare Earths, Titanium, Zirconium, Hafnium
0 Humphrey's Mining Company, Folkston, Georgia
The industry contacts/visits provided some rough estimates
of air, water, and solid waste materials associated with the
mineral mining industry, but most information was scanty and of a
site-specific nature. These contacts were helpful to PEDCo in
that they provided an insight into the general attitude and
philosophy of the mining industry toward control/treatment of
wastes. PEDCo also derived from these contacts/visits valuable
recommendations concerning R&D needs in the mineral mining
industry.
In addition to the sources of secondary information already
named, PEDCo also contacted several state pollution control
agencies and EPA regional offices regarding waste problems and
their control in the mineral mining industry. Considerable data
were acquired on quantities of waste, applicable control tech-
niques and efficiencies, and process descriptions.
The information obtained from all these sources was tabu-
lated and summarized into a data base report to support the
preparation of this document.
WASTE CHARACTERISTICS AND CONTROL
Sources of atmospheric emissions and liquid and solid wastes
are numerous in the mineral mining industry. Pollutants gener-
ated from these sources may or may not contain potentially
hazardous materials; however, uncontrolled wastes from the mining
and processing of ores can cause serious environmental damage
whether they contain hazardous contaminants or not. Although
state-of-the-art technology is now available to abate atmospheric
emissions and liquid and solid wastes associated with the mineral
mining industry, too often such technology is not applied, par-
ticularly at smaller facilities where the value of the end pro-
duct is too low to make controls economically feasible.
Control and treatment technologies that are assessed and
evaluated throughout this report fall into one of the following
categories:
1. State-of-the-art technology that is now widely, prac-
ticed in the mineral mining industry.
2. State-of-the-art technology that is available and
viable, but is not commonly practiced in the mineral
mining industry.
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Both in-plant and end-of-process technologies are identified in
the discussions, as are the limitations, problems, efficiencies
and reliability of each control or treatment (when known). The
effects of the application of various technologies on other
pollution problems (e.g. ultimate disposal of particulates en-
trapped by dry collection devices or ultimate disposal of sludges
generated by wet scrubbers) are also identified.
Air emissions and liquid and solid wastes generated by the
mineral mining industry are briefly summarized in the following
paragraphs. Related control and treatment technologies are also
mentioned.
Particulates from various phases of the mining process and
from any on-site beneficiation processes comprise the primary air
pollution in the mining industry. Emissions emanate from either
fugitive or process sources. For the purpose of this report,
fugitive emissions are defined as "particulate matter which
escapes from a defined process flow stream due to leakage,
materials charging/handling, inadequate operational control, lack
of reasonably available control technology, transfer or storage."
Process point emissions are those emitted from a definable point
source, such as a stack. Particulates emanating from process
and/or fugitive sources (such as free silica from sand, and gravel
operations and asbestos from asbestos mining and processing) can
pose health hazards. Particulates can also be aesthetically
displeasing or annoying to the public. Control of particulate
emissions involves a variety of techniques. Dust suppression
techniques, designed to prevent particulate matter from becoming
airborne, can be used on both fugitive and process sources.
Various dry and wet collection systems (fabric filters, scrub-
bers) are used where particulates can be contained and captured.
Liquid wastes generated by the construction materials and
npnferrous metals industries differ in one major way: construc-
tion materials operations generate effluents that normally con-
tain only suspended inert solids, whereas nonferrous metals
mining and processing facilities generate acidic discharges that
usually contain dissolved heavy metals. Liquid wastes associated
with the mineral mining industry can be separated into three
major categories: 1) mine dewatering (mine pumpout from surface
and underground mines); 2) process wastewaters (spent waters used
in transportation, classification, washing, separation, and pro-
cessing of ores); and 3) surface runoff (precipitation that falls
onto mine and mill properties and has the potential of traveling
overland to surface water systems or percolating into aquifers).
Leakage from tailings ponds and incidental water used for such
purposes as machinery cooling and dust supression are also
sources of water pollution. Mine dewatering and surface runoff,
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the major sources of liquid waste at many operations, are also
often the most difficult to control and treat. Wastewaters from
these two sources can be extremely detrimental to aquatic life,
especially if they contain heavy metals. Most liquid wastes from
processing operations range from alkaline to neutral and have a
high slurried solids level. These wastes may contain metal ions,
reagents such as cyanide, and high levels of dissolved solids.
They are normally discharged to tailings ponds, where the super-
natant is treated before it is recycled or discharged to re-
ceiving streams. The treatment, however, is often insufficient
to prevent degradation of the receiving waters. Settling ponds
or lagoons are used most commonly to treat effluents from mining
and beneficiating operations. These ponds remove suspended
solids and allow for pH control. Some operators use flocculating
agents to facilitate settling. Secondary treatment methods such
as clarifiers, supernatant and/or process wastewaters.
Overburden and gangue are the major solid wastes generated
by the mineral mining industry. The solid wastes (tailings)
generated during beneficiation cpnsist primarily of host rock
material. Other solid wastes are produced from wastewater
treatment (sludges from settling pond dredging and dewatering
devices) and air pollution control systems (particulates col-
lected by fabric filters and scrubbers). The treatment and
control of solid wastes usually involves disposal into off-site
landfills, on-site disposal (impoundment on the surface or re-
turning the solids to the mine), and, in a few instances, re-
covery of the solids as a by-product. On-site disposal of solids
can cause other pollution problems, such as runoff, seepage, and
fugitive dust.
ENVIRONMENTAL INDEX
An environmental index was prepared using the information
assimilated during the multimedia assessment of the mineral
mining industry. It consists of a tabulation of the sources,
types, and amounts of atmospheric emissions and liquid and solid
wastes associated with the mining and processing of construction
materials and nonferrous metals. The information contained in
the environmental index tabulations reflected the conclusions we
reached concerning research and development needs.
CONCLUSIONS AND RESEARCH AND DEVELOPMENT NEEDS
Dimension Stone
The environmental impact from this industry is relatively
minor. Conventional methods are sufficient to control atmos-
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pheric emissions and liquid and solid wastes. Other than an
investigation
of the feasibility of making bricks from the sludge from the
sawing and finishing operations, no research is recommended.
Crushed Stone
Technologies currently applied in the crushed stone industry
are adequate to maintain environmental standards. The only
research recommended involves locating a steady market for the
sludge from the settling ponds and the particulate matter col-
lected by the fabric filters.
Construction Sand and Gravel
Although many sand and gravel operators are maintaining good
pollution control programs, some environmental problems still
persist. The major problems involve 1) dewatering settling pond
sludge, which consists of colloidal fines; 2) the disposal of
dewatered waste fines; 3) the silt load from storm runoff and pit
pumpout from part-time or temporary sand and gravel operations;
4) contamination of ground water resulting from seepage and
percolation from settling basins; and 5) the introduction of
large amounts of suspended solids into public waterways during
dredging operations.
In connection with problem 1), research is needed to deter-
mine the properties in colloidal particles that make the slime so
difficult to dewater, and to develop an economical mechanism for
dewatering this material. Research concerning problem 2) should
be aimed at determining the effectiveness of waste fines (with or
without additives) as a soil builder or fertilizer and to find
other uses, such as building bricks and road base filler. An
important part of this research effort is to find markets for
possible by-products in the immediate vicinity of the sand and
gravel plants. For problem 3) research efforts should be con-
centrated on determining the practicality of constructing diver-
sion ditches and/or retaining dikes to contain and control runoff
at temporary facilities. In connection with potential ground
water contamination as a result of problem 4), an evaluation
should be made of the nature and extent of seepage/percolation
from settling ponds, followed by research relating to possible
preventive measures. To provide an answer to problem 5), re-
search should be initiated to find an effective and economical
means of removing or containing suspended solids generated from
dredging operations.
Industrial Sand
The problems are the same as those in the construction sand
and gravel industry, and the same research recommendations apply.
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Gypsum
Gypsum is mined and beneficiated by environmentally
acceptable methods, and no hazardous pollutants are generated.
State-of-the-art control technologies are applied to contain air
emissions, and liquid wastes are completely recycled as process
water. The only area for possible research is the disposal/
utilization of overburden and waste rock materials removed from
open-pit mines.
Asphaltic Minerals
This industry appears to cause no serious pollution problem,
partially because of its small size and the location of its mines
in remote dry areas. If, however, the vague boundary between oil
shale and asphaltic minerals becomes even more vague and the
deposits become of value as a fuel source, the industry could
expand both geographically and in size. When and if that occurs,
research will be needed to quantify specific waste streams.
Asbestos and Wollastonite
Asbestos has recently been recognized as a potential carcin-
ogen, and asbestos fibers can be liberated into the air in
dangerous amounts at all stages of mining and beneficiation of
the ore. Because of the carcinogenic properties of this mineral,
research should be directly related to reducing adverse health
effects.
The one wollastonite mine in the United States does not
warrant research and development effort.
Lightweight Aggregate Minerals
Other than the usual problem of judicious disposal of over-
burden and consideration for the ultimate condition of the
abandoned mine site, the major problem associated with light-
weight aggregate mining and beneficiation has to do with the
generation of large quantities of fines. The fines are collected
by dry dust collection devices, but they still present a solid
waste disposal problem. Some fine particulates are returned to
the process or sold as a by-product, but most have no use and
must be disposed of onsite. Research should be aimed at
developing a market for these fines.
Mica and Sericite
Very little mica and sericite are mined in the United
States, so the environmental impact from this industry is minor.
Conventional state-of-the-art techniques are sufficient to con-
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trol major pollutants. However, two areas for research do exist.
One involves an investigation into the feasibility of recycling
the large quantities of treated effluent resulting from the
flotation process, and the other concerns an alternative to water
for controlling fugitive dust, during periods when the ambient
temperature falls below freezing.
Aluminum
Available techniques of land reclamation and lime treatment
of mine runoff are adequate to maintain environmental standards
in the bauxite mining and beneficiation industry, and air emis-
sions are also easily controlled. One promising area for re-
search, however, involves reducing the volume of water produced
by the mining operation. Groundwater control techniques now
being used to increase the stability of open-pit slopes should be
expanded to minimize the production of acid mine discharge. This
will require an investigation of the use of gravity wells and
drains.
Antimony
Pollution problems from the mining of antimony in the United
States are insignificant because of the small quantities in-
volved. Hence, no areas of research are recommended.
Beryllium
The beryllium industry in this country is relatively small.
Because of the proprietary nature of some of the processes and
the fact that only one mine is currently in operation, a complete
environmental assessment is impossible. Wastewater is impounded,
and solid waste is blended into the topography during reclama-
tion. The only area that might be worthy of research is the
extent to which impoundments prevent leakage.
Copper
Fugitive dust control, large volumes of tailings (often
containing hazardous materials), the control of wastes from the
flotation process, the amount of solid waste created by using
ponds to settle the tailings from the flotation system, the use
of sodium cyanide as a flotation depressant, and reclamation of
inactive tailings by revegetation or stabilization are all areas
of concern in the copper industry. Research and development
activity is suggested in each <• f these areas.
Fugitive dust control prc .ided by water is of a very tempo-
rary nature; therefore chemical stabilizers are used. Some
comparative studies of the more than 1000 proprietary stabilizers
now available would be of valu.-t.
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The danger of heavy metals leaching into groundwater from
unlined tailings ponds is always present. Techniques should be
researched either to remove the heavy metals from the tailings or
to seal the ponds to prevent leaching.
Tailings are commonly removed from flotation water by
allowing them to settle in a pond. If mechanical screening and
filtering equipment could be developed to separate tailings from
concentrator water, it would permit more effective control of
this solid waste.
Cyanide that enters a copper mill tailings pond is stable in
solution because the pH of the pond water is above 8; therefore,
cyanide escapes with any seepage that occurs. The development of
an alternative reagent to replace sodium cyanide as a flotation
depressant would eliminate this risk.
Many times the pH and associated parameters of copper tail-
ings are such that they present obstacles to revegetation and
stabilization of inactive tailings. Research and development of
soil binders and vegetation with a broad pH-range tolerance would
be beneficial.
Gold
Most of -the wastewater from gold mining and beneficiation
operations is discharged into a tailings pond, then recycled to
the mill or discharged into a watercourse. Solid waste is
usually discarded into the same pond. These solids could contain
gold or other recoverable minerals. One area of research could
concentrate on reclamation of solids that settle out in the
tailings pond. The other possible area of research involves
finding an economical method of controlling the wastewater, which
contains arsenic and cyanide.
Lead and Zinc
The problems and suggested areas of research and development
are much the same as those for the copper industry.
Magnesium
The magnesium mining and beneficiation industry causes fewer
environmental impacts than most other chemical industries. The
following are possible areas for research and development pro-
grams, however. Efforts could be made to characterize the feed
streams for the possible presence of unknown contaminants that
could be creating significant public health impacts. Sufficient
potentially hazardous chlorine is emitted to the atmosphere to be
detected by smell in the immediate vicinity. Research efforts
may be focused on reducing or controlling these emissions.
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Mercury
The mercury industry is comparatively small in the United
States, and the location of the mines in remote areas of arid
climate tends to minimize the environmental impact. The most
significant problenT for research is the control of hazardous
mercury vapor from open deposits. Wastewater from mining and
processing of the ore can be recycled; however, the potential is
great for release of mercury to the environment through impound-
ments. For this reason, research is also needed to develop an
efficient method of removing mercury from water.
Rare Earth Elements
The rare earth mineral mining industry is not considered a
source of adverse environmental impacts. One possible area of
research would be to develop a means of recycling or disposing of
the large quantities of overburden waste that rare earth mining
is projected to produce as the industry expands.
Silver
Liquid wastes create the largest pollution problem in the
silver mining industry. The irregular terrain of the arid areas
in which most mines are located make treatment by tailings ponds
difficult at best, and the scarcity of water makes it essential
to recycle as much as possible. Also, because silver is mined in
conjunction with several other minerals, separation is accom-
plished by a series of flotation cells, and many reagents are
accumulated in the final wastewater. This makes the recycling of
flotation water difficult.
Research could be aimed at finding an economical way to
recover or separate the reagents from the wastewater or the
development of degradable reagents that naturally deteriorate
after a short period of time. Another research possibility is
the combining of liquid wastes from several adjacent mines into
one large reverse-osmosis treatment facility. Collateral re-
search into managing the the resulting slurry and solid waste
disposal problem may be undertaken.
Titanium *
The size of the industry and the available solutions to any
pollutant control problems that are likely to develop preclude
the necessity of any research and development activity.
Nonferrous Metals (Refinery/Smelter By-Products)
Since these metals are recovered as smelter or refinery
by-products of ores that are mined for more economical attractive
xvii
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metals, any research and development needs would be included
under the primary metals.
Nonferrous Metals (Imports)
Because these metals are either imported in a finished or
semifinished form or are produced from imported raw ores, their
extraction does not pose an environmental hazard in the United
States.
ESTABLISHMENT OF R&D PRIORITIES
Because of the large number of mining industries covered in
this report, a system was developed to determine priorities for
purposes of research and development needs. Ten criteria were
chosen to provide EPA with a means to judging R&D needs for each
industry (Table 1). Each criterion was weighed and listed in the
order of its relative importance. Thus Criterion 1 is the most
important and Criterion 10 is the least. Three or four arbitrary
values are assigned within each criterion to indicate the degree
to which that criterion applies to each industry. For example,
Criterion 1 deals with hazardous wastes generated by mining and
beneficiation. If a specific industry generates little or no
hazardous wastes, it receives a basic value of 5 for that
criterion; if hazardous wastes are a minor problem, it receives a
value of 10; if hazardous wastes are a major'problem, it receives
a value of 80. Because the first five criteria are considered
critical as far as potential problems are concerned, they are
promising areas for research.
Various factors entered into the selection and rating of all
the criteria. For example, the generation of hazardous waste by
an industry is assumed to be the criterion of prime importance in
the establishment of R&D priorities because of the environmental
threat (lethal or sublethal) posed if such wastes are not con-
trolled. Although the control of nonhazardous atmospheric
emissions and liquid and solid wastes is considered necessary in
the mining industry, the environmental threat of these wastes is
not of the magnitude as that of hazardous wastes and the values
assigned to them are not as high.
The quantity of ore mined by a particular industry is also a
criterion', as it is directly related to the amount of waste
generated by that industry. The future of each industry is also
important in determining R&D needs. If projections indicate a
decline in an industry, the need for research and development is
not as great as it .would be for industries for which increased
activity is projected and thus the generation of more waste
materials.
xvi 11
-------
TABLE 1.
IMPACT PRIORITIES FOR R&D
X
H-
X
Criteria
1. Hazardous materials associated
with mining and benef iciation
2. Degree of control - atmospheric
emissions
3. Degree of control - liquid wastes
4. Degree of control - solid wastes
5. Domestic ore production
6. Growth of the specific mineral
7. Number of domestic mines
8. Number of principal producing
states
9. Total number of producing states
10. Present degree of information on
the industry
Impact Intensity
A
None to low
(5)
85-99%
(4)
85-99%
(3)
85-99%
(2)
0-300 Gg
(1)
Decline
(0)
<10
(0)
0
(0)
0
(0)
Info.
complete
(0)
B
Minor
(10)
80-84%
(8)
80-84%
(6)
80-84%
(4)
301-500 Gg
(2)
Stable (0%)
(0)
11-24
(0)
1
(0)
1
(0)
Minor gaps
(0)
C
Moderate
(20)
65-79%
(17)
65-79%
(14)
65-79%
(11)
501-2,700 C.o
(8)
0-5%
(5)
25-100
<2)
2
(0)
2
(0)
Moderate
gaps
(0)
D
Significant
(40)
34-64%
(36)
34-64%
(32)
34-64%
(28)
2701-5000 Gg
(24)
6-24%
(20)
101-999
(16)
3-4
(12)
3-9
(4)
Significant
gaps
«>
K
Major
(80)
0-33%
(75)
0-33%
(70)
0-33%
(65)
>sooo 09
(60)
>25%
(55)
>1000
(SO)
>4
(45)
>10
(35)
Major
gaps
(30)
(continued)
-------
TABLE 1. (continued)
Mineral/Criteria
Honferroua Metals
Aluninum
Antimony
Beryllium
Copper
Gold
Lead and Zinc
Magnesium
Mercury
Rare Earth Elements
Silver
Titanium
Nonmetals
Asbestos and Hollastonite
Asphaltic Minerals
Construction Sand t Gravel
Crushed Stone
Dimension Stone
Gypsum
Industrial Sand
Mica and Seriate
Perlite
Pumice
Vermiculite
Nonferroua Metals
(refinery/smelting
by-products0)
Nonferroua Metals
(imports)a
1
20
S
10
80
20
80
10
40
S
20
20
40
10
10
5
S
5
10
S
5
5
10
N/A
N/A
2
36
8
4
36
17
B
36
36
8
17
17
17
17
4
17
8
8
4
4
36
36
4
N/A
N/A
3
14
14
6
32
14
14
6
14
6
32
6
14
14
6
14
14
6
14
3
3
3
6
N/A
N/A
4
11
2
2
28
28
28
2
4
2
28
11
11
28
11
11
11
28
28
4
28
28
28
N/A
N/A
5
24
2
2
60
24'
60
24
1
1
8
a
2
2
60
60
8
24
8
1
8
24
1
N/A
N/A
Critical
Score3
105
31
24
236
103
190
78
95
22
105
62
84
71
91
107
46
71
64
17
80
96
49
N/A
N/A
6
5
S
5
5
5
5
5
0
5
5
5
5
0
20
5
0
5
5
0
20
5
20
N/A
N/A
7
0
0
0
2
2
2
0
0
0
16
0
0
0
50
50
16
2
16
0
0
16
0
N/A
N/A
8
12
• o
0
45
45
12
12
12
12
12
12
12
12
45
45
45
45
45
12
0
45
0
N/A
N/A
9
4
4
4
35
35
35
4
4
4
35
35
4
4
35
35
35
. 35
35
4
4
35
0
N/A
N/A
10
0
0
0
0
4
0
0
0
0
0
0
4
4
0
0
0
0
0
4
4
4
4
N/A
N/A
Total
Score
126
40
33
323
194
244
99
111
43
173
114
109
91
241
242
142
158
165
37
108
201
73
N/A
N/A
X
X
(continued)
-------
TABLE 1. (continued)
a Critical score provides an indication of the combined effects of potential hazard, degree of
environmental control, and extent of ore volume for particular minerals.
Total score provides only a general indication for ranking. Specific attention should be given
to the ten criteria. For example, if it was desired to identify 3 ranking minerals associated
with mining and beneficiation, copper; lead and zinc; and, crushed stone would yield the highest
relative ranking. Yet there is a wide variation of both critical and total scores of each.
Similarly, if impact from the mineral represented by the largest number of mines was sought,
construction sand and gravel or crushed stone may be selected.
X ° Several nonferrous metals covered in this report are not mined for their own economic value, but
X are constituents of an ore that is mined for a more economically attractive metal such as copper
H- or zinc. These metals are captured during the refining or smelting of ores containing other metal*.
The following is a listing:
Bismuth Hafnium . Tellurium
Cadmium Indium Thallium
Gallium Selenium Zirconium
Germanium
Several nonferrous metals covered in this report are not currently mined in the United States.
These metals are either imported in a finished or semifinished form or are produced from
imported ores; therefore, their extraction does not pose an environmental hazard to the
United States. These metals are as follows:
Arsenic Radium Scandium
Cesium Rubidium Tin
Platinum-group metals
-------
The number of domestic mines, the principal producing
states, and the total number of producing states are important
criteria in that the wider the geographic distribution of an
industry, the more widespread will be the pollution problems
associated with that industry and the greater need for control.
The amount of data available on each industry is a necessary
criterion for several reasons. Lack of understanding regarding
an industry's process means a lack of knowledge about its waste
streams; and the less that is known about the waste streams, the
greater the possibility that hazardous and nonhazardous waste
streams are either inadequately controlled or completely uncon-
trolled.
After values have been assigned to each criterion, the
values of a particular industry are totaled. A comparison of
industry totals then provides a partial guidance for determining
R&D efforts (Table 1).
xxi i
-------
CONTENTS
Page
Foreward iii
Executive Summary . iv
Figures xxv
Tables -xxvii
Acknowledgment xxx
Metric-to-English Conversion Table xxxi
1. Introduction 1
2. General Industry Process Description 8
Premining activities 10
Extraction processes 12
Beneficiation 25
3. General Waste Characteristics and Control 32
Air emissions and control technology 32
Liquid wastes and control technology 44
Solid wastes and control technology 49
Hazardous wastes 52
4. Nonmetals 54
Dimension stone 54
Crushed stone 60
Construction sand and gravel 67
Industrial sand 84
Gypsum . 93
Asphaltic minerals 99
Asbestos and wollastonite 106
Lightweight aggregates 114
Mica and sericite 125
5. Nonferrous Metals 132
Aluminum 132
Antimony 143
xxi 11
-------
CONTENTS (continued)
Beryllium 150
Copper 155
Gold 174
Lead and zinc 183
Magnesium 200
Mercury 207
Rare earth elements . 212
Silver 218
Titanium 228
6. Nonferrous Metals (Refinery/Smelter
By-Products) 238
Bismuth 238
Cadmium 238
Gallium. • - . . . . 238
Germanium 239
Hafnium 239
Indium ...... 239
Selenium 239
Tellurium 239
Thallium 239
Zirconium 240
7. Nonferrous Metals (Nondomestic) 241
Arsenic 241
Cesium 241
Platinum-group metals 241
Radium 242
Rubidium '. 242
Scandium 242
Tin 242
Appendix A Explanation of criteria used to
establish R&D priorities 243
xxiv
-------
FIGURES
No.
1 Scope of mining activities 9
2 Room-and-pillar mining method 15
3 Open stope mining method 15
4 Stull stoping 17
5 Shrinkage stoping 18
6 Block caving underground 18
7 Open-pit mining 20
8 Glory hole mining 20
9 Types of dredges used in excavation 23
10 Beneficiation processes . 26
11 Mining and beneficiating of dimension stone 56
12 Mining and beneficiating of crushed stone 62
13 Mining and beneficiating of construction sand
and gravel 71
14 Mining and beneficiating of industrial sand 87
15 Mining and beneficiating of gypsum 95
16 Mining and beneficiating of asphaltic minerals .... 101
17 Mining and beneficiating of asbestos 108
XXV
-------
FIGURES (continued)
No. Page
18 Mining and beneficiating of wollastonite 109
19 Mining and beneficiating of lightweight aggregates
(perlite, pumice, and vermiculite) 118
20 Mining and beneficiating of mica and sericite 127
21 Mining and beneficiating of bauxite 134
22 Mining and beneficiating of antimony from sulfide
and complex ores
23 Mining and beneficiating of beryllium ore 152
24 Mining and beneficiating of copper ores 157
25 Mining and beneficiating of gold ores 176
26 Mining and beneficiating of lead-zinc ores 188
27 Mining and beneficiating of magnesium 202
28 Mining and beneficiating of mercury ores 209
29 Mining and beneficiating of rare earth elements .... 215
30 Mining and beneficiating of silver 221
31 Mining and beneficiating of heavy-mineral beach
sand (placer) deposits 230
32 Mining and beneficiating of ilmenite rock (lode)
deposits 231
XXVI
-------
TABLES
No. Page
1 Priorities for R&D Efforts . . . : xix
2 Subject Minerals 2
3 Production Statistics for Construction Materials ... 3
4 Production Statistics for Nonferrous Metals 4
5 Domestic Mine Production of Nonferrous Metals 5
6 Fugitive and Process Point Sources 33
7 Summary of Multimedia Wastes From Mining and
Beneficiating of Dimension Stone 57
8 Dimension Stone Water Use Data 58
9 Summary of Multimedia Wastes From Mining and
Beneficiating of Crushed Stone 63
10 Particulate Emission Factors for Stone Crushing
Processes 64
11 Summary of Multimedia Wastes From Mining and
Beneficiating of Construction Sand and Gravel .... 74
12 Major Producing States of Industrial Sands 85
13 Summary of Multimedia Wastes From Mining and
Beneficiating of Industrial Sand 89
14 Summary of Multimedia Wastes From Mining and
Beneficiating of Gypsum 97
15 Summary of Multimedia Wastes From Mining and
Beneficiating of Asphaltic Minerals 10?
16 Summary of Multimedia Wastes From Mining and
Beneficiating of Asbestos and Wollastonite
XXVI1
-------
TABLES (continued)
No. Page
17 Summary of Multimedia Wastes From Mining and
Beneficiating of Lightweight Aggregates
(Perlite, Pumice, Vermiulite) 120
18 Summary of Multimedia Wastes From Mining and
Beneficiating of Mica and Sericite 129
19 Summary of Multimedia Wastes From Mining and
Beneficiating of Bauxite 136
20 Summary of Multimedia Wastes From Mining and
Beneficiating of Antimony Ores 147
21 Summary of Multimedia Wastes From Mining and
Beneficiating of Beryllium Ore . . . 149
22 Concentrating Alternatives for Copper Ores 153
23 Summary of Multimedia Wastes From Mining and
Beneficiating of Copper Ores 161
24 Emission Factors for Tailings Piles . . 162
25 Raw Waste Load in Water Pumped From Selected
Copper Mines 164
26 Examples of Chemical Agents That Are Employed
in Copper Flotation 165
27 Analysis of Tailings Discharged From a Copper
Concentration 166
28 Analytical Data on Tailings Solids for Copper
Mining Operations 167
29 Summary of Multimedia Wastes From Mining and
Beneficiating of Gold Ores 179
xxviii
-------
TABLES (continued)
No. Page
30 Chemical Composition of Raw Mine Water From
Two Underground Gold Mines ............. 18 1
31 Summary of Multimedia Wastes From Mining and
Beneficiating of Lead-Zinc Ores ..........
32 Range of Chemical Characteristics of Raw Mine
Waters From Four Operations Indicating High
Solubilization Potential ...... ........ 194
33 Range of Chemical Characteristics of Sampled Raw
Mine Water From Three Lead/Zinc Mines Showing
Low Solubilization ....... ' .......... 195
34 Ranges of Constituents of Wastewaters and Raw
Waste Loads From Five Selected Mills ........ 197
35 Uses for Magnesium Compounds ....... ...... 200
36 Summary of Multimedia Wastes From Mining and
Beneficiating of Magnesium ............. 204
37 Summary of Multimedia Wastes From Mining and
Beneficiating of Mercury .............. 210
38 Uses of Rare Earth Elements ............. 213
39 Summary of Multimedia Wastes From Mining and
Beneficiating of Rare-Earth Ores .......... 216
40 Chemical Composition of Raw Wastewater From a
Flotation Mill ................... 217
41 Summary of Multimedia Wastes From Mining and
Beneficiating of Silver Ores ............ 223
42 Summary of Multimedia Wastes From Mining and
Beneficiating of Titanium Ores ........... 232
XXIX
-------
ACKNOWLEDGMENT
This report presents the results of a multimedia environ-
mental assessment of the mineral mining industry. The specific
mining industries covered in the report include the nonferrous
metals and nonmetals industries.
The study was prepared for the U.S. Environmental Protection
Agency (EPA) by PEDCo Environmental, Inc., Cincinnati, Ohio under
Contract No. 68-03-2479. The EPA project officer was S. Jackson
Hubbard of the Resource Extraction and Handling Division, Indus-
trial Environmental Research Laboratory.
The PEDCo director for this project was Mr. Richard 0.
Toftner and the project manager was Robert S. Amick. The
principal project investigators and authors were Jack S. Greber,
Vijay P. Patel and Ed. A. Pfetzing. Technical assistance was
provided by Dr. Roy E. Williams, Senior Mining Consultant.
.Many other individuals and organizations contributed to this
study. The following were especially helpful: S. Jackson
Hubbard and John Martin, U.S. EPA, lERL-Ci, for their guidance
and advice throughout the project; Karl W. Mote - Northwest
Mining Association, David R. Cole - Colorado Mining Association,
William H. McDonald - Indiana Limestone Institute of America,
Inc., Edward K. Davison - National Sand and Gravel Association,
and Fredrick J. Rogers - Gypsum Association, for their advice and
assistance in arranging contacts with the mining industry. A
number of Federal and State Governmental agencies provided
valuable data, as referenced in the report. Finally, the co-
operation of mining companies and their representatives who
provided pertinent information during site visits is gratefully
acknowledged.
XXX
-------
METRIC-TO-ENGLISH CONVERSION TABLE
To convert
Hectares
Cu. meters
Cu. cms/sec
Cu. meters
Meters
Cu. meters
Centimeters
Kilometers
Kilograms
Megagrams
Liters
To
Acres
Cubic feet
Cubic feet/min.
Cubic yards
Feet
Gallons
Inches
Miles (statute)
Founds
Tons (short)
Gallons
Multiply by
2.471
3.531 X 10]
2.119 x 10
1.308
3.281
2.642 x 10:
3.937 x 10
6.215 x 10
2.204
1.106
2.642 x 10
-3
-1
-1
-1
XXXI
-------
SECTION 1
INTRODUCTION
This report presents a multimedia environmental assessment
of mineral mines producing nonferrous metals and construction
materials. This assessment encompasses the identification of
wastes and waste sources, quantities, and characteristics, as
well as applicable control technology. An Environmental Index
summarizes the wastes and the waste sources, quantities, and
characteristics for each mineral.
The nonferrous metals and construction materials included in
the. study are listed in Table 2. The mining processes covered
are ore extraction and those mine-site beneficiating operations
that prepare the minerals for shipment as salable products or as
raw material for final processing. Final processing operations
such as refining, smelting, and exfoliation, which are located
away from mine sites are not considered in this report.
Many of the nonferrous metals are commonly found in asso-
ciation in the same ore. For example, some complex copper ores
yield not only copper but also selenium, tellurium, gold, silver,
and other nonferrous metals. Among nonferrous metals that are
not mined for their own economic value are bismuth, cadmium,
gallium, germanium, hafnium, indium, selenium, tellurium, and
thallium. No domestic mines operate solely for the extraction of
any of these metals; rather, they are captured during the re-
fining or smelting of more economically attractive ores like
copper or zinc. Ore production statistics are therefore not
presented for these metals.
Several nonferrous metals are not presently recovered from
domestic ores and are either imported in a finished or semi-
finished form or are produced from imported raw ores. They are
arsenic, cesium, platinum-group metals, radium, rubidium, scan-
dium, and tin. Since their extraction poses no environmental
hazard to the United States, they have been excluded from the
discussion.
Salient production statistics for construction materials and
nonferrous metals are presented in Tables 3, 4, and 5. These
data were derived from Bureau of Mines publications, particularly
from Mineral Facts and Problems, 1975 edition, and telephone
interviews with the appropriate commodity specialists at the U.S.
Bureau of Mines in Washington, D.C.
-------
TABLE 2. SUBJECT MINERALS
1) Construction Materials
Dimension stone
Crushed stone
Construction sand and gravel
Industrial sand
Gypsum
Asphaltic minerals
Asbestos and wollastonite
Lightweight aggregate minerals
Mica and sericite
2) Nonferrous Metals
Aluminum
Antimony
Arsenic
Beryllium
Bismuth
Cadmium
Cesium
Copper
Gallium
Germanium
Gold
Hafnium
Indium
Lead
Magnesium
Mercury
Platinum-group metals
Radium
Rare-earth elements
Rubidium
Scandium
Selenium
Silver
Tellurium
Thallium
Tin
Titanium
Zinc
Zirconium
-------
TABLE 3. PRODUCTION STATISTICS FOR CONSTRUCTION MATERIALS
Crushed stone1'3
Dimension stone >a
Sand and (travel and industrial
Gypsum
Asphaltic minerals
Asbestos4 'a
Nollastonite3
Lightweight aggregate
Minerals
Perlite5'6
Pumice '
Vermiculite6'8
Mica and sericite9'3
Sheet mica '
Scrap and flake9'3
Domestic
mine
production
(1974), Gg
944,755
1,737
887,730
10,883
N.A.
102
W
613
3,571
309
N
124
Domestic
mine
production
(1975), Gg
817,648
1,273
716,018
8,844
N.A.
90
W
640
3,530
308
.002
122
Domestic
mine
production
(1985) , Gg
1,405,850
• 1,361
1,260,730
10,857
N.A.
145
• W
816
5,986
531
0
168
Major producing states
Illinois, Pennsylvania, Texas,
Missouri, Ohio
Indiana, Georgia, Vermont, Ohio
Pennsylvania
California, Michigan, Illinois,
Texas, Minnesota
Michigan, California, Texas,
Iowa, Oklahoma
Texas, Utah, Oklahoma
California, Arizona, Vermont
New York
New Mexico
Arizona, California, Oregon,
Hawaii
Montana, South Carolina
North Carolina
Type of mine
Surface, (95%)
Underground, (5%)
Surface, (100%)
Surface, (90%)
Dredging (10%)
Surface, (80%)
Underground, (20%)
Surface, (70%)
Underground, (30%)
Surface, (80%)
Underground, (20%)
Underground, (100%)
Surface, (100%)
Surface, (100%)
Surface. (100%)
Surface, (100%)
Surface, (100%)
a Information obtained via telephone conversations between PEDCo staff and personnel of the U.S. Bureau of Mines,
Washington, D.C.
N.A. - Not available.
H - Information.withheld.
-------
TABLE 4. PRODUCTION STATISTICS FOR
NONFERROUS METALS
Metal
Aluminum '
Antimonyli-t
Ber>-lliuroi:>b
Copper13'"
Gold'4'"
uadl5-»
16, b
Magnesium
(product)
Nonmetal
Metal
17 b
Mercury
Rare earth
elementslo.b
Silver19'11
Titanium20'*1
Zinc21-»
1974 ore"
production ,
Gg
2917
Confiden-
tial
Confiden-
tial
244000
4200
8441
864
159
26
234
620
676
453
1975 ore*
production,
G9
2652
Confiden-
tial
tial
218000
5200
7654
795
166
70
176
709
650
426
Estimated 1985
ore production.
Go
2993.
Confidential
317000
5900
9110
1273
253
214
384
941
838
544
t of total
primary
domestic
metal
100
20
100
98
55
85
100
100
100
100
33
100
52
Major
Gallium
Lead, silver
None
Gold, silver,
selenium, lead,
tellurium,
platinum-group
metals
Copper, lead,
silver,
platinum-group
metals
Antimony, bis-
muth , 90 Id ,
silver, tellu-
rium, zinc
copper, gallium
None
None
None
Titanium, hafni-
um, zirconium
Copper* lead,
zinc, antimony
Hafnium,
zirconium
Cadmium, copper,
gallium, germa-
nium, indium,
lead, silver,
thallium
Major
producing
Arkansas ,
Alabama,
Georgia
Montana,
Idaho
Type of mine
Surface, lOOt
Underground, 100*
Utah Surface, 100*
Arizona,
Utah, New
Mexico,
Nevada,
Michigan
South Dakota,
Nevada.
Arizona
Missouri,
Idaho,
Colorado,
Utah
California ,
Texas, Utah,
Michigan
Texas
fornia , Alaska
California,
Florida
Idaho,
Montana
New York,
Florida,
New Jersey
Missouri,
Colorado,
Tennessee,
Idaho. New
York
Surface, 80*
Underground, 20*
Surface, 66t
Underground, 23*
Dredging, l\
Underground , 1 00 «
Brines. N.A.
Surface, N.A.
Brines, N.A.
Surface, N.A.
Underground, 66(
Surface , 90*
Dredging , 10%
Underground , 1 0 0 »
Dredging, 80*
Surface. 20*
Underground, 100%
metal is the major or primary constituent of the ore. It does
'here the designated metal is a constituent of the ore and is
* Represents that ore mined for designated metal where that
not represent the tonnage of ore mined for other metals wl
recovered only as a by-product or coproduct.
b Information obtained via telephone conversations between PEDCo staff and personnel of the U.S. Bureau of Nines,
Washington, D.C.
N.A. - Hot available.
-------
TABLE 5. DOMESTIC MINE PRODUCTION OF
NONFERROUS METALS
Aluminum
Antimony
Beryllium
Bismuth
Cadmium
Copper
Gallium
Germanium
Gold
Hafnium
Indium
Lead
Magnesium
Nonmetal
Metal
Mercury
Rare earths
Selenium
Silver
Tellurium
Thallium
Titanium
Zinc
1974 domestic
primary
production ,
Gga
1945
0.6
c
c
3.023d
1448
C
0.013
0.035
0
c
602
•
964
159
151
20. 418
584
1.05
173d
c
23320
454
1975 domestic
primary
production ,
eg*
1768
0.8
a
a
1.989d
1282
c
0.014
0.033
0
c
563
795
166
508
15. 3e
325
1.09
1.19*
c
23320
425
Ref. 22 (except as noted).
Ref. 6 (except as noted).
Withheld to avoid disclosing company confidential data.
Refinery production.
e Information obtained via telephone conversations between
PEDCo staff and personnel of the U.S. Bureau of Mines,
Washington, D.C.
-------
Table 3 presents 1974 and 1975 domestic mine production
figures for construction materials and projected production
figures for 1985. The table also shows the leading producing
states and the method of extraction. Ore tonnages are not avail-
able.
The crushed stone segment of the industry produces the
largest annual tonnage of product, followed closely by the sand
and gravel industry, positions they are expected to retain
through this century. Since they are closely aligned to con-
struction activity, stone and sand and gravel ope'r-ations are
usually concentrated near urban centers. This sometimes creates
a land-use conflict with promoters of local business expansion,
residential construction, and public works projects such as parks
and recreation areas. Consequently, the slight but growing trend
is away from open pit quarries to underground mining of these
materials. As a result, subsidence may become a future environ-
mental impact in the future.
Growth in the construction material industries should paral-
lel the growth in the Nation's economy with two exceptions. One
is the dimension stone industry; the demand is decreasing because
of the introduction of alternative construction materials such as
glass and steel. The other exception is the sheet mica industry.
Only 0.002 gigagram was produced in 1975, and by 1985 this
country will probably no longer produce sheet mica. It is
assumed that asphaltic minerals are following the normal growth
pattern, although no production data are available. The same is
true of wollastonite since only one company (in New York) pro-
duces this material, and its production data are confidential.
Production statistics for nonferrous metals outlined in
Table 4 quantify the amount of ore mined for each metal except
where such data are considered confidential by the producer. The
data presented in Table 4 represent only ore in which the desig-
nated metal is the primary constituent; the table does not in-
clude the amount of ore mined for those metals where the desig-
nated metal is a coproduct or by-product. For example, in 1975,
7854 gigagrams of ore was extracted from mines in which lead was
the primary metal. The table includes only the percentage that
this ore contributes to the total domestic primary metal produc-
tion of lead (i.e., lead ores contributed 85 percent of the total
domestic lime output of lead; the remaining 15 percent was taken
from lead-zinc, zinc, copper-lead, copper-zinc, or copper-lead-
zinc ores). Table 4 also lists the leading producing states, the
types of mines, and the associated metals for each nonferrous
metal. Statistics for the production of primary metals from
domestic ore are presented in Table 5.
-------
Production statistics for beryllium .are not available for
publication. The Brush-Wellman, Inc., mine in Utah is the sole
domestic producer of this mineral. Statistics for the primary
antimony industry also are incomplete. Total domestic mine
production is known, but the amount of ore processed each year
cannot be determined. Although much of our domestic antimony
comes from the lead-silver ores of Idaho, a substantial amount is
also taken from antimony ores near Towson Falls, Montana. One
Montana producer is known to extract ores solely for their anti-
mony content, but he elects to keep production data proprietary.
Although production of most nonferrous metals declined in
1974 and 1975 because of the general economic downturn, it should
return to normal levels as the economy regains its strength.
Only mercury shows any signs of dramatically increasing produc-
tion through 1985. This sudden surge is not a function of rising
demand; rather it is directly attributable to the opening of a
large mercury mine in Nevada. An annual output of 689 megagrams
from this mine will greatly reduce dependence on imported mer-
cury.
Copper producers are by far the largest extractors of non-
ferrous metals. The copper industry produced 218,000 gigagrams
of ore in 1975 compared with 7854 gigagrams of ore processed by
the lead industry, which ranks second. In terms of volume of
ore, the smallest producers are the mercury industry (69.7 giga-
grams in 1975) and the rare-earth group (176 gigagrams in 1975).
-------
SECTION 2
GENERAL INDUSTRY PROCESS DESCRIPTION
Mining activities encompass prospecting and exploring for a
mineral deposit through finding, proving, developing, extracting,
and processing the ore. As indicated on Figure 1, which depicts
the scope of activities, the mining industry can be divided into
three major phases:
Phase I - Before Mining
Phase II - Mining
Phase III - After Mining
These three phases are common to the mining of both construction
and nonferrous minerals, although the manner in which they are
accomplished may vary.
Premining activities (Phase I) involve prospecting and
exploration required to locate, characterize, and prove a
potential ore body. Once proof of an ore deposit has been es-
tablished, the property is prepared for ore extraction and pro-
cessing. This site-development step includes trenching, drill-
ing, clearing and grubbing, removing overburden, and constructing
buildings.
Phase II refers to actual ore extraction and related simul-
taneous activities (e.g., blasting, loading, conveying). Extrac-
tion processes for both construction and nonferrous minerals
include underground mining, surface mining (primarily open-pit),
and some dredging.
Activities subsequent to mining (Phase III) involve pro-
cessing and preparing the raw mineral ore for the end product or
for shipment to final processing facilities. Processing normally
includes operations such as size reduction, classification,
concentration, leaching,* and smelting and refining. Smelting
and refining are not considered in this document, since the major
areas of concern are mining operations and initial beneficiation
processing conducted at the mine site and integrated with mining
operations (e.g., size reduction, classification, concentration).
*Leaching involves the recovery of mineral values from rock by
hydrometallurgical processes. Leaching, considered, as a
beneficiation method as well as a secondary mining method, is
discussed in the beneficiation section of this report.
8
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PHASE I
BEFORE MINING
PHASE II
MINING
PHASE HI
AFTER MINING
vo
FINDING
PROVING
PLANNING
OPENING AND
DEVELOPING
DRILLING
SAMPLING
SHAFTING AND/OR TUNNELING
SELECTION OF OPERATING METHODS
DESIGN AND ENGINEERING
SHAFT SINKING AND TUNNELING
CLEARING AND GRUBBING
STRIPPING
UNDERGROUND AND SURFACE
CONSTRUCTION
EXTRACTION ORE
SURFACE PROCE
UNDERGROUND
DREDGING
BREAKING
LOADING
TRANSPORTING
UNLOADING
TO
SSING^ PROCESSING
TO FURTHER PROCESSING
OR CONSUMER PRODUCTS
SIZE REDUCTION
SCREENING
CLASSIFYING
CONCENTRATING
DEWATERING
THERMAL DRYING
LEACHING
Figure 1. Scope of mining activities.
Source: Ref. 23.
-------
Details specific to the activities addressed in this report
are discussed in the following pages.
PREMINING ACTIVITIES (23,24)
Potential mine sites are evaluated to determine the presence
of economical recoverable mineral deposits. This work, referred
to as prospecting, usually includes ground and geochemical recon-
naissance, examination of aerial photographs, and in certain
special situations, sampling and drilling. Most modern pros-
pecting activities leave the ground relatively undisturbed.
After making an initial rough estimate of the general form and
character of the expected ore body, the prospector or geologist
submits his findings to those involved in the physical explora-
tion and development.
The selection of an area for surveying may result from
regional reconnaissance, a spot check of promising geologic
situations described in published literature, submittal of site
data by a prospector or independent geologist, or the decision to
restudy an old mine or mining district. The area selected usu-
ally embraces ground beyond the site of actual interest. A total
of less than 3000 hectares or as much as 30,000 hectares may be
involved, depending on the type of mineral deposit being ex-
plored. When an area has been chosen, the site is prepared for
the exploration team. This may involve activities such as con-
structing an access road, bringing in utilities (electricity and
water), locating or developing housing for the exploration team,
constructing helicopter pads, and establishing a communication
system. Once preliminary site preparation is completed, explora-
tion for a potential ore begins. The following is a list of some
exploration methods and their definitions.
I
1) Geological method - A study of the geology of the ore
deposit and its general setting. Involves geologic
mapping and plotting by the use of various tools such
as a transit, stadia, compass, and tape.
2) Geochemical method - A study of the chemistry of rocks,
soils, waters, and the atmosphere.
3) Biochemical method - A study of plant material to
determine trace metal content.
4) Geophysical method - A study of the physical character-
istics of rocks and minerals. Six basic geophysical
exploration methods are commonly employed in the search
for minerals: gravity, seismic, magnetic, electro-
magnetic, electric, and radiometric.
10
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At this stage a preliminary environmental assessment. is
undertaken to establish baseline conditions and to project po-
tential impact from both exploration and possible later mining.
The physical work involved in the exploration methods de
fined usually includes trenching, pitting, and drilling.
Trenching establishes the trend, width, and mineral character of
an ore protruding from soil. This is normally accomplished with
bulldozers and backhoes of various sizes, or sometimes mechanical
or hydraulic rippers in rough ground. Drilling and blasting are
rarely necessary because adequate samples are usually collected
at the point where the rock becomes too hard to be moved by a
ripper or blade. If irregular deposits are believed to extend
beneath the soil cover or the alluvium is suspected to contain
values such as placer gold, shallow pits (3 to 5 meters) are dug
with small backhoes or circular shafts (in the range of 30
meters) are excavated with septic tank diggers. These machines
can remove only the uppermost weathered bedrock. If penetration
into the rock itself is required, shafting is usually done by
pneumatic drilling and blasting with stick dynamite and standard
fuse and blasting caps.
Other exploration techniques include overburden and explora-
tion drilling. Overburden drilling is a shallow exploration
method for obtaining small bedrock samples for geochemical anal-
ysis or in various geophysical interpretations. Exploration
drilling, which is deeper, is used to study the ore itself.
Percussion, rotary, and diamond drilling are the three most
common methods used today. Equipment ranges in size and com-
plexity from simple hand-operated augers to small-scale versions
of oil-fired rigs.
Results of the exploration study are tabulated and used to
locate and characterize (prove) the ore deposit. Data obtained
from exploration studies may also be of value in planning extrac-
tion and hauling facilities, developing beneficiation operations,
and establishing methods of waste handling and disposal.
After exploration has provided information on the shape and
size of an ore deposit, its general geological characteristics,
its average grade, etc., site development for mining begins.
Mine development depends largely upon the kind of ore body and
the mining method to be applied. Some common approaches to mine
development are development drilling; access road construction;
clearing and grubbing; adit or shaft development; overburden
removal; establishment of utilities and communication; and con-
struction of facilities such as the grinding mill, concentrating
mill, and general office. The different types of equipment
required range from small, simple units such as backhoes and dump
trucks to sophisticated systems involving earth movers, drag-
lines, and power shovels.
•
11
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Although an effort is made to develop mine sites in harmony
with the environment, some alteration and disturbance of the
topography are unavoidable. An Environmental Impact Statement
(EIS) or a Negative Declaration (ND) frequently is required at
this stage of activities, depending on the significance of the
Environmental Assessment (EA). This involves a detailed study of
soil, water, air, vegetation, and wildlife in the vicinity of the
site and the potential impacts of access roads and other develop-
mental features, including socioeconomic impacts during and after
the mine is closed down. Generally, premining activities are
halted temporarily (for a year or more) while the study is con-
ducted. Considerably more detail may be required if Federal land
is involved, but in almost all cases an EA is a part of the
premining operation and leads to a formal EIS when the impacts
are significant or the project is controversial.
EXTRACTION PROCESSES
For purposes of this report, three specific mining cate-
gories are considered: underground mining, surface mining, and
dredging. These extraction methods are described individually in
this section, following the discussions on the various activities
carried out simultaneously with ore extraction (drilling, blast-
ing, and ore loading and transport).
Drilling, Blasting, and Ore Loading and Transport (25)
It is necessary to drill and blast to loosen portions of
most mineral deposits before they can be removed, although some
can be removed by power equipment such as front-end loaders, drag
lines, and dredges.
Drilling consists of boring blast holes into the bedded
minerals. The holes are subsequently charged with explosives and
detonated. Tractor or truck-mounted pneumatic rotary or per-
cussion drills are commonly used for this purpose. A rotary
drill rotates a drill rod to which a bit (usually a roller-cone
type) is attached and produces the borehole by the abrasive
cutting action of the rotating bit. Percussion drills use com-
pressed air to drive a piston that transmits a series of impacts
or hammer blows, either through the drill rod, or, as in "down-
the-hole" drilling, directly to the bit. The borehole is formed
by the chipping and pulverizing action of the chisel-like bit
impacting against the mineral surface. Normally, rotary drills
are used in softer mineral deposits and percussion drills in
harder deposits. The number, depth, spacing, and diameter of
blast holes depend on the characteristics of the explosive used,
the type of burden or mineral to be fragmented, and character-
istics of the deposit such as the location of dips, joints, and
seams.
12
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Blasting is used to displace minerals from their deposits
and to fragment them into sizes that require a minimum of second-
ary breakage and that can be readily handled by loading and
hauling equipment. Once engineered, blasting practices consist
simply of loading blast holes with a predetermined amount of
explosives and stemming, then detonating them. Dynamites and
blasting agents are the most commonly used explosives. Dyna-
mites, which are highly explosive, come in a variety of types and
grades, many of which contain nitroglycerine. Blasting agents
are insensitive chemical mixtures of fuels and oxidizers. Mix-
tures of ammonium nitrate and fuel oil (ANFO) are the most common
and consist of coated or uncoated fertilizer grade ammonium
nitrate pellets, prills, or granules mixed with 4 to 6 percent
fuel oil.
Blasting frequency ranges from several shots per day to one
per week, depending on the plant capacity and the size of indivi-
dual shots. The effectiveness of a shot depends on the charac-
teristics of the explosive and the mineral.
The excavation and loading of broken minerals is normally
performed by shovels and front-end loaders. At most surface
mines, large haulage vehicles with a capacity of 18 to 68 mega-
grams are used to transport minerals from the mine to the primary
crusher. At underground mines crude ore is transported to the
surface in buckets or cars called "skips." Ore is transported to
the skip by conveyors or haulage vehicles.
Underground Mining
An underground mine is a facility constructed to permit the
extraction and removal of a mineral or metal ore from a natural
deposit beneath the earth's surface. The mine also includes the
area of land over which these extraction and removal activities
occur or where these activities disturb the natural land surface.
In some cases, the mine may also encompass areas affected by
ancillary surface operations-haul roads or access roads, work-
ings, impoundments, dams, ventilation shafts, drainage tunnels,
entryways, refuse banks, dumps, stockpiles, overburden piles,
spoil banks, culm banks, tailings, holes or depressions, repair
areas, storage areas, and structures (23).
The choice of the underground mining method to be applied
depends on a number of factors (23):
1. The assay (quality), size, and geometry of the ore
deposit.
2. The amount and distribution of the minerals in that
deposit.
13
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•3. The mechanical engineering, and chemical properties of
the ore and the parent rock.
4. The economic situation of the mining operation.
5. Safety, health, and government regulations.
6. Special considerations (environmental impacts including
socioeconomic, etc.).
Several methods are employed in underground extraction of
mineral deposits, and descriptions of the more common ones follow.
Room-and-Pillar—
Room-and-pillar mining involves removal of an ore stratum
with the exception of occasional columns or pillars; these
pillars then provide support for the overlying rock strata. The
method is commonly applied when ores are flat-lying or in gently
dipping beds (Figure 2). The supports may be left in place or
removed (or partially removed) for their mineral value. The
structure of some areas requires that the pillars be left in
place so that subsidence does not cause disturbance of original
land surface. The pillars are left in place in a regular pattern
while the rooms are mined out. If the pillars are to be removed,
those farthest from the haulage exits are mined first, allowing
the roof to cave in. Room-and-pillar mining is well-adapted to
mechanization, and many different types of ore deposits are mined
by this method.
Conveyors carry the ore mined in the rooms to the entry belt
or mine car-loading station. Haulage in the rooms may be by
conveyor, shuttle car, or load-tram unit. Elaborate water
collection and pumping systems keep the mine dry during extrac-
tion of rooms and pillars.
Hydraulic Mining--
Another method of breaking minerals out of a solid body of
rock is by hydraulic jets. This method can also provide imme-
diate transportation of the materials, with the rate of removal
dependent upon the material, the grade of the opening, and the
water flow. If the material is highly flammable, such as the
asphaltic mineral gilsonite, hydraulic mining is usually the
preferred method of extraction. Although this method can be
employed in either flat or vertical veins, additional water is
required to flush out the mined material in a flat vein. Cutting
can be accomplished with hand-held jets; however, jet cars, which
are controlled either remotely or by an operator, or water
cannons are more efficient. In vertical veins, the ore may be
loosened by drilling before the jet cutting operation.
14
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MULTIPLE' ORILLN(JUMBO
V. vvvvvvvvvvv.--"--
HAUL-DUMP MACHINE
Figure 2. Room-and-pillar mining method.
Source: Ref. 24.
SECTION A-A1
PLAN
SURFACE
,////////,,,,,
^ADINGf^
ii OPEN STOPE
.BENCH
SECTION B-B1
Figure 3. Open stope mining method.
Source: Ref. 24.
15
-------
-Whereas in level to moderately pitched veins the room-and-
pillar method is the basic approach, for the more steeply pitched
veins hand-held jet nozzles, jet cars, and water cannons are
normally used.
In hydraulic mining, higher pressure through the nozzle
lessens the amount of water required to maintain the same produc-
tion rate. New Units are being developed that use short bursts
of water in a pulsating action. Several such units can be
mounted on a crawler chassis.
Stoping—
in open-stope mining, small ore bodies are mined out com-
pletely, leaving no pillar of ore in place to support the walls
of the stope. In some varieties of rock it is possible to mine
out huge stopes, which may remain open for years (Figure 3).
When the ore being mined is of low grade, some of the ore body is
left in place as random pillars to support the walls. Sometimes
the pillars are "robbed" just before abandoning a portion of the
mine so the collapse of the stope/walls will not affect the
operation.
Sometimes narrow veins can be mined by the stoping method by
placing an occasional wooden beam across from one end of the
stope to another to support the vein walls. This is called stull
stoping (Figure 4).
Shrinkage -stoping (Figure 5) refers to stoping the ore
deposit from beneath and allowing the broken ore to support the
stope walls, a method mostly used in steeply dipping vein de-
posits where the walls and mineral body require little or no
support. Space is left above the broken ore so that a miner can
stand and drill overhead. The broken ore is drawn off as needed
to maintain the headroom needed for drilling. After the stoping
is completed, all the broken ore is removed and the walls are
allowed to collapse.
Other variations of stoping include cut-and-fill stoping
(used in wider, irregular ore bodies), rill stoping, hydraulic
filling, and square-set stoping (24).
Block Caving—
The block caving method is used to mine large ore bodies
over which barren or low-grade capping is too thick to strip away
from the surface. Mining is accomplished by making a series of
evenly spaced crosscuts below the bottom of the ore to be caved,
from which raises are driven up to the ore. Then the entire ore
body is undercut so that it will slowly cave into the raises
(Figure 6). The weight of the ore provides enough force to break
it up and move it downward, where it is drawn from beneath,
16
-------
8m
STORE SUBDRIFT
ELEVATION
LACED MANWAYS
AND CHUTES
RAISE CUMBER
v , CUT OUT
SUNSHINE MINE
ALIMAK RAISING
VEIN
Figure 4. Stull stoping.
Source: Ref. 26.
17
-------
]MMmmmm&
iMiwHiiM* (iw'Alw
Figure 5. Shrinkage stoping.
Source: Ref. 24.
SURFACE
ALL ORE WITHDRAWN
Figure 6. Block caving underground
Source: Ref. 24.
18
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trammed to the shaft, and hoisted or hauled to the surface. As
the broken ore is removed, the overburden will eventually descend
until fragments of it come up from the raises, indicating that
the ore body is mined out. This type of mining often leaves
behind a surface depression because of the sinking overburden
material. In mines containing pyrite and located in areas of
sufficient precipitation to produce surface runoff, these de-
pressions become a source of recharge for production of acid mine
drainage, which must be collected, pumped, and treated during
both mining and post-mining operations. Treatment of the acidic
drainage is required for an indefinite (usually long) period of
time.
Surface Mining
A surface mine is an open-air operation for extraction of
metallic or nonmetallic minerals. Deposits recovered by this
method may be in any rock type and are usually less than 150
meters deep, so that overburden removal is not prohibitively
expensive (23). Minerals that are surface-mined are coal,
copper, iron and aluminum ores; placer deposits of gold, tin, and
platinum; and sand, gravel, stone, gypsum, and clays. Very large
and efficient earth-moving machinery and auxiliary equipment
recently developed make it possible to recover many ore deposits
that could not be economically mined underground.
In general, a surface mine operation includes removing the
overburden material covering the deposit, removing the mineral
being recovered, and subsequently transporting the mineral to
beneficiation processing operations. The following subsections
cover specific types of surface mining.
Open-Pit Mines and Quarries--
Both of these surface mining methods involve open-air exca-
vations. Open-pit mining refers to the extraction of metallic
ores (Figure 7). Quarrying refers to the extraction of non-
metallic ores and construction materials.
Metallic minerals mined by open-pit methods include copper
(porphyry) ores, iron ores (hematite and taconite), beryllium ore
(bertrandite), mercury ore (cinnabar), aluminum (bauxite) ores,
and to a lesser extent ores containing antimony, magnesium rare-
earth metals, vanadium, and zinc. Nonmetallic minerals and
construction materials that are quarried include sand and gravel,
dimension stone, gypsum, clays, asphaltic materials, limestone,
and asbestos.
The methodology of mineral extraction is essentially identi-
cal in open pits and quarries except that open pits normally are
much deeper and require larger equipment.
19
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TOO DEEPLY BURIED UNDER
WASTE TO BE STRIPPED AND MINED
Figure 7. Open-pit mining.
Source: Ref. 24.
SOIL
Figure 9. Glory hole mining.
Source: Ref. 24.
20
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Glory Holing—
A glory hole (Figure 8) is an open pit from which ore is
excavated so that it falls by gravity into a raise (inclined or
vertical shaft). The raise leads to an underground conveying
system that transports the ore to the surface. This mining
technique is applied to deposits that could also be mined by
open-pit methods or to ore deposits that are narrow and nearly
vertical. Both metallic and nonmetallic minerals can be re-
covered by glory holing.
Strip Mining—
In a strip mine, overburden is removed, frequently in great
quantity, to expose a coal bed for extraction. Because coal
mining is not included within the scope of this report, strip
mining procedures are not discussed.
Placer Mining—
Placer mining involves the recovery of a placer deposit,
which consists of alluvial or glacial minerals. Placer deposits
are concentrations of heavy minerals in detrital (loosely packed)
materials. The desired ores have been selectively settled in
running water because of their high specific gravity. Gold, tin,
platinum, diamonds, and various industrial metallic minerals such
as zircon (ZrSi04), ilmenite (FeTi03), and rutile (Ti02) are
recovered by placer mining techniques. No diamond deposits are
worked in the United States. Industrial metallic minerals are
recovered by dredging, a type of placer mining covered separately
in this Section of the report.
Panning, suction dredging, sluicing, and "hydraulicking" are
the primary placer mining methods for recovering gold, tin, and
platinum deposits and other low concentration ores. These
methods are described briefly.
Panning and sluicing--Panning, the legendary method of gold
mining, involves filling a pan with creek or river-bottom gravel
and swirling it in water with sufficient force to wash away the
lighter detrital material and leave behind the heavier gold.
Most surface deposits rich enough to be mined and concentrated by
this method were exhausted long ago (24).
Sluicing is a method whereby ore and surrounding gravel are
shoveled into an inclined sluice box; the heavy ore is trapped on
small ridges along the water's path as the lighter gravel is
washed on down the incline. Few unmined deposits remain in the
United States where sluicing is economically feasible (24).
Hydraulic mining—The basic technique of surface "hydrau-
licking" is identical to hydraulic underground mining described
earlier.
21
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In surface hydraulic mining, the high-pressure water stream
is directed against the base of the placer gravel bank to disin-
tegrate the deposit. The broken material is washed to and
through sluice boxes situated in convenient positions down slope.
Many Western States have passed laws closely regulating hydraulic
mining because it eventually disturbs a large surface area and
land restoration is somewhat difficult (24).
Dredging
Dredging is a type of placer mining (a subcategory of sur-
face mining) that involves the underwater extraction of minerals
from placer deposits (alluvial or glacial deposits of sand and
gravel containing particles of valuable minerals) (23). The
deposits dredged are usually low-grade and lie near the surface.
They are large in both a real extent and thickness. Minerals
obtained by this method include placer deposits of gold,
titanium, sand and gravel, and rare earths. (See Tables 3 and 4
for a complete listing.) Dredging operations may be conducted on
public waterways (e.g. streams, lakes, rivers, estuaries) or in
areas adjacent to public waterways that have been cleared,
excavated, and flooded.
A classical dredge is basically a continuous digging machine
that excavates large volumes of bottom deposits and transports
them to the surface for beneficiation. Dredges can remove
material from 3.7 to 30.5 meters below the surface of the water
and have successfully removed material from a depth of 49 meters
(23). Capacities of different types of dredges vary. Suction-
type dredges, for example, are capable of extracting 272 to 454
megagrams of material per hour (27). Once the ore has been
transported to the surface- it can be partially or completely
processed on board the dredge. At some operations, only initial
waste/raw material separation takes place on board, and most of
the beneficiation occurs at a land-based facility (25).
A variety of dredges are being used in the mineral mining
industry. Factors that influence selection of the type and size
of dredge include clay content of the deposit, particle size of
the material being extracted, and the amount of water available
to float the dredge. The two basic categories of dredges in use
today are mechanical and hydraulic. Various types within these
categories are illustrated in Figure 9 and described in the
following- paragraphs.
Mechanical Dredges—
Grapple dredge—This type of dredge consists of a clamshell
bucket suspended from a derrick mounted on a barge. Clamshell
dredges are most suitable for excavating medium-soft materials in
confined areas near docks and breakwaters. Little waste material
is discharged back into the body of water being dredged because
22
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MECHANICAL
THE GRAPPLE DREDGE
THE DIPPER DREDGE
HYDRAULIC
THE PLAIN SUCTION DREDGE
THE CUTTERHEAD PIPELINE DREDGE
THE BUCKET DREDGE
Figure 9. Types of dredges used in excavation.
Source: Ref. 28.
23
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all the raw material is transported on the barge to a land-based
processing facility (27). Excess water and fines leave the barge
while on the river.
Dipper dredge—This dredge has a powerful bucket mounted at
the forward end, which gives the dipper its main advantage, a
strong "crowding action" produced as the bucket is forced into
material being moved (28). This dredge provides efficient re-
moval of rock and other hard materials. The dipper's ability to
handle larger rock reduces the need for blasting.
Bucket dredge—The bucket dredge, commonly referred to as
the bucket-line or bucket-ladder dredge, consists of a series of
buckets mounted on an endless closed-loop chain. Each bucket
digs, conveys-, and dumps its own load. This dredge is very
efficient and operates at the lowest unit cost in mining placer
deposits that principally lie below the water level. Minerals
excavated by bucket-line dredges are usually processed on board.
Tailings are discarded back to the water, and the product is
loaded onto barges and hauled away.
Two principal types of bucket dredges are used. One has an
inclined belt-conveyor stacker to discharge the coarse fraction
of washed tailings well astern of the haul, and sluices to dis-
charge the sand fraction a short distance astern. The other has
only sluices for stern discharge of tailings. Bucket dredges are
used for mining gold, tin, heavy industrial minerals (e.g.,
titanium, rare earths, zirconium), and sand and gravel (23).
Hydraulic Dredges—
Hydraulic dredges are designed for excavating materials
lying under the water and transporting the solids in a pulp or
slurry through a continuous system to a point of discharge (23).
The pulp or slurry may be discharged into hoppers on board or
into barges moored alongside or sent via a floating pipeline to a
point ashore, to a treatment plant on board, or to one on a barge
moored nearby. The hydraulic excavating system can be mounted on
a barge, with or without propulsion, or on a self-propelled ship.
It can be designed for operation in inland waters, protected
coastal waters, or open seas. The two principal classifications
of hydraulic dredges, based on method of imparting energy to the
pulp, are pump dredges and air-jet or water-jet lift dredges.
The dredges are additionally categorized by the manner in which
material is dislodged and excavated from the bottom deposit:
plain suction dredge and cutterhead dredge. The plain suction
type consists of a suction pipe that is lowered to the surface of
the deposit to be worked and a powerful pump that draws up the
material mixed with water and discharges it through a pipeline
(25). These units are used for digging soft deposits that con-
tain no large boulders. The cutterhead dredge works on the same
24
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principle but is equipped with a powerful rotating cutter that
loosens the material, which is then sucked through the dredging
pump (25). These dredges are capable of digging all types of
alluvial materials, as well as clay, hardpan, and other compacted
deposits.
Portable suction dredges—Portable suction dredges are
vacuum cleaner-like pipes or sluicera that operate on small
floating rafts or barges anchored in a stream channel. The
suction hose is operated on the river bottom by a scuba diver who
selectively vacuums gold-laden sediments from the river bottom.
The gold is separated on the raft by gravitational methods.
Suction dredges are common on the streams of the northwestern
United States.
BENEFICIATION
After ores are mined or dredged, they usually must be
crushed, classified, concentrated .and dried. Although all ores
dp not require such extensive beneficiation, a general flow
diagram of .the beneficiation process for nonferrous ores and
construction materials is shown in Figure 10. Most of the pro-
cesses shown are conducted at one site. Some size reduction
takes place in blasting and mining the ore for transport, and in
some underground operations primary crushing occurs below ground;
however, for the most part beneficiation can be viewed as an
operation usually composed of six major steps: size reduction,
screening, classification, concentration, dewatering, and thermal
drying. All beneficiation processes involve at least one .of
these major steps.
Most ores must first be reduced in size. In some under-
ground mines size reduction is necessary before the ore can be
transported to the surface. Size reduction (or comminution) of
minerals is necessary either to separate desirable material from
undesirable material (gangue) or to increase the surface area of
the ore for further processing.
The four classifications within size reduction are primary
crushing, secondary crushing, dry grinding, and wet grinding. A
conventional pulverizing plant usually consists of one or more
primary crushers, secondary crushers, and fine grinders.
Size reduction is initiated on run-of-mine ore in the pri-
mary crushing stage. The most common primary crusher in current
use is the jaw crusher. Since primary crushers handle the
largest particles, they must be capable of exerting the greatest
force. The mechanical stress applied to a rock to strain it
beyond its breaking point may be either compression or impact
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stress. These differ in the duration of time needed to apply the
breaking force. In impacting, the breaking force is applied
almost instantaneously, whereas in compression, the rock particle
is slowly squeezed and forced to fracture. All crushers use both
compression and impaction of various degrees. In primary crush-
ing some reduction also occurs by attrition, the rubbing of stone
on stone or metal surfaces. Crushers are usually loaded gradu-
ally between nonparallel crushing surfaces, except occasionally
when impact breakers and roll crushers are used in the primary
stage (23). Primary crushers are typically charged by means of a
receiving hopper. At large mines, more than one hopper or dump
bin may serve separate primary crushers placed in parallel.
Depending on the ultimate size requirements of the product, the
material from the primary crushers may be screened, with the
undersize going directly to the screening plant and the oversize
to secondary crushing, or all of the material may be routed to
the secondary crushers.
Secondary crushers take all or a portion of the crushed
material from the primary crushers and further reduce it. This
may be the final comminution process or only an intermediate
step. The term "secondary crushing" does not refer to the size
of either the crusher or the crushed ore but only the sequence in
which the crushing occurs. Generally, however, the average
diameter of the feed is unlikely to exceed 12 centimeters, and
the product usually has a top size range from 2.5 to 3.5 centi-
meters. Tonnage capacity of the secondary crusher need not match
that of the primary unit; in most cases it is substantially less
because screening is a common practice between the primary and
secondary stages (23).
Grinding, which can be either wet or dry, reduces the ore to
the optimum size for further treatment. Unlike the equipment
used in primary and secondary crushing, grinders do not reduce
product to a maximum size, a sizing apparatus such as a mechan-
ical classifier or a cyclone must be used to limit the maximum
size of the discharge. Oversized particles are then recycled
through the grinder. Creation of a wet pulp or suspension in a
ball, rod, or pebble mill operation has definite advantages when
concentrating or extractive steps are conducted in the same
environment as the grinding. It aids the longitudinal flow
through the mill, has a cushioning effect on the tumbling bodies
in the grinding, controls dust, and facilitates the addition of
chemical reagents for futher processing (23).
Solids are usually separated according to size to obtain
maximum production from the crushing and grinding equipment.
Commercial crushing and grinding always produces a distribution
of sizes, irrespective of the characteristics of the feed. This
characteristic of the crushing and grinding units requires that
27
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screening and classification be used in almost all beneficiation
processes.
The several screening devices available are classified as
stationary, mechanical, high-speed mechanical, and electrically
vibrated. The trend is from stationary grizzles to vibrating,
multideck, mechanical screens on which deck motions can be
straight-line, circular, or elliptical. High speed mechanical
screens are widely used for separations of 4-mesh and finer.
Electrically vibrated machines are used for separations of 8-mesh
and finer (29).
Wet screening is used extensively for mineral processing.
Using a wet slurry can increase the amount of material that is
made to pass through a unit area of screen surface. Depending on
the size of the screened particle, this capacity can be increased
by from 25 to 350 percent (29).
Mechanical classifiers or cyclones frequently are used for
size separation of fine particulate matter. Water is the sus-
pending medium with mechanical classifiers, and either water or
air with cyclones. With both types of units, the separation size
is based on the relative velocity with which a particle moves
through the suspending medium.
Mechanical classifiers consist primarily of .rake or spiral
types. Larger particles settle out in a settling tank and are
then removed by either a mechanical rake or a spiral.
As a sizing device, the hydroclone generally is preferred
over the mechanical classifier because it takes less floor space
and costs less. The hydroclone usually operates at pressures
exceeding 34.5 kilo pascals and converts this energy into rota-
tional fluid-solid motion. Consequently, particles are separated
according to their mass. The centrifugal force acting on the
particles in a hydroclone is much greater than the normal gravi-
tational force responsible for sedimentation in the mechanical
classifier (29).
Concentration is used primarily in the beneficiation of
nonferrous metals rather than construction materials. Deposits
normally consist of mixtures of various minerals. To become
usable these minerals must be separated from the unwanted gangue.
Various concentration methods for this purpose include flotation,
gravity concentration, magnetic separation, electrostatic separa-
tion, extractive metallurgy (pyrometallurgy, hydrometallurgy,
electrometallurgy), and agglomeration.
Froth flotation is used most widely to beneficiate complex
and low-grade ores. Flotation is a complex physicochemical
28
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process that takes place in an ore pulped with water, by which
the surfaces of one or more minerals in the pulp are made water-
repellent and the minerals attach themselves to air bubbles.
When the mineral-laden bubbles (froth) rise to the surface they
.are skimmed off and sent to further concentration steps. Collec-
tors are used to selectively coat the surfaces of the minerals to
be floated with a water-repellent surface. Activators, pH con-
trollers, depressants, and dispersants are used to make the
collectors selective under a given set of physical conditions.
By changing any of these conditions (such as pH) a sequential
series of flotations may be obtained from a given pulp. Frothers
are also used to keep the air bubbles, intact so that the floated
minerals will remain on the surface for removal (23).
Gravity concentration separates solids of different specific
gravities in a fluid medium, usually water or air, but sometimes
a heavy medium is used. Mineral mixtures susceptible to separa-
tion by gravity methods are those in which valuable minerals and
gangue differ appreciably in specific gravity. For simple
methods, a specific gravity differential of at least 1.5 is
desirable. Methods of gravity concentration include the simple
sluice, pinched sluice, Humphrey's spiral, sink-float mechanism,
jig, shaking table, and various dry concentration methods (23).
Magnetic separation sorts one solid from another by means of
a magnetic field. This method is based on the principle that
particles placed in a magnetic field are either attracted or
repelled by it. The only important highly magnetic mineral is
magnetite. Many other minerals are measurably susceptible to
magnetic action but fewer than 20 are amenable to magnetic sep-
aration, and these are classed as weakly magnetic. Magnets are
also used to remove tramp iron from an ore feed (23).
Electrostatic separation of mineral grains is an integral
part of the treatment of beach sands. Dry particles subjected to
a surface electrical charge, on or before entering an electro-
static field, behave in accordance with their ability to conduct
electricity. Conductive particles are repelled by the active
electrode emitting the charge. Different minerals become charged
to different degrees and are separated on this basis. Electro-
static separation is used to recover ilmenite, rutile, and zircon
from beach sands and to remove feldspar and mica from quartz
(23).
Extractive metallurgy is used to alter chemically the min-
eral constituents of an ore to facilitate their separation from
the gangue. The three categories of extractive metallurgy are
pyrometallurgy, hydr©metallurgy, and electrometallurgy. Pyro-
metallurgy involves operations that use refractory furnaces and
high temperatures created by electrical energy or by burning
29
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fuels to produce refined metals from ores and concentrates. The
major processes include drying, roasting, sintering, distilling,
smelting, and fire refining (23). These techniques are generally
considered final metal refining processes rather than part of
beneficiation. The electrometallurgy process uses electric
current to recover metals. The two basic types of electrometal-
lurgy are categorized on the basis of depending on how the elec-
tric current is used. If it is used as a source of heat, the
process is referred to as electrothermic. If the electric
current is used to transport metal ions from anodes and/or elec-
trolytes for deposition on cathodes, it is referred to as elec-
trolytic processing (23). Electrometallurgy, like pyrometallur-
gy, is considered more a final purification operation than a
beneficiation process.
The final extractive metallurgical operation to be con-
sidered is hydrometallurgy, which involves the recovery of metals
from ore and concentrates by selective dissolution. The pro-
cesses involved in hydrometallurgy include preparation of the
feed, leaching, separation of the metal-bearing solution from the
leach residue, and purification of the solution following metal
recovery (23). Leaching, which is considered a beneficiation
process, is the main process of concern in this report.
Leaching refers to dissolving away of gangue or metal values
in aqueous acids or bases, liquid metals, or other special solu-
tions (29). The leaching solutions may be either*strong general
solvents (e.g. sulfuric acid) or weaker specific solvents (e.g.
calcium). The specific solvents will attack only one or a few
ore constituents whereas the general ones will attack a number of
constituents. The action of solvents can be enhanced by heating,
agitating, or applying pressure. Leaching can be accomplished by
a variety of techniques. In-vat leaching takes place in a con-
tainer, which may or may not be equipped for heating, agitating,
or pressurizing. Leaching that takes place in the ore body is
referred to as in situ leaching. The solvent is introduced into
the ore body by pumping or percolation through overburden. Heap
or dump leaching involves the leaching of stored tailings or ore
on a surface that has been lined with an impervious material
(clay or plastic sheeting). In this technique the solvent is
sprinkled over the heap and the leached material is collected in
furrows or troughs. Metals covered in this report that require
some recovery by leaching are gold, copper, mercury, and silver.
The final concentration process considered here is agglom-
eration. Agglomeration forms masses or clusters from fine parti-
cles. The four main agglomeration processes are sintering,
pelletizing, briquetting, and modulizing. As with chemical
beneficiation, most agglomeration processes are a part of refin-
ing rather than beneficiation (23). Agglomeration is also used
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in a different sense to describe thickening of flotation tailings
by use of agglomerating agents such as polyelectrolytes.
If wet screening, classification, or concentration tech-
niques are used or if the moisture content is high in the initial
ore (as dredged material), dewatering must precede the drying
process. Mechanical dewatering removes water by means of gravity
and centrifugal forces. Thickeners also are used to increase the
concentration of solids in a slurry, whereas clarifiers are used
to remove solids from a slurry. Mechanical dewatering is accom-
plished with screens, centrifuges, and classifiers, and by sedi-
mentation, filtration, and flocculation (23).
When concentrates are dried commercially, heat is trans-
ferred by convection by direct contact between the wet solid and
hot air. The various types of thermal dryers include rotary,
flash, continuous-tray, and fluidized-bed dryers. After drying,
the mineral is generally stored for shipment (23).
As mentioned previously, not all beneficiation techniques
for mineral ores containing nonferrous metals and construction
materials require all of the processes outlined. Many construc-
tion materials require only size reduction, screening, and dry-
ing; whereas many nonferrous metals require extensive concentra-
tion steps. It is only necessary, however, to delete those steps
from the generalized flow chart that are unnecessary for a
specific mineral.
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SECTION 3
GENERAL WASTE CHARACTERISTICS AND CONTROL
Many different types of pollution problems arise from the
large volume of construction materials and nonferrous metals
mined and beneficiated in the United States. Pollutants include
fugitive particulates from drilling and blasting, spent process
water from concentrating operations, and gangue and overburden
generated as a result of ore extraction. Some of the pollutants
may be contaminated with materials considered potentially hazard-
ous. For example, fugitive emissions may contain asbestos fibers
or free silica particles, and some process wastewater may contain
various heavy metals and/or toxic reagents like cyanide. In most
cases the potential environmental effects of mining can be main-
tained at acceptable levels by the application of established
waste management practices.
This chapter describes the sources and characteristics of
air, liquid, and solid waste and the treatment and control tech-
nology typically used in the mineral mining industry to abate
waste problems. Since the characteristics of liquid wastes from
mining of construction materials and nonferrous metals are dif-
ferent, they are discussed separately.
AIR EMISSIONS AND CONTROL TECHNOLOGY
Emissions
Air pollution emissions in the mineral mining industry
consist primarily of particulates from various phases of the
mining process and from on-site beneficiation processes. Emis-
sion sources are categorized as fugitive or point sources. Table
6 lists the operations included within each category. Fugitive
emissions, for the purpose of this report, are defined as ...
"Particulate matter which escapes from a defined process flow
stream due to leakage, materials charging/handling, inadequate
operational control, lack of reasonably available control tech-
nology, transfer of storage" (25). Process point emissions are
those emitted from a definable point, such as a stack.
Factors Affecting Fugitive and Process Emissions--
Emissions common to most mining and beneficiation operations
are affected by the moisture content of the ore, the type of ore,
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the amount processed, the type of equipment, operating practices
and a variety of geographical and seasonal factors. These fac-
tors, discussed in more detail below, apply to both fugitive and
process sources and usually combine to determine the total emis-
sion problem of a facility.
TABLE 6. FUGITIVE AND PROCESS POINT EMISSION SOURCES
Fugitive sources
Process point sources
Drilling
Blasting
Loading and hauling
Stock and waste piles
Overburden removal3
Mine roads
Wind erosion of unprotected
surfaces
Land reclamation
Crushing and grinding
Screening
Conveying
Drying
a Applicable only to surface mines.
The inherent moisture content of the ore processed has a
substantial impact on total uncontrolled emissions especially
during mining, material handling, and initial plant process
operations such as primary crushing. Surface wetness causes fine
particles to agglomerate or to adhere to larger particles with a
concomitant dust suppression effect. As new fine particles are
created by crushing and attrition and moisture content is reduced
by evaporation, this suppressive effect diminishes and may even
disappear.
The type of ore processed is also significant. Soft ores
produce a higher percentage of screenings than • hard minerals
because of a greater tendency to crumble and a lower resistance
to fracture. Thus, the processing of soft rocks produces a
greater potential for emissions than the processing of hard rock.
The type of ore also governs the hazardous constituents contained
in particulate emissions. For example, particulates from some
talc and sand and gravel processing are known to contain asbestos
and free silica, respectively.
33
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Equipment types and operating practices also affect uncon-
trolled emissions. Equipment selection is based on parameters
such as quarry characteristics, minerals processed, and desired
end products. Emissions from process equipment such as crushers,
screens, and conveyors, are generally a function of the amount of
material processed, its size distribution, and the amount of
mechanically induced velocity applied. The crushing mechanism
(compression or impact) of the crushers also affects emissions.
Climate is the most significant geographical factor affect-
ing uncontrolled particulate emissions. The wind velocity, wind
direction, amount and intensity of precipitation, and relative
humidity can affect emissions significantly, especially fugitive
emissions. For example, the level of emissions can be expected
to be greater in arid regions than in temperate ones. Other
geographical elements that affect fugitive emissions include the
topography and the extent and type of vegetation around a facil-
ity.
Seasonal changes affect emissions in several ways. For
instance, the lower moisture content of the ore and high evapora-
tion rate during the summer months cause uncontrolled emissions
to be higher than at other times of the year. Shutdown of many
operations during the winter months also affects total annual
emissions. ,
Fugitive Emissions—
Fugitive dust constitutes a large portion of the emission
problem in the nonmetallic mineral industry. Drilling, blasting,
loading, hauling, dumping, storage piles, waste piles, overburden
removal, wind erosion of unprotected surfaces, and land reclama-
tion activities all contribute fugitive dust.
Particulate emissions from drilling operations are caused
primarily by air flushing the bottom of the hole to remove cut-
tings and dust. Compressed air is released down the hollow drill
center, forcing cuttings and dust up and out the annular space
formed between the hole wall and drill.
Emissions from blasting are inherently unavoidable. Factors
affecting emissions include the size of the shot, blasting pro-
cedures, rock type, and meteorological conditions, especially
wind.
Considerable fugitive dust emissions may result from loading
and hauling operations. Emissions emanate from load gathering,
loading operations, vehicular transport over the unpaved roads
associated with mining operations, and air motion across the load
during hauling. The most significant factor affecting emissions
during loading is the wetness of the ore. Factors affecting
34
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emissions from hauling operations are type of road surface,
wetness of the surface, and volume and speed of vehicle traffic.
Truck dumping generates dust as the material tumbles from
the truck bed and strikes the ground or the side of the receiving
hopper. Dust emissions may also occur at the edge of a spoils
slope when a truck dumps waste material or overburden. This
simple operation has been identified as a significant fugitive
dust source (30, 31).
Fugitive dust emissions from the storage area occur as a
result of several activities, which include, in order of de-
creasing significance, equipment and vehicle movement in the
storage area, wind erosion, loadout from the storage piles, and
loading onto the storage piles. The emissions from waste and
tailings piles are similar in mineralized identity to those from
primary storage piles, but because the particles are finer they
travel further.
Fugitive emissions associated with reclamation operations
result from wind erosion of unvegetated or partially vegetated
land. These emissions are related to wind speed, surface tex-
ture, and degree of vegetation cover (if any).
Emission factors for various phases of mining and process
operations are presented in subsequent sections of this report
covering individual minerals.
Process Emissions—
Although emissions from process point sources are signi-
ficant, they are easily controlled because the processes are
primarily stationary and the emissions emanate from a defined
point. Sources include crushing, grinding, screening, conveying,
and drying.
Generation of particulate emissions is inherent in the
crushing process. Emissions are most apparent at crusher or
grinder feed and discharge points. Factors that influence emis-
sions include the moisture content of the rock, the type of rock
processed, and the type of crusher used.
The most important element affecting emissions from crushing
and grinding equipment is whether the reduction mechanism is
compression or impact. This has a substantial effect on the size
reduction achieved, the particle size distribution of the product
(especially the proportion of fines produced), and the amount of
mechanically induced energy imparted to these fines.
Dust emitted from screening operations results from agita-
tion of dry rock particles. The level of uncontrolled emissions
35
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is dependent on the particle size of the material screened, the
amount of mechanically induced energy transmitted, and other
factors discussed earlier.
Generally, screening of fines produces higher emissions than
screening of coarse sizes. Also, screens agitated at large
amplitudes and high frequencies emit more dust than those oper-
ated at lesser amplitudes and frequencies.
Particulate emissions can occur in all material handling and
transfer operations. As with screening, the level of uncon-
trolled emissions depends on the size of the material and how
much it is agitated. The most emissions probably occur at con-
veyor belt transfer points where material is discharged from the
conveyor at the head pulley or received at the tail pulley. The
conveyor belt speed and the free-fall distance between transfer
points affect the volume of emissions from these sources.
Emission Control Technology
The diverse particulate emission sources in mining and
processing operations have resulted in the application of a
variety of control methods and techniques. Dust suppression
techniques for preventing particulate matter from becoming air-
borne are used to control both fugitive and process dust sources.
Collection systems are used to control particulate emissions that
can be contained and captured. _.
Control of Fugitive Dust Sources—
Almost all fugitive dust controls involve one (or a com-
bination) of three basic techniques: watering, chemical stabili-
zation, and reduction of surface wind speed across exposed sur-
faces. Watering costs the least but also provides the least
permanent dust control. Depending on the source of the dust,
water may effectively suppress the dust for only a few hours or
for several days. A film of moisture creates a direct cohesive
force that holds surface particles together; it also forms a thin
surface crust that is more compact and mechanically stable than
the material below and therefore less subject to producing dust
after drying. Since this crust and its dust-reducing capability
are easily destroyed by movement over the surface or by abrasion
from loose particles blown across the surface, repeated watering
is required to maintain the moisture film or surface crust.
Several types of chemicals are effective fugitive dust
reducers. These are applied directly to the surface of the dust
source. Some of the materials can "heal" (re-encrust) if the
treated surface is disturbed, but many will not reform a crust.
The effect of natural weathering on the life of the treated
surface also varies widely with different chemicals. The primary
36
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use of chemical stabilizers in the mining industry is for land
reclamation after the mining potential of an area has been ex-
hausted; however, chemicals may also be applied to piles of
overburden, waste, and tailings.
Air movement, or wind, contributes significantly to the
incidence of fugitive dust from all sources, thus the reduction
of wind speed across the source is a means of reducing emissions.
Construction of windbreaks and enclosures or coverings for the
sources, and the planting of grasses or grains on or adjacent to
the exposed surfaces are some methods of reducing wind speed. If
vegetative techniques are applied, the soil must provide nutri-
ents moisture, and proper texture, and must be free of materials
toxic to plant life.
The following paragraphs discuss in more detail how one or
more of the foregoing techniques control fugitive dust.
Control of drilling operations—The two methods generally
available for controlling particulate emissions from drilling
operations are water injection and aspiration to a control de-
vice.
Water injection is a wet drilling technique in which water
or water plus a wetting agent or surfactant is injected into the
compressed air stream used for flushing the drill cuttings from
the hole. The injection of the fluid into the airstream produces
a mist that dampens the ore particles and causes them to agglom-
erate. As the particles are blown from the hole, they drop at
the drill collar as damp pellets rather than becoming airborne.
The addition of a wetting agent increases the wetting ability of
water by reducing its surface tension (32).
Dry collection systems also may be used to coritrol emissions
from the drilling process. A shroud or hood encloses the drill
rod at the hole collar. Emissions are captured under vacuum and
vented through a flexible duct to a control device for collec-
tion. The most commonly used are cyclones or fabric filters
preceded by a settling chamber. In this application collection
efficiencies of cyclone collectors are usually not high. They
are more suitable for coarse-to-medium-sized particles than for
fine particulates. Fabric filter collectors, on the other hand,
exhibit collection efficiencies in excess of 99 percent.
Control of blasting operations—No effective methods are
currently available for controlling particulate emissions from
blasting. Good blasting practices, however, can minimize noise,
vibration, air shock, and dust emissions. Multidelay detonation
devices that detonate the explosive charges in millisecond time
intervals may reduce these adverse effects. Scheduling of blast-
ing operations to coincide with such favorable meteorological
37
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conditions as low wind speed and low inversion potential can
substantially reduce the impact of emissions from blasting.
Control of loading operations—The loading of dry raw mate-
rials generates fugitive dust emissions regardless of the method.
Limited control may be attained by wetting the materials before
loading. Water trucks equipped with hoses or movable watering
systems may be used.
Control of hauling operations—The hauling of raw materials
from the mine or quarry to the processing plant is responsible
for a large portion of the fugitive dust generated by the indus-
try. Temporary haul roads are built to accommodate advancing
quarry faces, and they are usually unimproved. The movement of
large, rubber-tired vehicles over these roads is a major source
of dust. The amount of these emissions relates directly to the
condition of the road surface and the volume and speed of vehicle
traffic. Consequently, control measures involve improving road
surfaces, supressing dust, and changing operations to minimize
the effect of vehicle traffic.
Various road treatment methods to control fugitive emissions
from haulage roads include watering, surface treatment with
chemical dust suppressants, soil stabilization, and paving.
Watering is the most common. Water is sprayed onto the road by
water trucks equipped with either gravity spray bars or pressure
sprays. The amount of water required, frequency of application,
and effectiveness depend on weather elements, road bed condition
and the willingness of the operator to allocate the necessary
resources to do an effective job.
Road dust can also be suppressed by periodically applying
wet or dry surface-treatment chemicals. Oiling is the most
common surface treatment. The frequency of application may range
from once a week to only several times a season, depending on
weather conditions. A potential adverse environmental impact of
this treatment is the floating away of the oil into streams or
percolation into aquifers. Oiling is sometimes supplemented by
watering; however, care must be exercised with this approach
since improper application can cause slippery, dangerous road
conditions.
Other treatments include the application of hygroscopic
chemicals (substances that absorb moisture from the air) such as
organic sulfonates and calcium chloride. When spread directly
over unpaved road surfaces, these chemicals dissolve in the
moisture they absorb and form a clear liquid that is resistant to
evaporation. Consequently, these chemicals are most effective in
areas with relatively high humidity. Since the chemicals are
water soluble, repeated application may be required in areas with
38
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frequent rainfall. Also these agents can contribute to corrosion
of expensive haulage vehicles.
Other alternatives include the following:
1. Soil stabilizers—These agents, which usually consist
of a water-dilutable emulsion of either synthetic or
petroleum resins and act as an adhesive or binder, are
applied once daily to the road surface. In addition to
being environmentally beneficial, these stabilizers
offer considerable savings and operating benefits over
traditional watering methods. Operators report reduced
labor costs, lower maintenance costs on haulage ve-
hicles, and safer road conditions.
2. Paving--Although it is probably the most effective
means of reducing particulate emissions, paving entails
high initial cost and requires subsequent maintenance
and repair of damage caused by heavy vehicle traffic.
3. Control of traffic speed and reduction of volume--
Replacing smaller haulage vehicles with units of larger
capacity would reduce the number of trips required and
the total emissions per ton of rock hauled. A
stringent program to control traffic speed also would
reduce dust emissions. According to a study on emis-
sions from conventional vehicle traffic on- unpaved
roads, reducing the average speed from 48 kilometers
per hour (for which an emission level of 1.0 kilogram
per vehicle kilometer was established) to 40, 32, and
24 kilometers per hour resulted in emission reductions
of 25, 33, and 40 percent, respectively (33). Although
the situations may not be completely analogous, it can
be concluded that an enforced speed limit of 8 to 16
kilometers per hour would substantially reduce fugitive
dust emissions from quarry vehicle traffic and provide
the additional benefits of increased safety and longer
vehicle life.
4. Wind breaks—Planting of rapidly growing hedges or
construction of temporary wooden walls upwind of major
dust sources can reduce emissions by limiting the
movement of air across the dust-laden surfaces.
Control of aggregate storage piles—Aggregate stockpiles are
a significant source of fugitive dust. Emissions occur during
creation of stockpiles and from wind erosion of formed piles.
During the construction of stockpiles by stacking conveyors,
particulate emissions are generated by wind blowing across a.
39
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stream of falling material and causing the segregation of fine
from coarse particles, and from the impact of falling aggregate
on the pile. Control methods include wet dust suppression and
devices designed to minimize the free-fall distance and thus
reduce both exposure to wind and force of impact.
Control devices include stone ladders, telescoping chutes,
and hinged-boom stacker conveyors. A stone ladder consists
simply of a section of vertical pipe into which material from the
stacking conveyor is discharged. The pipe has square or rec-
tangular openings at different levels through which the material
may flow. In the telescoping chute, material is discharged to a
retractable chute and falls freely to the top of the pile. As
the height of the stockpile increases or decreases, the chute is
gradually raised or lowered accordingly. A similar device, the
stacker conveyor, is equipped with an adjustable hinged boom to
raise or lower the conveyor according to the height of the stock-
pile.
An alternative is to install water sprays at the stacking
conveyor discharge pulley to wet the product. A pug mill can be
used to eliminate particulate emissions from very fine products
like stone sand by mixing the product with water before stock-
piling. Finely ground material that cannot be wetted should be
stored in silos until shipped.
Application of water is the technique most commonly used for
controlling windblown emissions from active stockpiles. A water
truck equipped with a hose or other spray device applies the
water.
The location of stockpiles behind natural or manufactured
wind breaks helps to reduce windblown dust. Also, active piles
should be worked from the leeward side. Even though they may
create load-out problems, stockpile enclosures or silos are the
only effective controls for very fine materials or materials that
must be stored dry.
Control of yard and other open areas—Fugitive dust emis-
sions from plant yard areas are generated by vehicle traffic and
wind. Generally, simply maintaining good housekeeping practices
will control emissions from these areas. Spillage and other
potential dust sources should be cleaned up. Brush-type or
vacuum-type street sweeping is effective on paved or other smooth
yard surfaces. Treating with soil stabilizers and planting
vegetation are viable control options for large open areas and
overburden piles. Many chemical stabilizers on the market pro-
vide some aid to the emergence and growth of vegetation and offer
effective control against rain and wind erosion (34).
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The application of soil stabilizers made of petroleum or
synthetic resins in emulsion is moderately effective for storage
piles that are inactive for long periods of time and for per-
manent waste piles or spoil banks. These chemical binders cause
the topmost particles to adhere to one another to form a durable
surface crust that resists wind and rain erosion as long as the
surface crust remains intact. However, wind errosion and freez-
ing and thawing can break up the surface.
Control of conveying operations—Conveying operations may
produce fugitive dust emissions in addition to the emissions
generated at transfer points. These emissions may be either
mechanically induced or windblown.
Control methods include dust suppression and covering.
Covering open conveyors is the most effective way to provide
protection from wind and prevent particles from becoming air-
borne. Covered conveyors also yield certain operating benefits.
For example, during inclement weather the covers reduce potential
mud cake buildup on belts that can result in damage to conveyors,
hazardous operating conditions, screen blinding, and the produc-
tion of products that do not meet specifications because of
retention of fines.
Control of Particulates from Process Operations-
Operations at a typical nonmetallic mineral processing plant
generates dust at many points, including the crushers, grinders,
screens, conveyor transfer points, and storage facilities.
Consequently, effective emission control is complex and diffi-
cult. Control methods include wet dust suppression, dry collec-
tion, and a combination of the two. In wet dust suppression,
moisture is. introduced into the material flow, causing fine
•particulate matter to remain with the material flow rather than
become airborne. Dry collection involves hooding and enclosing
dustproducing points and exhausting emissions to a collection
device. Combination systems apply both methods at different
stages throughout the processing plant. Housing process equip-
ment in enclosed structures is another effective means of pre-
venting atmospheric emissions. Such buildings generally must be
vented through a control device.
Wet dust suppression--Wet dust suppression systems control
dust emissions by spraying moisture in the form of water or water
plus a wetting agent at critical dust-producing points in the
process flow, causing dust particles to adhere to larger mineral
pieces or to form agglomerates too heavy to become or remain
airborne. Thus, the objective of wet dust suppression is not to
capture and remove particulates emitted from a source, but rather
to prevent their emission by moist agglomeration at all process
stages.
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Water sprays are not practical in all cases because moisture
may interfere with further processing such as screening or grind-
ing, where agglomeration cannot be tolerated. Also the capacity
of the dryers used in some of the processing steps limits the
amount of water that can be sprayed onto the raw materials.
Since water cannot be added after the materials have passed
through the drying operations, other means of dust control must
be applied then.
The unusually high surface tension (72.75 dynes per square
centimeter at 20°C) requires that 5 to 8 percent moisture (by
weight), or greater, be added to adequately suppress dust (35).
In many installations this is not acceptable because excess
moisture can cause screening surfaces to blind, which reduces
both capacity and effectiveness, or can cause the coating of
mineral surfaces, which yields a marginal product or unacceptable
product. To counteract these deficiencies, small quantities of
specially formulated wetting agents or surfactants are blended
with the water to reduce surface tension and improve wetting
efficiency, thereby minimizing the moisture necessary to suppress
dust particles. Although composition of these agents may vary,
their molecules are characteristically composed of two groups, a
hydrophobic group (usually a long-chain hydrocarbon) and a hydro-
philic group (usually a sulfate, sulfonate, hydroxide, or ethy-
lene oxide). When introduced into water, these agents reduce its
surface tension appreciably (to as low as 27 dynes per square
centimeter) (36).
One or more spray headers fitted with pressure spray nozzles
distribute the dust suppressant mixture at each treatment point
at the rate and in the configuration required to effect dust
control. Spray actuation and control are important to prevent
waste and undesirable muddiness, especially during intermittent
material flow. Spray headers at each application point normally
are equipped with an on-off controller interlocked with a sensing
mechanism, allowing sprays to operate only when material is
flowing.
Dry collection systems—Particulate emissions generated at
plant process facilities (crushers, screens, conveyor transfer
points and bins) are controlled by capturing and exhausting the
emissions to a collection device. Depending on the physical
layout of the plant, emission sources are manifolded to one
centrally located collector or to a number of strategically
placed units. Dry collection systems consist of an exhaust
system with hoods and enclosures to confine and capture emissions
and ducting and fans to convey the captured emissions to a col-
lection device for particulate removal before the airstream
exhausts to the atmosphere.
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The proper design and balance of local exhaust systems,
including hooding and ducting, are required to assure that a
collection system effectively controls discharge of particulates
to the atmosphere. Process equipment should be enclosed as
completely as practicable, allowing access for routine mainte-
nance and inspection. Generally a minimum indraft velocity of 61
meters per minute should be maintained through all open-hood
areas (37). Proper design of hoods and enclosures minimizes
exhaust volumes required and, consequently, power consumption.
Proper hooding also minimizes the effects of cross drafts (wind)
and induced air (i.e., air placed in motion as a result of
machine movement or falling material). Good duct design dictates
that adequate conveying velocities be maintained to prevent
transported dust particles from falling out and settling in the
ducts en route to the collection device. Information on crushed
stone recommends conveying velocities for mineral particles in
the range of 1100 to 1400 meters per minute (37).
For proper dust control from process sources, hoods should
be installed at conveyor transfer points, screens, crushers,
grinders, and bagging operations. The fabric filter or baghouse
is the most effective dust collection device in the mineral
industry. Most crushing plants use mechanical shaker-type col-
lectors, which require periodic shutdown for cleaning (after four
or five hours of operation). These units normally are equipped
with cotton sateen bags and operated at an air-to-cloth ratio of
two or three to one. A cleaning cycle usually requires no more
than 2 to 3 minutes of bag shaking, which is normally actuated
automatically when the exhaust fan is turned off.
For applications where turning off the collector is imprac-
tical, continuous-cleaning fabric filters are used. Jet-pulse
units are preferred over compartmented mechanical shakers.
Jet-pulse units ordinarily use wool or synthetic felted bags for
a filtering medium and may be operated at a filtering ratio of as
high as six or ten to one. With either type of baghouse, greater
than 99 percent efficiency can be attained, even on submicron
particle sizes (38).
Other collection devices include cyclones and low-energy
scrubbers. Although these collectors demonstrate high efficien-
cies (95 to 99 percent) for coarse particles (40-micrometer and
larger), their efficiencies are poor (less the 85 percent) for
medium and fine particles (20-micrometer and smaller) (38).
High-energy scrubbers and electrostatic precipitators could
conceivably achieve results similar to that of a fabric filter,
but these methods do not appear to be used in the industry.
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LIQUID WASTES AND CONTROL TECHNOLOGY
Liquid Wastes
Liquid wastes from construction materials and non-ferrous
metals mining show one major difference: effluent from construc-
tion materials generally contain only suspended inert solids,
whereas effluents from nonferrous metals are often acidic and
contain dissolved heavy metals (29, 39).
Liquid wastes come from three major sources:
1) Mine dewatering: For many mines this is the only
source of wastewater. It is usually low in suspended
solids, but may contain dissolved minerals or metals
(29, 39).
2) Process waters; This is water used in transportation,
classification, washing, beneficiation, separation, and
processing of ores. The effluent usually contains
heavy loadings of suspended solids, and in nonferrous
metals mining, dissolved metals (39).
3) Precipitation runoff; Since mining operations require
large surface areas, precipitation constitutes a major
source of wastewater and pollutant loading. This water
also contains suspended solids such as minerals, silt,
sand, and clay, and possibly hazardous metals, depend-
ing on the type of ore mined (39).
Other major sources of water pollution primarily associated
with mining and beneficiation operations are acid mine drainage
and tailings pond leakage. Surface runoff near beneficiation and
processing facilities is another potential problem area.
Acid runoff can be produced by the leaching of precipitation
through any mine waste containing sufficient pyrite or other
sulfide. The presence of heavy metals compound the pollution
potential because at a low pH, the metals tend to dissolve in the
water (40, 41).
Solid wastes are commonly disposed of in tailings ponds.
Wastewater streams are also treated in these ponds. The super-
natant decanted from these tailings ponds contain suspended
solids and sometimes cyanide or ammonia introduced to the water
during ore processing (42).
Percolation of wastewater from impoundments may occur if
tailings ponds, settling ponds, and lagoons are not designed
properly (29).
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Construction Materials—
Liquid wastes generated by construction materials mining are
primarily from mine dewatering, ore processing, and precipitation
runoff. They usually contain only inert suspended solids.
Process water and mine dewatering are controlled and contained by
pumping or gravity flow through pipes, channels, ditches, and
ponds. Surface runoff near ore processing facilities, haul
roads, conveyors, and storage piles are a potential pollution
source also. Surface runoff is generally untreated; however,
methods used to minimize erosion control suspended solids load-
ings in the effluent (39). Usually no .further treatment is
necessary to achieve a high effluent quality from tailings ponds
if the ponds are well-designed and the water does not contain
excessive concentrations of dissolved metals or other undesirable
ions (29, 42, 43).
Relative quantities and composition of the wastewater
generated vary from one mining category to another. Chapter 4
deals specifically with wastewater characteristics.
Nonferrous Metals—
Although effluents from the mining and processing of non-
ferrous ores generally contain such hazardous metals as lead,
copper, zinc, and nickel, these materials can be controlled to
acceptable levels by established waste management practices.
Wastewater generated by such ore processing operations as con-
centration, separation, and beneficiation are generally alkaline
and often contain dissolved metal ions and process reagents,
i.e., cyanide, methanol, and ammonia. Usually these waste
streams are discharged to a tailings pond for pH control and
solids settling. The supernatant is either treated before dis-
charge or is recycled to the mill. Partially oxidized sulfur
compounds may be present in mill effluent; unless they are
stabilized in a waste treatment system, they can cause acidic
conditions miles from the point of discharge (40).
Acid mine drainage is often a problem in mining nonferrous
metals because the ores usually contain sulfur compounds. The
impact of acid mine drainage depends on whether a pyrite is
associated with the ore being mined and the control techniques
applied to minimize acid formation.
Relative quantities and composition of these wastewater
sources vary from one mining category to another. Chapters 4 and
5 of this report contain more specific information on this sub-
ject.
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Control Technology
Control of water pollution can be achieved by proper mining
and land reclaiming methods, minimizing water contamination at
the source,- and treating of effluents in well-designed and main-
tained facilities.
Control of contaminated runoff can be maintained effectively
by diking and diverting the surface flow to prevent the runoff
from higher elevated or undisturbed areas from coming in contact
with exposed surfaces, to reduce the surface flow velocity, and
to divert the contaminated runoff through sediment-detention
structures. These methods also minimize erosion (44).
The now extensive reclamation of mined-out areas not only
has aesthetic value but also reduces water pollution potential.
Sometimes the land is landscaped and revegetated; at other times
recreational lakes are developed from abandoned open-pit mines.
Other reclamation alternatives are physical-chemical soil stabi-
lization and soil amelioration (43).
The most common method of treating process wastewater is to
discharge it into the tailings pond to settle out the suspended
solids. Although discharge from the pond is usually of accept-
able quality to recycle or discharge, secondary treatment could
be necessary. Secondary treatment methods include clarifiers,
aerators, thickeners, and liming, which are installed for tail-
ings pond supernatant and/or process wastewaters. When the
effluent must be of high quality, it can be treated further by
ion exchange or reverse osmosis to remove dissolved metals.
Construction Materials—
Treatment and control of wastewaters generated from the
mining and milling of construction materials are normally not as
critical or complex as for nonferrous metals. Many mines have
only mine dewatering discharge. Discharges from tailings dis-
posal areas are sometimes a problem because of decreased resi-
dence time during high-flow periods. Chemical flocculation,
thickeners, clarifiers, centrifuges, and other suspended solids
removal techniques are rarely used (39).
The following are wastewater treatment methods for construc-
tion materials:
Settling ponds—Settling ponds are widely used to remove
total suspended solids (TSS) because they are easier to construct
and less expensive to operate than other technologies. Effec-
tiveness depends on the settling characteristics of the solids
and the retention time. Settling ponds generally achieve reduc-
tions in TSS to 50 milligrams per liter or less; however, for
some wastewaters, the TSS content of the discharge is as high as
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150 milligrams per liter. Most facilities achieve a 95 percent
or better reduction in TSS. Settling ponds also provide equal-
ization, water storage capacity, and solid waste storage.
Flocculation—Flocculating agents, such as ferric chloride
(FeCL,), alum [A1NH4(S04)4], and ferrous sulfate (FeSO.), and a
variety of polyelectrolytls increase the efficiency of^ settling
facilities and are most often used after the larger, more readily
settled particles have been removed.
Clarifiers and thickeners--Clarifiers or thickeners are
sometimes used to remove suspended solids. Consisting primarily
of tanks with internal baffles to provide efficient concentration
of solids and clarification of the liquid, these devices are
usually used by phosphate and industrial sand operations when
sufficient land for ponds is not available or when suspended
particles are too small to settle under gravity and flocculating
agents must be added.
pH control--Since some wastewaters, including mine drainage,
are either acidic or alkaline, they need to be brought to a pH of
6 to 9 before disposal or discharge. Acidic streams are usually
treated with alkaline materials such as limestone, soda ash,
sodium hydroxide, or lime. Alkaline streams are treated with an
acid such as sulfuric acid. Dissolved solids such as lead, zinc,
copper, manganese, and iron, are precipitated as hydroxides.
Lime is the most widely used reagent for acid water.
Precipitation—Sulfates, fluorides, hydroxides, and carbon-
ates can be precipitated by lime treatment (39). Sodium sulfate
is used to precipitate copper, lead, and other toxic metals. The
suspended precipitates are then removed by settling ponds, clari-
fiers, or thickeners, along with flocculating agents if neces-
sary.
Nonferrous metals—
Wastewaters generated from various beneficiation processes
are commonly discharged to a tailings pond to control pH. Heavy
metals are precipitated as hydroxide when pH is raised with
limes. Consistently high effluent quality can reach pH ranges
from 9.5 to 10.5 to precipitate copper, lead, zinc, and nickel
compounds.
Process wastewaters can also be treated with a mechanical
system, which includes settling, flotation, aeration, and, less
frequently, reverse osmosis or ion exchange. Cyanide and ammonia
used as flotation agents in the milling process may form toxic
compounds and residuals that cannot be stabilized in the waste
treatment system. The use of these compounds is discouraged
(41).
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The use of tailings impoundments is becoming less attractive
because of acid generation and metal leaching, which cause long-
term seepage problems and prevent vegetation of the area.
In control of water pollution, emphasis should be placed on
minimizing water usage and discharges and preventing pollution at
the sources.
The use of settling ponds, pH control, clarifiers, thick-
eners, flocculation, and precipitation, as described under Con-
struction Materials, are also used in nonferrous mining and
beneficiation operations. Other treatment methods include'oxi-
dation, adsorption, and reverse osmosis. These methods are
described in the following paragraphs:
Precipitation—Starch xanthate complexes are reported to be
effective in aiding precipitation of a variety o£ metals, includ-
ing cadmium, chromium, copper, lead, mercury, nickel, silver, and
zinc (45). Oxidation can be used in conjunction with starch
xanthate in special cases to produce less soluble heavy-metal
products.
Oxidation—Several waste components produced by mining and
beneficiating of nonferrous materials can be removed or rendered
less harmful by oxidation (39). Among these are cyanide, sul-
fide, ammonia, and other compounds that cause high chemical
oxygen demand (COD) levels. Cyanide can be removed effectively
by rapid chlorinatiori at a pH of 10.5. Generally when high COD
levels are occurring, aeration or the use of strong oxidants are
of value. |
Adsorption--The application of activated carbon adsorption
to mining and processing wastewater treatment is more limited by
cost than feasibility (39). The removal of flotation reagents or
solvent extraction compounds is practical in some operations if
the waste streams are segregated.
Ion exchange—Ion exchange equipment will remove various
ionic species (39). The disadvantages of using ion exchangers to
treat wastewaters generated by mining and beneficiating opera-
tions are high costs, limited resin capacity, and inadequate
specificity. The feasibility of applying ion exchangers depends
upon the resin loading achievable and pretreatment required.
Waste segregation and recycling enhance the practicability.
Since calcium ions are usually present in greater concentrations
than other metal ions, this method would not be feasible.
Reverse osmosis—A reverse osmosis plant for acid mine
drainage consists of pumps and filters for removal -of suspended
solids (43). Effluent from the filter enters a pressure chamber
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at the point of exposure to the membrane cells. Concentrated
brine passes from the unit and is treated or injected into a deep
well. The product water can be brought to potable quality by a
small increase in pH. Very high removal of dissolved solids,
sulfates, calcium, magnesium, and iron has been achieved by
reverse osmosis, but this method is not economical unless acid
mine drainage is to be used to supply potable water for municipal
use.
SOLID WASTES AND CONTROL TECHNOLOGY
Solid Wastes
In the mining industry, the major solid waste disposal
problem involves handling and relocation of overburden and
gangue. Overburden is the rock which overlies the ore body in
open pit, underground, and strip mines. In beneficiation opera-
tions such as screening and concentrating, the solid wastes
generated (tailings) essentially consist of the host rock. Other
solid wastes are produced from wastewater treatment and air
pollution control systems. All solid wastes that cannot be
recycled within a process must ultimately be disposed of by
landfilling or by impoundment on the surface (43).
Since huge volumes of wastes are produced, large-scale
impoundment facilities must be maintained. In underground mining
operations, the trend is to return the coarse tailings to the
areas underground as they are mined out and abandoned (29).
Characteristics of solid wastes from mining and benefi-
ciating operations vary according to industry and location.
Aside from the problem of containment, solid waste impound-
ments pose a potential water pollution problem in the form of
runoff, seepage, and leaching. Tailings pond effluent, as dis-
cussed earlier, has an acid-generating potential that can cause
metal dissolution.
Solid wastes from the mining of construction materials and
nonferrous metals are discussed below.
Construction Materials—
Generally, tailings and gangues from construction materials,
mining, and ore processing are relatively inert. Solid wastes
are impounded perpetually in tailings pond, and effluent from the
pond usually requires no additional treatment.
49
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Nonferrous Metals—
Solid wastes generated from nonferrous metals mining are
generally more hazardous than those from construction materials
mining. If the solid waste contains sufficient pyrite, sulfuric
acid can be generated and heavy metal can be leached out of the
rocks, as discussed earlier.
Control Technology
In general> the industry produces large quantities of solid
waste. Certain mining techniques can be used to minimize solid
waste generation; however, properly designed and maintained
containment and treatment facilities are necessary. Tailings
that contain a sufficient percentage of course materials (sands)
can be separated and the course sands used as embankment material
for the fines.
Impoundment basins must be designed to reduce or prevent
leakage, seepage, groundwater percolation, infiltration, and
overflow. Effluent sometimes requires additional treatment
before it is discharged to a stream or recycled to the process.
Dikes must be designed so as to maximize stability, and if solid
residue piles are not managed properly, they constitute sources
of fugitive dust and stream sediment in runoff. Vegetative
stabilization is often used to minimize these problems (39).
The principal methods of solid waste utilization are dis-
cussed in the following paragraphs.
Revegetation—Implanting a vegetative cover on mineral
mining wastes or mined areas is called revegetation. This method
serves to stabilize erodible slopes, minimize water pollution,
control dust, and facilitate crop-producing potential.
Chemical and physical waste stabilization—Chemical and
physical waste stabilization of mine wastes is sometimes used
instead of revegetation to minimize fugitive dust and water
pollution (43). Also, chemical stabilization is often used in
conjunction with vegetation to protect the plants.
Physical stabilization is a method that involves covering
the wastes with erosion-resistant waste rock from the mining
operation, when it is available. Coverage with topsoil and bark
is also considered a physical method that offers aesthetic advan-
tages .
Chemical stabilization ranges from the use of soil sealants
to the application of fertilizers for amelioration of soil to
enhance plant growth. Chemical stabilizers, however, are gen-
erally defined as chemical agents that bind waste surfaces to
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prevent erosion. The main advantage of chemical stabilizers is
that they protect the vegetative covers during early stages of
growth. They normally cannot be expected to be permanent.
Soil Amelioration
Amelioration of soil properties is essential before revege-
tation on some mine wastes. Salinity, pH, and nutrient content
are critical factors that require amelioration. Some ameliora-
ting agents that increase pH are lime, crushed limestone, asbes-
tos, tailings, fly ash, and sewage. Agents that decrease pH are
pyrite-rich tailings, powdered sulfur and acids. Nutrients can
be added by fertilizing or applying sewage sludge.
Construction Materials—
Solid waste disposal techniques are not significantly dif-
ferent from those just discussed. Wastes generated from this
category are generally less hazardous and pose fewer environ-
mental problems than nonferrous metals mining. When acid mine
drainage is a potential problem, special attention to disposal
methods and maintenance is needed. Sometimes, too, specific
problems are associated with certain mining categories. In
asbestos mining, for example, asbestos fibers in the solid waste
present fugitive dust and water pollution problems if not managed
properly.
Nonferrous Metals—
Although impoundments are often the only alternative, they
become unattractive when tailings contain significant concentra-
tions of pyrite or similar sulfides that lead to acid generation
and leaching of metal values. Long-term environmental problems
are prevalent and difficult to solve (41).
The processing of tailings to recover, the metal values has
been found to be economically infeasible. With the combined
effect of higher market values, improved technologies, and long-
term environmental implications, metal recovery may become more
attractive in the future (41). Some reworking of tailings oc-
curred when flotation technology replaced the gravity separation
techniques of early mining days. Hydr©metallurgy may produce an
analogous activity in the future.
Rehabilitation includes revegetation of tailings areas;
control of contaminated surface, mine pit, and underground dis-
charges; control of mining subsidence; improvement of the general
aesthetics; and area redevelopment (41). The uptake of toxic
materials in the vegetation is a source of concern where vegeta-
tion can be harvested or consumed by wildlife or domestic ani-
mals.
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HAZARDOUS WASTES (43, 46, 47)
The term hazardous wastes means any waste or combination of
wastes which pose a substantial present or potential hazard to
human health or living organisms because such wastes are lethal,
nondegradable, persistent in nature, biologically magnified, or
otherwise cause or tend to cause detrimental cumulative effects.
General categories of hazardous wastes are toxic chemicals,
flammable, radioactive, explosives, and biological. These wastes
can take the form of solids, liquids, gases or sludges.
There are numerous sources of hazardous wastes in the mining
of construction materials and nonferrous metals. These wastes
could originate from the mining or extraction of the ore, pro-
cessing of the ore and as the constituents of waste streams.
These wastes may be in the form of fugitive particulates, gaseous
and liquid wastes as well as solid wastes.
The toxicity and adverse environmental effects of some of
the potentially hazardous materials associated with the mining
activity are summarized below:
0 Solid wastes from mining activities, which consist
mainly of overburden and gangue are in general not
toxic; however they may be hazardous to health on
another basis (e.g. asbestiform minerals) or become a
source for toxic emissions as they weather and other-
wise alter with time to give up undesirable chemicals.
0 The most significant source of liquid wastes in the
mining industry is acid mine drainage. Acid mine
drainage can be extremely damaging to aquatic life.
Heavy metal (copper, nickel, lead, zinc) ions found in
acid mine drainage are often in concentrations suffi-
cient to be harmful or even toxic to aquatic life. At
pH levels below 5, most fish life dies.
0 Particulates generated as a result of mining of asbes-
tos are a known health hazard in air and possibly
water.
0 Cyanide is used as a flotation reagent in many base
metal mines, including cyanidation circuits for gold
extraction. Cyanide is highly toxic and its use is
generally discouraged in favor of alternate reagents.
0 Free silica which is emitted as fugitive dust from sand
and gravel operations may result in development of a
pulmonary fibrosis (silicosis) if exposed for a pro-
longed time.
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Mill* effluent has characteristics that have a chemical
or a biochemical oxygen demand, some of which may be
toxic to animals or plants.
Milling practices for the recovery of gold may produce
a cyanide-leach problem. Process wastes from mining
activities are often ponded at many facilities. There
is a strong tendency for leaching out heavy metals to
nearby streams, which can make it unsuitable for fish
and other aquatic organisms.
Toxic effects caused by the discharge of reagents or
residuals other than heavy metals can alter the re-
ceiving stream environment making it unsuitable for
habitation by native biota.
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SECTION 4
NONMETALS
DIMENSION STONE
Industry Description
"Dimension stone" is rock which has been specially cut or
shaped for use in buildings, bridges, curbing, and other con-
struction or for special applications. Large quarry blocks
suitable for cutting to specific dimensions also fall into this
classification. The principal dimension stones are limestone,
granite, marble, sandstone, slate, and basalt.
The dimension stone industry accounted for less than 0.5
percent of total stone output in 1974, and 4 percent of the total
value. It consisted of'approximately 500 plants in 44 states and
produced $100 million worth of construction, monumental, and
speciality products (1). Section 1 presents production statis-
tics for dimension stone.
Nearly every state in the Union produces dimension stone.
Igneous and metamorphic rocks are predominant in the Appalachian
and Rocky Mountain belts, but granite is also produced in
Missouri and in several of the North-Central states. Nearly all
of the slate now comes from six Atlantic states from North
Carolina to Maine, however, a small quantity is still produced in
Utah. Michigan and several southern states also produced small
amounts in the past. Limestone and sandstone are the predominant
dimension stones in the sedimentary formations of the Midwest and
also occur widely elsewhere in the United States.
Construction consumes more than 75 percent of the dimension
stone in the United States, with exterior and interior facing
panels for buildings taking the major share. Curbing, flagging,
and slate roofing comprise the other significant construction
uses. Monument works consume another 20 percent of the dimension
stone output, mostly for gravestones and markers. Miscellaneous
uses that account for the rest of the output include slate,
electrical panels, blackboards, billiard tabletops, and various
decorative panels for furniture, such as tops for dressers and
tables (1).
54
-------
Clays, lithium, and gypsum are the only significant by-
products in dimension stone production. Flake mica, which occurs
in igneous and metamorphic rocks, is a potential by-product
worthy of attention. Stone is obtained in conjunction with
production of many metallic and nonmetallic ores (1).
Process Description
Dimension stone is obtained from open-pit quarries. (Figure
11 presents a simple diagram of the steps involved in its mining
and beneficiation.) Quarrying can be accomplished by one of the
following techniques (39):
0 Drilling with or without broaching
0 Channeling by machine (semi-automated, multiple-head
chisels)
0 Sawing with wire
0 Using low level explosives
0 Using high-velocity jet flames to cut channels
0 Using splitting techniques
After a large block of stone is freed, it is either hoisted
onto a truck and driven from the floor of the quarry to the
processing facility, or it is removed from the quarry by means of
a derrick, then loaded onto a truck.
At the processing facility (usually located at or near the
quarry) the blocks of stones are first sawed into slates by gang
saws, wire saws, or, occasionally, rotating diamond saws. All
sawing systems require considerable water for cooling and par-
ticle removal; however, the water is usually recycled.
After the blocks have been sawed into slabs of predetermined
thicknesses, they are ready for finishing. Finishing operations
vary and depend either on the properties of the stone itself or
on the characteristics of the end product. Some of the finishing
operations are splitting, trimming, and polishing (39).
Waste Streams
Table 7 presents a summary of multimedia wastes from the
mining and beneficiation of dimension stone, and the following
paragraphs explain in more detail the various air, liquid, and
solid wastes associated with this industry.
55
-------
ui
o\
OVERBURDEN
REMOVAL
EXTRACTION
OF ORE
\
?
/
LEGEND
LIQUID WASTES
GASESCUS EMISSION
SOLID HASTES
LOADING
OF ORE
TRANSPORT
OR ORE
WATER
V
SETTLING
PONO
DISCHARGE
WATER
SETTLING
POND
DISCHARGE
PRODUCT
Figure 11 . Mining and beneficiating of dimension stone.
-------
TABLE 7. SUMMARY OF MULTIMEDIA WASTES FROM MINING AND
BENEFICIATING OF DIMENSION STONE
Air
Source
Overburden
removal
Ore
extraction
Ore
loading
Ore
transport
Pollutant
Particulates
Uncontrolled
emission
rate
N.A.
Liquid
Source
Overburden
removal
Ore
extraction
Sawing
Finishing
Pollutant/
parameter
TSS
TSS
TSS
Uncontrolled
discharge
a
< 25 rog/l
N.A.
N.A.
Solid
Source
Overburden
removal
Ore
extraction
Settling
pond
Pollutant
Haste rock
Sludge
Uncontrolled
quantity
N.A.
N.A.
01
• Ref. ».
N.A. - Not available.
-------
Air Emissions—
The quarrying operation is the major source of air emissions
in the dimension stone industry, as all other operations are
accomplished using water. No data are available on the quantity
of particulate emissions however.
Liquid Wastes-
Pit pumpout is a seasonal occurrence in some dimension stone
facilities. The quality of the mine water depends more on stone
type than any other factor. For example, pumpout at one granite
quarry contains 26 mg/liter total .suspended solids. However,
limestone, marble, and dolomitic limestone quarry water is gener-
ally very clear and much lower in suspended solids (39). Most
limestone and some granite quarries use water for channel cutting
and water is also used in small quantities during wet drilling.
All sawing operations require water. The raw waste load
from these operations contains a significant load of suspended
solids, as do the untreated effluents from finishing facilities.
Sawing and the finishing operations are often under the same roof
and water effluents are combined.
Water usage varies according to stone processes, water
availability, and owner or operator attitudes on water usage.
Table 8 shows water usage data for various dimension stone faci-
lities (39).
TABLE 8. DIMENSION STONE WATER USE DATA
Stone type
Mica Schist
Limestone
Granite
Marble
Water use, liter/Mg of stone
processed
Saw plant
4,460
16,600
7,350
100,000
Finish plant
None
1,600
7,360
Unknown
Source: Ref. 39.
Solid Wastes—
Overburden and waste rock are generated from the quarrying
operation. Another source of solid wastes is the settling pond,
which generates sludge. Quantitative data on these wastes have
not been reported.
58
-------
Control Technology
Control technologies applied to the dimension stone industry
are explained in the following paragraphs.
Air Emissions Control—
Particulate emissions from quarrying operations and haul
roads are controlled by wetting.
Liquid Waste Control—
Effluent from the quarry is discharged into a sump for
continuous recycling and is rarely discharged.
Wastewater from both sawing and finishing operations is
first discharged into a settling pond, where most of the sus-
pended solids are allowed to settle out. Sometimes effluents
from these operations are combined and discharged into a common
pond. The settling pond is reported to reduce total suspended
solids by more than 96 percent (39). Treated wastewater is
recycled as process water.
Solid Waste Control—
The overburden and waste rock from quarrying operations is
either stockpiled on site or crushed and screened to smaller
sizes for use as aggregates.* Settling pond sludge is hauled to
an on-site dumping area, where runoff water is controlled to
reduce TSS levels to any nearby streams.
Conclusions and Recommendations
Environmental impacts from the dimension stone industry are
minor compared to the crushed stone industry. Air, liquid, and
solid wastes are amenable to conventional treatment technologies.
Effluent from sawing and finishing operations is sent to
settling ponds (usually in series) for treatment. Sludge that
accumulates in the pond is removed periodically and disposed of
on-site. The properties of the sludge are such that bricks might
possibly be made from it. Using sludge and other solid waste for
this purpose warrants further investigation to determine its
technical and economic feasibility.
*Telephone conversation between Vijay Patel of PEDCo and
Mr. Max Jurras, Division of Air and Solid Wastes, State of
Vermont, Montpelier, Vermont. April 1977.
59
-------
CRUSHED STONE
Industry Description
Crushed stone is derived principally from limestone, dolo-
mite, granite, trap rock, sandstone, quartz, and guartzite (48).
Less than 5 percent comes from calcereous marl, marble, shell,
and slake.
Crushed and broken stone refers to rock that has been re-
duced in size after mining to meet various consumer requirements
(1). The United States is the leading producer of crushed stone,
and this industry is responsible for more than 99 percent of all
stone produced in this country. Firms range in size from small
independent producers with single plants to large diversified
corporations with 50 or more plants. Plant capacities range from
less than 2.27 x 104 to about 1.36 x 106 megagrams per year (1).
Section 1 presents production statistics for crushed stone.
Plants are widespread geographically, with all but one state
reporting production in 1974. Crushed granite comes primarily
from the Rocky Mountain and Appalachian areas, basalt from the
northeast sections of the Rocky Mountains and Hawaii (where it is
the principal crushed stone), and shell from the Gulf Coast and
Atlantic Coast States. Arkansas, California, and Pennsylvania
produce over half of the total output of quartzitic'stone, and
the balance of the production is scattered over 32 other states
(i).
Construction consumes 86 percent of the crushed stone pro-
duced in the United States, with highway construction leading in
quantity, followed by building construction. All major types of
crushed stone (limestone, quartzite, granite, etc.) are used for
construction. Closely related to the direct construction use is
the quantity that goes into cement production. Crushed stone is
also used as a source of calcium in agriculture; as flux in the
iron and steel industry; as a water softening agent; and in the
making of glass, refractories, and chemicals.
The only significant by-products are clays, lithium, and
gypsum. Some stone is obtained in conjunction with the produc-
tion of metallic ores and nonmetallic minerals. Although most of
it is dumped as waste for lack of local demand, small quantities
are marketed.
Process Description
Although most crushed and broken stone is presently mined
from open quarries a trend is growing in many areas toward large-
scale production by underground mining methods. In 1974 about 5
60
-------
percent of all crushed stone production came from underground
mines (1). Shell dredging, mainly from coastal waterways,
accounts for approximately 1 percent of total production (39).
The crushed stone is beneficiated by both dry and wet processes.
In the quarrying operation, the overburden is removed and
the raw material is loosened by drilling and blasting. The
steep, almost vertical walls of the quarry may be several hundred
meters deep. The mine is normally excavated on a number of
horizontal levels (called benches) at various depths. The
material is loaded into trucks for transport to the processing
facility. Occasionally a portable processing facility, which can
be situated near the blasting site, is set up on one of the
quarry benches or on the quarry floor. Specific methods vary
with the nature and location of the deposit (39).
At the processing facility (Figure 12) the raw material
passes through screening and crushing operations before final
sizing and stockpiling. Consumer demands for various product
grades determine the number and position of the screens and
crushers. No process water is used in the crushing and screening
of dry-process crushed stone.
Excavation and transportation of crushed stone for wet
processing are identical to those for dry processing. The pro-
cess is also the same except water is added to the system to wash
the stone. This washing is normally done by spray bars that are
added to the final screening operation after crushing. Since not
all of the product is washed, a separate washing facility or
tower is incorporated that receives only the material to be
washed. This separate system usually consists only of a set of
sizing screens equipped with spray bars. A portable processing
facility can also incorporate a portable washing facility to
satisfy the demands for a washed product.
Waste Streams
Table 9 summarizes multimedia wastes from the mining and
beneficiation of crushed stone. The following paragraphs explain
in more detail the various air emissions and liquid and solid
wastes associated with this industry.
Air Emissions—
The major pollutant emitted during the production of crushed
stone is respirable dust containing free silica. Both open-pit
and underground mining activities generate considerable particu-
late emissions. Sources include drilling, blasting, secondary
breaking, and loading and hauling of the minerals to the proces-
sing plant.
61
-------
a\
N)
CIHAUST
\
T
FAIIB 1C FUUR
OUBfUHOtN
REHOun
ODE
CIT8ACHOK
one
CIIRKCIION
OKI
LOADING
one
LOADING
IRAIilPORI
ID iUR(*Ci
UHOIRWOUNO MINING
ty
I
one 1
iRANii>niii 1
c
CRUSHER
j)
C
j)
(
CRUSHER
j) C
SCRECtl
0» PROCESS
c
CRUSHEB
)
c
SC»[[N
1
(
CRUSHER
UAIER
[ * ^
iCKlH
»',0
HASH
\
SEITIIiG
PONO
»
LEGEND
LIQUID WASTES
GASESOUS EMISSION
SOLID WASTES
I
Figure 12. Mining and beneficiating of crushed stone.
-------
TABLE 9. SUMMARY OF MULTIMEDIA WASTES FROM MINING AND
BENEFICIATING OF CRUSHED STONE
Air
Source
Overburden
removal
Ore
extraction
Ore
loading
Ore
transport
Underground •
mining
Crusher
Screen
Pollutant
Fugitive
particulates
Fugitive
particulates
Particulates
Uncontrolled
emission
rate
N.A.
N.A.
0.25 to 3.04
kg/Mga
Liquid
Source
Overburden
removal
Ore
extraction.
Ore
loading
Ore
transport
Underground
mining
Screen and
wash
Pollutant/
parameter
TSS
(Mine
• pumpout)
N.A.
Uncontrol led
discharge
1 to 128 mg/t
N.A.
Solid
Source
Overburden
removal
Ore
extraction
Fabric
filter
Settling
pond
Pollutant
Gangue
Particulatea
Sludge
Uncontrolled
quantity
N.A.
N.A.
N.A.
cn
ui
" Ret. 33.
N.A. - Not' available.
-------
Particulate emissions from drilling operations are primarily
caused by air-flushing to remove cuttings and dust from the
bottom of the hole. The level of uncontrolled emissions depends
on the type of ore, its moisture content, the type of drill used,
the diameter of the hole, and the penetration rate. Emissions
from blasting depend on the size of the shot, blasting practices,
mineral type, and meteorological conditions (especially wind).
Emissions from secondary breaking are relatively insignificant
(25).
Considerable fugitive dust emissions result from loading the
product and hauling it over unpaved roads. The most significant
factor affecting emissions during loading is moisture content of
the ore. Although no data were found on hauling operations, an
emission factor of 0.55 kilogram per vehicle kilometer has been
reported for conventional vehicle traffic on unpaved country
roads (33). It can be assumed that mineral hauling emissions are
higher because of the greater size of the rubber-tired units and
the finer texture of the typical road bed. Factors affecting
fugitive dust emissions from hauling operations include the
composition and wetness of the road surface and the volume and
speed of vehicle traffic (25).
The generation of particulate emissions is inherent in the
crushing process. These emissions, which are most apparent at
crusher feed and discharge points, may be influenced by such
factors as the moisture content of the rock, the type of rock
processed, and the type of crusher used.
Dust is emitted from screening operations as a result of the
agitation of dry stone. The level of uncontrolled emissions
depends largely on particle size of the material screened and the
amount of mechanically induced energy. Emission factors for
various crushing and screening operations are shown in Table 10.
TABLE 10. PARTICULATE EMISSION FACTORS FOR
STONE CRUSHING PROCESSES
Process Operation
Uncontrolled emission
factor, kg/Mg of ore processed
Primary crushing
Secondary crushing and
screening
Tertiary crushing and
screening
0.25
0.76
3.04
Source: Ref. 49.
64
-------
Liquid Wastes—
Mine pumpout is the major source of liquid wastes in both
open-pit and underground mines. Mine water comes from ground-
water, precipitation, or surface runoff. Data from several mines
indicate a total suspended solids range of 1 to 128 parts per
million (39).
The dry process does not produce any other liquid wastes. In
the wet process, however, the crushed stone is washed by spray
bars in the final screening operation. The quantity of water
required for washing depends upon the deposit from which the raw
material is extracted. The quantity of wash water reported in
several facilities has ranged from 0.041 to 1.26 cubic meters per
megagram of product (39).
Solid Waste —
Overburden and gangue are the major sources of solid wastes
in open-pit and underground mines. Although typical overburden
ranges from 0.9 to 1.5 meters, it can be as high as 3 to 4.5
meters.*
Other sources of solid wastes include the dust collected by
the dry collection device (fabric filter) and sludge accumulation
in settling ponds. Quantitative data on these wastes are . not
available.
Control Technology
Control technologies applied in the crushed stone industry
are covered in the following paragraphs.
Air Emissions Control--
Water injection and aspiration to a control device are the
two methods normally used to control particulate emissions from
drilling operations. The most common control devices are cy-
clones or fabric filters preceded by a settling chamber. Whereas
collection efficiencies of cyclones seldom exceed 80 percent, the
efficiencies of fabric filters are usually over 99 percent. Air
volumes required for effective control range from 14 to 42 cubic
meters per minute depending upon the type of rock drilled, the
hole size, and the penetration rate (48).
No effective method for controlling particulate emissions
from blasting is yet known; however, good blasting practices can
minimize the effects of noise, vibration, air shock and dust
emissions.
*Telephone conversation between Vijay Patel of PEDCo and
Frederick Allen, North Carolina Aggregate Association,
Raleigh, North Carolina. April 1977.
65
-------
Wetting the rock prior to loading helps to control fugitive
dust from loading operations. This is done with water trucks
equipped with hoses or movable watering systems (48).
Various road treatments used to control fugitive emissions
from haulage roads include watering, surface treatment with
chemical dust suppressants, soil stabilization, and paving.
Process emissions from crushers, screens, conveyor transfer
points and storage facilities are controlled by devices such as
wet dust suppression, dry collection, and a combination of the
two. The wet dust suppression device introduces moisture into
the material flow, causing fine particulate matter to be confined
and remain with the material flow rather than become airborne.
Dry collection involves hooding and enclosing dust-producing
points and exhausting emissions to a collection device. Using
enclosed structures for process equipment is also an effective
means of control (48).
Hooding and air volume requirements for the control of
crusher emissions vary greatly according to judgment and exper-
ience. The only established criterion is that of maintaining a
minimum indraft velocity of 61 meters per minute through all open
hood areas (48).
Screening operations generally apply a full coverage hood to
control emissions. Required exhaust volumes vary with the sur-
face area of the screen and the amount of open area around the
periphery of the enclosure. A minimum exhaust rate of 15.56
cubic meters per minute per square meter of screen area is
commonly used, with no increase for multiple decks (1).
The most commonly used dust collection device in the crushed
stone industry is the fabric filter, which is more than 99 per-
cent efficient. Other reported collection devices include cy-
clones and low energy scrubbers (48).
Liquid Waste Control—
Pit pumpout is discharged directly without treatment, dis-
charged after treatment, or discharged along with treated efflu-
ent from the washing operation. In this last method, quarry
water combines with the untreated facility effluent and then
flows through a settling pond system prior to discharge. In this
type of facility, much of the combined pond water is recycled
rather than discharged <39).
All facilities send effluent from washing operations through
a settling pond system prior to discharge. The system design
generally includes at least two settling ponds in series to
reduce the suspended solids in the final discharge to less than
66
-------
50 milligrams per liter. Reduction in the concentration of
suspended solids has been reported to exceed 95 percent (39).
Many facilities recycle a portion of their treated effluent. In
many instances, evaporation and percolation tend to reduce the
flow rate of the final discharge.
Solid Waste Control—
The solid waste (overburden) from open-pit mining is either
stockpiled on site or used in reclamation. Small quantities of
solid waste from underground mining operations are usually left
within the mine site.
The large quantities of solids collected in the fabric
filters are sometimes marketed. When a market is not available,
the waste is dumped on site. Sludge from the settling ponds is
also disposed of on site. These wastes can cause an adverse
environmental impact if they become airborne or if harmful con-
stituents wash into surface waters and leach into groundwater.
Conclusions and Recommendations
Treatment technologies currently available in the crushed
stone industry are generally adequate to maintain environmental
standards.
An area that might be researched is locating a. steady market
for sludge from the settling ponds and particulate matter col-
lected in the fabric filter.
CONSTRUCTION SAND AND GRAVEL
Industry Description
On a product weight basis, the sand and gravel industry is
the second largest nonfuel mineral industry in the United States.
Historically, these products have been the principal construction
materials in the United States, and from all indications they
will continue to be. The industry is one of the fastest growing
in the mineral field, producing enough sand and gravel to satisfy
the total domestic requirement. Every state in the Union re-
ported some production in 1974, and active or latent deposits are
located in nearly every county. Although resources are inex-
haustible on a national basis, some local shortages exist.
Since sand and gravel are produced by weathering of rock,
they are predominantly silica; however, they often contain other
minerals such as iron oxides, mica and feldspar. The particle
size of sand ranges from 0.065 to 2 millimeters, whereas gravel
consists of naturally occurring rock particles larger than 4
67
-------
millimeters but less than 64 millimeters in diameter (2). Par-
ticles finer than sand are referred to as silt, and particles
larger than gravel as cobbles and boulders.
In 1974, 4844 sand and gravel companies operated 6697 sep-
arate facilities. Annual production of individual companies
varies greatly (the range was 4.54 to 3.63 x 10 megagrams in
1974), but the average company is small (2).
Total sand and gravel resources that can be reached at
current exploritation costs are estimated to be 5.90 x 10
megagrams which is adequate to meet ,the projected cumulative
requirements through 2000 (3.61 x 10 megagrams). By 2000,
approximately half of the sand and gravel requirements will still
come from deposits of material similiar to those now being ex-
ploited and the remainder from lower grade deposits and possibly
offshore resources.
The sand and gravel industry extends into every state.
Production in 19745ranged from 1,1 x 10 megagrams in California
to about 9.9 x 10 megagrams in Hawaii. Following California,
the next five states in terms of total output are Wisconsin,
Michigan, Illinois, Ohio, and New York.
Sand and gravel have both construction and industrial uses.
However, construction consumes more than 95 percent of the total
volume, leaving less than 5 percent for industrial applications.
Specific uses of construction sand and gravel are covered in this
section; industrial uses will be covered later under Industrial
Sand.
The end use of construction sand and gravel is determined by
such factors as the ratio of sand to gravel, particle size,
particle shape, rock type, and chemical .composition. Sand and
gravel can be used directly after limited processing (e.g.,
cleaning and sizing) or mixed with other materials to form a
different product, such as portland cement. In 1974, highway and
street construction accounted for 63 percent of the total demand.
Sand and gravel aggregates go into concrete and bituminous paving
mixes, concrete structures such as bridges and tunnels, road-base
material, and fill. As the second largest consumer, general
building and other heavy construction industries accounted for
about 25 percent of the total 1974 demand. Most of the sand and
gravel is used as aggregate in concrete, with small quantities
used for fill, septic fields, and other building construction
purposes. About 7 percent is consumed by the building industry
for concrete construction materials such as brick and concrete
block.
68
-------
Although sand and gravel generally are used in combination
as a single product, they can be used separately. Sand has the
wider range of usage. It is used in architectural structures,
mortar, plaster, all forms of road and pavement construction, and
for purposes other than construction.
Almost no by-products or coproducts are recovered in the
sand and gravel industry. Traces of gold and silver have been
recovered during extraction, but quantities are miniscule.
Potential salable by-products/coproducts include heavy minerals,
flake mica, and clay, but little attempt has been made to recover
any of these (2). The increasingly stringent regulations on land
disturbance and solid waste disposal may soon require more com-
plete recovery of salable materials.
Process Description
Sand and gravel producers may turn out one product or a
range of products. Some operations sell only bank-run material,
which requires no processing, whereas others sell material that
has been subjected to various processing techniques. Most pro-
ducers are engaged exclusively in the sand and gravel business,
but some are diversified.
When sand and gravel deposits are large, permanent installa-
tions are built and operated for many years. Portable and semi-
portable units are used in pits that have an intermediate working
life. Many facilities operate year round, and others operate on
a limited basis depending on such factors as weather and/or
product demand.
Sand and gravel are usually found in the same deposit, but
proportions vary greatly. This sand to gravel ratio, the chemi-
cal and physical characteristics of the gravel deposit, and the
specifications of the user govern extraction and processing
equipment/methodology at a specific site.
Currently, three methods of sand and gravel excavation are
practiced: (1) dry pit (sand and gravel are extracted above the
water table); (2) wet pit (raw material is extracted by means of
a dragline or barge-mounted dredging equipment both above and
below the water table); and (3) dredging (sand and gravel are
recovered from public waterways such as lakes, rivers, and es-
tuaries ). The breakdown in the United States is as follows: 50
percent by dry pit; 30 to 40 percent by wet pit; and 10 to 20
percent by dredging of public waterways (51).
Although the extracted raw material can be processed by
various methods, most are similar in that they involve some form
of transporting, screening, washing, crushing, blending, and
69
-------
stockpiling. The most common extraction/processing methods are
illustrated in Figure 13a and 13b and described in the following
paragraphs.
Dry Process—
After a site is cleared and overburden is removed, sand and
gravel are extracted from the deposit by front-end loaders, power
shovels, or scrapers. The raw ore is then transported to a
processing facility by conveyor or truck.
In the initial step of dry beneficiation sand is separated
from gravel via inclined vibrating screens. The sand and gravel
are then sized as they pass through a number of screens of vary-
ing mesh sizes. Material too large to pass through the screens
is crushed and resized.
Wet Process—
The site is cleared, overburden is pushed back, and the pit
is flooded. The sand and gravel are then recovered by dragline,
suction dredge, or bucket dredge. The raw material is trans-
ported to a processing facility by conveyor belts, slurry lines,
trucks, or barges. There the sand and gravel are first dumped
into a hopper or coarse ore bin covered by a grizzly, where the
raw material is subjected to primary and secondary screening and
crushing (52). Primary crushing reduces the particle size to
less than 5 centimeters and secondary crushing reduces it to less
than 3-3/4 centimeters (52). Primary crushing is performed by
cone or gyratory crushers and secondary crushing by roll
crushers. Screens can be horizontal or sloped, single or multi-
deck. They also may be either vibrating or revolving, and they
are frequently heated to prevent clogging. Wash water is sprayed
on the product throughout the screening/crushing operation. The
material is sometimes washed further by passing it through log
washers or rotary scrubbers.
Following initial screening, crushing, and washing, the
material is fed to a battery of screens for product sizing. The
different sizes of gravel are discharged from these screens into
bins or conveyed to stockpiles or sometimes to crushers and other
screens for further processing. The sand fraction coming off of
the battery of screens is fed to classifiers, separatory cones,
or hydroseparators for additional washing, sizing, and water
removal. At most facilities, two size categories of sand are
stockpiled: coarse (1 to 0 centimeter) and fine (1/3 to 0 centi-
meter) (52). The sized sand and gravel are then ready for
various degrees of blending as required for use in building
construction or concrete and bituminous paving.
At several facilities heavymedia separation (HMS) is used
prior to wet processing to remove very fine deleterious materials
70
-------
(OPEN PIT-DRY)
PREMIriING
PROCEDURES
ORE
EXTRACTION
*" AND
LOADING
p o t>Q o
TRANSFORM
*" TION
COARSE
»• ORE
STORAGE
SAND/GRAVEL
SEPARATION
CLUNING AND FRONT-END LOADERS CONVEYORS BIN INCLINED
GRUBBING POUER SHOVELS TRUCKS STOCK PILE VIBRATING
OVERBURDEN SCRAPPERS SCREEN
REMOVAL
•*
~*
SIZING
SCREEN
C
SIZING
SCREEN
r ^
SAND
PRODUCT
JP ^
GRAVEL
PRODUCT
(OPEN PIT-WET)
1
PREM1NING
PROCEDURES
r
ORE
EXTRACTION
AND
LOADING
CLEARING AND DRAG LINE
GRUBBING SUCTION DREDGI
OVERBURDEN BUCKET DREDGE
REMOVAL
(DREDGING)
f
ORE
EXTRACTION
SIZING
SCREEN
/>
/>
TRANSPORTA
TION
CONVEYOR
TRUCK
BARGE
CRUSHER
1
SCREEN
SUCTION DREDGE
BUCKET DREDGE
CLAIM SHELL
P
1
COARSE ORE
STORAGE
BIN
STOCKPILE
1
PRIMARY
J>
SCREENING
i
PRIMARY
CRUSHING
SECONDARY
SCREENING
'
1
SECONDARY
CRUSHING
CONE CRUSHER
GYRATORV CRUSHER
?
KD
\
T
LEGEND
LIQUID WASTES
GASESOUS EMISSION
SOLID WASTES
Figure 13a. Mining and beneficiating of construction sand and gravel.
-------
ro
H20
HEAVY
MEDIA
SEPARATION
Q
\
T
LEGEND
LIQUID WASTES
GASESOUS EMISSION
SOLID HASTES
LOG WASHER
ROTARY SCRUBBER
HYDRAULIC
SAND
CLASSIFIER
COARSE
SAND
o
__J
CYCLONE
UNDERFLOW'
/•^ t^jT
y \
SPIRAL
.CLASSIFIER
FINE
SAND
Figure 13b. Mining and beneficiating of construction sand and gravel.
-------
that would not be washed away by normal scrubbing and screening
operations. These fine particles include soft fragments, thin
and friable particles, shale, argillaceous sandstones and limes,
porous and unsound cherts, coated particles, coal, lignite and
other low-density impurities (39). HMS (sink-float) removes the
deleterious materials as a result of the different specific
gravities of the particles involved. The sand and gravel product
(sink fraction) and the impurities (float fraction) pass over
separate screens, where the heavy-media materials are removed by
separation and recycled. The impurities are usually disposed of
on site and the product is transported to a wet processing facil-
ity for further washing, crushing, and sizing.
Dredging with On Land/On Board Processing—
Raw material is extracted from public waterways using float-
ing, movable dredges, which excavate the bottom sand and gravel
deposit by one of the following methods: a suction dredge with
or without cutter-heads, a clamshell bucket, or a bucket-ladder
dredge. After the sand and gravel have been brought onto the
dredge, they can be transported directly to an on-land processing
facility (via barges or a slurry line) or be partially or com-
pletely processed on board the dredge. When transported to an
on-land facility, the raw material is processed in a manner
similar to that described under Wet Process. Partial on-board
processing involves primary sizing and/or crushing performed by
vibrating or rotary screens and cone or gyratory crushers.
Oversize boulders are returned to the water. Following these
initial steps the ore usually is transported to on-land facili-
ties for additional processing; however, the product sometimes is
ready for sale following on-board processing. When raw material
is processed completely on board, it is treated in a manner
similar to that described earlier under Wet Process. Following
the on-board beneficiation, sized sand and gravel are loaded onto
tow-barges and delivered to the user or stockpiled on land.
Waste Streams
Various atmospheric, liquid, and solid waste materials
result from sand and gravel extraction and processing. These
waste streams are shown in Table 11 and discussed in detail in
the following paragraphs.
Air Emissions—
Particulate emission sources in the sand and gravel industry
parallel those in the crushed stone industry. They may be fugi-
tive or process in origin. Process sources include crushers,
screens, conveyors, and loading mills (25). Fugitive sources
include haul roads, stockpiles, and open loading areas.
73
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TABLE 11. SUMMARY OF MULTIMEDIA WASTES FROM MINING AND BENEFICIATING
OF CONSTRUCTION SAND AND GRAVEL
I'lOCI'S*
t l.livi
iui:-la!ij
prunes* ing >
Dredging
U.i.-b«..»rd
processing)
S«»urvf
<-.|ui|.n.-ni
Slot'k|ji los
Vehicle
i>l her t a«u- j
rt|iiip>
t't|.)ltive
par i iculatei
r'ugi t ive
f'ii<|i Live
Fu.|itw«i
Fugitive
DM.-oni mlU.,1
on 1MB ion
rate
product3
O.Ob to 2.6 lui/Mti
of product*3
O.Sf, to 2.1 >
N.A.
product**
of product*1
O.S6 lo 2.11
N.A.
product4
0.06 to 2.6 kn/Mti
0.56 to 2.1J c
14. A.
Source
water**
ing**
waterc
Sutt 1 inq (Mind
I'urcoldt ion
inq'J
Settlinq pond
discharqe
Settl inij |.o n<1
Dredqe k
Dredge dis-
charge
Dredqe dis-
turbance*
Ll.lUI.I
I'ol lut.int/
I'JidOu-tor
T-iSf
water
TSSf
TSSf
TSSf
water
TSS1
TSS(
TSS'
TSSf
TSSf
liii.-ont i<>! U-ii
uiu<:h.>i-|t-
TJW mat«.-rijlh
0. 006 to 0.26 M/Mg
N.A.
fet-'d^
0.10 to 22.0 k<]/rhj of
(jroducth
N.A.
100 to 460 fc.i/Mti of
12S kg /Mil of rdw
mater tal *
•I. A.
Sourco
Crush i n-i/
a ct vu ninn
t-r Oi.'Oilui us
Dewatertnq
Jov ic<>s and
stft 1 1 intj ponds
Oc'wa t or i n>j
.UtvicL-s and
set tl in
-------
Of the three basic types of sand and gravel facilities
[open-pit (dry),, open-pit (wet), and public waterway dredging
with on-board/on-land processing], open-pit (dry) operations
generate the most particulate emissions because the moisture
content of the raw material is lower and no water is used in the
beneficiation process. Particulate emissions emanate from both
process and fugitive sources.
Processing operations at open-pit (wet) facilities normally
do not produce any particulate emissions because of the high
moisture content of the material being processed. Most particu-
late emissions come from fugitive sources.
Those facilities that practice dredging with complete on-
board processing experience few problems with particulate emis-
sions because the moisture content of the material is always very
high.
Little information is available on emission factors from
sand and gravel plants. One report lists overall emissions as
0.03 kilograms per megagram of material through the facility
(53). The sources of dust are listed as the secondary and re-
ducing crushers and the elevator boot on the "dry side."
Seventy-five percent of the dust is estimated to come from the
crushers. More recently, Midwest Research Institute (MRI) pro-
vided an estimated overall emission factor of 0.05 kilograms of
dust per megagram of product (53). This factor is based on
process sources only and does not include fugitive sources such
as stockpiles or haul roads.
Sand and gravel particulate emissions data from fugitive
sources are even more scarce than for process sources, however,
emission factors are available for a few sources, such as stock-
piles and vehicle transport. One state agency estimates emis-
sions from stockpiles to be approximately 0.1 percent of finished
product for sand and 0.5 percent for gravel (54). More recently,
MRI compiled and evaluated data for emissions from aggregate
storage piles (55). Based on the results of this study, they
developed an empirical expression for estimating fugitive emis-
sions from aggregate stockpiles:
E = °-165
/ PE .2
1 100 '
where: E = Emission factor, kilograms per megagram
placed in storage
PE = Thornthwaite's Precipitation-Evaporation
Index
75
-------
Based on PE values of 25 and 150 (which are representative of a
broad range of areas where sand and gravel are extracted), stock-
pile emission rates would be equal to 2.6 and 0.06 kilograms per
megagram of product placed in storage, respectively.
Vehicle transport is another contributor to the total par-
ticulate emissions emanating from sand and gravel operations, and
often is the major source of particulates. The emission factor
for respirable particulate emissions from transport of sand and
gravel is 0.56 gram per vehicle-meter, with a range of 0.14 to
2.13 grams per vehicle-meter (56). Even though these values
represent emissions resulting from the transport of the product
from finished stockpiles to the consumer, they are likely also to
be representative of emissions generated by vehicular transport
within the boundries of sand and gravel plants.
Other sources of fugitive emissions associated with the sand
and gravel industry include overburden removal, transfer and
conveying and abandoned or dry tailings dumps. Although data on
emissions from these sources are not available for the sand and
gravel industry, they are for other industries (crushed stone,
copper, and phosphate) whose operations parallel those in the
sand and gravel industry. Therefore, fugitive particulate emis-
sions data for these industries provide the best available bases
for estimating fugitive 'emissions .for the sand and gravel indus-
try.
Although limited data are available on the characteristics
of particulate emissions from sand and gravel plants, it is
feasible to assume they would be similar to the characteristics
of the raw material being handled. Although sand and gravel
consist primarily of silica, other constituents are sometimes
present such as limestone or combined silica in the form of
feldspar, mica, and other mineral silicates and aluminosilicates
(2). Free silica is the only potentially hazardous constituent
in emitted particulates. The .average free silica content of
emissions resulting from vehicular transport is 14 percent, with
a range of 1.4 to 47 percent by weight (56).
Liquid Waste Streams—
Since processing water is not used at dry open-pit opera-
tions, no major aqueous waste streams are associated with these
facilities. Dry processing produces some incidental wastewater,
which includes mine pumpout, surface runoff, noncontact cooling
water, and water used for dust suspression (39). These effluents
are usually discharged directly to the watershed.
Incidental water may also be a source of liquid waste at wet
open-pit operations. At most wet facilities incidental water is
discharged to a settling pond rather than to the watershed. The
76
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major liquid waste associated with wet facilities is process
wastewater. The wastewater may be discharged from process opera-
tions directly to receiving waters, or it may be discharged
through constructed tailings ponds or extraction pits (active or
abandoned working pits). The amount of process wastewater gener-
ated as a result of wet beneficiation of sands and gravel ranges
between 50 and 480 kilograms per megagram of raw material pro-
cessed (based on monitoring at five separate facilities (39).
Process wastewater at many operations is recycled back to the
process after treatment; however, some facilities discharge
treated wastewater. Treated wastewater discharges were monitored
at several plants and ranged between 0.006 and 0.26 kilograms TSS
per megagram of product (39). An additional source of aqueous
waste at wet facilities is water that escapes from settling ponds
by percolation. The quantity of wastewater from this source has
not been measured.
Plants that combine dredging with on-land processing opera-
tions generate aqueous waste from their land-based processing
facilities that is similar to effluents from wet plants. These
facilities also generate processing wastes at the dredge itself
as a result of partial on-board processing. The following is a
tabulation of these waste loads at several operations (39):
Waste generated Waste generated
at dredge, at land facility,
Operation_no. . kg/Mg of feed kg/Mg of feed
1 460 100
2 . None 400
3 None 150
4 None 110
5 None 120
6 250 60
7 180 120
Process wastewater at land-based facilities is normally treated
and recycled. The total suspended solids level of recycled
wastewater measured at four separate operations ranged between 50
and 400 megagrams per liter (39). Two facilities are known to
discharge treated wastewater. The TSS level of discharge is 22
kilograms per megagram of product at one plant and 0.10 at the
other.
Effluents from dredging units with complete on-board pro-
cessing contain essentially the same high suspended solids con-
centrations as those generated by land-based operations, and
additional solids are placed into suspension by the action of the
recovery assemblies. No information is available for effluents
from dredging operations with complete on-board processing. It
77
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problems. Sometimes sol-id waste generated by these devices is
transported to off-site dumps, but if the fines are of top soil
or fill dirt quality, they can be readily and profitably sold in
the immediate area. The fines can also be mixed with coarser
material to facilitate drying and enhance the quality of the
finished product. Some operators have added organic debris such
as leaves and commercial fertilizers to waste fines to yield a
profitable product. Waste fines have also been used to produce
building bricks, an activity which may increase proportionately
with the demand for construction materials, especially since sand
and gravel operations are located near metropolitan areas.
Conclusions and Recommendations
Most of the larger sand and gravel operations are maintain-
ing air, liquid, and solid wastes at acceptable levels by apply-
ing state-of-the-art control technology. Particulate emissions
from process sources are being minimized by applying well-
established control techniques (watering, wetting agents, exhaust
and collection systems, etc.). Although technology for the
control of fugitive emissions has not advanced to the level of
that for source emissions, it is improving rapidly. Process
wastewater and incidental wastewater are controlled by mechanical
devices followed by settling ponds. At some operations, pond ef-
fluent is completely recycled resulting in zero discharge. Solid
wastes (colloidal fines removed from settling ponds) are being
land spread at facilities with sufficient area or recovered as
useful by-products.
Even though many operations are maintaining good pollution
control programs, some environmental problems still persist.
These problems and related research and development needs are
discussed below.
A major problem that faces the sand and gravel industry is
the dewatering of settling pond sludge, which consists of colloi-
dal fines (-200 mesh). Reportedly, no technology is available
for economical dewatering of these silts. Efforts to use various
mechanical, devices such as vacuum filters and hydraulic cones
have been generally unsuccessful. Vacuum filtration is economi-
cally prohibitive because of the enormous quantities of sludge
that must be treated. Hydraulic cones effectively remove fine
sands (+200 mesh), but they are not efficient enough to remove
small colloidal particles. Some operators are now trying to
remove silts with centrifuges, which have been used successfully
for dewatering of coal mine slimes. This may be a practical
solution to the problem. Research is needed to identify the
properties of these colloidal particles to determine why it is so
difficult to dewater them. Dewatering devices such as vacuum
filters and and hydraulic cones have been partially effective;
82
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stress. These differ in the duration of time needed to apply the
breaking force. In impacting, the breaking force is applied
almost instantaneously, whereas in compression, the rock particle
is slowly squeezed and forced to fracture. All crushers use both
compression and impaction of various degrees. In primary crush-
ing some reduction also occurs by attrition, the rubbing of stone
on stone or metal surfaces. Crushers are usually loaded gradu-
ally between nonparallel crushing surfaces, except occasionally
when impact breakers and roll crushers are used in the primary
stage (23). Primary crushers are typically charged by means of a
receiving hopper. At large mines, more than one hopper or dump
bin may serve separate primary crushers placed in parallel.
Depending on the ultimate size requirements of the product, the
material from the primary crushers may be screened, with the
undersize going directly to the screening plant and the oversize
to secondary crushing, or all of the material may be routed to
the secondary crushers.
Secondary crushers take all or a portion of the crushed
material from the primary crushers and further reduce it. This
may be the final comminution process or only an intermediate
step. The term "secondary crushing" does not refer to the size
of either the crusher or the crushed ore but only the sequence in
which the crushing occurs. Generally, however, the average
diameter of the feed is unlikely to exceed 12 centimeters, and
the product usually has a top size range from 2.5 to 3.5 centi-
meters. Tonnage capacity of the secondary crusher need not match
that of the primary unit; in most cases it is substantially less
because screening is a common practice between the primary and
secondary stages (23).
Grinding, which can be either wet or dry, reduces the ore to
the optimum size for further treatment. Unlike the equipment
used in primary and secondary crushing, grinders do not reduce
product to a maximum size, a sizing apparatus such as a mechan-
ical classifier or a cyclone must be used to limit the maximum
size of the discharge. Oversized particles are then recycled
through the grinder. Creation of a wet pulp or suspension in a
ball, rod, or pebble mill operation has definite advantages when
concentrating or extractive steps are conducted in the same
environment as the grinding. It aids the longitudinal flow
through the mill, has a cushioning effect on the tumbling bodies
in the grinding, controls dust, and facilitates the addition of
chemical reagents for futher processing (23).
Solids are usually separated according to size to obtain
maximum production from the crushing and grinding equipment.
Commercial crushing and grinding always produces a distribution
of sizes, irrespective of the characteristics of the feed. This
characteristic of the crushing and grinding units requires that
27
-------
screening and classification be used in almost all beneficiation
processes.
The several screening devices available are classified as
stationary, mechanical, high-speed mechanical, and electrically
vibrated. The trend is from stationary grizzles to vibrating,
multideck, mechanical screens on which deck motions can be
straight-line, circular, or elliptical. High speed mechanical
screens are widely used for separations of 4-mesh and finer.
Electrically vibrated machines are used for separations of 8-mesh
and finer (29).
'Wet screening is used extensively for mineral processing.
Using a wet slurry can increase the amount of material that is
made to pass through a unit area of screen surface. Depending on
the size of the screened particle, this capacity can be increased
by from 25 to 350 percent (29).
Mechanical classifiers or cyclones frequently are used for
size separation of fine particulate matter. Water is the sus-
pending medium with mechanical classifiers, and either water or
air with cyclones. With both types of units, the separation size
is based on the relative velocity with which a particle moves
through the suspending medium.
Mechanical classifiers consist primarily of rake or spiral
types. Larger particles settle out in a settling tank and are
then removed by either a mechanical rake or a spiral.
As a sizing device, the hydroclone generally is preferred
over the mechanical classifier because it takes less floor space
and costs less. The hydroclone usually operates at pressures
exceeding 34.5 kilo pascals and converts this energy into rota-
tional fluid-solid motion. Consequently, particles are separated
according to their mass. The centrifugal force acting on the
particles in a hydroclone is much greater than the normal gravi-
tational force responsible for sedimentation in the mechanical
classifier (29).
Concentration is used primarily in the beneficiation of
nonferrous metals rather than construction materials. Deposits
normally consist of mixtures of various minerals. To become
usable these minerals must be separated from the unwanted gangue.
Various concentration methods for this purpose include flotation,
gravity concentration, magnetic separation, electrostatic separa-
tion, extractive metallurgy (pyr©metallurgy, hydrometallurgy,
electrometallurgy), and agglomeration.
Froth flotation is used most widely to beneficiate complex
and low-grade ores. Flotation is a complex physicochemical
28
-------
process that takes place in an ore pulped with water, by which
the surfaces of one or more minerals in the pulp are made water-
repellent and the minerals attach themselves to air bubbles.
When the mineral-laden bubbles (froth) rise to the surface they
are skimmed off and sent to further concentration steps. Collec-
tors are used to selectively coat the surfaces of the minerals to
be floated with a water-repellent surface. Activators, pH con-
trollers, depressants, and dispersants are used to make the
collectors selective under a given set of physical conditions.
By changing any of these conditions (such as pH) a sequential
series of flotations may be obtained from a given pulp. Frothers
are also used to keep the air bubbles_intact so that the floated
minerals will remain on the surface for removal (23).
Gravity concentration separates solids of different specific
gravities in a fluid medium, usually water or air, but sometimes
a heavy medium is used. Mineral mixtures susceptible to separa-
tion by gravity methods are those in which valuable minerals and
gangue differ appreciably in specific gravity. For simple
methods, a specific gravity differential of at least 1.5 is
desirable. Methods of gravity concentration include the simple
sluice, pinched sluice, Humphrey's spiral, sink-float mechanism,
jig, shaking table, and various dry concentration methods (23).
Magnetic separation sorts one solid from another by means of
a magnetic field. This method is based on the principle that
particles placed in a magnetic field are either attracted or
repelled by it. The only important highly magnetic mineral is
magnetite. Many other minerals are measurably susceptible to
magnetic action but fewer than 20 are amenable to magnetic sep-
aration, and these are classed as weakly magnetic. Magnets are
also used to remove tramp iron from an ore feed (23).
Electrostatic separation of mineral grains is an integral
part of the treatment of beach sands. Dry particles subjected to
a surface electrical charge, on or before entering an electro-
static field, behave in accordance with their ability to conduct
electricity. Conductive particles are repelled by the active
electrode emitting the charge. Different minerals become charged
to different degrees and are separated on this basis. Electro-
static separation is used to recover ilmenite, rutile, and zircon
from beach sands and to remove feldspar and mica from quartz
(23).
Extractive metallurgy is used to alter chemically the min-
eral constituents of an ore to facilitate their separation from
the gangue. The three categories of extractive metallurgy are
pyrometallurgy, hydrometallurgy, and electrometallurgy. Pyro-
metallurgy involves operations that use refractory furnaces and
high temperatures created by electrical energy or by burning
29
-------
fuels to produce refined metals from ores and concentrates. The
major processes include drying, roasting, sintering, distilling,
smelting, and fire refining (23). These techniques are generally
considered final metal refining processes rather than part of
beneficiation. The electrometallurgy process uses electric
current to recover metals. The two basic types of electrometal-
lurgy are categorized on the basis of depending on how the elec-
tric current is used. If it is used as a source of heat, the
process is referred to as electrothermic. If the electric
current is used to transport metal ions from anodes and/or elec-
trolytes for deposition on cathodes, it is referred to as elec-
trolytic processing (23). Electrometallurgy, like pyrometallur-
gy, is considered more a final purification operation than a
beneficiation process.
The final extractive metallurgical operation to be con-
sidered is hydrometallurgy, which involves the recovery of metals
from ore and concentrates by selective dissolution. The pro-
cesses involved in hydrometallurgy include preparation of the
feed, leaching, separation of the metal-bearing solution from the
leach residue, and purification of the solution following metal
recovery (23). Leaching, which is considered a beneficiation
process, is the main process of concern in this report.
Leaching refers to dissolving away of gangue or metal values
in aqueous acids or bases, liquid metals, or other special solu-
tions (29). The leaching solutions may be either*strong general
solvents (e.g. sulfuric acid) or weaker specific solvents (e.g.
calcium). The specific solvents will attack only one or a few
ore constituents whereas the general ones will attack a number of
constituents. The action of solvents can be enhanced by heating,
agitating, or applying pressure. Leaching can be accomplished by
a variety of techniques. In-vat leaching takes place in a con-
tainer, which may or may not be equipped for heating, agitating,
or pressurizing. Leaching that takes place in the ore body is
referred to as in situ leaching. The solvent is introduced into
the ore body by pumping or percolation through overburden. Heap
or dump leaching involves the leaching of stored tailings or ore
on a surface that has been lined with an impervious material
(clay or plastic sheeting). In this technique the solvent is
sprinkled over the heap and the leached material is collected in
furrows or troughs. Metals covered in this report that require
some recovery by leaching are gold, copper, mercury, and silver.
The final concentration process considered here is agglom-
eration. Agglomeration forms masses or clusters from fine parti-
cles. The four main agglomeration processes are sintering,
pelletizing, briquetting, and modulizing. As with chemical
beneficiation, most agglomeration processes are a part of refin-
ing rather than beneficiation (23). Agglomeration is also used
30
-------
in a different sense to describe thickening of flotation tailings
by use of agglomerating agents such as polyelectrolytes.
If wet screening, classification, or concentration tech-
niques are used or if the moisture content is high in the initial
ore (as dredged material), dewatering must precede the drying
process. Mechanical dewatering removes water by means of gravity
and centrifugal forces. Thickeners also are used to increase the
concentration of solids in a slurry, whereas clarifiers are used
to remove solids from a slurry. Mechanical dewatering is accom-
plished with screens, centrifuges, and classifiers, and by sedi-
mentation, filtration, and flocculation (23).
When concentrates are dried commercially, heat is trans-
ferred by convection by direct contact between the wet solid and
hot air. The various types of thermal dryers include rotary,
flash, continuous-tray, and fluidized-bed dryers. After drying,
the mineral is generally stored for shipment (23).
As mentioned previously, not all beneficiation techniques
for mineral ores containing nonferrous metals and construction
materials require all of the processes outlined. Many construc-
tion materials require only size reduction, screening, and dry-
ing; whereas many nonferrous metals require extensive concentra-
tion steps. It is only necessary, however, to delete those steps
from the generalized flow chart that are unnecessary for a
specific mineral.
31
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SECTION 3
GENERAL WASTE CHARACTERISTICS AND CONTROL
Many different types of pollution problems arise from the
large volume of construction materials and nonferrous metals
mined and beneficiated in the United States. Pollutants include
fugitive particulates from drilling and blasting, spent process
water from concentrating operations, and gangue and overburden
generated as a result of ore extraction. Some of the pollutants
may be contaminated with materials considered potentially hazard-
ous. For example, fugitive emissions may contain asbestos fibers
or free silica particles, and some process wastewater may contain
various heavy metals and/or toxic reagents like cyanide. In most
cases the potential environmental effects of mining can be main-
tained at acceptable levels by the application of established
waste management practices.
This chapter describes the sources and characteristics of
air, liquid, and solid waste and the treatment and control tech-
nology typically used in the mineral mining industry to 'abate
waste problems. Since the'characteristics of liquid wastes from
mining of construction materials and nonferrous metals are dif-
ferent, they are discussed separately.
AIR EMISSIONS AND CONTROL TECHNOLOGY
Emissions
Air pollution emissions in the mineral mining industry
consist primarily of particulates from various phases of the
mining process and from on-site beneficiation processes. Emis-
sion sources are categorized as fugitive or point sources. Table
6 lists the operations included within each category. Fugitive
emissions, for the purpose of this report, are defined as ...
"Particulate matter which escapes from a defined process flow
stream due to leakage, materials charging/handling, inadequate
operational control, lack of reasonably available control tech-
nology, transfer of storage" (25). Process point emissions are
those emitted from a definable point, such as a stack.
Factors Affecting Fugitive and Process Emissions--
Emissions common to most mining and beneficiation operations
are affected by the moisture content of the ore, the type of ore,
32
-------
the amount processed, the type of equipment, operating practices
and a variety of geographical and seasonal factors. These fac-
tors, discussed in more detail below, apply to both fugitive and
process sources and usually combine to determine the total emis-
sion problem of a 'facility.
TABLE 6. FUGITIVE AND PROCESS POINT EMISSION SOURCES
Fugitive sources
Process point sources
Drilling
Blasting
Loading and hauling
Stock and waste piles
Overburden removal3
Mine roads
Wind erosion of unprotected
surfaces
Land reclamation
Crushing and grinding
Screening
Conveying
Drying
a Applicable only to surface mines.
The inherent moisture content of the ore processed has a
substantial impact on total uncontrolled emissions especially
during mining, material handling, and initial plant process
operations such as primary crushing. Surface wetness causes fine
particles to agglomerate or to adhere to larger particles with a
concomitant dust suppression effect. As new fine particles are
created by crushing and attrition and moisture content is reduced
by evaporation, this suppressive effect diminishes and may even
disappear.
The type of ore processed is also significant. Soft ores
produce a higher percentage of screenings than hard minerals
because of a greater tendency to crumble and a lower resistance
to fracture. Thus, the processing of soft rocks produces a
greater potential for emissions than the processing of hard rock.
The type of ore also governs the hazardous constituents contained
in particulate emissions. For example, particulates from some
talc and sand and gravel processing are known to contain asbestos
and free silica, respectively.
33
-------
Equipment types and operating practices also affect uncon-
trolled emissions. Equipment selection is based on parameters
such as quarry characteristics, minerals processed, and desired
end products. Emissions from process equipment such as crushers,
screens, and conveyors, are generally a function of the amount of
material processed, its size distribution, and the amount of
mechanically induced velocity applied. The crushing mechanism
(compression or impact) of the crushers also affects emissions.
Climate is the most significant geographical factor affect-
ing uncontrolled particulate emissions. The wind velocity, wind
direction, amount and intensity of precipitation, and relative
humidity can affect emissions significantly, especially fugitive
emissions. For example, the level of emissions can be expected
to be greater in arid regions than in temperate ones. Other
geographical elements that affect fugitive emissions include the
topography and the extent and type of vegetation around a facil-
ity.
Seasonal changes affect emissions in several ways. For
instance, the lower moisture content of the ore and high evapora-
tion rate during the summer months cause uncontrolled emissions
to be higher than at other times of the year. Shutdown of many
operations during the winter months also affects total annual
emissions. ,
Fugitive Emissions— -
Fugitive dUSt constitutes a large portion of the emission
problem in the nonmetallic mineral industry. Drilling, blasting,
loading, hauling, dumping, storage piles, waste piles, overburden
removal, wind erosion of unprotected surfaces, and land reclama-
tion activities all contribute fugitive dust.
Particulate emissions from drilling operations are caused
primarily by air flushing the bottom of the hole to remove cut-
tings and dust. Compressed air is released down the hollow drill
center, forcing cuttings and dust up and out the annular space
formed between the hole wall and drill.
Emissions from blasting are inherently unavoidable. Factors
affecting emissions include the size of the shot, blasting pro-
cedures, rock type, and meteorological conditions, especially
wind.
Considerable fugitive dust emissions may result from loading
and hauling operations. Emissions emanate from load gathering,
loading operations, vehicular transport over the unpaved roads
associated with mining operations, and air motion across the load
during hauling. The most significant factor affecting emissions
during loading is the wetness of the ore. Factors affecting
34
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emissions from hauling operations are type of road surface,
wetness of the surface, and volume and speed of vehicle traffic.
Truck dumping generates dust as the material tumbles from
the truck bed and strikes the ground or the side of the receiving
hopper. Dust emissions may also occur at the edge of a spoils
slope when a truck dumps waste material or overburden. This
simple operation has been identified as a significant fugitive
dust source (30, 31).
Fugitive dust emissions from the storage area occur as a
result of several activities, which include, in order of de-
creasing significance, equipment and vehicle movement in the
storage area, wind erosion, loadout from the storage piles, and
loading onto the storage piles. The emissions from waste and
tailings piles are similar in mineralized identity to those from
primary storage piles, but because the particles are finer they
travel further.
Fugitive emissions associated with reclamation operations
result from wind erosion of unvegetated or partially vegetated
land. These emissions are related to wind speed, surface tex-
ture, and degree of vegetation cover (if any).
Emission factors for various phases of mining and process
operations are presented in subsequent sections of this report
covering individual minerals.
Process Emissions—
Although emissions from process point sources are signi-
ficant, they are easily controlled because the processes are
primarily stationary and the emissions emanate from a defined
point. Sources include crushing, grinding, screening, conveying,
and drying.
Generation of particulate emissions is inherent in the
crushing process. Emissions are most apparent at crusher or
grinder feed and discharge points. Factors that influence emis-
sions include the moisture content of the rock, the type of rock
processed, and the type of crusher used.
The most important element affecting emissions from crushing
and grinding equipment is whether the reduction mechanism is
compression or impact. This has a substantial effect on the size
reduction achieved, the particle size distribution of the product
(especially the proportion of fines produced), and the amount of
mechanically induced energy imparted to these fines.
Dust emitted from screening operations results from agita-
tion of dry rock particles. The level of uncontrolled emissions
35
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is dependent on the particle size of the material screened, the
amount of mechanically induced energy transmitted, and other
factors discussed earlier.
Generally, screening of fines produces higher emissions than
screening of coarse sizes. Also, screens agitated at large
amplitudes and high frequencies emit more dust than those oper-
ated at lesser amplitudes and frequencies.
Particulate emissions can occur in all material handling and
transfer operations. As with screening, the level of uncon-
trolled emissions depends on the size of the material and how
much it is agitated. The most emissions probably occur at con-
veyor belt transfer points where material is discharged from the
conveyor at the head pulley or received at the tail pulley. The
conveyor belt speed and the free-fall distance between transfer
points affect the volume of emissions from these sources.
Emission Control Technology
The diverse particulate emission sources in mining and
processing operations have resulted in the application of a
variety of control methods and techniques. Dust suppression
techniques for preventing particulate matter from becoming air-
borne are used to control both fugitive and process dust sources.
Collection systems are used to control particulate emissions that
can be contained and captured.
Control of Fugitive Dust Sources—
Almost all fugitive dust controls involve one (or a com-
bination) of three basic techniques: watering, chemical stabili-
zation, and reduction of surface wind speed across exposed sur-
faces. Watering costs the least but also provides the least
permanent dust control. Depending on the source of the dust,
water may effectively suppress the dust for only a few hours or
for several days. A film of moisture creates a direct cohesive
force that holds surface particles together; it also forms a thin
surface crust that is more compact and mechanically stable than
the material below and therefore less subject to producing dust
after drying. Since this crust and its dust-reducing capability
are easily destroyed by movement over the surface or by abrasion
from loose particles blown across the surface, repeated watering
is required to maintain the moisture film or surface crust.
Several types of chemicals are effective fugitive dust
reducers. These are applied directly to the surface of the dust
source. Some of the materials can "heal" (re-encrust) if the
treated surface is disturbed, but many will not reform a crust.
The effect of natural weathering on the life of the treated
surface also varies widely with different chemicals. The primary
36
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use of chemical stabilizers in the mining industry is for land
reclamation after the mining potential of an area has been ex-
hausted; however, chemicals may also be applied to piles of
overburden, waste, and tailings.
Air movement, or wind, contributes significantly to the
incidence of fugitive dust from all sources, thus the reduction
of wind speed across the source is a means of reducing emissions.
Construction of windbreaks and enclosures or coverings for the
sources, and the planting of grasses or grains on or adjacent to
the exposed surfaces are some methods of reducing wind speed, if
vegetative techniques are applied, the soil must provide nutri-
ents moisture, and proper texture, and must be free of materials
toxic to plant life.
The following paragraphs discuss in more detail how one or
more of the foregoing techniques control fugitive dust.
Control of drilling operations—The two methods generally
available for controlling particulate emissions from drilling
operations are water injection and aspiration to a control de-
vice.
Water injection is a wet drilling technique in which water
or water plus a wetting agent or surfactant is injected into the
compressed air stream used for flushing the drill cuttings from
the hole. The injection of the fluid into the airstream produces
a mist that dampens the ore particles and causes them to agglom-
erate. As the particles are blown from the hole, they drop at
the drill collar as damp pellets rather than becoming airborne.
The addition of a wetting agent increases the wetting ability of
water by reducing its surface tension (32).
Dry collection systems also may be used to control emissions
from the drilling process. A shroud or hood encloses the drill
rod at the hole collar. Emissions are captured under vacuum and
vented through a flexible duct to a control device for collec-
tion. The most commonly used are cyclones or fabric filters
preceded by a settling chamber. In this application collection
efficiencies of cyclone collectors are usually not high. They
are more suitable for coarse-to-mediura-sized particles than for
fine particulates. Fabric filter collectors, on the other hand,
exhibit collection efficiencies in excess of 99 percent.
Control of blasting operations—No effective methods are
currently available for controlling particulate emissions from
blasting. Good blasting practices, however, can minimize noise,
vibration, air shock, and dust emissions. Multidelay detonation
devices that detonate the explosive charges in millisecond time
intervals may reduce these adverse effects. Scheduling of blast-
ing operations to coincide with such favorable meteorological
37
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conditions as low wind speed and low inversion potential can
substantially reduce the impact of emissions from blasting.
Control of loading operations—The loading of dry raw mate-
rials generates fugitive dust emissions regardless of the method.
Limited control may be attained by wetting the materials before
loading. Water trucks equipped with hoses or movable watering
systems may be used.
Control of hauling operations—The hauling of raw materials
from the mine or quarry to the processing plant is responsible
for a large portion of the fugitive dust generated by the indus-
try. Temporary haul roads are built to accommodate advancing
quarry faces, and they are usually unimproved. The movement of
large, rubber-tired vehicles over these roads is a major source
of dust. The amount of these emissions relates directly to the
condition of the road surface and the volume and speed of vehicle
traffic. Consequently, control measures involve improving road
surfaces, supressing dust, and changing operations to minimize
the effect of vehicle traffic.
Various road treatment methods to control fugitive emissions
from haulage roads include watering, surface treatment with
chemical dust suppressants, soil stabilization, and paving.
Watering is the most common. Water is sprayed onto the road by
water trucks equipped with either gravity spray bars or pressure
sprays. The amount of water required, frequency of application,
and effectiveness depend on weather elements, road bed condition
and the willingness of the operator to allocate the necessary
resources to do an effective job.
Road dust can also be suppressed by periodically applying
wet or dry surface-treatment chemicals. Oiling is the most
common surface treatment. The frequency of application may range
from once a week to only several times a season, depending on
weather conditions. A potential adverse environmental impact of
this treatment is the floating away of the oil into streams or
percolation into aquifers. Oiling is sometimes supplemented by
watering; however, care must be exercised with this approach
since improper application can cause slippery, dangerous road
conditions.
Other treatments include the application of hygroscopic
chemicals (substances that absorb moisture from the air) such as
organic sulfonates and calcium chloride. When spread directly
over unpaved road surfaces, these chemicals dissolve in the
moisture they absorb and form a clear liquid that is resistant to
evaporation. Consequently, these chemicals are most effective in
areas with relatively high humidity. Since the chemicals are
water soluble, repeated application may be required in areas with
38
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frequent rainfall. Also these agents can contribute to corrosion
of expensive haulage vehicles.
Other alternatives include the following:
1. Soil stabilizers—These agents, which usually consist
of a water-dilutable emulsion of either synthetic or
petroleum resins and act as an adhesive or binder, are
applied once daily to the road surface. In addition to
being environmentally beneficial, these stabilizers
offer considerable savings and operating benefits over
traditional watering methods. Operators report reduced
labor costs, lower maintenance costs on haulage ve-
hicles, and safer road conditions.
2. Paving--Although it is probably the most effective
means of reducing particulate emissions, paving entails
high initial cost and requires subsequent maintenance
and repair of damage caused by heavy vehicle traffic.
3. Control of traffic speed and reduction of volume—
Replacing smaller haulage vehicles with units of larger
capacity would reduce the number of trips required and
the total emissions per ton of rock hauled. A
stringent program to control traffic speed also would
reduce dust emissions. According to a study on emis-
sions from conventional vehicle traffic on unpaved
roads, reducing the average speed from 48 kilometers
per hour (for which an emission level of 1.0 kilogram
per vehicle kilometer was established) to 40, 32, and
24 kilometers per hour resulted in emission reductions
of 25, 33, and 40 percent, respectively (33). Although
the situations may not be completely analogous, it can
be concluded that an enforced speed limit of 8 to 16
kilometers per hour would substantially reduce fugitive
dust emissions from quarry vehicle traffic and provide
the additional benefits of increased safety and longer
vehicle life.
4. Wind breaks—Planting of rapidly growing hedges or
construction of temporary wooden walls upwind of major
dust sources can reduce emissions by limiting the
movement of air across the dust-laden surfaces.
Control of aggregate storage piles—Aggregate stockpiles are
a significant source of fugitive dust. Emissions occur during
creation of stockpiles and from wind erosion of formed piles.
During the construction of stockpiles by stacking conveyors,
particulate emissions are generated by wind blowing across a
39
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stream of falling material and causing the segregation of fine
from coarse particles, and from the impact of falling aggregate
on the pile. Control methods include wet dust suppression and
devices designed to minimize the free-fall distance and thus
reduce both exposure to wind and force of impact.
Control devices include stone ladders, telescoping chutes,
and hinged-boom stacker conveyors. A stone ladder consists
simply of a section of vertical pipe into which material from the
stacking conveyor is discharged. The pipe has square or rec-
tangular openings at different levels through which the material
may flow. In the telescoping chute, material is discharged to a
retractable chute and falls freely to the top of the pile. As
the height of the stockpile increases or decreases, the chute is
gradually raised or lowered accordingly. A similar device, the
stacker conveyor, is equipped with an adjustable hinged boom to
raise or lower the conveyor according to the height of the stock-
pile.
An alternative is to install water sprays at the stacking
conveyor discharge pulley to wet the product. A pug mill can be
used to eliminate particulate emissions from very fine products
like stone sand by mixing the product with water before stock-
piling. Finely ground material that cannot be wetted should be
stored in silos until shipped.
Application of water is the technique most commonly used for
controlling windblown emissions from active stockpiles. A water
truck equipped with a hose or other spray device applies the
water.
The location of stockpiles behind natural or manufactured
wind breaks helps to reduce windblown dust. Also, active piles
should be worked from the leeward side. Even though they may
create load-out problems, stockpile enclosures or silos are the
only effective controls for very fine materials or materials that
must be stored dry.
Control of yard and other open areas—Fugitive dust emis-
sions from plant yard areas are generated by vehicle traffic and
wind. Generally, simply maintaining good housekeeping practices
will control emissions from 'these areas. Spillage and other
potential dust sources should be cleaned up. Brush-type or
vacuum-type street sweeping is effective on paved or other smooth
yard surfaces. Treating with soil stabilizers and planting
vegetation are viable control options for large open areas and
overburden piles. Many chemical stabilizers on the market pro-
vide some aid to the emergence and growth of vegetation and offer
effective control against rain and wind erosion (34).
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The application of soil stabilizers made of petroleum or
synthetic resins in emulsion is moderately effective for storage
piles that are inactive for long periods of time and for per-
manent waste piles or spoil banks. These chemical binders cause
the topmost particles to adhere to one another to form a durable
surface crust that resists wind and rain erosion as long as the
surface crust remains intact. However, wind errosion and freez-
ing and thawing can break up the surface.
Control of conveying pperations--Conveying operations may
produce fugitive dust emissions in addition to the emissions
generated at transfer points. These emissions may be either
mechanically induced or windblown.
Control methods include dust suppression and covering.
Covering open conveyors is the most effective way to provide
protection from wind and prevent particles from becoming air-
borne. Covered conveyors also yield certain operating benefits.
For example, during inclement weather the covers reduce potential
mud cake buildup on belts that can result in damage to conveyors,
hazardous operating conditions, screen blinding, and the produc-
tion of products that do not meet specifications because of
retention of fines.
Control of Particulates from Process Operations—
Operations at a typical nonmetallic mineral processing plant
generates dust at many points, including the crushers, grinders,
screens, conveyor transfer points, and storage facilities.
Consequently, effective emission control is complex and diffi-
cult. Control methods include wet dust suppression, dry collec-
tion, and a combination of the two. In wet dust suppression,
moisture is introduced into the material flow, causing fine
particulate matter to remain with the material flow rather than
become airborne. Dry collection involves hooding and enclosing
dustproducing points and exhausting emissions to a collection
device. Combination systems apply both methods at different
stages throughout the processing plant. Housing process equip-
ment in enclosed structures is another effective means of pre-
venting atmospheric emissions. Such buildings generally must be
vented through a control device.
Wet dust suppression--Wet dust suppression systems control
dust emissions by spraying moisture in the form of water or water
plus a wetting agent at critical dust-producing points in the
process flow, causing dust particles to adhere to larger mineral
pieces or to form agglomerates too heavy to become or remain
airborne. Thus, the objective of wet dust suppression is not to
capture and remove particulates emitted from a source, but rather
to prevent their emission by moist agglomeration at all process
stages.
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Water sprays are not practical in all cases because moisture
may interfere with further processing such as screening or grind-
ing, where agglomeration cannot be tolerated. Also the capacity
of the dryers used in some of the processing steps limits the
amount of water that can be sprayed onto the raw materials.
Since water cannot be added after the materials have passed
through the drying operations, other means of dust control must
be applied then.
The unusually high surface tension (72.75 dynes per square
centimeter at 20°C) requires that 5 to 8 percent moisture (by
weight), or greater, be added to adequately suppress dust (35).
In many installations this is not acceptable because excess
moisture can cause screening surfaces to blind, which reduces
both capacity and effectiveness, or can cause the coating of
mineral surfaces, which yields a marginal product or unacceptable
product. To counteract these deficiencies, small quantities of
specially formulated wetting agents or surfactants are blended
with the water to reduce surface tension and improve wetting
efficiency, thereby minimizing the moisture necessary to suppress
dust particles. Although composition of these agents may vary,
their molecules are characteristically composed of two groups, a
hydrophobic group (usually a long-chain hydrocarbon) and a hydro-
philic group (usually a sulfate, sulfonate, hydroxide, or ethy-
lene oxide). When introduced into water, these agents reduce its
surface tension appreciably (to as low as 27 dynes per square
centimeter) (36).
One or more spray headers fitted with pressure spray nozzles
distribute the dust suppressant mixture at each treatment point
at the rate and in the configuration required to effect dust
control. Spray actuation and control are important to prevent
waste and undesirable muddiness, especially during intermittent
material flow. Spray headers at each application point normally
are equipped with an on-off controller interlocked with a sensing
mechanism, allowing sprays to operate only when material is
flowing.
Dry collection systems—Particulate emissions generated at
plant process facilities (crushers, screens, conveyor transfer
points and bins) are controlled by capturing and exhausting the
emissions to a collection device. Depending on the physical
layout of the plant, emission sources are manifolded to one
centrally located collector or to a number of strategically
placed units. Dry collection systems consist of an exhaust
system with hoods and enclosures to confine and capture emissions
and ducting and fans to convey the captured emissions to a col-
lection device for particulate removal before the airstream
exhausts to the atmosphere.
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The proper design and balance of local exhaust systems,
including hooding and ducting, are required to assure that a
collection system effectively controls discharge of particulates
to the atmosphere. Process equipment should be enclosed as
completely as practicable, allowing access for routine mainte-
nance and inspection. Generally a minimum indraft velocity of 61
meters per minute should be maintained through all open-hood
areas (37). Proper design of hoods and enclosures minimizes
exhaust volumes required and, consequently, power consumption.
Proper hooding also minimizes the effects of cross drafts (wind)
and induced air (i.e., air placed in motion as a result of
machine movement or falling material). Good duct design dictates
that adequate conveying velocities be maintained to prevent
transported dust particles from falling out and settling in the
ducts en route to the collection device. Information on crushed
stone recommends conveying velocities for mineral particles in
the range of 1100 to 1400 meters per minute (37).
For proper dust control from process sources, hoods should
be installed at conveyor transfer points, screens, crushers,
grinders, and bagging operations. The fabric filter or baghouse
is the most effective dust collection device in the mineral
industry. Most crushing plants use mechanical shaker-type col-
lectors, which require periodic shutdown for cleaning (after four
or five hours of operation). These units normally are equipped
with cotton sateen bags and operated at an air-to-clpth ratio of
two or three to one. . A cleaning cycle usually requires no more
than 2 to 3 minutes of bag shaking, which is normally actuated
automatically when the exhaust fan is turned off.
For applications where turning off the collector is imprac-
tical, continuous-cleaning fabric filters are used. Jet-pulse
units are preferred over compartmented mechanical shakers.
Jet-pulse units ordinarily use wool or synthetic felted bags for
a filtering medium and may be operated at a filtering ratio of as
high as six or ten to one. With either type of baghouse, greater
than 99 percent efficiency can be attained, even on submicron
particle sizes (38).
Other collection devices include cyclones and low-energy
scrubbers. Although these collectors demonstrate high efficien-
cies (95 to 99 percent) for coarse particles (40-micrometer and
larger), their efficiencies are poor (less the 85 percent) for
medium and fine particles (20-micrometer and smaller) (38).
High-energy scrubbers and electrostatic precipitators could
conceivably achieve results similar to that of a fabric filter,
but these methods do not appear to be used in the industry.
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LIQUID WASTES AND CONTROL TECHNOLOGY
Liquid Wastes
Liquid wastes from construction materials and non-ferrous
metals mining show one major difference: effluent from construc-
tion materials generally contain only suspended inert solids,
whereas effluents from nonferrous metals are often acidic and
contain dissolved heavy metals (29, 39).
Liquid wastes come from three major sources:
1) Mine dewatering; For many mines this is the only
source of wastewater. It is usually low in suspended
solids, but may contain dissolved minerals or metals
(29, 39).
2) Process waters; This is water used in transportation,
classification, washing, beneficiation, separation, and
processing of ores. The effluent usually contains
heavy loadings of suspended solids, and in nonferrous
metals mining, dissolved metals (39).
3) Precipitation runoff; Since mining operations require
large surface areas, precipitation constitutes a major
• source of wastewater and pollutant loading. This water
also contains suspended solids such as minerals, silt,
sand, and clay, and possibly hazardous metals, depend-
ing on the type of ore mined (39).
Other major sources of water pollution primarily associated
with mining and beneficiation operations are acid mine drainage
and tailings pond leakage. Surface runoff near beneficiation and
processing facilities is another potential problem area.
Acid runoff can be produced by the leaching of precipitation
through any mine waste containing sufficient pyrite or other
sulfide. The presence of heavy metals compound the pollution
potential because at a low pH, the metals tend to dissolve in the
water.(40, 41).
Solid wastes are commonly disposed of in tailings ponds.
Wastewater streams are also treated in these ponds. The super-
natant decanted from these tailings ponds contain suspended
solids and sometimes cyanide or ammonia introduced to the water
during ore processing (42).
Percolation of wastewater from impoundments may occur if
tailings ponds, settling ponds, and lagoons are not designed
properly (29).
44
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Construction Materials—
Liquid wastes generated by construction materials mining are
primarily from mine dewatering, ore processing, and precipitation
runoff. They usually contain only inert suspended solids.
Process water and mine dewatering are controlled and contained by
pumping or gravity flow through pipes, channels, ditches, and
ponds. Surface runoff near ore processing facilities, haul
roads, conveyors, and storage piles are a potential pollution
source also. Surface runoff is generally untreated; however,
methods used to minimize erosion control suspended solids load-
ings in the effluent (39). Usually no .further treatment is
necessary to achieve a high effluent quality from tailings ponds
if the ponds are well-designed and the water does not contain
excessive concentrations of dissolved metals or other undesirable
ions (29, 42, 43).
Relative quantities and composition of the wastewater
generated vary from one mining category to another. Chapter 4
deals specifically with wastewater characteristics.
Nonferrous Metals—
Although effluents from the mining and processing of non-
ferrous ores generally contain such hazardous metals as lead,
copper, zinc, and nickel, these materials can be controlled to
acceptable levels by established waste management practices.
Wastewater generated by such ore processing operations as con-
centration, separation, and beneficiation are generally alkaline
and often contain dissolved metal ions and process reagents,
i.e., cyanide, methanol, and ammonia. Usually these waste
streams are discharged to a tailings pond for pH control and
solids settling. The supernatant is either treated before dis-
charge or is recycled to the mill. Partially oxidized sulfur
compounds may be present in mill effluent; unless they are
stabilized in a waste treatment system, they can cause acidic
conditions miles from the point of discharge (40).
Acid mine drainage is often a problem in mining nonferrous
metals because the ores usually contain sulfur compounds. The
impact of acid mine drainage depends on whether a pyrite is
associated with the ore being mined and the control techniques
applied to minimize acid formation.
Relative quantities and composition of these wastewater
sources vary from one mining category to another. Chapters 4 and
5 of this report contain more specific information on this sub-
ject.
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Control Technology
Control of water pollution can be achieved by proper mining
and land reclaiming methods, minimizing water contamination at
the source, and treating of effluents in well-designed and main-
tained facilities.
Control of contaminated runoff can be maintained effectively
by diking and diverting the surface flow to prevent the runoff
from higher elevated or undisturbed areas from coming in contact
with exposed surfaces, to reduce the surface flow velocity, and
to divert the contaminated runoff through sediment-detention
structures. These methods also minimize erosion (44).
The now extensive reclamation of mined-out areas not only
has aesthetic value but also reduces water pollution potential.
Sometimes the land is landscaped and revegetated; at other times
recreational lakes are developed from abandoned open-pit mines.
Other reclamation alternatives are physical-chemical soil stabi-
lization and soil amelioration (43).
The most common method of treating process wastewater is to
discharge it into the tailings pond to settle out the suspended
solids. Although discharge from the pond is usually of accept-
able quality to recycle or discharge, secondary treatment could
be necessary. Secondary treatment methods include clarifiers,
aerators, thickeners, and liming, which are installed for tail-
ings pond supernatant and/or process wastewaters. When the
effluent must be of high quality, it can be treated further by
ion exchange or reverse osmosis to remove dissolved metals.
Construction Materials—
Treatment and control of wastewaters generated from the
mining and milling of construction materials are normally not as
critical or complex as for nonferrous metals. Many mines have
only mine dewatering discharge. Discharges from tailings dis-
posal areas are sometimes a problem because of decreased resi-
dence time during high-flow periods. Chemical flocculation,
thickeners, clarifiers, centrifuges, and other suspended solids
removal techniques are rarely used (39).
'The following are wastewater treatment methods for construc-
tion materials:
Settling ponds—Settling ponds are widely used to remove
total suspended solids (TSS) because they are easier to construct
and less expensive to operate than other technologies. Effec-
tiveness depends on the settling characteristics of the solids
and the retention time. Settling ponds generally achieve reduc-
tions in TSS to 50 milligrams per liter or less; however, for
some wastewaters, the TSS content of the discharge is as high as
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150 milligrams per liter. Most facilities achieve a 95 percent
or better reduction in TSS. Settling ponds also provide equal-
ization, water storage capacity, and solid waste storage.
Flocculation—Flocculating agents, such as ferric chloride
(FeClo), alum [A1NH4(S04)4], and ferrous sulfate (FeSCO, and a
variety of polyelectrolytes increase the efficiency of^ settling
facilities and are most often used after the larger, more readily
settled particles have been removed.
Clarifiers and thickeners—Clarifiers or thickeners are
sometimes used to remove suspended solids. Consisting primarily
of tanks with internal baffles to provide efficient concentration
of solids and clarification of the liquid, these devices are
usually used by phosphate and industrial sand operations when
sufficient land for ponds is not available or when suspended
particles are too small to settle under gravity and flocculating
agents must be added.
pH control--Since some wastewaters, including mine drainage,
are either acidic or alkaline, they need to be brought to a pH of
6 to 9 before disposal or discharge. Acidic streams are usually
treated with alkaline materials such as limestone, soda ash,
sodium hydroxide, or lime. Alkaline streams are treated with an
acid such as sulfuric acid. Dissolved solids such as lead, zinc,
copper, manganese, and iron, are precipitated as hydroxides.
Lime is the most widely used reagent for acid water.
Precipitation—Sulfates, fluorides, hydroxides, and carbon-
ates can be precipitated by lime treatment (39). Sodium sulfate
is used to precipitate copper, lead, and other toxic metals. The
suspended precipitates are then removed by settling ponds, clari-
fiers, or thickeners, along with flocculating agents if neces-
sary.
Nonferrous metals—
Wastewaters generated from various beneficiation processes
are commonly discharged to a tailings pond to control pH. Heavy
metals are precipitated as hydroxide when pH is raised with
limes. Consistently high effluent quality can reach pH ranges
from 9.5 to 10.5 to precipitate copper, lead, zinc, and nickel
compounds.
Process wastewaters can also be treated with a mechanical
system, which includes settling, flotation, aeration, and, less
frequently, reverse osmosis or ion exchange. Cyanide and ammonia
used as flotation agents in the milling process may form toxic
compounds and residuals that cannot be stabilized in the waste
treatment system. The use of these compounds is discouraged
(41).
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The use of tailings impoundments is becoming less attractive
because of acid generation and metal leaching, which cause long-
term seepage problems and prevent vegetation of the area.
In control of water pollution, emphasis should be placed on
minimizing water usage and discharges and preventing pollution at
the sources.
The use of settling ponds, pH control, clarifiers, thick-
eners, flocculation, and precipitation, as described under Con-
struction Materials, are also used in nonferrous mining and
beneficiation operations. Other treatment methods include'oxi-
dation, adsorption, and reverse osmosis. These methods are
described in the following paragraphs:
Precipitation—Starch xanthate complexes are reported to be
effective in aiding precipitation of a variety of metals, includ-
ing cadmium, chromium, copper, lead, mercury, nickel, silver, and
zinc (45). Oxidation can be used in conjunction with starch
xanthate in special cases to produce less soluble, heavy-metal
products.
Oxidation—Several waste components produced by mining and
beneficiating of nonferrous materials can be removed or rendered
less harmful by oxidation (39). Among these are cyanide, sul-
fide, ammonia, and other compounds that cause high chemical
oxygen demand (COD) levels. Cyanide can be removed effectively
by rapid chlorination at a pH of 10.5. Generally when high COD
levels are occurring, aeration or the use of strong oxidants are
of value. (
Adsorption--The application of activated carbon adsorption
to mining and processing wastewater treatment is more limited by
cost than feasibility (39). The removal of flotation reagents or
solvent extraction compounds is practical in some operations if
the waste streams are segregated.
Ion exchange—Ion exchange equipment will remove various
ionic species (39). The disadvantages of using ion exchangers to
treat wastewaters generated by mining and beneficiating opera-
tions are high costs, limited resin capacity, and inadequate
specificity. The feasibility of applying ion exchangers depends
upon the resin loading achievable and pretreatment required.
Waste segregation and recycling enhance the practicability.
Since calcium ions are usually present in greater concentrations
than other metal ions, this method would not be feasible.
Reverse osmosis—A reverse osmosis plant for acid mine
drainage consists of pumps and filters for removal -of suspended
solids (43). Effluent from the filter enters a pressure chamber
48
-------
at the point of exposure to the membrane cells. Concentrated
brine passes from the unit and is treated or injected into a deep
well. The product water can be brought to potable quality by a
small increase in pH. Very high removal of dissolved solids,
sulfates, calcium, magnesium, and iron has been achieved by
reverse osmosis, but this method is not economical unless acid
mine drainage is to be used to supply potable water for municipal
use.
SOLID WASTES AND CONTROL TECHNOLOGY
Solid Wastes
In the mining industry, the major solid waste disposal
problem involves handling and relocation of overburden and
gangue. Overburden is the rock which overlies the ore body in
open pit, underground, and strip mines. In beneficiation opera-
tions such as screening and concentrating, the solid wastes
generated (tailings) essentially consist of the host rock. Other
solid wastes are produced from wastewater treatment and air
pollution control systems. All solid wastes that cannot be
recycled within a process must ultimately be disposed of by
landfilling or by impoundment on the surface (43).
Since huge volumes of wastes are produced, large-scale
impoundment facilities raust.be maintained. In underground mining
operations, the trend is to return the coarse tailings to the
areas underground as they are mined out and abandoned (29).
Characteristics of solid wastes from mining and benefi-
ciating operations vary according to industry and location.
Aside from the problem of containment, solid waste impound-
ments pose a potential water pollution problem in the form of
runoff, seepage, and leaching. Tailings pond effluent, as dis-
cussed earlier, has an acid-generating potential that can cause
metal dissolution.
Solid wastes from the mining of construction materials and
nonferrous metals are discussed below.
Construction Materials—
Generally, tailings and gangues from construction materials,
mining, and ore processing are relatively inert. Solid wastes
are impounded perpetually in tailings pond, and effluent from the
pond usually requires no additional treatment.
49
-------
Nonferrous Metals—
Solid wastes generated from nonferrous metals mining are
generally more hazardous than those from construction materials
mining. If the solid waste contains sufficient pyrite, sulfuric
acid can be generated and heavy metal can be leached out of the
rocks, as discussed earlier.
Control Technology
In general> the industry produces large quantities of solid
waste. Certain mining techniques can be used to minimize solid
waste generation; however, properly designed and maintained
containment and treatment facilities are necessary. Tailings
that contain a sufficient percentage of course materials (sands)
can be separated and the course sands used as embankment material
for the fines.
Impoundment basins must be designed to reduce or prevent
leakage, seepage, groundwater percolation, infiltration, and
overflow. Effluent sometimes requires additional treatment
before it is discharged to a stream or recycled to the process.
Dikes must be designed SO as to maximize stability, and if solid
residue piles are not managed properly, they constitute sources
of fugitive dust and stream sediment in runoff. Vegetative
stabilization is often used to minimize these problems (39).
The principal methods of solid waste utilization are dis-
cussed in the following paragraphs.
Revegetation—Implanting a vegetative cover on mineral
mining wastes or mined areas is called revegetation. This method
serves to stabilize erodible slopes, minimize water pollution,
control dust, and facilitate crop-producing potential.
Chemical and physical waste stabilization—Chemical and
physical waste stabilization of mine wastes is sometimes used
instead of revegetation to minimize fugitive dust and water
pollution (43). Also, chemical stabilization is often used in
conjunction with vegetation to protect the plants.
Physical stabilization is a method that involves covering
the wastes with erosion-resistant waste rock from the mining
operation, when it is available. Coverage with topsoil and bark
is also considered a physical method that offers aesthetic advan-
tages .
Chemical stabilization ranges from the use of soil sealants
to the application of fertilizers for amelioration of soil to
enhance plant growth. Chemical stabilizers, however, are gen-
erally defined as chemical agents that bind waste surfaces to
50
-------
prevent erosion. The main advantage of chemical stabilizers is
that they protect the vegetative covers during early stages of
growth. They normally cannot be expected to be permanent.
Soil Amelioration
Amelioration of soil properties is essential before revege-
tation on some mine wastes. Salinity, pH, and nutrient content
are critical factors that require amelioration. Some ameliora-
ting agents that increase pH are lime, crushed limestone, asbes-
tos, tailings, fly ash, and sewage. Agents that decrease pH are
pyrite-rich tailings, powdered sulfur and acids. Nutrients can
be added by fertilizing or applying sewage sludge.
Construction Materials—
Solid waste disposal techniques are not significantly dif-
ferent from those just discussed. Wastes generated from this
category are generally less hazardous and pose fewer environ-
mental problems than nonferrous metals mining. When acid mine
drainage is a potential problem, special attention to disposal
methods and maintenance is needed. Sometimes, too, specific
problems are associated with certain mining categories. In
asbestos mining, for example, asbestos fibers in the solid waste
present fugitive dust and water pollution problems if not managed
properly.
Nonferrous Metals—
Although impoundments are often the only alternative, they
become unattractive when tailings contain significant concentra-
tions of pyrite or similar sulfides that lead to acid generation
and leaching of metal values. Long-term environmental problems
are prevalent and difficult to solve (41).
The processing of tailings to recover the metal values has
been found to be economically infeasible. With the combined
effect of higher market values, improved technologies, and long-
term environmental implications, metal recovery may become more
attractive in the future (41). Some reworking of tailings oc-
curred when flotation technology replaced the gravity separation
techniques of early mining days. Hydrometallurgy may produce an
analogous activity in the future.
Rehabilitation includes revegetation of tailings areas;
control of contaminated surface, mine pit, and underground dis-
charges; control of mining subsidence; improvement of the general
aesthetics; and area redevelopment (41). The uptake of toxic
materials in the vegetation is a source of concern where vegeta-
tion can be harvested or consumed by wildlife or domestic ani-
mals.
51
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HAZARDOUS WASTES (43, 46, 47)
The term hazardous wastes means any waste or combination of
wastes which pose a substantial present or potential hazard to
human health or living organisms because such wastes are lethal,
nondegradable, persistent in nature, biologically magnified, or
otherwise cause or tend to cause detrimental cumulative effects.
General categories of hazardous wastes are toxic chemicals,
flammable, radioactive, explosives, and biological. These wastes
can take the form of solids, liquids, gases or sludges.
There are numerous sources of hazardous wastes in the mining
of construction materials and nonferrous metals. These wastes
could originate from the mining or extraction of the ore, pro-
cessing of the ore and as the constituents of waste streams.
These wastes may be in the form of fugitive particulates, gaseous
and liquid wastes as well as solid wastes.
The toxicity and adverse environmental effects of some of
the potentially hazardous materials associated with the mining
activity are summarized below:
0 Solid wastes from mining activities, which consist
mainly of overburden and gangue are in general not
toxic; however they may be hazardous to health. on
another basis (e.g. asbestiform minerals) or become a
source for toxic emissions as they weather and other-
wise alter with time to give up undesirable chemicals.
0 The most significant source of liquid wastes in the
mining industry is acid mine drainage. Acid mine
drainage can be extremely damaging to aquatic life.
Heavy metal (copper, nickel, lead, zinc) ions found in
acid mine drainage are often in concentrations suffi-
cient to be harmful or even toxic to aquatic life. At
pH levels below 5, most fish life dies.
0 Particulates generated as a result of mining of asbes-
tos are a known health hazard in air and possibly
water.
0 Cyanide is used as a flotation reagent in many base
metal mines, including cyanidation circuits for gold
extraction. Cyanide is highly toxic and its use is
generally discouraged in favor of alternate reagents.
0 Free silica which is emitted as fugitive dust from sand
and gravel operations may result in development of a
pulmonary fibrosis (silicosis) if exposed for a pro-
longed time.
52
-------
Mill effluent has characteristics that have a chemical
or a biochemical oxygen demand, some of which may be
toxic to animals or plants.
Milling practices for the recovery of gold may produce
a cyanide-leach problem. Process wastes from mining
activities are often ponded at many facilities. There
is a strong tendency for leaching out heavy metals to
nearby streams, which can make it unsuitable for fish
and other aquatic organisms.
Toxic effects caused by the discharge of reagents or
residuals other than heavy metals can alter the re-
ceiving stream environment making it unsuitable for
habitation by native biota.
53
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SECTION 4
NONMETALS
DIMENSION STONE
Industry Description
"Dimension stone" is rock which has been specially cut or
shaped for use in buildings, bridges, curbing, and other con-
struction or for special applications. Large quarry blocks
suitable for cutting to specific dimensions also fall into this
classification. The principal dimension stones are limestone,
granite, marble, sandstone, slate, and basalt.
The dimension stone industry accounted for less than 0.5
percent of total stone output in 1974, and 4 percent of the total
value. It consisted of approximately 500 plants in 44 states and
produced $100 million worth of construction, monumental, and
speciality products (1). Section 1 presents production statis-
tics for dimension stone.
Nearly every state in the Union produces dimension stone.
Igneous and metamorphic rocks are predominant in the Appalachian
and Rocky Mountain belts, but granite is also produced in
Missouri and in several of the North-Central states. Nearly all
of the slate now comes from six Atlantic states from North
Carolina to Maine, however, a small quantity is still produced in
Utah. Michigan and several southern states also produced small
amounts in the past. Limestone and sandstone are the predominant
dimension stones in the sedimentary formations of the Midwest and
also occur widely elsewhere in the United States.
Construction consumes more than 75 percent of the dimension
stone in the United States, with exterior and interior facing
panels for buildings taking the major share. Curbing, flagging,
and slate roofing comprise the other significant construction
uses. Monument works consume another 20 percent of the dimension
stone output, mostly for gravestones and markers. Miscellaneous
uses that account for the rest of the output include slate,
electrical panels, blackboards, billiard tabletops, and various
decorative panels for furniture, such as tops for dressers and
tables (1).
54
-------
Clays, lithium, and gypsum are the only significant by-
products in dimension stone production. Flake mica, which occurs
in igneous and metamorphic rocks, is a potential by-product
worthy of attention. Stone is obtained in conjunction with
production of many metallic and nonmetallic ores (1).
Process Description
Dimension stone is obtained from open-pit quarries. (Figure
11 presents a simple diagram of the steps involved in its mining
and beneficiation.) Quarrying can be accomplished by one of the
following techniques (39):
0 Drilling with or without broaching
0 Channeling by machine (semi-automated, multiple-head
chisels)
0 Sawing with wire
0 Using low level explosives
0 Using high-velocity jet flames to cut channels
0 Using splitting techniques
After a large block of stone-is freed, it is either hoisted
onto a truck and driven from the floor of the quarry to the
processing facility, or it is removed from the quarry by means of
a derrick, then loaded onto a truck.
At the processing facility (usually located at or near the
quarry) the blocks of stones are first sawed into slates by gang
saws, wire saws, or, occasionally, rotating diamond saws. All
sawing systems require considerable water for cooling and par-
ticle removal; however, the water is usually recycled.
After the blocks have been sawed into slabs of predetermined
thicknesses, they are ready for finishing. Finishing operations
vary and depend either on the properties of the stone itself or
on the characteristics of the end product. Some of the finishing
operations are splitting, trimming, and polishing (39)'.
Waste Streams
Table 7 presents a summary of multimedia wastes from the
mining and beneficiation of dimension stone, and the following
paragraphs explain in more detail the various air, liquid, and
solid wastes associated with this industry.
55
-------
WATER
WATER
Ln
cflP *& ? ? \ \
OVERBURDEN EXTRACTION LOADING _ TRANSPORT
REMOVAL OF ORE "" OF ORE OR ORE ->AW1NG
1 *
„.,„«
1 ^P
LEGEND _V
k . SETTLING
\. LIQUID WASTES fOND
T GASESOUS EMISSION 1
1 DISCHARGE
/ SOLID HASTES
i
I
K
SETTLING
POND
1
DISCHARGE
PRODUCT
f
Figure 11 . Mining and beneficiating of dimension stone.
-------
TABLE 7. SUMMARY OF MULTIMEDIA WASTES FROM MINING AND
BENEFICIATING OF DIMENSION STONE
Air
Source
Overburden
removal
Ore
extraction
Ore
loading
Ore
transport
Pollutant
Particulatea
Uncontrolled
emission
rate
N.A.
Liquid
Source
Overburden
removal
Ore
extraction
Sawing
Finishing
Pollutant/
parameter
TSS '
TSS
TSS
Uncontrolled
discharge
a
< 25 mg/t
N.A.
N.A.
.Solid
Source
Overburden
removal
Ore
extraction
Settling
pond
Pollutant
Waste rock
Sludge
Uncontrolled
quantity
M.A.
N.A.
Ul
* Ref. 30.
N.A. - Not available.
-------
Air Emissions—
The quarrying operation is the major source of air emissions
in the dimension stone industry, as all other operations are
accomplished using water. No data are available on the quantity
of particulate emissions however.
Liquid Wastes—
Pit pumpout is a seasonal occurrence in some dimension stone
facilities. The quality of the mine water depends more on stone
type than any other factor. For example, pumpout at one granite
quarry contains 26 mg/liter total suspended solids. However,
limestone, marble, and dolomitic limestone quarry water is gener-
ally very clear and much lower in suspended solids (39). Most
limestone and some granite quarries use water for channel cutting
and water is also used in small quantities during wet drilling.
All sawing operations require water. The raw waste load
from these operations contains a significant load of suspended
solids, as do the untreated effluents from finishing facilities.
Sawing and the finishing operations are often under the same roof
and water effluents are combined.
Water usage varies according to stone processes, water
availability, and owner or operator attitudes on water usage.
Table 8 shows water usage data for various dimension stone faci-
lities (39).
TABLE 8. DIMENSION STONE WATER USE DATA
Stone type
Mica Schist
Limestone
Granite
Marble
Water use, liter/Mg of stone
processed
Saw plant
4,460
16,600
7,350
100,000
Finish plant
None
1,600
7,360
Unknown
Source: Ref. 39.
Solid Wastes—
Overburden and waste rock are generated from the quarrying
operation. Another source of solid wastes is the settling pond,
which generates sludge. Quantitative data on these wastes have
not been reported.
58
-------
Control Technology
Control technologies applied to the dimension stone industry
are explained in the following paragraphs.
Air Emissions Control—
Farticulate emissions from quarrying operations and haul
roads are controlled by wetting.
Liquid Waste Control—
Effluent from the quarry is discharged into a sump for
continuous recycling and is rarely discharged.
wastewater from both sawing and finishing operations is
first discharged into a settling pond, where most of the sus-
pended solids are allowed to settle out. Sometimes effluents
from these operations are combined and discharged into a common
pond. The settling pond is reported to reduce total suspended
solids by more than 96 percent (39). Treated wastewater is
recycled as process water.
Solid Waste Control—
The overburden and waste rock from quarrying operations is
either stockpiled on site or crushed and screened to smaller
sizes for use as aggregates.* Settling pond sludge is hauled to
an on-site dumping area, where runoff water is controlled to
reduce TSS levels to any nearby streams.
Conclusions and Recommendations
Environmental impacts from the dimension stone industry are
minor compared to the crushed stone industry. Air, liquid, and
solid wastes are amenable to conventional treatment technologies.
Effluent from sawing and finishing operations is sent to
settling ponds (usually in series) for treatment. Sludge that
accumulates in the pond is removed periodically and disposed of
on-site. The properties of the sludge are such that bricks might
possibly be made from it. Using sludge and other solid waste for
this purpose warrants further investigation to determine its
technical and economic feasibility.
*Telephone conversation between Vijay Patel of PEDCo and
Mr. Max Jurras, Division of Air and Solid Wastes, State of
Vermont, Montpelier, Vermont. April 1977.
59
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CRUSHED STONE
Industry Description
Crushed stone is derived principally from limestone, dolo-
mite, granite, trap rock, sandstone, quartz, and guartzite (48).
Less than 5 percent comes from calcereous marl, marble, shell,
and slake.
Crushed and broken stone refers to rock that has been re-
duced in size after mining to meet various consumer requirements
(1). The United States is the leading producer of crushed stone,
and this industry is responsible for more than 99 percent of all
stone produced in this country. Firms range in size from small
independent producers with single plants to large diversified
corporations with 50 or more plants. Plant capacities range from
less than 2.27 x 104 to about 1.36 x 106 megagrams per year (1).
Section 1 presents production statistics for crushed stone.
Plants are widespread geographically, with all but one state
reporting production in 1974. Crushed granite comes primarily
from the Rocky Mountain and Appalachian areas, basalt from the
northeast sections of the Rocky Mountains and Hawaii (where it is
the principal crushed stone), and shell from the Gulf Coast and
Atlantic Coast States. Arkansas, California, and Pennsylvania
produce over half of the total output of quartzitic stone, and
the balance of the production is scattered over 32 other states
(1).
Construction consumes 86 percent of the crushed stone pro-
duced in the United States, with highway construction leading in
quantity, followed by building construction. All major types of
crushed stone (limestone, quartzite, granite, etc.) are used for
construction. Closely related to the direct construction use is
the quantity that goes into cement production. Crushed stone is
also used as a source of calcium in agriculture; as flux in the
iron and steel industry; as a water softening agent; and in the
making of glass, refractories, and chemicals.
The only significant by-products are clays, lithium, and
gypsum. Some stone is obtained in conjunction with the produc-
tion of metallic ores and nonmetallic minerals. Although most of
it is dumped as waste for lack of local demand, small quantities
are marketed.
Process Description
Although most crushed and broken stone is presently mined
from open quarries a trend is growing in many areas toward large-
scale production by underground mining methods. In 1974 about 5
60
-------
percent of all crushed stone production came from underground
mines (1). Shell dredging, mainly from coastal waterways,
accounts for approximately 1 percent of total production (39).
The crushed stone is beneficiated by both dry and wet processes.
In the quarrying operation, the overburden is removed and
the raw material is loosened by drilling and blasting. The
steep, almost vertical walls of the quarry may be several hundred
meters deep. The mine is normally excavated on a number of
horizontal levels (called benches) at various depths. The
material is loaded into trucks for transport to the processing
facility. Occasionally a portable processing facility, which can
be situated near the blasting site, is set up on one of the
quarry benches or on the quarry floor. Specific methods vary
with the nature and location of the deposit (39).
At the processing facility (Figure 12) the raw material
passes through screening and crushing operations before final
sizing and stockpiling. Consumer demands for various product
grades determine the number and position of the screens and
crushers. No process water is used in the crushing and screening
of dry-process crushed stone.
Excavation and transportation of crushed stone for wet
processing are identical to those for dry processing. The pro-
cess is also the same except water is added to the system to wash
the stone. This washing is normally done by spray bars that are
added to the final screening operation after crushing. Since not
all of the product is washed, a separate washing facility or
tower is incorporated that receives only the material to be
washed. This separate system usually consists only of a set of
sizing screens equipped with spray bars. A portable processing
facility can also incorporate a portable washing facility to
satisfy the demands for a washed product.
Waste Streams
Table 9 summarizes multimedia wastes from the mining and
beneficiation of crushed stone. The following paragraphs explain
in more detail the various air emissions and liquid and solid
wastes associated with this industry.
Air Emissions--
The major pollutant emitted during the production of crushed
stone is respirable dust containing free silica. Both open-pit
and underground mining activities generate considerable particu-
late emissions. Sources include drilling, blasting, secondary
breaking, and loading and hauling of the minerals to the proces-
sing plant.
61
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\
LEGEND
LIQUID WASTES
CIHAUST
GASESOUS EMISSION
a\
M
i •
^
OURFUHKN
RENOV»I.
one
EIIBACIIOII
r
UHDISG
<
out
ciiRACiioN
ORE
LOAOIkC
40UUD HININC
r
c
ORE
LOADING
IHAI.iWM!
TO SURFACE
1
^
1
1
1
1
1
1
J
?
one I
iRANbRonr 1
fA""ICfIlIC" ? SOLID
HOOO "I
1 1
1
o 9 9 9 i
i
i
1 "" i
i
D«» PROCESS J
WAUR
o o 9 i t>
SCf[[N 1
WASH 1
i y
SEI:II;C
POtlD
1
CFFLUtNT
Mtl "ttfSS _1
Figure 12. Mining and beneficiating of crushed stone.
-------
TABLE 9. SUMMARY OF MULTIMEDIA WASTES FROM MINING AND
BENEFICIATING OF CRUSHED STONE
Air
Source
Overburden
removal
Ore
extraction
Ore
loading
Ore
transport
Underground
mining
Crusher
Screen
Pollutant
Fugitive
particulates
Fugitive
particulates
Particulates
Uncontrolled
emission
rate
N.A.
N.A.
0.2S to 3.04
kg/Mga
Liquid
Source
Overburden
removal
Ore
extraction
Ore
loading
Ore
transport
Underground
mining
Screen and
wash
Pollutant/
parameter
TSS
(Mine
pumpout)
N.A.
Uncontrolled
discharge
1 to 128 mg/t
N.A.
Solid
Source
Overburden
removal
Ore
extraction
Fabric
filter
Settling
pond
Pollutant
Gangue
Particulatea
Sludge
Uncontrolled
quantity
•
N.A.
N.A.
N.A.
CJ
a Kef. 33,
N.A. - Not'available.
-------
Particulate emissions from drilling operations are primarily
caused by air-flushing to remove cuttings and dust from the
bottom of the hole. The level of uncontrolled emissions depends
on the type of ore, its moisture content, the type of drill used,
the diameter of the hole, and the penetration rate. Emissions
from blasting depend on the size of the shot, blasting practices,
mineral type, and meteorological conditions (especially wind).
Emissions from secondary breaking are relatively insignificant
(25).
Considerable fugitive dust emissions result from loading the
product and hauling it over unpaved roads. The most significant
factor affecting emissions during loading is moisture content of
the ore. Although no data were found on hauling operations, an
emission factor of 0.55 kilogram per vehicle kilometer has been
reported for conventional vehicle traffic on unpaved country
roads (33). It can be assumed that mineral hauling emissions are
higher because of the greater size of the rubber-tired units and
the finer texture of the typical road bed. Factors affecting
fugitive dust emissions from hauling operations include the
composition and wetness of the road surface and the volume and
speed of vehicle traffic (25).
The generation of particulate emissions is inherent in the
crushing process. These emissions, which are most apparent at
crusher feed and discharge points, may be influenced. by such
factors as the moisture content of the rock, the type of rock
processed, and "the type of crusher used.
Dust is emitted from screening operations as a result of the
agitation of dry stone. The level of uncontrolled emissions
depends largely on particle size of the material screened and the
amount of mechanically induced energy. Emission factors for
various crushing and screening operations are shown in Table 10.
TABLE 10. PARTICULATE EMISSION FACTORS FOR
STONE CRUSHING PROCESSES
Process Operation
Uncontrolled emission
factor, kg/Mg of ore processed
Primary crushing
Secondary crushing and
screening
Tertiary crushing and
screening
0.25
0.76
3.04
Source: Ref. 49.
64
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Liquid Wastes—
Mine pumpout is the major source of liquid wastes in both
open-pit and underground mines. Mine water comes from ground-
water, precipitation, or surface runoff. Data from several mines
indicate a total suspended solids range of 1 to 128 parts per
million (39).
The dry process does not produce any other liquid wastes. In
the wet process, however, the crushed stone is washed by spray
bars in the final screening operation. The quantity of water
required for washing depends upon the deposit from which the raw
material is extracted. The quantity of wash water reported in
several facilities has ranged from 0.041 to 1.26 cubic meters per
megagram of product (39).
Solid Waste —
Overburden and gangue are the major sources of solid wastes
in open-pit and underground mines. Although typical overburden
ranges from 0.9 to 1.5 meters, it can be as high as 3 to 4.5
meters.*
Other sources of solid wastes include the dust collected by
the dry collection device (fabric filter) and sludge accumulation
in settling ponds. Quantitative data on these wastes are not
available.
Control Technology
Control technologies applied in the crushed stone industry
are covered in the following paragraphs.
Air Emissions Control—
Water injection and aspiration to a control device are the
two methods normally used to control particulate emissions from
drilling operations. The most common control devices are cy-
clones or fabric filters preceded by a settling chamber. Whereas
collection efficiencies of cyclones seldom exceed 80 percent, the
efficiencies of fabric filters are usually over 99 percent. Air
volumes required for effective control range from 14 to 42 cubic
meters per minute depending upon the type ^of rock drilled, the
hole size, and the penetration rate (48).
No effective method for controlling particulate emissions
from blasting' is yet known; however, good blasting practices can
minimize the effects of noise, vibration, air shock and dust
emissions.
*Telephone conversation between Vijay Patel of PEDCo and
Frederick Allen, North Carolina Aggregate Association,
Raleigh, North Carolina. April 1977.
65
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Wetting the rock prior to loading helps to control fugitive
dust from loading operations. This is done with water trucks
equipped with hoses or movable watering systems (48).
Various road treatments used to control fugitive emissions
from haulage roads include watering, surface treatment with
chemical dust suppressants, soil stabilization, and paving.
Process emissions from crushers, screens, conveyor transfer
points and storage facilities are controlled by devices such as
wet dust suppression, dry collection, and a combination of the
two. The wet dust suppression device introduces moisture into
the material flow, causing fine particulate matter to be confined
and remain with the material flow rather than become airborne.
Dry collection involves hooding and enclosing dust-producing
points and exhausting emissions to a collection device. Using
enclosed structures for process equipment is also an effective
means of control (48).
Hooding and air volume requirements for the control of
crusher emissions vary greatly according to judgment and exper-
ience. The only established criterion is that of maintaining a
minimum indraft velocity of 61 meters per minute through all open
hood areas (48).
Screening operations generally apply a full coverage hood to
control emissions. Required exhaust volumes vary with the sur-
face area of the screen and the amount of open area around the
periphery of the enclosure. A minimum exhaust rate of 15.56
cubic meters per minute per square meter of screen area is
commonly used, with no increase for multiple decks (1).
The most commonly used dust collection device in the crushed
stone industry is the fabric filter, which is more than 99 per-
cent efficient. Other reported collection devices include cy-
clones and low energy scrubbers (48).
Liquid Waste Control—
Pit pumpout is discharged directly without treatment, dis-
charged after treatment, or discharged along with treated efflu-
ent from the washing operation. In this last method, quarry
water combines with the untreated facility effluent and then
flows through a settling pond system prior to discharge. In this
type of 'facility, much of the combined pond water is recycled
rather than discharged (39).
All facilities send effluent from washing operations through
a settling pond system prior to discharge. The system design
generally includes at least two settling ponds in series to
reduce the suspended solids in the final discharge to less than
66
-------
50 milligrams per liter. Reduction in the concentration of
suspended solids has been reported to exceed 95 percent (39).
Many facilities recycle a portion of their treated effluent. In
many instances, evaporation and percolation tend to reduce the
flow rate of the final discharge.
Solid Waste Control—
The solid waste (overburden) from open-pit mining is either
stockpiled on site or used in reclamation. Small quantities of
solid waste from underground mining operations are usually left
within the mine site.
The large quantities of solids collected in the fabric
filters are sometimes marketed. When a market is not available,
the waste is dumped on site. Sludge from the settling ponds is
also disposed Of on site. These wastes can cause an adverse
environmental impact if they become airborne or if harmful con-
stituents wash into surface waters and leach into groundwater.
Conclusions and Recommendations
Treatment technologies currently available in the crushed
stone industry are generally adequate to maintain environmental
standards.
An area that might be researched is locating a steady market.
for sludge from the settling ponds and particulate matter col-
lected in the fabric filter.
CONSTRUCTION SAND AND GRAVEL
Industry Description
On a product weight basis, the sand and gravel industry is
the second largest nonfuel mineral industry in the United States.
Historically, these products have been the principal construction
materials in the United States, and from all indications they
will continue to be. The industry is one of the fastest growing
in the mineral field, producing enough sand and gravel to satisfy
the total domestic requirement. Every state in the Union re-
ported some production in 1974, and active or latent deposits are
located in nearly every county. Although resources are inex-
haustible on a national basis, some local shortages exist.
,Since sand and gravel are produced by weathering of rock,
they are predominantly silica; however, they often contain other
minerals such as iron oxides, mica and feldspar. The particle
size of sand ranges from 0.065 to 2 millimeters, whereas gravel
consists of naturally occurring rock particles larger than 4
67
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millimeters but less than 64 millimeters in diameter (2). Par-
ticles finer than sand are referred to as silt, and particles
larger than gravel as cobbles and boulders.
In 1974, 4844 sand and gravel companies operated 6697 sep-
arate facilities. Annual production of individual companies
varies greatly (the range was 4.54 to 3.63 x 10 megagrams in
1974), but the average company is small (2).
Total sand and gravel resources that can be reached at
current exploritation costs are estimated to be 5.90 x 10
megagrams which is adequate to meet ,the projected cumulative
requirements through 2000 (3.61 x 10 megagrams). By 2000,
approximately half of the sand and gravel requirements will still
come from deposits of material similiar to those now being ex-
ploited and the remainder from lower grade deposits and possibly
offshore resources.
The sand and gravel industry extends into every state.
Production in 19745ranged from 1.1 x 10 megagrams in California
to about 9.9 x 10 megagrams in Hawaii. Following California,
the next five states in terms of total output are Wisconsin,
Michigan, Illinois, Ohio, and New York.
Sand and gravel have both construction and industrial uses.
However, construction consumes more than 95 percent of the total
volume, leaving less than 5 percent for industrial applications.
Specific uses of construction sand and gravel are covered in this
section; industrial uses will be covered later under Industrial
Sand.
The end use of construction sand and gravel is determined by
such factors as the ratio of sand to gravel, particle size,
particle shape, rock type, and chemical composition. Sand and
gravel can be used directly after limited processing (e.g.,
cleaning and sizing) or mixed with other materials to form a
different product, such as portland cement. In 1974, highway and
street construction accounted for 63 percent of the total demand.
Sand and gravel aggregates go into concrete and bituminous paving
mixes, concrete structures such as bridges and tunnels, road-base
material, and fill. As the second largest consumer, general
building and other heavy construction industries accounted for
about 25 percent of the total 1974 demand. Most of the sand and
gravel is used as aggregate in concrete, with small quantities
used for fill, septic fields, and "other building construction
purposes. About 7 percent is consumed by the building industry
for concrete construction materials such as brick and concrete
block.
68
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Although sand and gravel generally are used in combination
as a single product, they can be used separately. Sand has the
wider range of usage. It is used in architectural structures,
mortar, plaster, all forms of road and pavement construction, and
for purposes other than construction.
Almost no by-products or coproducts are recovered in the
sand and gravel industry. Traces of gold and silver have been
recovered during extraction, but quantities are miniscule.
Potential salable by-products/coproducts include heavy minerals,
flake mica, and clay, but little attempt has been made to recover
any of these (2). The increasingly stringent regulations on land
disturbance and solid waste disposal may soon require more com-
plete recovery of salable materials.
Process Description
Sand and gravel producers may turn out one product or a
range of products. Some operations sell only bank-run material,
which requires no processing, whereas others sell material that
has been subjected to various processing techniques. Most pro-
ducers are engaged exclusively in the sand and gravel business,
but some are diversified.
When sand and gravel deposits are large, permanent installa-
tions are built and operated for. many years. Portable and semi-
portable units are used in pits that have an intermediate working
life. Many facilities operate year round, and others operate on
a limited basis depending on such factors as weather and/or
product demand.
Sand and gravel are usually found in the same deposit, but
proportions vary greatly. This sand to gravel ratio, the chemi-
cal and physical characteristics of the gravel deposit, and the
specifications of the user govern extraction and processing
equipment/methodology at a specific site.
Currently, three methods of sand and gravel excavation are
practiced: (1) dry pit (sand and gravel are extracted above the
water table); (2) wet pit (raw material is extracted by means of
a dragline or barge-mounted dredging equipment both above and
below the water table); and (3) dredging (sand and gravel are
recovered from public waterways such as lakes, rivers, and es-
tuaries ). The breakdown in the United States is as follows: 50
percent by dry pit; 30 to 40 percent by wet pit; and 10 to 20
percent by dredging of public waterways (51).
Although the extracted raw material can be processed by
various methods, most are similar in that they involve some form
of transporting, screening., washing, crushing, blending, and
69
-------
stockpiling. The most common extraction/processing methods are
illustrated in Figure 13a and 13b and described in the following
paragraphs.
Dry Process—
After a site is cleared and overburden is removed, sand and
gravel are extracted from the deposit by front-end loaders, power
shovels, or scrapers. The raw ore is then transported to a
processing facility by conveyor or truck.
In the initial step of dry beneficiation sand is separated
from gravel via inclined vibrating screens. The sand and gravel
are then sized as they pass through a number of screens of vary-
ing mesh sizes. Material too large to pass through the screens
is crushed and resized.
Wet Process—
The site is cleared, overburden is pushed back, and the pit
is flooded. The sand and gravel are then recovered by dragline,
suction dredge, or bucket dredge. The raw material is trans-
ported to a processing facility by conveyor belts, slurry lines,
trucks, or barges. There the sand and gravel are first dumped
into a hopper or coarse ore bin covered by a grizzly, where the
raw material is subjected to primary and secondary screening and
crushing (52). Primary crushing reduces the particle size to
less than 5 centimeters and secondary crushing reduces it to less
than 3-3/4 centimeters (52). Primary crushing is performed by
cone or gyratory crushers and secondary crushing by roll
Crushers. Screens can be horizontal or sloped, single or multi-
deck. They also may be either vibrating or revolving, and they
are frequently heated to prevent clogging. Wash water is sprayed
on the product throughout•the screening/crushing operation. The
material is sometimes washed further by passing it through log
washers or rotary scrubbers.
Following initial screening, crushing, and washing, the
material is fed to a battery of screens for product sizing. The
different sizes of gravel are discharged from these screens into
bins or conveyed to stockpiles or sometimes to crushers and other
screens for further processing. The sand fraction coming off of
the battery of screens is fed to classifiers, separatory cones,
or hydroseparators for additional washing, sizing, and water
removal. At most facilities, two size categories of sand are
stockpiled: coarse (1 to 0 centimeter) and fine (1/3 to 0 centi-
meter) (52). The sized sand and gravel are then ready for
various degrees of blending as required for use in building
construction or concrete and bituminous paving.
At several facilities heavymedia separation (HMS) is used
prior to wet processing to remove very fine deleterious materials
70
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(OPEN PIT-DRY)
PREMUING
PROCEDURES
ORE
EXTRACTION
* AND
LOADING
p o c?0 o
TRANSPORTA
* TION
COARSE
»• ORE
STORAGE
SAND/GRAVEL
SEPARATION
CLLAKlNG AND FRONT-END LOADERS CONVEYORS BIN INCLINED
GRUBBING POWER SHOVELS TRUCKS STOCK PILE VIBRATING
OVERBURDEN SCRAPPERS SCREEN
REMOVAL
-*
-*
TRANSPORTA
TION
CONVEYOR
TRUCK
BARGE
CRUSHER
'
SCREEN
^
COARSE ORE
STORAGE
BIN
STOCKPILE
r
PRIMARY
SCREENING
PRIMARY
CRUSHING
SECONDARY
SCREENING
1
1
SECONDARY
CRUSHING
f
~ CONE CRUSHER
y GYRATORY CRUSHER
\
T
LEGEND
LIQUID WASTES
GASESOUS EMISSION
SOLID HASTES
Figure 13a. Mining and beneficiating of construction sand and gravel.
AWBERC LIBRARY US, EPA
-------
fO
HEAVY
MEDIA
SEPARATION
Q
ROADSTONE
LOG WASHER
ROTARY SCRUBBER
PEA
GRAVEL
I
I ROD OR BALL j
I MILL
\
LEGEND
LIQUID WASTES
GASESOUS EMISSION
SOLID WASTES
COARSE
SAND
3
O
_l
u.
UN
CYCLONE
OERFLOW*
SPIRAL
CLASSIFIER
0 C^
FINE
SAND
Figure 13b. Mining and beneficiating of construction sand and gravel.
-------
that would not be washed away by normal scrubbing and screening
operations. These fine particles include soft fragments, thin
and friable particles, shale, argillaceous sandstones and limes,
porous and unsound cherts, coated particles, coal, lignite and
other low-density impurities (39). HMS (sink-float) removes the
deleterious materials as a result of the different specific
gravities of the particles involved. The sand and gravel product
(sink fraction) and the impurities (float fraction) pass over
separate screens, where the heavy-media materials are removed by
separation and recycled. The impurities are usually disposed of
on site and the product is transported to a wet processing facil-
ity for further washing, crushing, and sizing.
Dredging with On Land/On Board Processing—
Raw material is extracted from public waterways using float-
ing, movable dredges, which excavate the bottom sand and gravel
deposit by one of the following methods: a suction dredge with
or without cutter-heads, a clamshell bucket, or a bucket-ladder
dredge. After the sand and gravel have been brought onto the
dredge, they can be transported directly to an on-land processing
facility (via barges or a slurry line) or be partially or com-
pletely processed on board the dredge. When transported to an
on-land facility, the raw material is processed in a manner
similar to that described under Wet Process. Partial on-board
processing involves primary sizing and/or crushing performed by
vibrating or rotary screens and cone or gyratory crushers.
Oversize boulders are returned to the water. Following these
initial steps the ore usually is transported to on-land facili-
ties for additional processing; however, the product sometimes is
ready for sale following on-board processing. When raw material
is processed completely on board, it is treated in a manner
similar to that described earlier under Wet Process. Following
the on-board beneficiation, sized sand and gravel are loaded onto
tow-barges and delivered to the user or stockpiled on land.
Waste Streams
Various atmospheric, liquid, and solid waste materials
result from sand and gravel extraction and processing. These
waste streams are shown in Table 11 and discussed in detail in
the following paragraphs.
Air Emissions—
Particulate emission sources in the sand and gravel industry
parallel those in the crushed stone industry. They may be fugi-
tive or process in origin. Process sources include crushers,
screens, conveyors, and loading mills (25). Fugitive sources
include haul roads, stockpiles, and open loading areas.
73
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TABLE 11. SUMMARY OF MULTIMEDIA WASTES FROM MINING AND BENEFICIATING
OF CONSTRUCTION SAND AND GRAVEL
riPCCSft
O|H.»n pit liHyt
iur.-ld!iJ
proi-essm*})
Drrdtiing
Un.-tx.-ird
processing)
Soiir.rt*
i'n»i.-,-ji«iina
fi|kii|-nifni
S I oc k \t i \ c s
Vfhiirlf
Othiir fj<|i- d
«'vjui|xnt:nt
Stockpi Ics
Vtrhiclt*
I ransport
t-quipnuint
vehicle
Other luqi- rf
An
I'ol Ititani
1,111 ...Ut. 11.'*
t'u.|l t i vo
pjrt iculdti'S
I'ti.li t ivt-
1
Ku-iitive
l*iii|t I ive
Fuqi t ive
part iculdtes
particulars
Fuqi t ivu
Fjqltive
UiK-oni rol li'd
PHI ssion
rale
0.0^ k.l f'M Of
product4
O.Oh to 2.6 ko/M^i
of proJuctt)
O.-ifc to 2.11
N.A.
product"
0.06 to 2.6 k«i/Hii
O.S6 to 2.1)
qr am/ vehicle -meter1"
N.A.
product*
of product b
0.*6 to 2.11
IJ.A,
Source
Incidental
water"
inq1*
Inc ident A!
Settl inq (Kind
di«char<(«,;
fi-rcoldt ion*
inq^
discharqe
Sett! inq |iond
Dredqe .
Dredge die-
charge
Dredqe di a-
turbancek
l.i.tui.l
I'ol lui.ua/
l>jf amt'i or
TSSf
water
TSS1
TSSf
TSS<
•
water
TBS1
TSSf
TSSf
TSS'
TSS'
DfK-'.l.l |.ll Ic-d
di li'.'h.ii -jc
N.A.
raw mdtorijt"
N.A.
0.006 to 0.26 kq/Mtl
of product
N.A.
fe«d*»
product*1
N.A.
160 to 460 k-i/Kv! of
12% kcj/M
Dry tAi 1 in'in
< so i 1 4 roo k 1
Slud-ifta*
Sludqes1"
Uncontrol led
quant ity
N.A.
N.A.
N.A.
N.A.
* Kef. S). Tin* vdlue ia an overall ••timate of source particulate enissions Jnd includes operations such oa conveying
screening, and crushing.
b fti-f. *>',. These emiaoiur. factors arc based on PE values of 150 and 25, respectively. See tent for explanation.
CKcf. '..,.
Other fuqitive sources coutd include overburden removal, transfer and conveying, truck loadinq, and abandoned waste disposal
e Incidental water refers to wastewater qeiterated by various miscellaneous sources such as vine punpuut, surface runoff, non-
contact coolinq water and water used for dust supression.
TSS • total Bus|J4*ndo
-------
Of the three -basic types of sand and gravel facilities
[open-pit (dry), open-pit (wet), and public waterway dredging
with on-board/on-land processing], open-pit (dry) operations
generate the most particulate emissions because the moisture
content of the raw material is lower and no water is used in the
beneficiation process. Particulate emissions emanate from both
process and fugitive sources.
Processing operations at open-pit (wet) facilities normally
do not produce any particulate emissions because of the high
moisture content of the material being processed. Most particu-
late emissions come from fugitive sources.
Those facilities that practice dredging with complete on-
board processing experience few problems with particulate emis-
sions because the moisture content of the material is always very
high.
Little information is available on emission factors from
sand and gravel plants. One report lists overall emissions as
0.03 kilograms per megagram of material through the facility
(53). The sources of dust are listed as the secondary and re-
ducing crushers and the elevator boot on the "dry side."
Seventy-five percent of the dust is estimated to come from the
crushers. More recently, Midwest Research Institute (MRI) pro-
vided an estimated overall emission factor of 0.05 kilograms of
dust per megagram of product (53). This factor is based on
process sources only and does not include fugitive sources such
as stockpiles or haul roads.
Sand and gravel particulate emissions data from fugitive
sources are even more scarce than for process sources, however,
emission factors are available for a few sources, such as stock-
piles and vehicle transport. One state agency estimates emis-
sions from stockpiles to be approximately 0.1 percent of finished
product for sand and 0.5 percent for gravel (54). More recently,
MRI compiled and evaluated data for emissions from aggregate
storage piles (55). Based on the results of this study, they
developed an empirical expression for estimating fugitive emis-
sions from aggregate stockpiles:
E = 0.165
, PE .2
1 100 ;
where: E = Emission factor, kilograms per megagram
placed in storage
PE = Thornthwaite's Precipitation-Evaporation
Index
75
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Based on PE values of 25 and 150 (which are representative of a
broad range of areas where sand and gravel are extracted), stock-
pile emission rates would be equal to 2.6 and 0.06 kilograms per
megagram of product placed in storage, respectively.
Vehicle transport is another contributor to the total par-
ticulate emissions emanating from sand and gravel operations, and
often is the major source of particulates. The emission factor
for respirable particulate emissions from transport of sand and
gravel is 0.56 gram per vehicle-meter, with a range of 0.14 to
2.13 grams per vehicle-meter (56). Even though these values
represent emissions resulting from the transport of the product
from finished stockpiles to the consumer, they are likely also to
be representative of emissions generated by vehicular transport
within the boundries of sand and gravel plants.
Other sources of fugitive emissions associated with the sand
and gravel industry include overburden removal, transfer and
conveying and abandoned or dry tailings dumps. Although data on
emissions from these sources are not available for the sand and
gravel industry, they are for other industries (crushed stone,
copper, and phosphate) whose operations parallel those in the
sand and gravel industry. Therefore, fugitive particulate emis-
sions data for these industries provide the best available bases
for estimating fugitive emissions for the sand and gravel indus-
try.. .
Although limited data are available on the characteristics
of particulate emissions from sand and gravel plants, it is
feasible to assume they would be similar to the characteristics
of the raw material being handled. Although sand and gravel
consist primarily of silica, other constituents are sometimes
present such as limestone or combined silica in the form of
feldspar, mica, and other mineral silicates and aluminosilicates
(2). Free silica is the only potentially hazardous constituent
in emitted particulates. The .average free silica content of
emissions resulting from vehicular transport is 14 percent, with
a range of 1.4 to 47 percent by weight (56).
Liquid Waste Streams--
Since processing water is not used at dry open-pit opera-
tions, no major aqueous waste streams are associated with these
facilities. Dry processing produces some incidental wastewater,
which includes mine pumpout, surface runoff, noncontact cooling
water, and water used for dust suspression (39). These effluents
are usually discharged directly to the watershed.
Incidental water may also be a source of liquid waste at wet
open-pit operations. At most wet facilities incidental water is
discharged to a settling pond rather than to the watershed. The
76
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major liquid waste associated with wet facilities is process
wastewater. The wastewater may be discharged from process opera-
tions directly to receiving waters, or it may be discharged
through constructed tailings ponds or extraction pits (active or
abandoned working pits). The amount of process wastewater gener-
ated as a result of wet beneficiation of sands and gravel ranges
between 50 and 480 kilograms per megagram of raw material pro-
cessed (based on monitoring at five separate facilities (39).
Process wastewater at many operations is recycled back to the
process after treatment; however, some facilities discharge
treated wastewater. Treated wastewater discharges were monitored
at several plants and ranged between 0.006 and 0.26 kilograms TSS
per megagram of product (39). An additional source of aqueous
waste at wet facilities is water that escapes from settling ponds
by percolation. The quantity of wastewater from this source has
not been measured.
Plants that combine dredging with on-land processing opera-
tions generate aqueous waste from their land-based processing
facilities that is similar to effluents from wet plants. These
facilities also generate processing wastes at the dredge itself
as a result of partial on-board processing. The following is a
tabulation of these waste loads at several operations (39):
Waste generated Waste generated
at dredge, at land facility,
Operation no. kg/Mg of feed kg/Mg of feed
1 460 100
2 None 400
3 None 150
4 None 110
5 None 120
6 250 60
7 180 120
Process wastewater at land-based facilities is normally treated
and recycled. The total suspended solids level of recycled
wastewater measured at four separate operations ranged between 50
and 400 megagrams per liter (39). Two facilities are known to
discharge treated wastewater. The TSS level of discharge is 22
kilograms per megagram of product at one plant and 0.10 at the
other.
Effluents from dredging units with complete on-board pro-
cessing contain essentially the same high suspended solids con-
centrations as those generated by land-based operations, and
additional solids are placed into suspension by the action of the
recovery assemblies. No information is available for effluents
from dredging operations with complete on-board processing. It
77
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is estimated, though, that approximately 25 percent of the total
volume of material being dredged plus 10 percent of the material
going to processing is discarded back into the body of water
being dredged (39). The total discharge resulting from on-board
processing, based on these percentages, would be equal to 325
kilograms per megagram (32.5 percent) of initial feed. No esti-
mate is made of the suspended solids introduced into public
waterways by the action of dredging assemblies.
Although aqueous wastes discharged from sand and gravel
operations do not contain any toxic materials, they can be very
high in total suspended solids. Since the characteristics of the
suspended materials relate to the characteristics of the raw
material being extracted and processed, discharges are expected
to contain silica, limestone, feldspar, mica, and other mineral
silicates and aluminosilicates.
Solid Wastes—
Solid wastes generated by mining and beneficiation of sand
and gravel may include overburden, oversized rock removed during
initial waste/raw material separation, and tailings resulting
from dry processing operations. Solids removed from process
wastewaters by mechanical dewatering devices and/or settling
ponds also add to the solid waste when plants have operations
such as scrubbing, dewatering, desliming, and heavy media separa-
tion. No data were found on the amounts of solid waste generated
by these sources. ...
Control Technology
Many of the larger, permanent sand and gravel operations
greatly reduce their waste problems by applying extensive control
technology. Some plants are limited in their ability to treat
wastes by the best available methods because, for example, they
do not have sufficient land for settling ponds. Other plants,
particularly those that operate on intermittent or part-time
schedules, practice little or no waste control.
The best control technology now available is discussed in
the following paragraphs.
Air Emission Control—
Particulate emissions from both process sources (screening,
crushing/ transferring, etc.) and fugitive sources (haul roads,
stockpiles, waste dumps, etc.) are the major atmospheric wastes
of concern at sand and gravel plants. Emission control method-
ology used to reduce these particulates include dry collection
systems, wet dust suppression, wind reduction, and various com-
binations thereof.
78
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Dry collection systems—Particulate emissions generated by
process operations can be controlled by capturing and exhausting
emissions to a collection device. The most effective dust col-
lection device in the sand and gravel industry is the fabric
filter or baghouse. Mechanical shaker-type collectors which
require periodic shutdown for cleaning, are the most common.
Baghouses give greater than 99 percent efficiency, even on sub-
micrometer particle sizes (38). Cyclones and low-energy scrub-
bers, which are sometimes used, demonstrate efficiencies of 95 to
99 percent for coarse particles (+40 micrometer), but their
efficiencies are usually less than 85 percent for medium and fine
particles (-20 micrometer) (38).
Wet dust suppression—Wet dust suppression techniques,
designed to prevent particulate matter from becoming airborne,
may be used to control both process and fugitive sources. Dust
emissions are controlled by spraying moisture (water or water
plus a wetting agent) on critical dust-producing points in the
process flow. One California plant, which operates a wetting
system to control particulate emissions from both process and
fugitive sources, mixes a wetting agent called compound MR with
water at a ratio of 1 cubic meter of solution to 100 cubic meters
of water (57). Approximately 4 cubic meters of this mixture is
applied to every 1000 megagrams of crushed material by means of
sprays at the top and bottom of the secondary cone crushers. The
system has the advantage of a carry-over effect in subsequent
transfer, screening, and storage operations. Also, it does not
blind the screens because it operates at a level of 1/2 to 1
percent total moisture.
Wet dust suppression systems have been used extensively for
many years to control dust from fugitive sources. Applying plain
water on haul roads has been a common practice. Although water
application has also been used to control dust from overburden
removal, stockpiles, and waste disposal, such practice is not
widespread. Among the reasons many operations do not use plain
water for dust control is its ultimate high cost. Initial cost
is low, but control is temporary and the need for frequent appli-
cations adds materially to the cost. For this reason, many sand
and gravel operators are turning to chemical wetting agents,
which provide better wetting of fines and longer retention of the
moisture film. Wetting aids can be applied directly to the
surface being controlled or they can be worked into the material
being treated. Chemical treatment programs reduce total particu-
late emissions from fugitive sources by up to 90 percent, whereas
watering provides a dust-control efficiency of only 50 percent.
Reduction of wind speed—Wind contributes significantly to
all particulate dust sources at a sand and gravel operations, by
erosion of the exposed surfaces of stockpiles, tailings piles,
79
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and reclaimed areas, and by direct transport of the dust gener-
ated by other extraction and processing operations. Windbreaks,
enclosures or coverings for the sources, and planting of tall
grasses or grains on or adjacent to exposed surfaces can reduce
surface wind speed and result in control efficiencies of between
65 and 90 percent.
Control method combinations—Some sand and gravel facilities
use a combination of several of the control methods mentioned.
For example, wet dust suppression techniques are used to prevent
emissions at primary crushers, screens, transfer points, and
crusher inlets, and dry collection is applied to control emis-
sions at the discharge of secondary and tertiary crushers, where
new dry surfaces and fine particulates are formed.
Some operations control fugitive dust from abandoned tail-
ings dumps by combinations of watering, chemical stabilizers, and
vegetation cover. These combination methods often achieve 90 to
95 percent efficiency (58).
Liquid Waste Control--
Sources of liquid waste at sand and gravel operations in-
clude incidental water (surface runoff, mine pumpout, non-contact
cooling water, etc.), process wastewater, settling pond dis-
charge, percolation from settling basins, and dredging of public
waterways. Many facilities discharge incidental wastewater
directly to the watershed without prior treatment. Other plants
combine incidental wastewater with process wastewater, then pump
the wastes to treatment. Settling ponds are the predominant
method for treating wastewater. The ponding method requires the
construction of new ponds or utilization of active/ abandoned ex-
traction pits. The size, configuration, and number of treatment
ponds needed depend on such factors as total suspended solids
content of the inflow, retention time, land availability, and
climate. Some plants facilitate settling and minimize the size
of settling ponds by introducing settling aids into the water.
Some operations utilize mechanical devices such as dewater-
ing screws, cyclones, and classifiers followed by settling basins
to treat process wastewater. The mechanical devices remove a
large portion of the fine sands (+200 mesh) and the settling
ponds remove the colloidal material (-200 mesh). Mechanical
devices decrease the solids load going to the pond and expedite
the settling of colloidal material in the pond, thereby decreas-
ing the frequency of pond cleanout. Many operations that combine
mechanical devices with settling ponds for process wastewater
treatment achieve a final pond discharge of high enough quality
(<200 micrograms per liter of total suspended solids) to be
recycled and used as process water.
80
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Effluents from settling ponds are discharged to abandoned or
active excavation pits, recycled, or released to the watershed.
Discharge may be intermittent (only during heavy rains) or con-
tinuous, depending on the size of the operation, degree of pro-
cessing, and climatic conditions of the area. Effluents released
to the watershed usually do not receive any treatment after they
leave the settling ponds, and at some facilities (particularly
intermittent and temporary operations) process wastewater is
discharged directly to navigable waters without any treatment.
Percolation from settling basins occurs at some sand and
gravel operations. The best control method is to locate the
settling basin over impervious bedrock whenever possible.
Dredging of public waterways introduces large amounts of
suspended solids into the water. The raw wastes result from the
discharge of process wastewater (generated by on-board process-
ing) and disturbance of the substrate by the action of the dredg-
ing assemblies. Efforts to control these sediments include
diking, silt curtains, and bubble barriers, none of which has
been totally successful (51).
Solid Waste Control—
Solid wastes associated with the sand and gravel industry
include overburden, oversized rock, and dry waste fines (tailings
from dry open-pit operations). The removal of waste fines from
process wastewater by mechanical devices and/or settling ponds
results in additional solid waste (sludges) at wet sand and
gravel operations.
Overburden, oversized rock, and dry waste fines are stock-
piled at some operations and used to reshape the contour of the
land during reclamation procedures. At other facilities these
wastes are disposed of in active/abandoned pits or in any low
area that will take fill. If adequate space is not available for
disposal on site, this material is hauled to an off-site dump.
In some instances, it is transported away from the site and sold.
The ultimate disposal of sand and colloidal fines removed
from process wastewater is a major problem. Colloidal fines are
more difficult to deal with than sand fines because they are
harder to dewater. Many operations have available land for
disposal of waste fines. Some use previously mined areas or
obsolete sedimentation ponds, or disperse the sludge to open land
areas for drying. At operations where sufficient land is avail-
able, exhausted tailings ponds are abandoned and new ones con-
structed. At facilities where land for settling ponds is lim-
ited, it is necessary to extract as much marketable material as
possible. Classifiers and/or cyclones that remove product mate-
rial down to the 100-mesh range help to minimize solid waste
81
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problems. Sometimes solid waste generated by these devices is
transported to off-site dumps, but if the fines are of top soil
or fill dirt quality, they can be readily and profitably sold in
the immediate area. The fines can also be mixed with coarser
material to facilitate drying and enhance the quality of the
finished product. Some operators have added organic debris-such
as leaves and commercial fertilizers to waste fines to yield a
profitable product. Waste fines have also been used to produce
building bricks, an activity which may increase proportionately
with the demand for construction materials, especially since sand
and gravel operations are located near metropolitan areas.
Conclusions and Recommendations
Most of the larger sand and gravel operations are maintain-
ing air, liquid, and solid wastes at acceptable levels by apply-
ing state-of-the-art control technology. Particulate emissions
from process sources are being minimized by applying well-
established control techniques (watering, wetting agents, exhaust
and collection systems, etc.). Although technology for the
control of fugitive emissions has not advanced to the level of
that for source emissions, it is improving rapidly. Process
wastewater and incidental wastewater are controlled by mechanical
devices followed by settling ponds. At some operations, pond ef-
fluent is completely recycled resulting in zero discharge. Solid
wastes (colloidal fines removed from settling ponds) are being
land spread at facilities with sufficient area or recovered as
useful by-products.
Even though many operations are maintaining good pollution
control programs, some environmental problems still persist.
These problems and related research and development needs are
discussed below.
A major problem that faces the sand and gravel industry is
the dewatering of settling pond sludge, which consists of colloi-
dal fines (-200 mesh). Reportedly, no technology is available
for economical dewatering of these silts. Efforts to use various
mechanical devices such as vacuum filters and hydraulic cones
have been generally unsuccessful. Vacuum filtration is economi-
cally prohibitive because of the enormous quantities of sludge
that must be treated. Hydraulic cones effectively remove fine
sands (+200 mesh), but they are not efficient enough to remove
small colloidal particles. Some operators are now trying to
remove silts with centrifuges, which have been used successfully
for dewatering of coal mine slimes. This may be a practical
solution to the problem. Research is needed to identify the
properties of these colloidal particles to determine why it is so
difficult to dewater them. Dewatering devices such as vacuum
filters and and hydraulic cones have been partially effective;
82
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however, additional laboratory and field research is needed.
Laboratory research is also needed to determine the effectiveness
of centrifuges, and a pilot plant should be developed if the
laboratory tests are promising.
Another serious problem involves the ultimate disposal of
dewatered waste fines. Where sufficient land is available, waste
fines are land-spread on site, thereby alleviating drying and
disposal problems by a single method of control. Nonetheless,
these deposits can result in fugitive dust if methods of suppres-
sion are not employed. At operations where sufficient area is
not available for this approach, waste fines are either hauled to
off-site dumps or recovered as a by-product of some type. If the
material being recovered is of topsoil quality, it can be sold
directly to farmers and land-spread without any additives. Some
operators mix their sediments with materials such as leaves,
municipal sludge, and commercial fertilizers to facilitate drying
and to enhance the quality of the product. Additional research
is needed to determine how effective waste fines (with or without
additives), are as soil builders or fertilizers. Research is
also needed to identify other uses. Construction materials such
as building bricks and road base fill should be investigated as
potential by-products. The biggest problem involves .finding an
accessible market for by-products in the immediate vicinity of
the sand and gravel plant. A survey should be made of industry
to determine what markets are available and where they are lo-
cated.
Numerous sand and gravel producers operate on a part-time or
temporary basis. These are usually dry-pit operations and efflu-
ents from process wastewaters are not a major problem; however,
considerable discharge can result from storm runoff and pit
pumpout. It is estimated that storm runoff from one of these
temporary operations is capable of producing a silt load exceed-
ing the yearly output of a well-managed permanent sand and gravel
plant (51). It should be noted also that silt discharge can
continue after an operation has been abandoned. Research is
needed to determine the practicality of constructing diversion
ditches and/or retaining dikes to contain and control runoff at
these temporary facilities.
Seepage and percolation from settling basins is a problem
that can cause surface and ground water to become contaminated at
some plants. The nature and extent of seepage/percolation from
settling ponds should be evaluated, followed by research relating
to possible preventive measures (e.g., synthetic or earthen
liners).
Dredging in public waterways introduces large amounts of
suspended solids into these waters, thereby posing an environ-
83
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mental threat. Research should be initiated to determine effec-
tive and economical means of removing or containing suspended
solids generated from dredging operations. Various devices that
have been partially effective but need additional research in-
clude dikes, silt curtains, and bubble barriers.
INDUSTRIAL SAND
Industry Description
Industrial sands differ from construction sands in that they
contain little or no impurities. Industrial sands are silicate
minerals that have been segregated and refined by natural pro-
cesses into nearly monomineralic deposits. Because of their high
degree of purity, they have special and somewhat restricted uses
(39). Most often, industrial sands occur naturally in sandstone,
conglomerate quartzite, quartz mica schist, or massive igneous
quartz. These ores are refined to produce a sand of suitable
composition and texture. Industrial sands are recovered also
from quartzose sand and gravel deposits, which can be exploited
and used with very little preparation and expense.
Although industrial sands amounted to only about 4.5 percent
of total sand and gravel production in 1974, they represented 10
percent of the total value. (Present and projected production
statistics for silica sands appear in Section 1 of this report.)
Industrial sands are vital to glass manufacture, ferrous and
nonferrous foundry operations, some chemical and metallurgical
processes, and as extenders in manufactured products (2). Glass
sands must be free from iron oxide and other impurities. Molding
sands for foundry use usually contain clay as the bonding agent.
Other industrial classifications include abrasive sand for sand-
blasting, sawing, and grinding; filter sand for treating water
supplies, and ground sand for filler in paint, asphalt, tile,
plastic,, and rubber.
Nearly half of the states in the Union are involved in the
recovery of industrial sands. No one state produces all of the
various types of silica sands in use today, although a single
state may be noted for several varieties. Table 12 lists some of
the major producing states of industrial sands by end-use (2).
Some materials or substitutes compete with silica sands, and
will probably have some impact on the future of the industrial
sand industry. For example, zircon and mullite are more refac-
tory than silica sand and are used in foundry molds where tem-
perature or other conditions exceed the limits of silica molding
sand. Crushed garnet, ceramic materials, and ion exchange resins
84
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TABLE 12 . MAJOR PRODUCING STATES OF INDUSTRIAL SANDS
End-Use
Location of Deposits
Blasting sand
Glass-melting and
chemical sands
Metallurgical
pebble
Refractory sands:
Core sand
Canister mix
Naturally bonded
molding sand
Processed mold-
ing sand
Refractory
pebble
Ohio, Illinois, Pennsylvania, West Virginia,
New Jersey
West Virginia, Pennsylvania, Virginia,
Illinois, Missouri
Ohio, Tennessee, New York, Pennsylvania,
North Carolina
Illinois, Ohio, Michigan, West Virginia,
Pennsylvania
California, Illinois, Ohio, Massachusetts,
Wisconsin
New York, New Jersey, Ohio
Illinois, New Jersey, Pennsylvania, Ohio,
West Virginia
Ohio, Indiana, Pennsylvania, Maryland
Wisconsin
Source: Ref. 2.
85
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are suitable substitutes for filter sand. Fused alumina, silicon
carbide, garnet, corundum, emery, and diamond represent alternate
abrasives.
Process Description
Industrial sands may be obtained from open pits (wet or
dry), beach deposits, or sandstone quarries (39). Prior to
extraction, mine sites are cleared and grubbed, overburden is
removed, and working roads are constructed. Raw material from
dry pits, sandstone quarries, and beach deposits is extracted by
front-end loaders, power shovels, or scrappers. Ore extraction
at wet pits is usually accomplished with hydraulic dredges. Raw
material is transported to processing facilities (some on site
and others located away from the mine site) by conveyor belts,
trucks, or slurry lines. Processing typically consists of some
combination of scalping/screening, crushing, scrubbing, dewater-
ing, sizing, and drying. Some facilities have additional opera-
tions such as rod milling, flotation, and magnetic separation.
The specific type and amount of processing at a facility is
controlled by the quantity of impurities in the deposit, grain
size of the material, and specifications of the user. Glass
sand, for example, must be of higher purity than foundry sand and
therefore requires more processing. The various methods of
processing silica sands are illustrated in Figure 14 and dis-
cussed in more detail in the following paragraphs.
Ore recovered from sandstone quarries is reduced to a size
of about 2.54 centimeters by a jaw crusher, then further reduced
to natural sand grain size by wet rod milling (28). Generally,
one-pass treatment through the crusher and mill is sufficient;
however, at large scale operations two-stage crushing and milling
may be practiced. Reduced ore is passed over a 20-mesh spiral
screen; oversize goes to waste or back to the mill and minus-20-
mesh material goes to further treatment.
Silica sand recovered from dry. open pits is generally loaded
into trucks and transported dry to a mill receiving bin. It is
then fed onto a vibrating screen along with sufficient water to
wash the sand through a 20-mesh screen cloth. The material is
further washed by water sprays, with oversize going to waste or
other use. The minus-20-mesh material (which may or may not be
dried first) goes to product storage or to further processing.
Sand that is recovered from deposits below the water table
(wet pits or beach sands) is usually extracted by hydraulic
dredges, then pumped to a 20-mesh vibrating screen. The oversize
fraction goes to waste and the material passing through the
screen (minus^-20-mesh) goes to either product storage or further
treatment.
86
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ORE EXTRACTION
BEACH \
DEPOSIT
SAX05TCNE 1
OUARRt >
OPEN PIT-
not
1
PREMINING
PROCEDURES
f
1
EITWCTION
OF ORE
Vj |
LOADING
OF ORE
I
C
TRANSPORT
OF ORE
[ *
ORE
STORAGE
1
ORE TO PROCESSING
OPE* PIT-
"
^
PREMINING
PROCEDURES
/
EXTRACTION
(DREDGING)
V
ORE
RECYCLE
t C( 1
ORE TO PROCESSING
DRY PROCESS
ORE FROM
SANDSTONE
OUAsar
ME FRON I
JEACH SAND) •
DEPOSITS
CRUSHING
DISCHARGE
DRY OUST
COLLECTION
(CYCLONE OR
BACHOUSE)
UASTE FINES
TO OUKP
DRYING
-J
C
SCALPING/
SCREENING
f A
PRODUCT
STOMGE
WET PROCESS
;RE FROM
SA'IOSTOIIE
3UM9T
MET BUST
COLLECTION
(SC5LS3ES)
COLLECTION
9
.^,
THICKESER OR
CLASSIFYING
\
SETTLIVG •
315-
FLOTATION PROCESS
CRUSHING AND
GRINDING
O ATH05PMERIC f.flSSlONS
A LIUIO PASTES
O SnilO 4ASTFS
ALTE8I1ATE HOUTl
«l
OESLIMING
^
FLOTATION
^
CnNO I TUNING
ANn
ALHALISE
FLOTATION
<*
PRft IHI1ARY
ACiS
I
OFUATEB
^
.OriOI'ICMUG
A'lD
MYOBf!FU'ORIC
<\
(CYCLO'iE OR
PJG-OUSE)
\
c
DRYING
J °5
••^
1
1
1
1
L_.
PRODUCT
STOBAGE
i
MGHETIC
FLCTATIO*
SEPARATION
Figure 14. Mining and beneficiating of industrial sand.
87
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After the sand has been recovered and treated by one of the
three methods described, it is sent to primary classification for
dewatering or classifying, by cyclones or by mechanical dewater-
ing classifiers (drag, screw, or rake classifiers). After clas-
sification the sand is introduced into an attrition scrubber for
removal of impurities. Scrubbed sand is then pumped to a second
set of cyclones or mechanical classifiers for further removal of
slimes. Sometimes the impurity content of the sand meets re-
quired specifications at this point, making the cyclone or clas-
sifier sand the final product. In other instances the sand may
require additional cleaning because of a high concentration of
difficult-to-treat impurities and/or high product specifications.
Additional purification can be accomplished by two-stage attri-
tion scrubbing with classification and slime removal between
stages or by a variety of flotation techniques. Currently, the
three flotation methods used are acid, alkaline, and hydroflouric
acid flotation (39). In each method, raw material is first
scrubbed according to standard procedures outlined above and then
slurried to flotation cells, where various reagents are added.
Flotation methods differ according to the types of conditioners
and frothers added. Some of the reagents introduced include
sulfuric acid, soda ash, sodium silicate, sulfonated oils, ter-
penes, and heavy alcohols. The silica sands are depressed and
sink in the flotation cells, and the impurities are "floated"
away. The sand recovered from the cells is pumped to a mechan-
ical dewatering classifier for final dewatering, and is then
either conveyed to a stock pile or drainage bin or is dried in a
rotary dryer (oil or gas) and stockpiled.
At some facilities, final product purification and sizing
are performed by magnetic separation and/or grinding.
Waste Streams
The air, liquid, and solid wastes associated with the indus-
trial sand industry are summarized in Table 13 and discussed in
more detail in the following paragraphs.
Air Emissions—
Mining and beneficiation of industrial sand produces both
fugitive and process particulate emissions. Particulate emis-
sions from industrial sand plants have had very little monitor-
ing; however, some estimates are available. In 1975 the total
annual release of particulates from industrial sand3operations
(all processes included) were reported to be 3.2 x 10 megagrams
(this value is based on a total annual production of 2.68 x 10
megagrams) (56). Dryers are reportedly the major contributing
source, but other process sources that generate significant
amounts of particulates include crushing, screening, and milling
operations. Particulate emissions from various fugitive sources
88
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TABLE 13. SUMMARY OF MULTIMEDIA WASTES FROM MINING AND
BENEFICIATING OF INDUSTRIAL SAND
00
.
Source
Overburden
or ore
Load inq of
ore
Transport
Cire
Convoy i ruj ,
screening ,
fc crushing
Drying
Product
**
Tai 1 inq
dump
Total
industry
(al 1 pro-
cesses)
Air
Pol lutant
Fuqi t ive
particulars
Fuq i t i ve
parttculates
FU'|I LlVf
Fuq 1 1 1 v»;
Pai ticulates
Part iculates
Fuqi t ive
Fiiq 1 1 1VC
part iculates
Participates
Uncontrol l«d
L-roi ssion
rate
N.A.
N.A.
O.S6 to 2.13 .(ram/
0.06 to 2.6 kq/Mq
pr uct
O.OS kq/Mq of
producta
N.A.
0.06 to 2. 6 kq/Mond>
Settl inq
Settl inci
Settl inil wiisi cwiit or
discharqecl
pll
TUS
TSS
Stil fate
Uncuntrull«d
Jiucliaitiu
N.A.
5478 kg/day0
10-S10 k
-------
TABLE 13. (Continued)
Air
Source
Pol 1 utant
Uncontrol l«d
i-iiii ss ion
rat*'
l.i<|ii id
Sourt'o
Si-t t 1 inq
pond'
S.'ttl ing
Washi nq
Flotation'
Flotation
Flotation
Magnetic ,
separation
Sett I ing
pond1
Sott) ing
• pond1
Set tl ing
pond1
Set tl inq
pond'
Settling
pond1
Settling
pond1
I'Ol |ul ml /
Oi 1 _fc qi c-abv
1 ron
Clays
Flotation
tai 1 ings
Acid i t lota-
tion agents
Flor itii: (as
hydro t 1 uor it:
acid)
1 ron ox idi*
Amount of trt-at-
rd wastcwater
d ischtif'tud
pll
TSS
Sulf ate
Nitrate
Chloride
Flor ide
Uncont rol led
I.I. »4/."
O.I mc)/.h
1CS kq/Hi] of
raw mater id I*1
1 15 k:|/Mq of
raw ma tt->r ial^
n. 10 k.|/Mc| of
raw mater i^ 1 ••
0.4%k I/M.| of
raw mattfriair1
M kq/Mt) of
raw material
0.91 kq/Hq of
(jroiluc t
7.0-7.8h
S-47 „.,/.'•
27- nr. „,,/."
0-9 mq/. h
57-76 my/:.h
1.8-6.1 m,|.'.h
Solid
Source-
Pollutant
Uncontrol led
quant i ty
Emission estimate Iroro construrtion sand and qravel industry. See Section IB.3.1.
Ref. 52. Total annual emissions for entire industry including all processes.
Faci1itles recover ing silica sands from open pits (wet and dry) or from sandstone quarr ies have periodic pumpouts.
Runoff may result from sources such as stockpiled overburden, extraction areas, ore and product storaqe piles, and
abandoned tailings dumps.
Ref. 2. Based on monitoring at onu facility discharging scrubber water directly to the watershed with no prior treatment.
Ref. 2. The liquid wastes associated with process sources are untreated (uncontrolled) process wastcwatcrs which are
combined and fed to either a settling (Hind or to a thicki-nor lollriw.-.l hy ^ ui*Mliii<| pond.
Ref . 2. The range in va luctj is based on mon i tor inq at four si-pa r.i trd I ;u: i 1 i I it:S.
kef. 2. This valuu is based on monitoring at one facility.
Re f . 2. Uischar qes from sett I inq p*inds lepreucitt t r«*ated (control led > wa.ste st i earns .
N.A. - Not avallable.
-------
(haul roads, conveyors, and stockpiles) also present periodic
dust problems. Generally, however, fugitive dust problems are
minimal because even at "dry" operations the surface moisture of
the material is sufficient to prevent dusting.
No emission data specific to individual process and fugitive
sources are available for the industrial sand industry. However,
because of the similarity in materials, methods of recovery, and
processing, atmospheric emissions of the industrial sand industry
are based on those of the construction sand and gravel data,
which are covered in the preceding section.
Liquid Wastes—
In sandstone quarries and dry pits, surface runoff and pit
pumpout are the only sources of liquid wastes associated with the
extraction of silica sands. These effluents are periodic and are
highest during periods of heavy rainfall. Although typically
high in suspended solids, they do not contain any potentially
hazardous materials. Specific data concerning these effluents
are not available.
Sources of liquid waste at facilities processing industrial
sands include washing, desliming, dewatering, flotation, and wet
milling operations. When wet scrubbers are used to control
emissions from dryers, an additional wastewater stream is gener-
ated.
Table 13 presents data for a facility releasing wet scrubber
water directly to the watershed with no prior treatment.
Monitoring results indicate that the discharge contains 5478
kilograms TSS per day (39). At most facilities process waste-
water and scrubber wastewater are treated and recirculated, but
in some cases they are discharged after treatment. Discharge may
be continuous or it may occur only during periods of heavy rain-
fall.
Table 13 describes in detail the untreated and treated
(settling pond discharge) waste streams for several sand process-
ing facilities, which use both scrubbing and flotation. The
total quantity of wastewater going to treatment ranges between 60
and 730 kilograms per megagrara of raw material (39). Treated
wastewater discharge ranges between about 1 and 7 cubic meters
per megagram of product. Untreated and treated waste streams
consist of muds separated in the initial washing operations, iron
oxides separated magnetically, impurities removed by flotation,
and various flotation reagents.
Solid Wastes--
Overburden and gangue are both sources of solid waste at
industrial sand operations. The quantities produced vary by
91
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site, depending on the type of deposit being mined (beach
deposit, sandstone quarry, or wet pit) and the amount of impuri-
ties associated with the deposit. Other solid wastes include
oversize and sand fines that are removed during dry separating
and classifying operations. Dry dust collection of particulates
from rotary dryers, by either cyclones or baghouses, also results
in minor amounts of solid waste at some operations. Reports
indicate that all these solid wastes are landfilled (39), but no
data are available on quantities.
Wet processing and flotation result in a variety of solid
wastes, including muds and waste fines removed during dewatering,
thickening, clarifying, and settling operations. Although the
wastes consist of impurities such as clays, iron oxides, and
feldspar, they also contain some of the reagents (acids, caus-
tics, oils, alcohols, etc.) used to remove the impurities. No
data are available on the amounts of solid waste generated by
these operations.
Control Technology
Control technology in the industrial sand industry is much
the same as that used in the construction sand and gravel indus-
try. The various air, liquid, and solid waste controls are
described in the following paragraphs.
Air Emissions Control—
Fugitive dusts generated by operations such as overburden
removal, ore extraction, loading/unloading, vehicular transport
and conveying are controlled by wet suppression and or wind
reduction techniques. Wet suppression consists of applying water
or water plus a chemical wetting agent. Watering usually
achieves a control efficiency of 50 percent, whereas water plus
chemical additives can attain up to 90 percent.
The particulates released by process sources such as crush-
ing and -screening are generally minor since the material has
enough surface moisture to prevent dusting (38). In some in-
stances, particularly at dry operations, control devices are
necessary. The usual method involves capturing and exhausting
the particulates to a baghouse.
Dryers are the major source of particulate emissions at
industrial sand operations.* Dust collection systems can be dry
(cyclones and baghouses) or wet (scrubbers). Baghouses achieve
*Telephone conversation between Jack Greber of PEDCo and
Edward Davison, National Sand and Gravel Association, Silver
Spring, Maryland. December 1976.
92
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an overall efficiency of up to 90 percent, whereas cyclones and
low-energy scrubbers achieve 95 to 99 percent for coarse par-
ticles (+40 micrometer) but less than 85 percent for medium and
fine particles (-20 micrometer) (58).
Liquid Waste Control--
Scrubber water, a major source of liquid waste at some
industrial sand operations, generally is pumped to settling
ponds, where suspended solids are settled, and then is decanted
back to the scrubber, thereby resulting in no discharge.
However, some facilities discharge scrubber,water directly to the
watershed with no prior treatment (39). In these cases, dis-
charge points are typically not discrete, so use of National
Pollutant Discharge System (NPDES) permits to enforce control is
not practical.
Liquid wastes generated by scrubbing, desliming, dewatering,
and flotation are treated by a variety of control methods.
Usually all waste streams are combined, then treated by some
combination of thickeners, clarifiers, and settling ponds. Some
operators also use a flocculating agent (e.g., alum) to facili-
tate the settling of suspended material. Current practice is to
recycle treated wastewater, either completely or partially.
Water that is not recycled is discharged to the watershed or to
active/abandoned working pits. The pH is adjusted before either
recirculation or discharge.
Solid Waste Control—
When sufficient land is available, facilities dispose of
their solid wastes on site. The residuals (waste fines, over-
size, sludge) are dumped into previously mined areas, obsolete
sedimentation ponds, or low-lying areas that need fill. other
operations must haul their solid waste to off-site landfills.
Any valuable materials that are locally marketable, are recovered
and sold.
Conclusions and Recommendations
Environmental problems associated with the industrial sand
industry are similar to those encountered in the construction
sand and gravel industry. The major concern lies in dewatering
and ultimate disposal of waste fines, for which the same research
and development recommendations apply as those presented for
construction sand and gravel.
GYPSUM
Industry Description
Gypsum is a naturally occuring mineral found near large salt
deposits. Formed as evaporites from marine waters, the deposits
93
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are found in stratigraphic beds with limestone and salt.
"Gypsum" is a broad term that describes several different phases
of the same material:
0 Anhydrite (calcium sulfate) - CaS04
0 Selenite (hydrated calcium sulfatej - CaS04'2H20
0 Calcined gypsum (hydrated calcium sulfate) - CaS04'l/2H20
Anhydrite and selenite usually occur together; calcined gypsum is
a manufactured product. Water is added to calcined gypsum to
form plaster of paris, which quickly sets and hardens to become
selenite again.
In 1974, crude gypsum was mined by 44 companies at 75 mines
in 22 states (3). Thirteen of these mines were underground
operations. California, Michigan, Iowa, Texas, and Oklahoma led
in output with 60 percent of the total. Calcined gypsum was
produced by 13 companies at 77 plants in 29 states, with
California, Texas, New York, and Iowa accounting for 37 percent
of the total. Production statistics for gypsum are presented in
Section 1 of this report.
Gypsum, one of the most common building materials, is used
universally for interior walls, partitions, and ceilings, either
as plaster or in prefabricated products. Crude gypsum is
marketed for use in cement, agriculture, or fillers. Calcined
gypsum is marketed in the form of plaster or prefabricated pro-
ducts, such as lath, veneer base, sheathing, and wallboard.
Also, beds of limestone or clay encountered in the overburden
during mining of crude gypsum may be marketed for road materials.
Process Description
About 80 percent of the gypsum in the United States comes
from open-pit mines and the rest from underground mines (59). In
1973, the stripping ratio for open-pit mines was 1.6 to 1, and
average overburden for a 3-meter gypsum bed was only 4.8 meters.
Open-pit mines use both draglines and tractors. Underground
mines apply standard room-and-piliar methods, with trackless
mining equipment. Figure 15 shows a flow diagram for mining and
processing.
Gypsum is mined by using low-density, slow-speed explosives
and drilling methods adapted to meet local conditions. The
broken rock is loaded onto trucks or rail cars and transported to
the processing facility.
Most gypsum mines use the "dry process" to beneficiate the
ore. The alternative "wet process" is known as heavy-media
separation. Both methods first crush the ore, usually at the
mine site. Although most mines use gyratory crushers, some use
jaw or impact crushers.
94
-------
DR« PROCESS
en
OPIN-PIT L,
MINING j^
?
UMXHGKOUND 1 .
MINING ™
i —
L..
?
HPHIHART 1
CRUSHING |*
*
1
1
1
1
1
1
H
c
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>
i i r
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ORUR
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HEAVY MEDIA SEPARATION PROCESS
|
CALCINING U raooucf
9 AIR EMISSION
P SOLID HASTE
CJ LIQUID HASTE
Figure 15. Mining and beneficiating of gypsum.
-------
Secondary crushing and screening operations usually take
place in an enclosed building (crush house) away from the mining
site. Rock from the primary crusher (which reduces the ore to
-3.8 centimeters) is conveyed to the crush house and discharged
onto a vibrating scalping screen. The screening operation re-
covers rock larger than 1.6 centimeters for the manufacture of
Portland cement. Rock less than 1.6 centimeters is conveyed from
screening to a secondary crusher for further size reduction.
Removal of free moisture by drying sometimes is done in the
primary or secondary crushing stages and almost always before the
final size reduction step. Rotary dryers are used most often,
with rock temperatures kept below 49°C to avoid dissociation of
the combined water. Drying is necessary because wet material
from the secondary crusher is not free-flowing and therefore
difficult to handle.
When a total containment/recycle system (heavy-media separa-
tion) is used, the ore from the primary crushing step is screened
and washed with recycled water, which removes undesirable par-
ticles from the main stream. The slurry then goes to a sink-
float system, where magnetite and ferrous silica are used to
separate impurities from the gypsum ore. The process consists of
floating the mineral from the "heavy liquid" formed by the sus-
pension of finely ground, heavy, ferromagnetic materials in
water. The impurities are passed over screens to recover the
magnetite and ferrous silica for recycling. The impurities are
disposed of in nearby ponds and the product is transported to the
facility for routine washing.
Final grinding, which reduces the rock size to 100 mesh, is
accomplished almost exclusively by hammermills. After milling,
some gypsum is washed or wet screened (when a white color is
required), but most of the mineral is sent to vertical kilns or
kettles to be calcined for 2 to 3 hours at 160°C to remove most
of the hydration water. The calcined mineral is then processed
into the desired final product.
Waste Streams
Table 14 presents a summary of multimedia wastes from the
mining and beneficiation of gypsum. The following paragraphs
explain in some detail, the air, liquid and solid waste streams.
Air Emissions—
Both open-pit and underground mining operations generate
fugitive dust. Beneficiation sources of particulate emissions
include primary and secondary crushing and screening. No emis-
sion estimates are available.
96
-------
TABLE 14. SUMMARY OF MULTIMEDIA WASTES FROM
MINING AND BENEFICIATING OF GYPSUM
Air
Source
Open pit
•ining
Underground
mining
Primary
crushing
Screening
Secondary
crushing
Rotary
dryer
Grinding
Calcining
Pollutant
Fugitive
particulates
Fugitive
particulatea
Particulatea
Particulates
Particulatea
Particulate*
Particulatea
Particulates
Uncontrolled
emission rate
N.A.»
Negli-
gible
N.A.'
N.A.*
N.A.*
20 g/kq
gypsum"
0.5 g/kg
gypsum"
45 g/kg
gypsum0
Liquid
Source
Open pit -N
mining /
(pumpout) /
Underground (
mining \
(pumpout) J
Pollutant/
parameter
i- TSS
pH
Uncontrolled
discharge
4 to 60
rag/t
7.4 to «.lc
Solid
Source
Open pit
mining
Ore extrac-
tion
Pollutant
Overburden
waste
Gangue
Uncontrolled
quantity
1100 kq/Mg
gypsum mined0
N.A.'
to
-J
4 See air, liquid, and solid waste sections.
D Ref. 59.
c Ref. 39. This range is for six facilities.
N.A.- Not available.
-------
Probably the most significant air emissions in gypsum bene-
ficiation emanate from the calcining operation, which generates
45 grams of particulate per kilogram of gypsum (68). The turbu-
lant gases created by the release of the crystallization water
carry calcined and partially calcined gypsum into the atmosphere.
Particles are relatively large compared with those from processes
in which the material is vaporized and condensed. However,
gypsum dust is believed to be harmless.
Liquid Wastes—
If gypsum is dry processed, no process water is required in
the mining, crushing, screening, or grinding operations. The
only sources of liquid wastes are small amounts of mine drainage
pumpout and runoff from storage piles.
In wet processing (heavy-media separation), water is needed
for screening, washing and media recovery. Most of the waste-
water is recycled along with runoff and no water is discharged
into a watercourse (39). However, it is possible for some waste-
water from the pond to leach out into the groundwater table.
Solid Wastes—
The only significant source of solid waste is the overburden
removal from open-pit mining operations. About 1.1 megagrams of
waste is generated for each megagram of gypsum mined (59).
Control Technology
The following paragraphs explain in some detail the various
control options used in mining and beneficiation of gypsum.
Air Emissions Control—
Emissions from both underground and open-pit mines are
minimized by using state-of-the-art control devices common to all
mining activities. These are described in Section 3.
Most crushing and screening operations take place in a fully
enclosed crush house, which is vented to a dry-dust collection
device such as a fabric filter or a cyclone. The efficiency of
these devices is not reported, but is estimated to be 90 to 95
percent based on knowledge of the process and equipment.
Liquid Waste Control—
Wastewater (pumpout and runoff) from both open-pit and
underground mines is discharged into a pond. In the dry method,
mine wastewater is discharged into a nearby watercourse after the
solids have settled out. If heavy-media separation is used, most
of the wastewater from the pond is recycled and used as process
water.
98
-------
Solid Waste Control--
Overburden waste and gangue are collected and allowed to
pile up within the mine site. Although there are no general
reclamation guidelines and standards, natural vegetation develops
on these sites within a short time.
Conclusions and Recommendations
Gypsum is mined and beneficiated by environmentally accept-
able methods in the United States, and no hazardous pollutants
are generated.
Air pollutants are contained by conventional state-of-the-
art techniques, and aqueous wastes are frequently recycled and
used as process water. The only area that possibly warrants
further research and development is the disposal/utilization of
the large quantities (1.1 megagrams per megagram of ore) of
overburden removed from open-pit mines, which now is allowed to
accumulate at the mine site.
ASPHALTIC MINERALS
Industry Description
Asphaltic minerals are mixtures of hydrocarbons (natural or
pyrogenous in origin) that are frequently accompanied by their
nonmetalic derivitives. Since these natural asphalts include a
wide variety of minerals, the term is sometimes expanded to
include rocks in which the percentage of impregnation is compara-
tively low. Asphaltic minerals include bituminous sand, bitumi-
nous sandstone, bituminous limestone, tar sands, gilsonite,
albertite, uintaite, elaterite, grahamite, impsonite, nigrite,
wurtzilite, tabbyite, aconite, and aegerite.
Substantial deposits of bituminous sand, sandstone, and
limestone are found in many areas of the world. In the United
States, deposits of commercial importance have been mined in
Texas, Oklahoma, Louisiana, Utah, Arkansas, California, and
Alabama. The bitumen content of these deposits, which are mined
from open quarries, ranges from 4 to 14 percent (39). The mate-
rial is used for paving in areas that are within economical
shipping distance of the mine.
Another asphaltic mineral, which is 99.9 percent hydrocarbon
but of lesser importance, is gilsonite. The only known deposits
of this hard, brittle bitumen are in the Uintah basin of Utah and
Colorado, where it is found in place, in veins, in locks, or in
rock (60). Gilsonite production has been declining since 1974.
99
-------
Grahamite is a mineral that resembles albertite in its
jet-black luster. Deposits are found in veinlike masses in many
areas, but rarely in large quantities (60). A large deposit in
West Virginia was mined out several years ago; and deposits in
Oklahoma, which were mined intensively in.years past, are rarely
mined now (39). Two deposits have been discovered in West Texas
but are not considered significant enough to mine (61).
Wurtziline (also known as elaterite, aconite, aegerite, and
tabbyite)is a pyrobitumen that is closely related to gilsonite
and uintaite and characterized by its hardness and infusibility.
The main deposit of commercial importance is located in Uintah
County, Utah. Wurtziline is used primarily in paints, varnishes,
hard rubber compounds (as an extender), and weatherproofing and
insulating compounds (39, 60).
Although U.S. production of native asphalt and related
bitumen has fallen somewhat, it has remained between 1.6 and 1.8
x 10 megagrams per year for the past ten years (62). This
production consists mainly of bituminous limestone, bituminous
sandstone, bituminous sand, and gilsonite; therefore, the dis-
cussion in this report concentrates on the mining and beneficia-
tion of these asphaltic minerals. Production statistics for the
industry are presented in Section 1 of this report.
Process Description
All asphaltic minerals except gilsonite are mined by open-
pit methods. The asphaltic mineral category is a broad one and
involves various mining and beneficiation techniques. Figure 16
presents a composite flow diagram for the mining and beneficia-
tion of asphaltic minerals.
As mentioned, the gilsonite deposits in Utah are mined
underground. Because some fatal accidents occurred as a result
of the explosive nature of the dust, it is now mined exclusively
by hydraulic methods. High pressure water is applied, sometimes
in conjunction with mechanical cutters, to fragment the ore. The
ore is then recovered as a slurry and pumped to the surface where
a portion is screened, dried, and packaged as a marketable sized
material in its native state.
Material unsatisfactory for marketing is shipped by truck to
Craig, Colorado, for further processing. Until recently it was
pumped in a slurry through a 115 kilometer pipeline to Grand
Junction, Colorado, for processing into coke and gasoline. The
pipeline is now used in conjunction with oil shale mining.
Asphaltic sands (tar sands) are presently mined in Missouri
and have been mined in Kentucky and Oklahoma. The terms "tar
100
-------
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Figure 16 . Mining and beneficiating of asphaltic minerals
-------
sand" or "asphaltic sand" are used loosely to describe sands that
contain both oil and asphalts. The rising cost of fuels will
probably increase the pressure to develop these deposits for
their value as fuel rather than paving, where virtually all of it
now goes. Oil can be extracted by heating with hot water.
Development of technology to economically recover fuels from
asphaltic minerals could greatly increase mining activity.
The primary end use of asphaltic sandstone and asphaltic
limestone is also in paving. Since crushed asphaltic limestone
makes a much better paving material than the asphaltic sandstone,
little asphaltic sandstone is mined where limestone deposits are
available. However, some sandstone is blended with the limestone
mixture for use in paving (63). Texas is the largest producer of
total asphaltic minerals, and West Texas has the largest concen-
tration of asphaltic limestone in the country. These limestone
deposits contain about 9 to 13 percent bitumens. They lie close
to the surface, so little overburden has to be removed. The
deposits, which are between 3 and 25 meters thick, contain both
rich and barren sections. Some Texas deposits have been reported
to be from 50 to 65 meters thick (61). Mines are the conven-
tional open-pit type, with crushing and screening on site.
Waste Streams
Table 15 summarizes multimedia wastes resulting from the
mining and beneficiation of asphaltic minerals, and the following
paragraphs explain in more detail the various air, liquid, and
solid waste emissions.
Air Emissions—
Because of the explosive nature of gilsonite, dust control
is an integral part of the mining and beneficiating process. The
high-pressure water extraction method was developed after some
fatal underground accidents, and all operations prior to drying
are performed wet, thereby precluding air emissions.
Emissions from gilsonite drying are sent through a scrubber
before discharge to the atmosphere. Some fugitive dust emissions
result from packaging and storage, but they have not been quanti-
fied.
Because of their physical properties, air emissions from
open-pit mining of bituminous sand, sandstone, and limestone are
less than you would expect from a typical open-pit operation.
Also, deposits are generally close to the surface, making fugi-
tive dust emissions from overburden removal lower than average.
This appears also to be true of the fragmentation and loading of
the ore. However, no specific data were found on emission rates
for any of these sources.
102
-------
TABLE 15. SUMMARY OF MULTIMEDIA WASTES FROM MINING AND
BENEFICIATING OF ASPHALTIC MINERALS
Air
Source
Underground
operations
Dryer
Overburden
removal
Fragmenta-
tion of ore
Loading of
ore
Transport
of ore
Ore storage
Crushing
Screening
Product
storage
On site
packaging
Tailings
pond
Pollutant
Fugitive par-
ticulate from
mine ventila-
tion
Particulates
Fugitive
particulates
Fugitive
particulates
Fugitive
particulates
Fugitive
particulates
Fugitive
particulates
Particulates
Particulates
Fugitive
particulates
Particulates
Fugitive
particulates
Uncontrolled
emission rati
Negligible
N.A!
N.A.
N.A.
N.A.
N.A.
N.A.
N.A.
N.A.
N.A.
N.A.
N.A.
Liquid
Source
Flotation
Scrubber
discharge
Overburden
removal
Fragmentation
of ore
Ore storage
Decantation
Tailings
Pollutant/-
parameter
TSS
BOD
pH
TDS
Cd
Chloride
Sulfate
Runoff
Runoff
Runoff
Oil/tailings
N.A.
i
Uncontrolled
discharge
17 mg/lb
43 mg/t°
B.2*>
2949 mg/tb
<0.001 mg/lb
0.15 mg/lb
363 mg/lb
To tailings
To tailings
To tailings
To tailings
No discharge0
Solid
Source
Underground
operations
Solids sepa-
ration gil-
sonite
Flotation
Overburden
removal
Fragmenta-
tion of ore
Solids sepa-
ration other
than gilson-
ite
Tailings
Pollutant
Gangue
Sand
Tailings
Topsoil,
subsoil 4
other
strata
Gangue
Sand, waste
Tailings
Uncontrolled
quantity
100-450 thousand
Mg/hrd
N.A.
N.A.
N.A.
N.A.
o
u>
For store complete information see air. liquid, solid waste sections.
Ref. 39. For gilsonite mine.
c Ref. 39. No discharge under normal operations..
d Ref. 64. For gilsonite mine 1974.
H.A. - Hot available.
-------
Fugitive emissions from truck transport of the ore to the
beneficiation site depend more on the location of the mine than
on the ore. With the majority of the asphaltic minerals mined in
arid or semiarid regions (Utah, West Texas), the fugitive emis-
sions from this source can be expected to be higher than for the
average mine. No specific emission data were found for either
transport or storage of asphaltic minerals.
Because of the explosive nature of gilsonite, water sprays
are used to control emissions from the crushing and screening
processes. No information was found on tl>e emissions from the
crushing and screening of other asphaltic minerals. In fact no
specific emission rates are available for any of the numerous
asphaltic minerals.
With minor exceptions, most asphaltic minerals are used for
highway paving. A few, notably gilsonite, are packaged on site
for ultimate use in a wide variety of products such as paints,
insulation, . auto sealers, building board insulation, foundry
processes, explosives, well cementing and printer's ink. No
specific data were found on emissions from either the packaging
or product storage of asphaltic minerals.
Because of the diversity of the tailings and the wide geo-
graphic distribution- of the mines, it is impossible to estimate
an emission factor for dried tailings.
Liquid Wastes—
All liquid wastes generated in gilsonite mining and benefi-
ciation are recycled, largely because the mine is located in an
arid region. Table 15 lists the concentrations of various pollu-
tants sent to tailings.
All other asphaltic mining processes require considerably
less process water than gilsonite beneficiation and under normal
operating conditions no waste discharge occurs.
Some runoff from the overburden and gangue may occur, but no
published data were found to support this. Nor were any found on
mine pumpout from surface mines. Since the bulk of the asphaltic
minerals is mined in arid or semiarid regions, mine pumpout and
runoff are probably not serious problems.
Solid Wastes—
Solid waste emissions from the mining and beneficiation of
asphaltic minerals consist of overburden, gangue, and tailings.
The overburden produced in open-pit mining is usually stored in
heaps adjacent to the pits. Deposits are normally close to the
surface, and the quantity of overburden has been compared to that
of a stone quarry.
104
-------
A substantial quantity of gahgue and tailing is generated in
the mining and beneficiation of gilsonite. Table 15 shows the
solid waste from this total operation. No information was found
on the quantity of solid waste generated from any other, asphaltic
mineral mining processes.
Control Technology
Little data were found on pollution controls used in the
asphaltic minerals industry. The following paragraphs explain
the various control technologies known and.their estimated effi-
ciencies.
Air Emissions--
Overburden removal and ore fragmentation are among the most
variable fugitive dust sources at surface mines. Dust emitted
varies with composition, texture, and moisture content of the
material; excavation procedures; equipment employed; etc. No
information on specific controls or efficiencies was found.
Oiling or watering haul roads reduces dust generated from
ore transport. An efficiency of 50 percent is assumed for con-
trol by watering.
Water sprays are used to suppress dust in gilsonite mining.
This approach also helps to prevent explosion of the small dust
particles.
Wet scrubbers are used to control dust emissions from the
drying process, and the process water is sent to tailings for
recycle. Control efficiency is unknown.
Air emissions from tailings can occur when the tailing pond
becomes dry (i.e. when operations have ceased). These emissions
can be reduced by either an intentionally or naturally formed
crust. Emissions can be reduced up to 80 percent by- this method
(65).
Liquid Wastes—
Liquid wastes in the asphaltic mining industry are con-
trolled by recycling process water and by tailings ponds. No
discharge occurs from these ponds.
Solid Wastes—
Because the majority of the asphaltic minerals are mined in
fairly remote areas, little pressure is applied toward reclaiming
the disturbed land. Even the largest producing state does not
require land reclamation. However, no information pointed to any
problems caused by the solid waste generated at these mines.
More data are definitely needed in this area.
105
-------
Conclusions and Recommendations
Asphaltic minerals mining apparently causes no serious
pollution problem. This is due in part to its small size and the
location of the mines in remote dry areas.
It is believed that the new vague boundary between oil shale
and asphaltic minerals may become even more vague as deposits
become more valuable for their fuel value. If this happens and
the industry expands both geographically and in size, research
will be needed into the basic quantification of specific waste
streams. At present, however, this research effort can be spent
better on other minerals.
ASBESTOS AND WOLLASTONITE.
Industry Description
Asbestos is a broad term applied to a number of fibrous
mineral silicates that are incombustible and can be separated by
suitable mechanical processing, into fibers of various lengths
and thickness. Six varieties of asbestos are recognized: the
finely fibrous form of serpentine known as chrysolite and five
members of the amphibole group, i.e., amosite, anthophyllite,
crocidolite, tremolite, and ackinolite. Chrysolite, which pre-
sently constitutes 93 percent of the world's asbestos production,
Wollastonite is
has the empirical formula 3MgO2Si02*2H20 (39).
a naturally occurring, fibrous calcium silicate,
CaSiO, (39).
The United States is one of the leading consumers of asbes-
tos yet in 1974 produced only 2 percent of the total world's
production (4). (Production statistics for asbestos and wolla-
stonite appear in Section 1 of this report.)
Seven U.S. companies engaged in the production of asbestos
in 1974. Four of the operations were in California and one each
in Arizona, North Carolina, and Vermont (4). U.S. wollastonite
is mined by one company in New York (39).
The construction industry presently uses most of the asbes-
tos fibers in such products as asbestos cement pipe and sheeting,
roofing products, flooring products, paints, and caulking. These
fibers are also used in textiles, clothing, theatre curtains,
woven brake linings, clutch facings, electrical insulation mate-
rials, and high-pressure marine insulation (4). Wollastonite is
useful as a ceramic raw material, as a filler for plastics and
asphalt products, as a filler and an extender for paints, and as
an ingredient in welding rod coatings. Because of its fibrous,
noncombustible nature, wollastonite is also being considered as a
possible substitute when asbestos is objectionable in certain
products (39).
106
-------
Process Description
Most asbestos mines in the United States are open-pit; a
single mine in Arizona uses underground methods (4).
The ore is conveyed from mine to mill by truck. Although
milling methods vary in detail, they are all identical in prin-
ciple. Four of the five U.S. facilities that mine and process
asbestos use a dry method, the fifth a wet method (39). Figure
17 shows the two methods.
In the dry process, the quarried asbestos ore is crushed in
jaw or gyratory crushers to a size of 3.8 to 5.1 centimeters.
The crushed ore is dried to 1 percent or less moisture in rotary
or vertical dryers before being crushed again in hammermills,
cone crushers, or gyratory crushers. The ore is sent from the
secondary crushers to a series of shaker screens, where the
asbestos fibers are separated from the rock and air-classified
into a series of grades according to length. The graded fibers
are bagged for shipment (39).
In the wet process, ore is "ploughed" in horizontal benches
and allowed to air-dry. It is then screened and transported to
the mill for processing. Processing consists of further screen-
ing, wet crushing, fiber classification, filtering, and drying.
Process water is used for wet processing and classifying of
asbestos fibers.
The only U.S. producer of wollastonite uses the underground
room and pillar method to extract the ore, then trucks it to the
processing facility. Processing is dry and consists of three
stage crushing with drying following the primary crushing. The
ore is screened, then various sizes are fed to high-intensity
magnetic separators to remove garnet and other ferromagnetic
impurities. The purified wollastonite is ground in pebble or
attrition mills to the desired product sizes. Figure 18 shows a
process flow diagram for wollastonite mining and beneficiating.
Waste Streams
Table 16 presents a summary of multimedia wastes from the
mining and beneficiation of asbestos and wollastonite. The
following paragraphs explain in more detail the various air,
liquid, and solid wastes associated with this industry.
Air Emissions--
Asbestos fibers and other particles are emitted during
removal of overburden and preparation of the ore body for open-
pit mining. Further release occurs during drilling and ore-
breaking. Particles are also released in underground mining
107
-------
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Figure 17 . Mining and.,beneficiating of asbestos
-------
9 AIR EMISSIONS
^ LIQUID HASTES
SOL ID HASTES
C1HAUST
UM
f KMUMO MUIW
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10 SUIfACt
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Figure 18. Mining and beneficiating of wollastonite.
-------
TABLE 16. SUMMARY OF MULTIMEDIA WASTES FROM MINING AND
BENEFICIATING OF ASBESTOS AND WOLLASTONITE
Air
Source
Overburden
removal
Ore extrac-
tion
Ore loading
Ore trans-
port
Underground
mining
Primary
crusher
Rotary
dryer
Secondary
crusher
Screen
Pollutant
Fugitive
particu-
lates
Particu-
lates
Particu-
lates
Particu-
lates
Particu-
lates
Particu-
lates
Uncontrolled
emission rate
N.A.
N.A.
N.A.
N.A.
N.A.
N.A.
Liquid
Source
Overburden
removal
Ore
extraction
Underground
mining
Classify
Filter
Pollutant/
parameter
TSSa
Fe
Asbestos
PH
N.A.
TSSa
Magnesium
Sodium
Chloride
Nickel
PH
N.A.
Uncontrol led
discharge
2.0 mg/l
0.15 mg/t ,
1.0 to 1.8 x 10
fibers/liter
8.4 to 8.7
N.A.
160 mg/t
48 mg/t
345 mg/t
104 mg/t
0.1 mg/t
7.8 •
N.A.
Solid
Source
Overburden
removal
Ore
extraction
Underground
mining
Fabric
filter
Settling
pond
Pollutant
Gangue
Gangue
Collected
particu-
lates
Sludge
Uncontrolled
quantity
Up to 96% of ore
N.A.
N.A.
N.A.
I-1
(-•
o
• Kef. 39.
b Telephone conversation between Vijay Patel of PEDCo and Chris Jones, Vermont Air Pollution Control Agency, Montpelier,
Vermont, April 1977.
N.A. - Not available.
-------
operations. The quantity of emissions has not been reported from
any of these sources.
Each piece of process equipment in the dry milling of asbes-
tos produces dust emissions.
Dust sources are minimized in the wet process by use of
water throughout the operation.
Virtually every process step in the mining and beneficiation
of wollastonite is a potential generator of particulate emis-
sions. Quantitative data on these emissions are not available,
however, because of the proprietary nature of the process.
Liquid Wastes—
Since no process water is used for dry processing asbestos,
sources of liquid wastes are few. The major source is mine
pumpout. At one facility the flow ranges from 380 to 2270 liters
per minute depending on rainfall (39). The following tabulates
the analytical data for this discharge:
TSS 2.0 mg/£
Fe 0.15 mg/jfc 6
Asbestos 1.0 to 1.8 x 10 fibers/liter
pH 8.4 to 8.7
In the wet process, large quantities of water are used.
Water consumption at one facility is reported to be 4300 liters
per megagram of asbestos milled (39). The wastewater discharge
from the same facility amounts to 860 liters per megagram of
asbestos milled. The rest of the water is either lost with the
product, recirculated, or lost in tailings.
The discharge parameters from this facility are:
TSS 1160 mg/£
Magnesium 48 mg/£
Sodium 345 mg/Jl
Chloride 104 mg/£
Nickel 0.1 mg/£
pH 7.8
The filtrate from the filtration process is recycled to the
crushing and screening process (39).
Mining and beneficiation of wollastonite does not involve
any water use. Noncontact cooling water amounts to 235 liters
per megagram of product (39).
Ill
-------
Solid Wastes—
Open-pit mining produces large quantities of overburden and
waste rock. One of the largest asbestos mines in the country
reports up to 96 percent of mined ore is discarded as waste.*
Underground mining produces only a small amount of waste rock.
In the dry process, one of the largest sources of solid
wastes is the dust collected by the fabric filters.
In the wet process, solid wastes accumulate in the form of
sludge in the settling ponds.
In the mining and beneficiation of wollastonite, approxi-
mately 40 percent of the ore mined is discarded as solid waste.**
Roughly 10 percent of this waste comes from mining and the rest
from beneficiation of the ore. The magnetic separation process
is the largest source of solid waste in the beneficiation opera-
tion.
Control Technology
Control technologies as applied to the asbestos and wolla-
stonite mining industry are explained in the following para-
graphs .
Air Emissions Control—
Various types of wetting agents reduce dust emissions at
most open-pit mines. One> mine uses a fabric filter to control
primary dust from the drilling operation.* At another mine in
California, the relatively high moisture content (15 percent) of
the ore keeps dust emissions at a minimum.***
Most mines use fabric filters to control dry milling opera-
tions. All conveyors are enclosed, and conveyor transfer points
are aspirated to the fabric filters.
*Telephone conversations between Vijay Patel of PEDCo and
Chris Jones, Vermont Air Pollution Control Agency, Montpelier,
Vermont. April 1977.
**Telephone conversation between Vijay Patel of PEDCo and Loren
Choate, Interforce Corporation, Willoboro, New York. May 1977.
***Telephone conversation between Vijay Patel of PEDCo and
Bob Bashran, Fresno County Air Pollution Conference Office,
Fresno, California. April 1977.
112
-------
The one existing U.S. wollastonite facility uses seven
fabric filters at various locations within the process to mini-
mize dust emissions.*
Liquid Waste Control—
One dry process facility is reported to treat quarry pumpout
discharge with sulfuric acid to lower the pH of the highly alka-
line ground water that collects in the quarry (39).
The wet processing facility treats process water discharge
in settling ponds. Suspended asbestos fibers settle out in the
primary settling pond before the clarified effluent is decanted
to the secondary settling pond. The facility does not discharge
to surface waters (39).
The one U.S. wollastonite mine discharges untreated noncon-
tact cooling water to a nearby river (39).
Solid Waste Controls—
Waste rock from open-pit mining is disposed of in a tailing
pond. Some facilities also send dust collected from the fabric
filters to the tailing pond, whereas other facilities plough the
dust back into the process.
Sludge accumulated in the settling ponds is periodically
dredged. The wastes are piled along side the pond, allowed to
dry, and then landfilled. Usually no mitigating measures are
undertaken to retard windblown materials.
Solid wastes from the mining and beneficiation of wolla-
stonite are sent to a tailings pile. From there it is hauled off
site to be used as fill material or as an agricultural fertiliz-
er.*
Dust collected in the fabric filters in the wollastonite
mine is either ploughed back into the process or sent to the
tailings pile.*
Conclusions and Recommendations
Asbestos has recently been recognized as a potential
carcinogen. Asbestos fibers may be liberated into the air in
dangerous amounts at all stages in the mining and milling of the
ore. Because of the carcinogenic properties of asbestos, most
research should be directly related to reducing adverse health
effects. •
*Telephone conversations between Vijay Patel of PEDCo and Loren
Choate, Interface Corporation, Willoboro, New York. May 1977.
113
-------
Methods of sampling, identifying and quantitating airborne
asbestos need to be developed further in coordination with con-
tinuing studies involving animals and man to ensure biological
relevance of environmental data.
Quantitative methods for measuring airborne asbestos should
be applied widely to determine the natural background and the
concentration and distribution of fibers in the air near various
sources.
The potential use of tailings from asbestos mines in the
manufacture of building products should be further investigated.
LIGHTWEIGHT AGGREGATES
Industry Description
Lightweight aggregates include several minerals or rock
materials used as fillers in concrete, plaster, insulation, and
for other structural materials, and as an insulator (25). Some
lightweight aggregates occur naturally (pumice) whereas others
are manufactured from natural minerals (perlite and vermiculite).
Minerals used for lightweight aggregate production are
extracted by open-pit methods. Preliminary, beneficiation (e.g.
crushing, screening, milling)' of perlite and vermiculite is
usually performed at the mine site, but final processing (expan-
sion) is normally accomplished at facilities located closer to
the consumer. Pumice, on the other hand, is processed completely
at facilities located adjacent to the mining operations.
Perlite—
The name perlite is commonly used to describe both unpro-
cessed (crude perlite) and processed (expanded perlite) material.
Crude perlite is a natural, glassy, rhyolitic rock that is essen-
tially a metastable amorphous aluminum silicate (5). Its abun-
dance of spherical or convoluted cracks causes it to break into
small pearl-like masses, usually less than a centimeter in dia-
meter, as a result of the rapid cooling of acidic lavas. The
chemical constituents of perlite include silicon oxide (71 to 75
percent), aluminum oxide (12.5 to 18 percent), potassium oxide (4
to 5 percent), and sodium and calcium oxides (1 to 4 percent)
(5). Perlite may also contain traces of various metal oxides.
Crude perlite has the unusual characteristic of expanding to
about 20 times its original volume when heated, and expanded
perlite has numerous constructional and industrial applications
because of its low density, low thermal conductivity, and high
sound adsorption.
114
-------
The United States leads the world in production and consump-
tion of perlite. The industry has enjoyed continuous growth in
its brief 30-year history, and upward trend of perlite production
is expected to continue over at least the next 10 years. (See
Section 1 of this report for present and future production sta-
tistics. )
The total domestic production of crude perlite in 1974 came
from twelve surface-mine operations in six Western States (5).
New Mexico, the major producing state, supplied 88 percent of the
total crude perlite mined. Other states with active perlite
mines include Colorado, Texas, Arizona, Nevada, and California.
Expanded perlite was produced at 76 facilities in 30 states in
1974. The principal producing states are Illinois, Mississippi,
Kentucky, Pennsylvania, and Colorado.
The commercial uses of perlite are numerous and depend upon
the properties of the expanded material. Approximately 70 per-
cent of the expanded perlite is consumed as an aggregate for
plaster and concrete and prefabricated insulating board (39).
Some perlite is used as an insulator, and as such provides a high
degree of fireproofing. Perlite is also used as a filter-aid
material in the treatment of industrial wastes water, and in the
beverage, food, and pharmaceutical processing industries.
No by-products/coproducts are associated with the perlite
industry.
Pumice—
Pumiceous materials (minerals of volcanic origin) include
pumice, pumicite, scroia, and cinder (7). These volcanic rocks
have a variety of applications dependent upon the unique charac-
teristics of the materials, such as abrasiveness, inertness, and
light weight. Commercial usages have resulted in the application
of the term pumice to all rocks of volcanic ash origin.
Pumice is essentially an aluminum silicate of igneous origin
with a cellular structure formed by a process of explosive vol-
canism (7). Pumicite is a pumice that has been subjected to
additional volcanism, which breaks down the cellular structure to
form a finely divided, unconsolidated material. Volcanic cinder
and scoria are uncemented volcanic fragments formed from a basic
igneous magma.
The United States is one of the world's largest producers
and consumers of pumiceous materials. Over the past 11 years
this country has produced an average of 21.5 percent of the world
production (7). Projections indicate the United States will
maintain its current position in production and consumption.
(See Section 1 of this report for production statistics.)
115
-------
In 1974 pumiceous materials were produced by 290 operations
in 12 states (7). The major producing states were Arizona,
California, Hawaii, Nevada, and New Mexico.
Both unprocessed (crude) and processed pumiceous materials
are sold on the commercial market. Principal end uses include
abrasives for cleaning and scouring compounds, concrete aggregate
and admixtures, railroad ballast, road construction, and land-
scaping. Additional uses of pumiceous materials include dil-
uents, absorbents, catalyst carriers, decolorizing and purifying
agents, and filler and extenders for paints, enamels, varnishes,
plastics, and rubber goods.
Vermiculite—
Vermiculite is a mica-like mineral and, like perlite, has
the unique property of exfoliating to a low-density material when
heated. The term Vermiculite is applied to both the crude ore
and the expanded product.
In 1974 the United States accounted for 62 percent of the
vermiculite output and 58 percent of the demand in the world
market (8). (See Section 1 of this report for production statis-
tics.) The United States is now self-sufficient in vermiculite
production and ore reserves are thought to be sufficient to meet
future needs.
In 1975 crude vermiculite was extracted from only two loca-
tions in the United States, a large mine near Libby, Montana (the
largest vermiculite mine in the world), and several small mines
near Enoree, South Carolina. Efforts are being made to develop a
vermiculite deposit near Louisa, Virginia, but zoning problems
are delaying this action. Crude vermiculite was processed (ex-
foliated) at 53 plants in 31 states in 1974 (8). The major
producing states, accounting for 46 percent of the total produc-
tion, were California, Florida, New Jersey, South Carolina, and
Texas. Most vermiculate exfoliating facilities produce less than
5000 megagrams annually.
Vermiculite has a broad range of uses since the expanded
product is noncombustible, lightweight, insoluble, freeflowing,
chemically inert, resilient, and nonabrasive. These characteris-
tics make it particularly useful in the construction and agricul-
tural industries. It has been used specifically in thermal
insulators, in additives for lightweight concretes and plasters,
and in fire barriers, and more recently, because of its excellent
adsorption characteristics, in chemical processing, water and air
purification, and other areas.
116
-------
Process Description
Deposits of lightweight aggregates considered in this study
(perlite, pumice, and vermiculite) are all similar in that they
1) result from volcanism, 2) lie close to the surface, and 3) are
covered with a relatively thin layer of unconsolidated material.
In the past a small amount of lightweight aggregate was recovered
from underground operations, but all current mining is open-pit.
Since the overburden and most deposits consist of unconsolidated
material, equipment such as bulldozers, pan scrapers, draglines,
and power shovels are used to remove overburden and loosen,
extract, and load the mineral. Periodically, some consolidated
material is encountered that requires loosening by rippers or
blasting. Extracted ore is loaded onto trucks, carryalls, or
conveyor chutes and transported to the processing mill, which is
usually located adjacent to the mine site. The processing of
perlite, pumice, and vermiculite is illustrated on Figure 19 and
described in the following paragraphs.
Perlite—
Perlite ore is reduced by a jaw crusher and, occasionally, a
secondary roll crusher. When necessary, the crude is passed
through a rotary dryer (usually oil-fired) to reduce the moisture
content from 2 to 5 percent to less than 1 percent. The dried
perlite is screened and further reduced by a ball or rod mill to
the specified size for expansion. Care must be taken during the
crushing steps to keep to a minimiurn particles that are too small
for expansion. These excessively fine particles (-100 mesh),
which are generally considered waste, are separated from useful
sizes (-4 to +100 mesh) by screening and/or air classification.
Following classification, the perlite usually is stored in un-
covered stockpiles until being trucked to off-site expansion
furnaces located closer to the consumer. This classification
practice minimizes transportation expenses. Waste fines gener-
ated throughout the processing circuit (up to 25 percent of the
mill feed) are either collected and bagged (if salable) or dumped
on site.
Pumice—
Processing of pumice first involves the use of scalping
screens to remove organic debris and oversized material. Primary
(and sometimes secondary) crushers are then applied to reduce the
oversize material. Occasionally the crude ore requires drying,
which is done in a rotary dryer either before or after the crush-
ing step. If the pumice is to be used in road surfacing, it is
removed at this point. If it is to be used as an abrasive,
however, it must be ground with a rod or ball mill before sizing
by either air classification or bolting machines. The end pro-
duct usually is bagged by size and stored until shipment.
117
-------
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Figure 19. Mining and beneficiating of lightweight
aggregates (perlite, pumice, and vermiculite).
118
-------
Vermiculite--
vermiculite ore is currently processed in only two locations
in the United States: Libby, Montana, and Enoree, South
Carolina. Although these facilities differ operationally, they
share some similarities. Processing at the Montana plant com-
bines dry and wet processes using crushers, screens, jigs, and
spirals. Since most of the extracted ore is in a disseminated
form, crushing usually is not required and the ore is passed
directly through the screening operation to the concentrators
(25). However, crushing is required occasionally to reduce
oversized material. The screened (and sometimes crushed) ore is
concentrated by jigs and spirals. The concentrate is then de-
watered (generally by centrifuges or rotary dryers), sized, and
stored for shipment to the expansion facilities. The South
Carolina operations differ from those described above in that
almost all the ore requires some size reduction and it is washed
to remove clay slimes before being concentrated. Following
grinding, washing, and screening the ore is concentrated in
flotation units. As in Montana, the concentrate is then de-
watered, .sized, and stored for shipment to expansion plants.
Waste Streams
The extraction and processing of lightweight aggregate
minerals result in the generation of various atmospheric, liquid,
and solid wastes. These waste streams are shown in Table 17 and
discussed in detail in the following paragraphs.
Air Emissions--
Sources of atmospheric emissions associated with the mining
of lightweight aggregates are similar to those related to other
mineral mining industries. Fugitive particulates may result from
any one of a number of operations such as overburden removal and
ore loosening, extraction, loading, and transportation. The
moisture content of crude perlite, vermiculite, and pumice ores
is usually high enough to make fugitive emissions minimal;
however, when the ore and associated waste materials dry, they
can generate large quantities of particulate dust. This is
especially true at perlite and pumice mines, which usually are
located in areas with semiarid to arid climate. Most of the
fugitive particulates generated at lightweight aggregate mining
sites result from truck transport of crude ore over unpaved
roads. No data are available concerning the emissions of fugi-
tive particulates from these various sources in the lightweight
aggregate industry.
Particulates are the major atmospheric pollutant associated
with the processing of lightweight aggregates. The drying opera-
tion is the largest source at all perlite, pumice, and vermicu-
lite mills. Perlite and vermiculite dryers have been found to
119
-------
TABLE 17. SUMMARY OF MULTIMEDIA WASTES FROM MINING AND BENEFICIATING OF
LIGHTWEIGHT AGGREGATES (PERLITE, PUMICE, VERMICULITE)
Lightweight
Aggregate
Mining
Perl
O
(continued)
-------
TABLE 17. (continued)
Purict
Processing
Veralcullte
Processing
Air
Source
Screening
Sedondary
crushing
Drying
Grinding
Air
classification
Bagging
facility
All conveyors
and elevators
Grinding
Screening
Drying
Loading
facility
Pollutant
Participates
Participates
Partlculates
Partlculates
Partlculates
Parttculates
Partlculates
Partlculates
Partlculates
Uncontrolled
emission rate
N.A.
0.75 kg/Mg
of feed*
N.A.
3.0 kg/Ng
of feed*
N.A.
N.A.
N.A.
0.25 kg/Ng
of feed*
0.33 kg/Mg
of feed'
8.6 kg/Mg
of feedc
0.20 kg/Mg
of feedc
Liquid
Source
Process
wastewate
Pollutant/
parameter
TSS
Uncontrolled
discharge
N.A.
Solid
Source
Pollutant
Uncontrolled
quantity
ro
Ref. 44. Based OH Mission factors for stone quarrying.
Telephone conversation between Jack Greber of PEOCo and David Ouran. State of New Mexico Environmental Improvement Agency. Sante Fe. New Mexico.
April 1977. Value based on observation of a single perltte mining and processing facility.
c Telephone conversation between Jack Greber of PEDCo and John Bolstad, Montana State Department of Health and Environmental Sciences, Helena.
Montana. April 1977. Based on values from a single vermlcullte mine.
Ref. 7. Calculated as 25 percent of the mill feed. Represents total partlculates collected from various stages throughout the processing
operations.
N.A. - Not available.
-------
emit total particulates at a rate of 55.97 kilograms* and 8.6
kilograms** per megagram of feed, respectively. Data are not
available on emissions from pumice dryers, but they are expected
to be similar to those reported for perlite dryers. Additional
sources of particulates at lightweight aggregate plants include
crushing, screening, grinding, conveying, classifying, and load-
ing operations. Emissions from these operations are most ap-
parent at feed and discharge points. As Table 17 indicates,
initial processes (primary crushing and screening) generate less
emissions than secondary and final processing operations (e.g.
drying, grinding, classifying) because the crude ore handled
during and after drying operations is of smaller particle size
and drier than the ore handled in initial operations. Other
factors that influence the amount of emissions released from the
various sources include the type of rock processed and the type
of processing equipment.
Fugitive particulates are also a problem at perlite, pumice,
and vermiculite processing facilities. The major source is
vehicular traffic. Fugitive dust is a greater problem at perlite
and pumice operations because they are located in areas with
semiarid to arid climate. No data are available on fugitive
particulates for the lightweight aggregates industry.
Atmospheric wastes associated with the mining and benefi-
ciating of perlite and pumice do not contain any potentially
hazardous materials; however, the ore recovered from the large
vermiculite mine near Libby, Montana is known to contain asbestos
fibers.** The amount of asbestos released to the atmosphere has
not been monitored at this facility, but microscopic analysis of
the ore revealed an asbestos concentration of less than 5 fibers
per cubic centimeter of ore.
Liquid Wastes—
Most perlite and pumice operations employ dry processing
methods and therefore produce no wastewater (39). Several plants
use minor amounts of water to control fugitive dust, but the
water is evaporated or absorbed quite rapidly and results in no
discharge. Some facilities have small amounts of discharge
resulting from the use of wet scrubbers. Pit pumpout and surface
runoff are not a problem at perlite and pumice operations because
of their location in areas with relatively dry climate.
*Telephone conversation between Jack Greber of PEDCo and
David Duran, State of New Mexico Environmental Improvement
Agency, Santa Fe, New Mexico. April 1977.
**Telephone conversation between Jack Greber of PEDCo and
John Bolstad, Montana State Department of Health and Environ-
mental Sciences, Helena, Montana. April 1977.
122
-------
Vermiculite mills do generate process wastewater; however,
the water is pumped to settling ponds and recycled, so no dis-
charge occurs. Pit pumpout and surface runoff are also collected
in settling ponds. No information is available on the amount of
wastewater generated at vermiculite operations.
Solid Wastes—
The lightweight aggregate mining industry is faced with the
usual problems of judicious disposal of overburden and associated
waste rock and consideration of the ultimate condition of aban-
doned mine sites. One vermiculite mine generated as much as 3.88
megagrams of overburden and gangue for each megagram of ore
extracted.* Amounts are not available for either perlite or
pumice mining.
Waste fines collected from processing operations such as
screening and drying present a solid waste disposal problem at
most perlite and pumice milling facilities. The volume of fines
generated can amount to as much as 25 percent of the mill feed.
Control Technology
Various waste control options used in mining and benefi-
ciating of lightweight aggregates are explained in the following
paragraphs.
Air Emissions Control-
Fugitive particulate emissions are not a major problem at
vermiculite mining operations because extracted ore has a fairly
high moisture content. The few minor problems are minimized by
wetting, sweeping, and general good housekeeping practices.
Fugitive dust is a major problem at perlite . and pumice
mining and beneficiating operations because these facilities are
located in areas with dry climates. Little attempt is made to
control the fugitive particulates in these areas since water
scarcity prevents the use of wetting, the most common control
practice.
Vermiculite processing operations generate some source
particulate emissions; however, most mills have reduced these
emissions by converting from dry to wet beneficiation techniques.
The major sources of particulates include drying and the opera-
tions subsequent to drying, such as sizing, loading, and trans-
fering. Source particulates are controlled by baghouses, cy-
clones, and venturi scrubbers. These control devices achieve
efficiencies ranging between 95.0 and 99.7 percent.
*Telephone conversation between Jack Greber of PEDCo and
John Bolstad, Montana State Department of Health and
Environmental Sciences, Helena, Montana. April 1977.
123
-------
Pumice and perlite processing generates source particulates
throughout the entire beneficiating operation. The major sources
are crushing, screening, grinding, and drying. Crushing, grind-
ing, and screening operations take place in enclosed buildings,
with emissions vented to baghouses. Particulates from drying
operations are usually controlled by a combination of a baghouse
and a cyclone. Efficiencies of the cyclones and baghouses have
been measured at 95 and 99.5 percent, respectively.
Liquid Waste Control—'
Beneficiation of perlite or pumice produces no wastewater
because water is not used in the process. Several pumice pro-
cessing facilities use scrubbers for particulate control,
however, and therefore have a minor amount of liquid waste to
treat. The waste streams at these facilities are pumped to
settling ponds, where the solids are impounded (39). The treated
water is recycled to the scrubbers. The amount of scrubber
wastewater treated is not known.
Vermiculite processing operations do generate some liquid
wastes as a result of wet beneficiation techniques. The process
wastewater is pumped to a series of settling ponds, where the
solids are impounded (39). Some facilities use flocculants such
as aluminum sulfate to facilitate settling. Because all clari-
fied water is recycled, no discharge results. As settling ponds
become filled, new ones are constructed. Some water may escape
from the ponds by seepage or percolation. No values are avail-
able on the amount of wastewater going to settling ponds or the
amount escaping from them.
Solid Waste Control—
The major sources of solid waste at lightweight aggregate
mines are overburden and gangue. These wastes are disposed of by
returning them to the mine during reclamation. Mine reclamation
procedures depend on state regulations but usually involve grad-
ing the land back to its original contour and revegetating it.
The fine particulates collected from the various processing
operations at lightweight aggregate mills present an additional
solid waste disposal problem. The fines are returned to the
process, sold as a by-product, or disposed of on site.
Conclusions and Recommendations
Lightweight aggregate mining has the usual problem of judi-
cious disposal of overburden and consideration of the ultimate
condition of the abandoned mine site. Most abandoned mines are
located on governmental property and the sites are returned to
the conditions that prevailed prior to mining activities. Some
mines, however, are located on private property, and many of
these sites are not reclaimed.
124
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The major problem associated with lightweight aggregate
mining and milling results from the generation of large amounts
of fines. These fines produce related dust problems, and the
fines collected by dry dust collection devices present a solid
waste disposal problem. Although some fine particulates are
returned to the process or are sold as a by-product, most have no
use and must be disposed of on site. A market needs to be devel-
oped for rejected fines from the lightweight aggregates industry.
MICA AND SERICITE
Industry Description
Mica is a name applied to a number of complex hydrous min-
erals in the pptassium-aluminum-silicate group with differing
chemical composition and physical properties. The principal
minerals in this group are muscovite (potassium mica), phlogopite
(magnesium mica), biotite (magnesium iron mica) and lepidolite
(lithium mica). Muscovite and phlogopite are the most important
commercially (9). For commercial purposes, mica is classified
broadly as sheet mica and flake and scrap mica (which includes
all other forms). Sheet mica is further classified as block
mica, film mica, or splittings, according to its thickness.
In 1974, block and film mica was consumed by 13 companies in
New Jersey, New York, North Carolina, Pennsylvania,
Massachusetts, Ohio and Virginia. Splittings were fabricated
into various built-up mica products by 11 companies with 12
plants located in New Hampshire, New York, Ohio, Michigan,
Massachusetts, North Carolina, and Virginia. North Carolina was
responsible for 56 percent of total scrap and flake production in
1974. The remaining output of scrap and flake mica came from
Alabama, Arizona, Connecticut, Georgia, New Mexico, South
Carolina and South Dakota (9).
U.S. production of sheet mica in 1974 and 1975 was insigni-
ficant. Decline in domestic production has resulted in almost
total dependence on imports to meet the demand. The United
States, which accounted for 53 percent of world production during
1974, is self-sufficient in the production of scrap and flake
mica for grinding purposes. Production statistics for mica
appear in Section 1 of this report.
Electrical and electronic industries use the most sheet
mica, predominantly in the form of built-up mica from splittings.
Most of the block and film mica is consumed in the fabrication of
vacuum tube spacers. Other uses include high-pressure steam
boilers, marker dials for navigation compasses, optical instru-
ments, pyrometers, thermal regulators, lamp chimneys, microwave
windows, and hair-dryer elements.
125
-------
Scrap and flake mica are generally processed into ground
mica for various end uses in: gypsum plasterboard cement, rolled
roofing and asphalt shingles, in the paint industry as a pigment
extender, and in the rubber industry as an inert filler. Other
uses include decorative coatings on wallpaper and on concrete
stucco and tile surfaces; as a coating for cores and molds in
metal castings; as an absorbent; and as an ingredient in well-
drilling muds.
Primary by-products and coproducts associated with mica-
bearing pegmatites are clay, feldspar,, and lithium. Other
minerals of eocnomic importance found in pegmatites include
beryl, spodumene, and tantalite.
Process Description
Sheet mica mines are usually small-scale, hand-sorting
operations. Open-pit mining is used when economically feasible,
but many mica-bearing pegmatites are mined by underground
methods. Presently no significant quantity of sheet mica is
mined in the United States (9). Because essentially all of the
sheet mica used in the United States is imported and processed by
the ultimate user, this report is concerned primarily with the
flake and scrap mica industry.
Flake and scrap mica is obtained from open-pit quarries
(Figure 20)., Bulldozers or draglines remove the overburden ahead
of the face. Power-driven equipment such as power shovels, drag
pans, and trucks then transport the ore from the deposit to the
beneficiation plant. Small amounts of scrap mica also occur as a
by-product of mining, trimming, and fabricating sheet mica. The
three methods used to process the ore are dry grinding, wet
grinding and wet beneficiation (39).
In dry grinding facilities, ore from the mine is initially
processed through both coarse and fine screens. Then it is
fragmented, dried, and sent to a hammer mill. In facilities that
process scrap and flake mica, the feed is sent directly into the
hammer mill. In wet and dry grinding facilities, the milled
product passes through a series of vibrating screens to separate
the product into various sizes for bagging. Ground mica yield
from beneficiated scrap is 95 to 96 percent.
In a- typical wet grinding facility, scrap and flake mica is
batch-milled in a water slurry. When the bulk of the mica has
been ground to the desired size, the charge is washed from the
mill into a decant tank where gritty impurities sink. The ground
mica is dewatered by centrifuging and steam drying, and the final
product is obtained by screening on enclosed multiple-deck
vibrating screens. It is then bagged for shipment.
126
-------
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Figure 20. Mining and beneficiating of mica and sericite,
-------
In the wet beneficiation process, ore from the mine is
crushed, screened, and classified to separate the mica from the
gangue. This process requires large amounts of water and re-
covers only about 50 percent of the mica from the ore (60). The
ore is sent next to spiral classifiers that separate large mica
flakes from the waste sands. The fine sand and clays are
deslimed, conditioned, and sent to the flotation section for mica
recovery. The mica concentrate recovered by flotation is cen-
trifuged, then fed to a rotary dryer. After the dryer discharge
is ground and screened, it is ready for shipment.
Waste Streams
Table 18 presents a summary of multimedia wastes from mining
and beneficiating mica and sericite. The following paragraphs
explain in more detail the various air, liquid, and solid wastes
associated with this industry.
Air Emissions—
Fugitive dust is the principal pollutant discharged from
open-pit mining. The dust contains mica, quartz and other
minerals (60).
Particulate emissions also result from the screening, crush-
ing, drying, and milling operations in the dry process. Quanti-
tive data on these emissions are not available, however.
Sources of air emissions in the wet process and the flota-
tion process are few since the processes are carried out in the
presence of water. The only sources of particulate emissions are
the dryer and the screen.
Liquid Wastes--
Runoff produces wastewater from open-pit mining; however, no
data are available regarding this effluent.
The dry process produces no wastewater discharges.
Water-use data from two wet-process facilities indicate
usage of 4.9 and 125 kiloliters per megagram of product, respec-
tively. At the former facility, about 80 percent of the water is
makeup water and the remainder is recycled water from the decant-
ing and dewatering operations. At the latter facility, 1500
liters of makeup water is used per megagram of product, and the
remainder is recycled from the settling pond (39). The waste
load from these facilities consists of mill tailings, thickener
overflows, and wastes from the dewatering units.
The amount of water consumed by facilities with a flotation
process depends upon the quantity and type of clay material in
128
-------
TABLE 18. SUMMARY OF MULTIMEDIA WASTES FROM MINING
AND BENEFICIATING OF MICA AND SERICITE
Air
Source
Overburden
removal
Ore
extraction
Ore
loading
Ore
transport
Screening/
crushing
Dryer
Mill
Screening
Pollutant
Fugitive
patticulatei
Particulatea
Participates
Particulatea
Participates
Uncontrolled
emission rate
N.A.
N.A.
N.A.
N.A.
N.A.
Liquid
Source
Overburden
removal
Ore
extraction
Grinding
mill
Decant
tank
Centrifuge
Crush/
screen/
classify
Spiral
classifier
Flotation
Centrifuge
Pollutant/
parameter
N.A.
N.A.
N.A.
N.A.
N.A.
N.A.
N.A.
Uncontrolled
discharge
N.A.
N.A.
N.A.
N.A.
N.A.
N.A.
N.A.
Solid
Source
Overburden
removal
Ore
extraction
Screening/
crushing
Settling
pond
Pollutant
Waste rock
Rock
Sludge
Uncontrolled
quantity
N.A.
N.A.
N.A.
N>
VO
N.A. - Not available.
-------
the crude ore. The range of consumption is 69.5 to 656 kilo-
liters per megagram of product (39). No data are available on
raw waste from these facilities.
Solid Wastes—
Overburden and waste rock are the major solid waste problems
from mica mining.
In the dry process, screens (the only source of solid
wastes), generate rocks and boulders.
In the wet process, the settling pond produces solid waste
in the form of sludge.
Control Technology
Control technologies as applied in the mining and beneficia-
tion of mica and sericite are explained in the following para-
graphs .
Air Emissions Control—
Fugitive dust from open-pit mining and processing is con-
trolled by wetting and spraying with water.*
Plant process sources (screening, crushing, and drying) are
hooded, and emissions are ducted to control devices such as
fabric filters or scrubbers.*
Liquid Waste Controls—
The raw waste stream from the wet process is collected in
surge tanks. A portion of the decanted water is recycled to the
process, and the remainder is pumped to a treatment facility.
The treatment facility usually consists of settling ponds, which
sometimes use polymers as a settling aid. Some of the treated
water from the pond is recycled and some is discharged (39).
Raw waste from the flotation process also is pumped to a
settling pond. Supernatant from the pond usually is recycled to
the facility; however, the pond is allowed to discharge during
exceptionally heavy rainfall (39).
Solid Waste Control-
Some of the overburden and waste rock from the mining and
processing operations is used to build berms for settling ponds
and the rest is piled on or off site.
*Telephone conversation between Vijay Patel of PEDCo and Bill
Anderson, North Carolina Air Pollution Control Agency, Ashville,
North Carolina. April 1977.
130
-------
Because the amount collected is small, sludge is allowed to
accumulate in the settling ponds.*
Conclusions and Recommendations
Very little mica and sericite are mined in the United
States, so the environmental impact from this industry is minor.
Conventional state-of-the-art techniques are used to control all
major pollutants.
Large quantities of makeup water are used in the flotation
process, and most of it is discharged after treatment in settling
ponds. An investigation might determine the feasibility of
recycling this treated effluent.,
Fugitive dust cannot be controlled by wetting with water
when the ambient temperature falls below freezing, therefore,
alternative wetting agents need to be investigated.
*Telephone conversation between Vijay Patel of PEDCo and Bill
Anderson, North Carolina Air Pollution Control Agency, Ashville,
North Carolina. April 1977.
131
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SECTION 5
NONFERROUS METALS
ALUMINUM
Industry Description
The principal aluminum ore, bauxite, consists mainly of
gibbsite [A1(OH)3], boehmite [AlO(OH)], and diaspore (A1203-H20).
The aluminum content in bauxite is enriched by removal or most of
the other elements in the parent rock, primarily by dissolution
of the water-soluble minerals. Impurities in the ore include
iron oxide, aluminum silicate, titanium dioxide, quartz, and
compounds of phosphorous, vanadium, and gallium. Bauxite is not
regarded as a 'distinct mineralogical species; however, it has
become customary to use this term for rocks in which alumina
(aluminum oxide material) predominates (66).
The United States produces and consumes the most aluminum
products, even though we are currently forced to import about 90
percent of the bauxite from the less industrialized nations where
most of the reserves are found. Statistics indicate that we
mined approximately 12 percent of our usage in 1973 (10). This
percentage will decline as the demand for bauxite rises and
domestic mining volume remains stable. Although domestic re-
serves of bauxite total about 50 million tons, supply is rela-
tively inelastic because most of this ore is of poor quality.
Also, only an estimated 20 percent of these reserves is con-
sidered now economically recoverable with the present extraction
and processing methods (10).
Arkansas produces most of the domestic bauxite (90%);
Alabama and Georgia contribute lesser amounts. Small deposits
also are found in northwestern Oregon, but the quality is poor so
the ore is not mined.
About 88 percent of the bauxite mined is used to produce
aluminum. The rest is used for nonmetal purposes such as abra-
sives, refractories, and numerous aluminum compounds.
Aluminum metal applications generally fall into six major
categories: transportation, construction, electrical equipment,
132
-------
containers and packaging, consumer durables, and mechanical
equipment. The widespread uses within these categories are well
known.
Much of the domestic gallium supply is derived from the
processing of bauxite into alumina. Section 1 of this report
presents production statistics for aluminum and associated
metals.
Process Description
Although underground mining is common in Europe and the
USSR, the open-pit method is used to mine 90 percent of the
bauxite in the United States. The remaining 10 percent comes
from the underground Hurricane Creek Mine in Arkansas. Figure 21
shows a composite flow diagram of bauxite mining and benefi-
ciating.
The stripping ratios of open-pit bauxite mines in the United
States run as high as 13 meters of overburden to 1 meter of ore.
Some surface pits in Arkansas have reached depths of about 60
meters (10). These parameters are believed to represent the
extremes of current economic limits for mining large ore de-
posits.
Overburden is removed by conventional methods—draglines,
shovels, and haulers. The next step usually involves loosening
the bauxite by blasting with low-strength dynamite (67). Some-
times blasting is necessary only to loosen the hardcap that
comprises the top few feet of the deposit.
Front-end loaders and dump trucks haul the ore to the pro-
cessing plant, where it is weighed, unloaded onto a stockpile,
and sampled for laboratory testing. After the quality of the
load is determined, it is transferred to a second stockpile for
feeding into the plant. These uncovered stockpiles often occupy
large areas.
Crushing is common to all bauxite processing. The steps
following the crushing, however, depend on the makeup of the ore
and vary widely. Most bauxite beneficiation involves only crush-
ing, washing, and drying operations. More costly techniques are
rarely required. Moreover, most impurities such as iron, sili-
con, and titanium are often too finely dispersed in the bauxite
to be readily separated by physical methods. Many bauxite ores
are upgraded, however, by washing or wet screening to remove sand
and some of the clay minerals. Heavy media separation and jig-
ging are sometimes used to separate the iron minerals. In
Arkansas, siderite (FeCO,) has been removed by spiral concentra-
tors and magnetic separators (10).
133
-------
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Figure 21. Mining and beneficiating of bauxite.
-------
After necessary physical separation of unwanted impurities,
the bauxite may be shipped as is, dried, or calcined. Bauxite
contains both free moisture and chemically combined water. For
use in refractories and abrasives, it must be calcined to remove
the water of hydration. When bauxite is used for other purposes
(primarily refining to produce aluminum), only that water is
removed which can be justified by lower shiping costs or improved
handling characteristics. Most bauxite ores are not dried at the
mine site because drying creates serious dust problems during
transportation and handling.
If the ore has been dried or calcined, the ore is covered
during final storage for protection. Storage is in an open shed
which completely controls runoff, but dust may still be a problem
during transfer.
Waste Streams
Table 19 presents a summary of multimedia wastes produced by
mining and beneficiating bauxite. These include air, liquid, and
solid waste emissions, which are covered in more detail in the
following paragraphs.
Air Emissions—
Air emissions from the mining and beneficiation of bauxite
are mostly fugitive dust. Overburden removal is a variable and
potentially large fugitive dust source at surface mines. Dust
emitted by this operation vary with the composition and texture
of the overburden, its moisture content, excavation procedures,
and the type of equipment used. However, the emission rate is
most closely related to volume. Overburden-to-ore ratios of 5:1
to 10:1 are common. The economic limit is about 13:1 (10).
A fugitive dust emission factor of 0.02 kilograms per mega-
gram of overburden removed is assumed (65). To convert this
emission factor to represent bauxite mining, one must assume an
average overburden-to-ore ratio of 7.5:1 (10). This yields a
factor of 0.2 kilograms per megagram of bauxite mined.
A published emission factor is not readily available for
fugitive dust from the extraction and loading of bauxite ore. To
obtain a range, we have assumed that bauxite emissions are some-
where between those of crushed stone and lignite. Published
figures for these minerals are 0.01 kilogram per megagram of
crushed stone and 0.025 kilograms per megagram of lignite (65).
Similar texture characteristics suggest that bauxite is more
likely to approximate dry crushed stone.
Again, no published emission factor has been determined for
transporting bauxite ore to a storage pile. This operation must
135
-------
TABLE 19. SUMMARY OF MULTIMEDIA WASTES FROM
MINING AND BENEFICIATING OF BAUXITE
Air
Source
Overburden
removal
Extraction of
ore
Loading of
ore
Transport of
ore
Underground
operations
Ore storage
Ore crushing
Dryer
Calcining
Product
storage
Tailings
Pollutant
Fugitive
participates
Fugitive
particulates
Fugitive
particulates
Fugitive
particulates
Fugitive par-
ticulates
from mine
ventilation
Fugitive
particulates
Particulates
Particulates
Particulates
Fugitive
particulates
Fugitive
particulates
Uncontrolled
emission
rate
^0.2 kg/Hg of ore*
.01 -.025 kg/Hg of
oreb
.01 -.025 kg/Hg of
oreb
Dumping - .01-. 02
kg/Mg of orec
Hauling - .31-. 62
kg/km
en
(Continued)
-------
TABLE 19. (Continued)
OJ
Source
Air
Pollutant
Uncontrolled"
emission
rate
Source
Underground
operations
Underground
operations
Ore storage
Mineral jig
Washing
Wet screening
Spiral con-
centration
Tailings
Tailings
Tailings
Tailings
Tailings
Tailings
Tailings
Tailings
Tailings
Liquid
Pollutant/
parameter
Sulfate
Fluoride
Runoff
Heavy metals
(Fe)
Sand-Clay
Sand-Clay
Heavy metals
(Fe)
TDS
TS5
Total Fe
Total Mn
Al
Zn
Ni
Sulfate
Fluoride
Uncontrolled
discharge
0.01-0.05 kg/Hg
bauxite'
0.00001-0.0005 kg/Hg
bauxite'
N.A.
Varies with ore
(Sent to tailings pond)
Varies with ore
(Sent to tailings pond)
Varies with ore
(Sent to tailings pond)
Varies with ore
(Sent to tailings pond)
2.3 kg/Hg bauxite1"
0.008 kg/Hg bauxitek
0.00055 kg/Mg bauxite*
0.0077 kg/Mg bauxite*
0.0017 kg/Hg bauxite*
0.00022 kg/Hg bauxite*
0.00055 kg/Hg bauxite*
1.49 kg/Hg bauxite*
0.00097 kg/Mg bauxite*
Source
Solid
Pollutant
Uncontrolled
quantity
'
' Ref. 65. Factor for general overburden coverted to typical volume for bauxite. Ref. 65.
69.
69.
10.
46.
Ref. 46.
H.A. - Not available.
Range for dried tailings in the southeastern U.S.
Ref. 65.
Ref. 65.
Ref. 65.
Ref. 65.
Ref. 69.
Range for crushed rock - lignite, total for extraction and loading.
Range for dumping crushed rock - lignite.
Range for hauling crushed rock - lignite.
Range for active to inactive crushed rock storage.
Uncontrolled emissions, usually controlled by a baghouse.
Ref.
Ref.
Ref.
Ref.
1
-------
be broken down into two separate tasks - hauling, which is pro-
portional to vehicle miles traveled (VMT), and dumping, which is
proportional to the quantity of ore transported. As with ore
loading, we have assumed that bauxite falls within the range
between crushed rock and lignite, which is 0.31 to 0.62 kilograms
per kilometer for hauling (65).
Visits to several underground mines for other minerals led
to the assumption that air emissions from underground bauxite
mine ventilation are negligible.
Bauxite ore is stored in open piles of about 7500 megagrams
each (68). These piles often cover large areas and cause con-
siderable fugitive dust problems. In a mine producing up to 1600
megagrams of ore per day, for instance, storage piles cover about
8 hectares. Again, no emission figures have been published on
bauxite ore storage.
Uncontrolled fugitive dust emissions from crushing and
conveying vary between 0.5 to 4 kilograms per megagram (69).
These emissions, usually controlled by a baghouse, evidence no
especially toxic materials. Because particulates fall largely in
the coarser size ranges, impacts are judged to be very localized
(46).
Ore drying is only done occasionally at the mine site, to
eliminate uncombined water. Uncontrolled dust emissions are
about 0.6 kilograms per megagram of feed (69). Impacts of these
emissions are believed to be intermittent and highly localized.
Calcining of bauxite generates large volumes of airborne
particulates, but the economic value of this dust is such that
extensive controls are applied to collect it, thus reducing
emissions to relatively small quantities. The uncontrolled
emission rate is about 100 kilograms per megagram of feed.
Control efficiencies range between 70 to 98 percent (69).
The final product is stored in covered sheds, and air emis-
sions from these enclosures are assumed to be negligible.
Emission estimates for dried tailings were developed from
the U.S. Department of Agriculture's wind erosion equation (70).
This equation was then applied to conditions present in the
southeastern part of the United States (65), yielding a range of
5.7 to 8.8 kilograms per hectare per year. When the tailings
form a crust, emissions are reduced by 80 percent (65).
Liquid Wastes—
Liquid wastes in bauxite mining and beneficiation are pri-
marily from runoff and groundwater. Of less importance are those
138
-------
resulting from various wet methods of removing sand, clay, and
heavy metal impurities. U.S. bauxite mines generally do not
require these wet methods. The liquid wastes from these sources
are directed to a settling pond where the water is treated by
settling and lime neutralization before it is discharged into
streams.
The present rate of discharge from bauxite mines averages
about 57,000 cubic meters of mine water daily, most of which is
from open-pit mining. Underground mining accounts for only a
small fraction (29).
The two classes of raw mine drainage generally correspond
closely to the mining technique. Open-pit mining drainage is
generally acid or ferruginous, with a pH in the range of 2 to 4.
Sulfuric acid is formed by oxidation of the pyrite contained in
lignite present in the soil overburden. This acid water dis-
solves other minerals, including those -containing aluminum,
calcium, manganese, and zinc. Although these same compounds
might be formed naturally, mining activity, which disturbs the
surface and exposes pyrite to oxygen and water, greatly accel-
erates the rate of sulfide-mineral dissolution (29). Table 19
presents a typical range of specific pollutants in open-pit
drainage.
Drainage from underground mining is characteristically
alkaline. Unlike open-pit drainage, which is exposed to sulfide-
bearing minerals _in the overburden, underground mines receive
drainage that has migrated through strata of unconsolidated sands
and clays and is not exposed simultaneously to pyrite and oxygen.
The pH of this drainage is generally about 7.5 (29). Raw mine
water accumulates slowly in underground mines and is pumped to
the surface at regular intervals for treatment. Table 19 pres-
ents a typical range of specific pollutants in underground mine
drainage.
As mentioned, liquid wastes also are generated by various
wet methods for removal of impurities. Technologies include wet
screening and washing to remove sand and some of the clay min-
erals, heavy-media separation and jigging to separate iron min-
erals, and the use of spiral concentrators and magnetic separa-
tors to remove siderite (10). Since these methods generally are
not necessary, however, no data have been published on the rate
of waste generation. When these methods are practiced, this
waste goes to tailings and is measured in the average concen-
trations of the tailings effluent.
A tailings pond can be considered a specific source of
liquid wastes, and effluents from this source have been measured.
Wastewater sent to tailings ponds presently are being treated
139
-------
only by settling and lime neutralization. In the near future it
may be possible to treat tailings by a mobile lime-treatment
plant. Typical amounts of specific pollutants released from
tailings ponds are given in Table 19.
Solid Wastes--
Solid waste generation resulting from the mining and benefi-
ciation of bauxite come from overburden, gangue, and tailings.
The overburden produced in open-pit mining normally is stored in
heaps adjacent to the pits and may be used in refilling and
recontouring mined-out areas. Because the pyrite in the over-
burden combines with water and creates an acid soil condition,
revegetation proceeds extremely slowly. The concomitant lack of
vegetation accelerates the weathering of the overburden, thereby
contributing to a liquid waste problem. Because of the large
volume of overburden generated (by removal of up to 4.0 meters of
overburden per 0.3 meter of ore) the runoff problem can be seri-
ous. Generally between 1.5 and 3.0 meters of overburden per
meter of bauxite are removed (10).
Once the overburden has been removed, the pyrite content of
the bauxite deposit is sufficiently low to make the liquid waste
problems associated with gangue appear not to be as serious as
with overburden. Pyrite is less abundant because it and other
soluble materials have been leached out during the formation of
the bauxite deposit. Therefore the environmental impact of
gangue produced by bauxite mining is less than that from over-
burden. No published figures were found from which to estimate
the volume of gangue produced per megagram of bauxite mined.
Solid waste is generated by various wet methods of benefi-
ciation. These wastes are transported in liquid form to the
tailings pond, where sedimentation and precipitation of the heavy
metals occur. No published figures were found to estimate the
volume of solid waste tailings formed per megagram of bauxite.
Control Technology
Control technology in the bauxite mining industry is much
the same as that used in other mining industries. The following
paragraphs explain these controls as applied to air, liquid, and
solid waste.
Air Emissions Control--
Overburden removal and ore extraction are among the most
variable fugitive dust sources at surface mines. Dust losses
from these operations vary with the composition, texture, and
moisture content of the material; excavation procedures; equip-
ment employed; etc. A literature search yielded no specific
devices for controlling fugitive dust from these sources (65).
140
-------
Dust is generated by many aspects of the truck-loading
operation, but mainly by moving the trucks into position for
loading, by scooping up the loose material into a shovel bucket,
and by dumping the load from the bucket into the truck bed. The
same emission factors apply as those given for overburden removal
because no specific control devices were found for loading either.
Watering or oiling the haul roads is used extensively to
reduce dust generated from ore transport. A control efficiency
of 50 percent is assumed for watering the haul roads. Using
portable beneficiation equipment to reduce the length of the haul
is another method of reducing emissions.
Visits to several underground mines for other minerals
indicate that control of air emissions from underground bauxite
mine ventilation is unnecessary.
No information found indicates that any form of dust control
presently is applied to the open bauxite ore storage piles.
Chemical dust suppressants are on the market that would solve any
localized problems, at least on a short-term basis. Control
efficiencies of these products are estimated at 50 to 80 percent
(71).
Dust emissions from crushing generally are caught in a
baghouse. No evidence points to the presence of especially toxic
materials., arid particulates are believed to fall largely in the
coarser size ranges (46). Efficiency of baghouse control is
estimated at 99 percent (49).
When bauxite is dried at the mine site, emissions can be
controlled adequately by available technology (e.g. baghouses).
The presence of highly toxic substances is not anticipated in
these emissions; particulates are expected to be in the larger
size ranges (46). Control efficiency for a baghouse is estimated
at 99 percent when no hygroscopic substances are present (49).
Emissions from calcining bauxite can be controlled by vari-
ous dry-dust-collection devices such as centrifugal collectors,
multiple cyclones, and electrostatic precipitators, or combina-
tions of these controls. Impacts of this dust are judged to be
moderate to low, because alumina is not considered to be harmful
unless very fine particles (i.e., less than 1 to 5 micrometers)
reach the lower respiratory tract. Efficiencies of these devices
are estimated to be between 70 to 98 percent (46).
Because calcined and dried bauxite is stored in covered
sheds until shipped, the air emission impact during storage is
considered negligible.
141
-------
Air emissions from tailings can be expected only when the
tailings pond becomes dry (i.e. when operations have ceased).
The intentional or natural formation of crust under these condi-
tions can reduce emissions by as much as 80 percent (69).
Liquid Waste Control—
Water contaminated by runoff from overburden removal and
mining can be controlled in three ways. First, precipitation
leaches out various pollutants because formerly buried minerals
are exposed, and oxygen reacts with the exposed minerals. If
this material is reburied, covered with top soil, and revegetat-
ed, much of the groundwater and runoff contamination will be
eliminated. This technology is practiced in the coal strip-
mining industry.
A second method is to treat the contaminated water with lime
in a settling pond before releasing it to the environment.
Lime treatment reduces metal content in most metals by more
than 90 percent. Sulfate and fluoride content is also reduced.
Settling reduces total suspended solids (TSS) by 85 percent,
whereas total dissolved solids (IDS) actually increase with lime
treatment. Water pumped from underground mines as well as water
from various wet beneficiation methods also is lime-treated in
settling ponds.
A third method, which reduces the volume of water that must
be treated, diverts the groundwater away from the mining area.
This is accomplished by a system of dewatering wells, strate-
gically placed, which divert water that would naturally flow into
the mine. Details of this method are presented in the literature
(43).
Solid Waste Control—
Because of the growing demand for complete land reclamation,
it is advisable to segregate the overburden material by removing
top soil and other subsoil components suitable for revegetation,
storing them separately, and then covering the contoured spoil
banks with these two layers during the reclamation process. This
procedure greatly increases the ability to revegetate and reclaim
the land (72).
Backfilling of the mined-out area or the underground mine is
a good disposal method for the solid waste generated by any .of
the mining processes. Even the tailings can be disposed of by
dredging and backfilling.
Estimation of a control efficiency for this type of opera-
tion is difficult; however, it is conceivable that all of the
solid waste generated could be reburied and revegetated. Product
economics and local public demands will probably determine how
much is properly reclaimed.
142
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Conclusions and Recommendations
The available techniques of land reclamation and lime treat-
ment of mine runoff are adequate to maintain environmental stand-
ards in the bauxite mining and beneficiation industry. Air
emissions also can be controlled conventionally.
One promising area of research involves the reduction of the
volume of water produced by mining. Ground water control tech-
niques will be required. These techniques are presently being
used to increase the stability of open-pit slopes and thereby aid
in the economical removal of bauxite. Also, dewatering of the
pits enables production to continue when winter rains would
normally cause it to be curtailed.
The technique consists of drilling wells in locations around
the ore body and pumping out the ground water before it can reach
the mine. Locations of wells are determined by techniques common
to ground water hyrology. A description of dewatering at three
bauxite mines in the Eufaula district in Alabama is contained in
Reference 72. Expansion of the use of the technique to minimize
the production of acid mine discharge will require investigation
of the use of gravity wells and drains as described in Reference
43.
ANTIMONY .
Industry Description
Antimony occurs in over a hundred minerals. Sometimes
native metallic antimony is found free; however, the most impor-
tant source of the metal is stibnite (Sb2S3). When exposed to
the atmosphere, stibnite converts to varioiis oxides. The impor-
tant oxide minerals are stibiconite (Sb.-OgtOH]), cervantite
(Sb204 or Sb2O3'Sb205), valentenite (SbJb-), senarmontite
(Sbfot), and kerffiasite (2Sb2S3-Sb2O,). Complex stibnite ores
containing lead, copper, silver, and"^ mercury also can be impor-
tant sources of antimony. When the antimony content is lean, it
may be recovered as a by-product (11).
In 1974 the United States consumed an estimated 26 percent
of the world's production of primary antimony, while producing
less than 1 percent. The bulk of the demand is met either by
scrap recovery or imports. Scrap recovery comes primarily from
batteries and provides approximately 50 percent of the U.S.
supply. No change is expected in this supply-demand relationship
in the foreseeable future (11).
143
-------
Virtually all U:S. antimony that is recovered from domestic
ores comes from deposits as a by-product of silver, lead, copper,
and zinc ores. Lead-silver mines in the Idaho Coeur d1 Alene
area produce the bulk of the mined antimony in the United States.
Idaho, Montana, and Nevada supply over 50 percent of the domestic
primary antimony. Antimony recovered at three domestic lead
refineries supplied the remainder (11).
Antimony is classified chemically as a nonmetal or metal-
loid, although it has metallic characteristics in the elemental
state (11). It is used primarily as an alloy in lead and other
metals. In 1974 nearly half of the total demand was used in
storage batteries. It also is used in power transmission and
communication equipment, type metal, solder, and ammunition.
Antimony, in its nonmetallic form, is used industrially in fire
retardant and industrial chemicals, rubber and plastic products,
and ceramic and glass products (11).
Because most of the world's supply of antimony is concen-
trated in the People's Republic of China, production in the
United States will continue to be dictated by domestic supply
rather than demand. Section 1 present production statistics for
antimony and associated metals.
Process Description
Only one U.S. mine operates solely for the recovery of
antimony ore (29). This northwestern Montana mine applies both
underground and open-pit methods; however, most of the ore is
mined underground (64). Figure 22 shows a composite flow diagram
for the mining and beneficiating of antimony ores.
Several mines in the United States produce antimony as a
coproduct or by-product of other ores. Mining methods at those
mines that produce antimony only as a minor constituent are
designed for recovery of the principal metal (lead, silver, or
gold). The typical small mine is entered by shallow shaft or
short adit, developed by drifting in the vein (11).
Emissions at mines, where antimony is a by-product, are not
related to.the mining of .the antimony. Although it is generally
economical to separate the antimony from the concentrate, the
economics of mining the ore are independent of the presence of
antimony.' Also, emissions associated with the separation of the
antimony to form a concentrate occur in the refining stages of
the primary metal production. Therefore, the emissions from the
mining and beneficiation of the complex ores that contain anti-
mony are not considered here. Process descriptions and emissions
for these ores are covered in their respective sections, (i.e.,
silver, gold, copper, lead, zinc).
144
-------
UNDERGROUND OPERATIONS
o
•U
01
ORE
1
1
L
i
i
L
fRAGMENTATIOt*
OF ORE
ORE
LOADING
r
u
TRANSPORT
TO
SURFACE
r
v9a
SMALL
QUANTITY
BY OPEN PIT
STORAGE
ORE MINED AS A BYPRODUCT OR COPRODUCT
COMPLEX ORES
(Sb IS SMALL
8 OF ORE)
MINING OF
ORES
f-«
ROUGHER
£
u.
CLFANER
Au
\ FROTH
SEPARATION
OF Ag. Pb,
Cu, Zn, Au
-
^
Sb
CONCENTRATE
1
, Ag, Pb, Cu, Zn
£
FTT.TFD
PS.
u.
•PUT<"1KFMFP
H 'o •
"2U
f0
A LIQUID WASTES
. O ATMOSPHERIC EMISS1
Q SOLID WASTES
«$
STORAGE
-.«. £ ».
ROUGHER
FLOTATION
CM
CLFANER
FLOTATION
f TAILINGS I
O
«
(•4
*x
SCAVENGER
FLOTATION
FILTER
TAIL
INGS ,
O
«
THICKENER
1
FILTRATE
-
WASTE
STORAGE
&
SHIPMENT
r
TAILINGS
POND
NO
DISCHARGE
Figure 22. Mining and beneficiating of antimony from sulfide and
complex ores.
-------
Antimony is considered a coproduct of silver in some complex
deposits in Idaho that also contain copper, lead, and gold.
Silver is the primary metal mined at these underground mines,
followed by copper (64). Final separation of the antimony is
accomplished by leaching with Na2S and electrolysis in the re-
fining stage, not in beneficiation. Processes and emissions are
covered later in this section.
In 1974, the one U.S. mine worked solely for antimony pro-
duced about 7000 megagrams of ore containing a little over 200
megagrams of antimony. Although this mine used the single-bench,
open-pit method, most U.S. ores mined for their antimony content
are recovered from underground methods.
Ore is hauled by truck to the primary crushers. It is
crushed, wet-ground, and classified before being sent to the
rougher flotation process. Oversized ore is returned by the
classifier to the grinder for regrinding.
Concentration of the antimonial ore is accomplished by froth
flotation. Antimony-rich rises in the froth in each of three
flotation steps. The concentrate then is filtered and sent to a
thickener for final concentration before shipment.
Waste Streams
Table 20 presents a summary of multimedia wastes from the
mining and beneficiating of antimony ores, and the following
paragraphs explain these air, liquid, and solid wastes in more
detail.
Air Emissions—
Few air emissions are associated with the mining and benefi-
ciating of antimony ore because it is mined underground and
beneficiated by wet techniques. Air emissions from mine ventila-
tion are negligible.
No information was found on air emissions emanating from ore
storage, ore crushing, or concentrate storage during antimony
beneficiation.
An emission estimate for dried tailings was developed from
the U.S. Department of Agricultural wind erosion equation (70).
When applied to conditions present in the Pacific northwest
mining area, this equation yielded a value of 28.5 kilograms per
hectare. If the tailings form a crust, emissions can be reduced
by as much as 80 percent (65).
146
-------
TABLE 20. SUMMARY OF MULTIMEDIA WASTES FROM MINING AND
BENEFICIATING OF ANTIMONY ORESa
Air
Source
Underground
operations
Ore storage
Ore crushing
Product
storage
Tailings pond
Pollutant
Fugitive participates
from nine ventilation
Fugitive participates
Particulates
Fugitive particulates
Fugitive particulates
Uncontrolled
emission rate
Negligible
N.A.
N.A.
N.A.
9
28. 5 kg/hm
(dried area
only)
Liquid
Source
Underground
operations
Ore storage
Scavenger
flotation
Filter
Thickener
Product
storage
Pollutant/
parameter
Sb. Fe. Zn.
Ag, Ha. Pb
Runoff
pH
TSS
COO
TOC
Fe
Pb
Sb
Zn
Cu
Mn
Ho
Uncontrolled
discharge
No discharge presently,
possible in the future
N.A.
8.3d
7.48 kg/Hg of ored ,
0.0322 kq/Mg of ore"
0.059 kg/Hg of ore*
0.141 kg/Hg of ored ,
0.00097 kg/Hg of ore
0.48 kg/Hg of ore**.
0.033 kg/Hg of ore"
0.009 kg/Hq of ored
0.003 kg/Mq of oredrf
<0.0015 kg/Hq of ore
Solid
Source
Underground
operations
Scavenger
flotation
Tailings pond
Pollutant
Gangue
Tailings
Tailings
Uncontrolled
quantity
97S of ore Is gangue;
most backfilled;
under 130 kg/Hg of
ore remaining. £
N.A.
N.A.
* For wire complete derivation of factors see Sections 6.3.1-6.3.3.
b Ref. 65. Range for dried tailings In the Pacific Northwest wining area.
e Ref. 29.
d Ref. 29.
' Ref. 64.
-------
Liquid Wastes->-
Presently no liquid wastes are created in the one under-
ground antimony mine in the United States (29). However, more
extensive development of this mine could create a discharge.
Such a discharge probably would contain arsenic, iron, antimony,
zinc. No information was found concerning runoff from storage
piles of antimony ore.
Forty-nine separate constituents were measured in the raw
discharge from an antimony flotation mill (29). Table 21 pres-
ents the major waste constituents from this mill. These figures
represent combined discharges from the flotation tanks, the
filter, and the thickener.
No information was found on runoff from product storage.
Also, although 286 to 343 cubic meters per day of liquid waste
was discharged from the flotation mill to the tailings pond at
the mine studied, no discharge occurred from the pond.
Solid Wastes—
Solid waste generated by the mining and beneficiation of
antimony ores consists of gangue from underground operations and
tailings from the flotation mill. Nothing indicates that any of
the waste is particularly hazardous.
Reference 64 contains the only estimate found regarding the
solid waste generated at the one U.S. antimony mine. Ninety-
seven percent of the ore is gangue, but most of this is back-
filled into the mine. At the one mine, which extracts about 7000
megagrams of ore per year, the quantity of solid waste remaining
after backfilling is 900 megagrams (64).
Control Technology
Control problems in antimony mining are similar to those in
other mining industries. Applicable controls include settling,
lime precipitation, sulfide precipitation, and backfilling.
Air Emissions Control—
Because antimony is mined undergound and beneficiation is by
wet methods, this industry generates very few air emissions. The
crushing operation is a possible source of emissions and some
fugitive dust could occur. Particulate emissions from crushing
can be controlled by any. of several conventional methods.
Air emissions from tailings occur only when the tailings
pond becomes dry, (i.e. when operations have ceased). A crust,
formed either intentionally or naturally, can reduce these emis-
sions as much as 80 percent (65).
148
-------
TABLE 21. SUMMARY OF MULTIMEDIA WASTES FROM MINING AND
BENEFICIATING OF BERYLLIUM ORE
Air
Source
Overburden
removal
Extraction
of ore
Solvent
extraction
Pollutant
Fugitive
particulates
Fugitive
particulates
Vapor from
alkaline
berylate
solution
Uncontrolled
emission
rate
N.A.
N.A.
N.A.
Liquid
Source
Crushing/
grinding/
screening
Acid
leaching
Solvent
extract-
tion
Pollutant/
parameter
N.A.
(spills)
TDS
Sulfate
Fluoride
Aluminum
Beryllium
Zinc
N.A.
Uncontrolled
discharge
N.A.
18,380 mg/fca
10,600 mg/»
45 mg/t
552 mg/l
36 mg/i
19 mg/t
N.A.
Solid
Source
Overburden
removal
Extraction
of ore
Pollutant
Gangue
Uncontrolled
quantity
Overburden
ratio 5:lt>
VO
" Ref. 29.
Meeting between Jack Greber of PEDCo and Ken Poulson, Brush We11man, Inc., Delta, Utah.
N.A. - Not available.
December 1976.
-------
Liquid Waste Control--
Presently, there is little runoff or mine drainage asso-
ciated with the mining of antimony. Should a discharge develop,
it can be controlled by settling, lime precipitation, or sulfide
precipitation. Settling and lime precipitation should reduce
pollutant levels in the following manner: TSS, 20 percent;
arsenic, 28 percent; iron, 33 percent; antimony, 16 percent;
zinc, 33 percent. Another recommended treatment is additional
sulfide precipitation of the effluent, but control efficiences
are not known (29).
Solid Waste Control—
As alluded to earlier, the antimony content of the ore from
the only antimony mine in the United States is 3 percent. There-
fore, of the approximately 7000 megagrams of ore mined per year,
almost 6800 megagrams would initially be waste. All but about
900 megagrams of this waste is returned to the mine for backfill;
therefore control efficiency is about 87 percent (64).
Conclusions and Recommendations
Pollution problems from the mining of antimony in the United
States are insignificant because of the small quantities in-
volved.
Air emissions,. liquid wastes, and solid wastes are all small
or nonexistant in both mining and beneficiating processes.
Hence, no areas of research are recommended for antimony.
BERYLLIUM
Industry Description
Beryllium occurs as an essential constituent in approx-
imately 40 minerals and an occasional constituent in 50 others
(73, 74). Beryl, Be-Al-SigO..^, and bertandite, Be4Si207(OH)2/
are the principal beryllium inrherals in the United States. Beryl
is commonly a constituent of pegmatites, and coarse-grained
pegmatites yield most of the beryl used in industry. Other
commonly known beryllium minerals include phenacite, barylite,
and chrysoberyl.
The beryllium industry is relatively small compared with
most of the other nonferrous industries. As of 1975, the United
States had only two major beryllium producers (12). One company
in Utah mines bertrandite and converts it to an impure beryllium
hydroxide at a plant near the town of Delta. The other company
imports beryl for conversion to beryllium materials at plants in
Reading and Hazelton, Pennsylvania. The U.S. production of
pegmatitic beryl now comes from the Black Hills area in South
150
-------
Dakota and from northern Colorado, but deposits are present also
in the Appalachians and in the mountains of New Mexico and
Wyoming (75). Pegmatites are not usually mined for their beryl
content (12). Beryl is generally recovered as a coproduct of
mining other pegmatite minerals such as feldspar, mica, lithium
minerals, columbite, tantalite, and cassiterite. Deposits of
these minerals yield varying quantities of cobbed ore broken from
beryl. Production statistics for beryllium are shown in Section
1 of this report.
Beryllium is used as a metal, as an alloying agent, and as
an oxide. Beryllium metal is used when a high stiffness-to-
weight ratio is required, as in the aerospace industry (e.g.
space optical devices, X-ray windows, aircraft brakes, and mis-
sile components). It is used also in nuclear applications when a
low thermal-neutron absorption and a high-neutron-scatter cross
section are required.
More than half of the beryllium is consumed in beryllium-
copper alloy products, to which beryllium imparts strength,
hardness, and resistance to fatigue, corrosion, and wear. Molds
fabricated from beryllium-copper give plastic furniture the
wood-grain appearance. The variety of markets for beryllium-
copper alloys increases constantly and now includes the business
machine, appliance, transportation, and communication industries.
These alloys are used in electrical and electronic systems for
connectors, sockets, switches, and temperature- and pressure-
sensing devices to facilitate miniaturization and to provide
reliability and long service life. Beryllium oxide ceramics are
used in parts for lasers and microwave tubes, and in semicon-
ductors .
Process Description
Beryllium ore currently is mined on a large scale at only
one domestic operation. The bertrandite at this mine contains
approximately 1 percent beryllium and occurs erratically in
altered tuff that lies close to the surface. It is recovered by
open-pit methods (29). The average stripping ratio is 5:1.*
The ore is mined by conventional open-pit mining techniques.
(Figure 23 illustrates the flow sheet for mining and benefication
of beryllium.) The ore is blasted free, extracted, and hauled by
truck to temporary storage piles. During storage it is blended
with different grades of ore to make it homogenous, then shipped
to a mill approximately 84 kilometers away.
*Meeting between Bob Amick and Jack Greber of PEDCo and Ken
Poulson, Bruce Wellman, Inc., Delta, Utah. December 1976.
151
-------
MATER
M
cn
to
C
OVEKUUHDEM
REMOVAL
1? \
EXTRACTION
OF ORE
Y 1 ^ 1 ^
-------
To free the bertrandite minerals from associated gangue, the
ore is wet-crushed, wet-ground, and wet-screened to a thixotropic
slurry in preparation for a leaching step. The ore slurry then
is leached in a 10 percent sulfuric acid solution to put the
beryllium in solution and separate it from the insoluble gangue.
After leaching, solids are separated and washed by countercurrent
displacement in a series of thickeners.
Beryllium sulfate is selectively extracted using an organic
chelating agent, di-2-ethylhexyl phosphoric acid in a kerosene
diluent. The extracted beryllium in the organic solvent is
separated from the spent leach liquor (raffinate) in settling
tanks. The following then occurs in subsequent steps: the
organic solution containing the chelated beryllium ions (free of
impurities) is remixed with an alkaline stripping solution to
produce a solution containing an alkaline berylate compound; the
stripped organic phase is recycled; beryllium hydroxide is pre-
cipitated from the alkaline berylate solution by boiling and is
separated from the filtrate by centrifuging and filtering; and
the alkaline filtrate is recycled (76).
Waste Streams
Table 21 presents a summary of multimedia wastes from the
mining and beneficiating of beryllium. The following paragraphs
cover the various air, liquid, and solid wastes in more detail.
Air Emissions—
Very little air pollution is generated from the mining and
beneficiation of bertrandite. No dust problems are associated
with open-pit mining of the ore because it contains an average of
18 percent moisture (range 16 to 22%) (75). However, some fugi-
tive dust is' emitted from the waste dump, access roads, and
blasting.
Since all beneficiation processes are wet, dust problems are
minimized. The solvent extraction process generates a nontoxic
vapor from boiling alkaline berylate solution (76).
Liquid Wastes--
All water within the mine site is either evaporated or
percolates into the ground because the climate of the region is
arid.
Crushing, grinding, and screening do not generate any liquid
wastes per se because the ore slurry goes on to the leaching
operation, however, spills are possible.
The acidic residues of leaching obtained from the thickeners
are combined with alkaline waste solutions generated in another
153
-------
part of the plant to form a slurry with a pH of 8 to 10 (75).
The waste stream from the leaching process is exceptionally high
in dissolved solids (18,380 mg per liter), consisting largely of
sulfate (10,600 mg per liter), fluoride (45 mg per liter), alum-
inum (552 mg per liter), beryllium (36 mg per liter), and zinc
(19 mg per liter) (29). This waste stream could be considered
potentially hazardous (77).
Liquid wastes from the solvent extraction process include
spent leach liquor (raffinate), spills of organic solution in the
extraction circuit, and spills of alkaline stripping solutions
(75).
Solid Wastes—
Considerable amounts of gangue are generated from open-pit
mining of bertrandite ore. The stripping ratio is 5:1.*
Control Technology
Control technologies applied in the mining and beneficiation
Of beryllium are explained in the following paragraphs.
Air Emissions Control—
Since no significant air emissions are generated, control
devices are not.required.
Liquid Waste Control—
The slurry of solids from the acid leaching process are
discharged to a waste storage lagoon. Water is removed from the
pond by natural evaporation and, possibly percolation into the
subsurface.
Solid Waste Control-
Waste rock (spoils) from open-pit mining is used in land
reclamation (12).
Conclusions and Recommendations
The beryllium industry in this country is relatively small.
The proprietary nature of some of the processes and the fact that
only one mine is currently operating in this country make a
complete environmental assessment impossible.
The wastewater and solid wastes at this mine appear to be
under control. Wastewater is impounded and allowed to evaporate,
and the solid waste is blended into the topography during recla-
mation. Air pollution poses no significant problem. The only
*Meeting between Bob Amick and Jack Greber of PEDCo and Ken
Poulson, Bruce Wellman, Inc., Delta, Utah. December 1976.
154
-------
problem that might be worthy of further research is the extent to
which impoundments prevent leakage and the resulting leaching
into groundwater.
COPPER
Industry Description
The principal copper-bearing minerals are chalcocite (Cu2S),
chalcopyrite (CuFeS,), bornite (Cu5FeSd), chrysocolla
(CuSiO,'2H20), azurlte [2CuCOaCu(OH)2T, and malachite
[CuC03Cu(OH)2]. Copper is most often coiibined chemically with
sulfur, but frequently with iron or arsenic, and sometimes with
other elements (78). Copper ore also provides significant quan-
tities of by-products and coproducts such as gold, silver, molyb-
denum, selenium, tellurium, and rhenium (13).
In 1974 the United States led the world in producing and
consuming copper. Twenty-five mines accounted for 93 percent of
the U.S. output; the five largest mines produced 41 percent and
four companies accounted for 64 percent (13). The principal
copper-producing states in 1974 were Arizona (54 percent of total
U.S. production), Utah (14 percent), New Mexico (12 percent),
Montana (8 percent), Nevada (5 percent), and Michigan (4 per-
cent). Most of the remaining 3 percent came from Missouri and
Tennessee. Production statistics appear in Section 1 of this
report.
The most copper goes into the manufacture of electrical
equipment and supplies. Electric motors, power generators,
motor-generator sets, dynamotors, fans, blowers, industrial
controls, and related apparatus perform better when copper is
used in their manufacture.
Because they are corrosion-resistant, copper and its alloys
have many uses in the construction industry. Construction mater-
ials for roofing and plumbing, and brass and bronze for decora-
tive and utilitarian items require significant quantities of
copper.
Copper is also consumed by the following applications in the
production of nonelectrical machinery, household and commercial
air-conditioning, and farm machinery, in automobile manufacture,
railroad transportation, airplane manufacture, and marine parts,
in watches, clocks, microscopes, projectors, jewelry, and coin-
age, and for miscellaneous uses such as chemicals and inorganic
pigments.
155
-------
Process Description
Both open-pit and underground methods are used to mine
various types of copper deposits. Open-pit mining accounts for
nearly 80 percent of the copper ore mined in the United States
(13). Most ore deposits contain less than one percent copper.
The copper content of the ore is 15 to 30 percent after concen-
tration.
Open-pit mining involves the removal of ore from deposits at
or near the surface by a series of operations consisting of
drilling blast holes, blasting the ore, loading the broken ore
onto trucks or rail cars, and transporting it to the concen-
trators (Figure 24). Occasionally blasting is not required, and
ore is ripped loose by bulldozers. Barren surface rock overlying
the deposit must be removed to uncover the ore body. Such over-
burden may go as deep as 150 meters (76).
Underground mining involves the removal of ores from deep
deposits by a number of techniques. The selection depends on the
characteristics of the ore body. The two main methods are caving
and supported stoping. Block caving is used in large, homo-
geneous, structurally weak ore bodies, and the stop-sluicing
caving method for smaller and more irregular ore bodies. Sup-
ported stoping methods are used to mine veins and horizontal
deposits of copper ore.
Following extraction, ore and overburden are loaded by power
shovels onto rail cars or trucks and hauled to the mill. Some
mines use belt conveyors and skip ways to transport the ore.
Large underground mines use rail haulage, hoisting facilities,
and shuttle cars.
Beneficiation of copper ores may be accomplished by physi-
cal-chemical separation of minerals from the gangue material
(used for copper sulfide ores) or by hydrometallurgical (leach-
ing) methods (oxide and mixed oxide-sulfide ores). Table 22
shows the various concentrating alternatives used in copper
recovery.
The bulk of the United States copper comes from sulfide
ores. Typical processing steps for sulfide ores are crushing,
grinding, classification, flotation, and dewatering. The ore
enters the mill and is discharged over a grizzly into a gyratory
crusher. Most of the crushing is done in three steps (79). The
first gyratory crusher reduces the ore to a 15.2 to 22.9 centi-
meter size. Following screening, gyratory or cone-type crushers
further crush the oversized pieces to yield a 2.54 to 5.1 centi-
meter product. Water and lime are mixed with the ore, and fine
grinding takes place in rod and/or ball mills. Primary and
156
-------
Ul
-J
«. comi ccwoiwu
*ii mission
IIOUIO HMItS
MUlfi
Figure 24. Mining and beneficiating of copper ores.
-------
TABLE 22. CONCENTRATING ALTERNATIVES FOR COPPER ORES
Ore type
Sulf ide-pyrite
Sulfide-pyrite
Sulfide-pyrite
Oxide
Oxide
Oxide
Oxide
Both
Both
Both
Oxide
Oxide
Oxide
Oxide
Oxide
Oxide
Oxide
Sulfide-pyrite
Oxide
Process
code
A
B
C
D
E
F
G
H
I
J
K
L
M
N
0
P
Q
R
S
Process
Flotation
Flotation
Dump leach
Vat leach
Heap leach
In situ leach
Dump leach
Iron precipitation
Electrowinning
Solvent extraction
I + J
D •»• I
E + K
E + H
G + H
F •»• H
F + K
C + H
D -t- H
Waste
material
Yes
Yes
No
Yes
No
No
No
Yes
No
NO
No
No
No
Yes
Yes
Yes
No
No
Yes
Potentially
hazardous waste
Yes
Yes
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
Source: Ref. 77,
158
-------
secondary ball mills are in closed circuit and are equipped with
classifiers so that the coarse material circulates for regrind-
ing, whereas the fine feed material is delivered for flotation.
The finely ground pulp is then conditioned to adjust its
alkalinity before it is fed to the flotation cells. Air and a
small amount of frother, which might be pine oil or a long chain
alcohol, are added in the flotation cells to produce a froth.
Small amounts of chemicals referred to as "collectors" are also
added, whereupon the copper sulfide particles attach themselves
to air bubbles and rise to the top of the tank as a froth, which
is skimmed off as concentrate. The gangue sinks to the bottom of
the tank and is removed as a tailing. Following flotation, the
concentrate is thickened, filtered, and shipped to a smelter.
Four principal hydrometallurgical methods are practiced:
(1) in situ leaching; (2) dump leaching; (3) heap leaching; and
(4) vat leaching (69). In all four methods the copper-containing
solids are leached with a dilute solution of sulfuric acid or
acidic ferric sulfate.
In-place leaching techniques are applicable to shattered,
broken, or porous ore bodies in place on the surface or in old
underground workings. Usually, abandoned underground ore bodies
previously mined by block-caving methods are leached. In under-
ground workings, leach solution is applied by sprays or other
means to the lower levels, from which the solution is pumped to
the precipitation plant at the surface. The leaching of surface
ore bodies is similar to a heap or dump leach, except permeabil-
ity sometimes must be created by blasting the ore body prior to
leaching.
Most leach dumps are deposited upon the surrounding topo-
graphy. Dump sites are selected to assure impermeable surfaces
and to utilize the natural slope of ridges and valleys for the
recovery and collection of pregnant liquors. The leach solution
is recycled from the precipitation or other recovery operation,
along with makeup water and sulfuric acid additions, and is
pumped to the top of dumps, where it is delivered by sprays,
flooding, or vertical pipes.
Heap leaching of waste dumps that are near ore grade usually
is conducted on specially prepared surfaces. Copper is dissolved
from porous oxide ore. The difference between heap and dump
leaching is insignificant.
Vat leaching techniques require crushing and grinding of
high-grade oxide ore. Dry or slurried crushed ore is placed in
lead-lined tanks, where it is leached with sulfuric acid. This
method is applied to nonporous oxide ores for better recovery of
159
-------
copper in shorter time periods. The pregnant copper solution
drawn off the tanks contains very high concentrations of copper
as well as some other metals. The copper is recovered by iron
precipitation or by electrowinning.
The acid solution from in-place dump and heap leaching is
piped to a cementation process, which converts soluble copper
into a metallic precipitate through a chemical reaction with
scrap iron. The resulting product, called cement copper, is sent
to a smelter for processing.
Waste Streams
Table 23 presents a summary of multimedia wastes from the
mining and beneficiation of copper ores. The following para-
graphs offer more details regarding the various atmospheric
emissions, liquid wastes, and solid wastes.
Air Emissions—
Open-pit copper mining operations generate fairly large
amounts of fugitive dust. An estimate of 0.11 kilogram of
fugitive dust per megagram of ore mined is presented as the
overall average for several nonferrous mining operations (80).
Overburden removal, blasting, and loading and transporting
operations contribute to fugitive dust emissions. The following
are the primary sources associated with overburden removal:
0 Dumping of dragline buckets or shovels filled with
overburden material into adjacent trenches or spoil
banks.
0 Operation of scrapers and bulldozers in topsoil and
subsoil removal and transfer.
The estimated emission factor for overburden removal at open-pit
copper mines (based on a single mine near Butte, Montana) is 0.40
gram per megagram of ore mined (79). Even though blasting and
drilling are periodic operations of short duration, they also
generate large amounts of fugitive dust at open-pit copper mines.
It is estimated that daily blasting at a large open-pit copper
mine emits about 90.7 kilograms of suspended material per blast,
or about 0.50 gram per megagram of ore (65). This estimate is
based on visual observation and is considered to be only an
order-of-magnitude value. Truck loading, another major source of
fugitive dust at open-pit copper mines, generates dust at many
points, but mainly during the scooping of loose material by
shovel, dumping from the shovel bucket into the truck bed, and
movement of the trucks into loading position. It is estimated
that loading operations contribute dust at an average emission
160
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TABLE 23.
SUMMARY OF MULTIMEDIA WASTES FROM MINING AND
BENEFICIATING OF COPPER ORES
Air
Source
Overburden
remova 1
Blasting
and drilling
Ore loading
Haul roads
Underground
mining
Crushing/
grinding/
classifying
Dried
tailings
Pollutant
Fugitive
particulates
Fugitive
particulates
Fugitive
particulates
Fugitive
particulates
Fugitive
particulates
Particulates
Fugitive
particulates
Uncontrolled
emission rate
0.40 g/Mg ore3
0.50 g/Mg ore3
0.025 kg/Mg
ore3
0.50 and 0.18
kg/annual .
vehicle mile
N.A.
1 kg/Mg orec
9-35.8 .
Mg/hectare/yr
Liquid
Source
Overburden
remova 1
Ore
extraction
Underground
mining
Crushing/
grinding/
classifying
Flotation/
concentra-
tion
Leaching
Solvent
extraction
Pollutant/
parameter
See
Table 25
N.A.
See
Table 27
N.A.
Heavy
metals
Uncontrolled
discharge
See
Table 25
N.A.
See
Table 27
N.A.
N.A.
Solid
Source
Overburden
removal
Ore
extraction
Flotation/
concentra-
tion
Vat leaching
Pollutant
Soils and
native rock
Waste rock
Concentrator
tailings
Tailings
Uncontrolled
quantity
0.12 Mg/Mg
ore6
0.95 Mg/Mg
oref
2.0 Mg/Mg
ore1
N.A.
Ref.
Ref.
Ref.
Ref.
Ref.
81.
81.
33.
65.
78.
These values represent emissions from haul trucks and pickup trucks, respectively.
These values were calculated using the wind erosion equation.
These are average quantities for 1973.
Ref. 77. Average based on total national solid wastes generated in 1974.
N.A. - Not available.
-------
rate of 0.025 kilogram per megagram of ore (65). Haul roads
(usually temporary unpaved roads between active mining areas),
tipple, waste disposal areas, and equipment service areas are
additional sources of fugitive dust. Fugitive emissions emana-
ting from haul roads vary with vehicle type, vehicle speed, and
moisture content of the road surface. Emission factors for haul
trucks and pickups are estimated at 0.5 and 0.18 kilogram per
annual vehicle mile traveled (65).
The major sources of fugitive dust associated with the
beneficiation of copper ores are crushing, grinding, and classi-
fying. Dust quantity emanating from these sources is reported to
be about 1 kilogram per megagram of ore (81).
Wind erosion of tailings piles results in large amounts of
suspended particulates at some copper mining operations.
Although no data are available on emissions from tailings piles,
estimates can be obtained by applying calculations from the wind
erosion equation that has been used to predict emissions from
tailings piles in previous publications. This is assumed to be a
valid approach as tailings pile emissions are caused by wind
erosion across flat, exposed surfaces (33). Table 24 presents
emission factors in megagrams per hectare per year for a wide
range of "C" factors and climatic conditions.
TABLE 24. EMISSION FACTORS FOR TAILINGS PILES
Climatic factor, (C)
30
40
50
60
70
80
90
100
120
Emissions,
Mg/hnu/yr
9.0
11.9
14.8
17.9
21.3
23.5
27.3
29.8
35.8
C = 0.345
W3
-------
The following characteristics were considered in calculating the
values presented in Table 24: sandy and loamy sand soils with
possible fines for surface cementation; a smooth unridged sur-
face; no vegetative cover; an unsheltered length of 610 meters;
and a climatic factor dependent on the geographic location of the
tailings pile.
Liquid Wastes—
Wastewater from copper mines originates from seepage or
runoff from the mine and from utility water sent into the mine.
The amount of wastewater from open-pit mines ranges from zero to
0.3 cubic meter of water per megagram of ore mined, and the
amount from underground mines ranges from 0.008 to 4.0 cubic
meters per megagram of ore (29).
The primary chemical characteristics of mine waters are a pH
varying from 2.0 to 9.5, a high dissolved solids content, the
presence of oil and grease, and the presence of dissolved metals.
Mine water often has a high sulfate content, and acid mine water
can cause the dissolution of metals such as aluminum, cadmium,
copper, iron, nickel, zinc, and cobalt (29). Table 25 presents
an analysis of waters from two copper mines.
The quantity and characteristics of effluent from grinding
operations have not been reported.
The flotation/concentration process contributes the greatest
volume of wastewater (29). Ore flotation water is used to sluice
the tailings into a pond. Although part of this water is re-
cycled to the plant, the rest is discharged. Excluding the
amount lost by evaporation and seepage in the tailings pond, the
volume of wastewater emitted by this process "equals the water
consumption and ranges from 100 to 500 cubic meters per megagram
of concentrate (81). Reported analyses indicate that wastewaters
from flotation operations usually contain high levels of sus-
pended solids and a variety of dissolved solids. The various
dissolved materials present are a function of the characteristics
of the ore being processed and the types of reagents added during
processing. Table 26 gives examples of chemical agents that are
used in copper flotation. Some of the elements that may be
present in flotation wastewaters, are potentially hazardous
(cadmium, copper, lead, and zinc). Table 27 represents an anal-
ysis of tailings discharged from a copper concentrator, and Table
28 presents analytical data on tailings in the impoundments of 15
different domestic mining operations.
Water usage in the vat leaching process at three mills is
reported to range from 52 to 206 cubic meters per megagram of
product (29). Since the leach solution from this process is sent
for further processing by electrowinning or cementation, no waste
163
-------
TABLE 25. RAW WASTE LOAD IN WATER PUMPED FROM SELECTED COPPER MINES*
Parameter
Flow
pH
TDS
TSS
Oil i grease
TOC
COD
B
Cu
Co
Se
Te
As
Zn
Sb
Fe
Mn
Cd
Ni
Mo
Sr
Hq
Pb
Underqround mine
Concentration,
mq/l
3,815.3m3/day
7.37b
29,250
69
<1.0
<4.5
819
2.19
0.87
<0.04
<0.077
0.60
<0.07
2.8
<0.5
<0.1
2.22
<0.02
<0.05
<0.5
119
<0.0001
<0.1
Raw waste load per unit ore mined,
kq/Mq
0.017 m3/Mg
7.37b
5.05
0.012
<0. 00017
<0. 00078
0.142
0.00038
0.00015
<0. 000007
< 0.00001 3
<0. 00010
<0. 00001
0.00048
<0. 000086
<0. 000017
0.00038
<0. 000003
<0. 000009
<0. 000086
0.0206
<0. 00000002
- 0.000017
Open-pit mine
Concentration,
mg/l
409 raJ/day
6.96b
1,350
2
7
10
4
0.07
1.05
<0.06
0.096
<0.2
•
-------
a\
ui
TABLE 26. EXAMPLES OF CHEMICAL AGENTS THAT ARE EMPLOYED IN
COPPER FLOTATION
Mineral
Born it*
Chalcocite
Chalcopyrite
Native copper
Azurite
Cuprite
Malachite
Precipitation agent
-
-
-
-
Sodium monoaulfide
Sodium monoaulfide
Sodium monoBulfide
pH regulation
Lime
Lime
Lime
L'"ie
Sodium carbonate
Sodium carbonate
Sodium carbonate
Disperaant
Sodium ailicate
Sodium ailicate
Sodium ailicate
Sodium ailicate
Sodium ailicate
Sodium ailicate
Sodium ailicate
Depressant
Sodium cyanide
Sodium cyanide
Sodium cyanide
Sodium cyanide
Quebracho
Quebracho
Tannic acid
Activator
-
-
-
-
Polyaulfide
Polyaulfide
Polyaulfide
Collector
Xanthate,
aero float a
Xanthate ,
aerofloata
Xanthate,
aerofloata
Xanthate,
aerofloata
Xanthate.
areofloata,
fatty acida
Patty acids
and salts.
xanthatea
Patty acids
and salts,
xanthatea
Prother -
Pine oil
Pine oil
Pine oil
Pine oil
Pine oil.
vapor oil,
creaylic
acid
Pine oil.
vapor oil.
cresylic
acid
Pine oil,
vapor oil,
oreaylic
acid
Source: Ref. 29.
-------
TABLE 27. ANALYSIS OF TAILINGS DISCHARGED FROM
A COPPER CONCENTRATOR
Element
Cadmium
Cadmium
Copper
Iron
Potassium
Magnesium
Manganese
Sodium
Lead
Antimony
Zinc
Concentration, ppm
Concentrator
1172
1.4
2179
264,667
115
6051
19,129
75
1349
462
868
Background
1500
21
11,800
1800
3700
490
151
51
150
Source: Ref. 13.
166
-------
Ch
TABLE 28. ANALYTICAL DATA ON TAILINGS SOLID
FOR 15 COPPER MINING OPERATIONS
Copper
Molybdenum
Sulfur
Iron
Gold (oz/ton)
Silver (oz/ton)
Rhenium (oz/ton)
Aluminum
Arsenic
Cadmium
Lead
Magnesium
Phosphorus
Potassium
Silicon
Sodium
Titanium
Zinc
Zirconium
Cyanides
Mercury
Selenium
Chromium
Concentration, ppm unless indicated
750
0.47
8000
29,000
0.005
0.02
0.004
7000
-
5000
12,000
10,000
50,000
32,000
20,000
10,000
-
5000
700
Nil
200
2300
Nil
2600
930
1900
2000
500
i
i
1000
2100
1
|
i
i
1500
1300
1850
i
1300
1800
j i
! 1
i 1
1
* !
7
60
100
!
!
30
0.01
i 'l
!
30
290
1500
2500
2000
Source: Ref. 77.
-------
is discharged directly. The only waste occurs from possible
leakage in spent leach solution.
The barren leach solution from in-place, dump, and heap
leaching is always recycled. Buildup of iron salts in leach
solutions causes the worst problem in leaching operations. The
pH must be maintained below 2.4 to prevent the formation of iron
salts, which can precipitate in pipelines, on the dump surface,
or within the dump, and cause uneven distribution of solution.
Iron salts may also be removed by use of bleed streams or set-
tling or holding ponds, where the iron salts may precipitate
before recycling. Other metals such as cadmium, nickel, cobalt,
manganese, and zinc are often found in high concentrations in
leach solutions. Total and dissolved solids often build up to
the extent that a bleed cannot be avoided. A small amount of
solution containing dissolved solids may be sent to a holding or
evaporation pond for control purposes (29).
No liquid wastes can be directly attributed to the cementa-
tion process, except possibly from spills. Stripped solutions
are ponded for recycling.
A small amount of liquid waste may be discharged in connec-
tion with cleaning of the completed cathodes from the electro-
winning process. However, no reports of this source have been
published.
The solvent extraction process is likely to produce a bleed
of the concentrated acid to prevent accumulation of some heavy
metals contained in the solvent.
Solid Wastes—
Large volumes of solid waste are produced annually by the
mining and beneficiating of copper ores. The major sources are
overburden, waste rock, and concentrator tailings. The amount
generated from these sources varies from mine to mine and depends
on three factors: whether the mine is underground or open-pit;
the ore grade; and whether ore is oxide, sulfide, or mixed
oxide-sulfide (77). Usually, less solid waste is generated at
underground mines than at surface mines because no overburden is
removed at underground mines and the generally higher grade of
the ore results in the production of less waste rock and less
concentrator waste. Ore type determines the method of concen-
trating, and the method determines the amount of concentrator
waste generated. Concentration by flotation, for example, gener-
ates more solid wastes than concentration by leaching or precipi-
tation.
In 1974, a total of 383 million megagrams of copper ore was
produced. The total amount of solid waste generated that year,
168
-------
including all major sources (overburden, waste rock, and concen-
trator tailings), was 1423 million megagrams (77). This repre-
sents a ratio of 3.7 to 1. The breakdown of total solid waste
produced in 1974 is 44.5 million megagrams of overburden (0.12
megagram of waste per megagram of ore); 365.7 megagrams of waste
rock (0.95 megagram of waste per megagram of ore); and 772.4
megagrams of concentrator tailings (2.0 megagrams of waste per
megagram of ore) (77). These data indicate that concentrator
tailings represent the largest source, approximately 54 percent
of the total.
Overburden and waste rock contain small and varying amounts
of copper minerals, occasionally small amounts of minerals of
other metals, and large amounts of native rock. Concentrator
tailings are composed primarily of the common rock-forming miner-
als, but they also contain approximately 15 percent of the heavy
metals originally found in the ore and much of the pyrite. The
tailings also contain the various reagents added throughout the
concentration operation. Since the minerals in concentrator
solid waste have been pulverized and intimately mixed, they are
subject to weathering much more rapidly than natural rock masses
of similar composition. The soil that they form is usually
highly acidic, has no plant nutrients, and is phytotoxic (78).
It is believed that overburden waste and waste rock contain no
potentially hazardous materials. _ On the other hand, 65 percent
of concentrator waste, is estimated to be composed of hazardous
materials. Approximately 461 million megagrams of the 772 mil-
lion megagrams of concentrator waste generated in 1974 is be-
lieved to have been potentially hazardous material (77).
Vat leaching produces a large amount of tailings that is
sluiced into a tailings pond. This material is comparable to the
waste from a concentrator plant. Frequently the same pond is
used for both concentrator and vat-leached tailings (78).
None of the other leaching operations produce any solid
wastes as such because solids are carried either as suspended
particles or as dissolved solids in solution.
Control Technology
Typical control technologies as applied to the mining and
beneficiation of copper ores are described in the following
paragraphs.
Air Emissions Control—
Particulate emissions at copper mines are generated by a
variety of individual operations (blasting, hauling, loading,
etc.). Nearly all of the facilities that control emissions apply
one or a combination of three basic techniques: watering, chemi-
169
-------
cal stabilization, and reduction of surface wind speed across
exposed surfaces (65).
Watering generally requires the least initial cost, but it
also provides the most temporary dust control. Depending on its
source, dust can be suppressed effectively by watering for only a
few hours or for several days. Therefore, the frequent watering
required to reform the moisture film can become costly. Also,
dust control by watering is usually less than 50 percent effi-
cient.
It should also be pointed out that fugitive dust problems
related to copper mining are most prevalent in regions with arid
climates and the resulting lack of natural surface moisture. As
a corollary to this, water is scarce and therefore not readily
available for dust control. Watering is practiced primarily to
control dust emissions from haul roads. The water is usually
applied by large tank trucks equipped with a pump and directional
nozzles that spray the road surface and adjacent shoulders and
berms. Fixed pipeline spray systems are sometimes used on rela-
tively permanent main haul roads. Some facilities pave haul
roads to control fugitive dust. Such roads are frequently swept
and watered to minimize emissions. Although watering is also
used to control dust emissions from overburden removal, storage,
and waste disposal operations, it is rarely the only technique
applied to suppress dust from these sources. The vast area and
quantities of material to be covered and logistics and related
costs of supplying the necessary volumes of water to the remote
areas where these operations are usually located preclude its
singular use.
The application of chemical stabilizers is more effective
than watering in reducing fugitive dust, usually resulting in a
control efficiency of 90 percent. Different properties in the
chemicals promote dust suppression. They are generally categor-
ized by their composition — bituminous, polymer, resin, enzy-
matic, emulsion, surface-active agent, ligninsulfonate, latex,
etc. The wide range of characteristics available in commercial
products, make it possible to select a chemical stabilizer with
maximum efficiency for each specific dust control application.
Chemical stabilizers are used to a limited extent to control dust
from mining haul roads, storage piles, and inactive tailings
piles. The chemical stabilizers can be added to water or applied
independently to improve binding and reduce dusting. The chemi-
cals can be applied to the surface of the source being treated or
be worked into the soil to a depth of 5 to 15 centimeters (65).
Stabilizers are usually applied by truck or piping spray systems,
but they can also be applied by plane. A Kennecott Copper mine
west of Salt Lake City successfully stabilized 405 hectares of
inactive tailings by aerial application of chemicals (65).
170
-------
When treating storage piles with stabilizers, the chemicals
are usually added in water spray systems. Some chemicals remain
effective without reapplication for weeks, sometimes months.
As explained in the air emissions section, wind contributes
significantly to all fugitive dust sources in the mining indus-
try, by erosion of exposed surfaces of storage areas, tailings
piles, and reclaimed areas and by direct transport of the dust
generated by the other mining operations. Therefore, reduction
of surface wind speed across the source is a logical means of
reducing emissions. This speed reduction is achieved by wind-
breaks, enclosures or coverings for the sources, and planting of
tall grasses or grains on or adjacent to exposed surfaces.
Vegetative techniques require soil that supports growth, meaning
they must contain nutrients, moisture, and proper texture, and be
free of phytotoxicants. These requirements, especially adequate
moisture, are often difficult to meet in many copper mining
areas, making natural protection against wind erosion insuf-
ficient.
The large size of most fugitive dust sources in the mining
industry precludes the widespread use of enclosures or wind
barriers as practical solutions (65). Exceptions include the use
of mats for safety purposes during minor blasting operations at
some sites; the construction of some silos and other enclosed
facilities for storage of relatively small quantities of mined
material; the enclosure of conveying systems, with hooding
connected to control devices such as scrubbers or baghouses; and
the application of hooding to control the fugitive dust from
truck dumping and crushing. The depressed location of overburden
removal and shovel/truck loading operations usually creates a
natural wind barrier for these sources.
Dust generated by the beneficiation of copper ores, partic-
ularly that resulting from crushing and grinding operations, is
generally reduced by drawing air through the equipment and col-
lecting the dust with cyclone separators. This is both a means
of dust control and an integral part of the process, since it
allows these small particles to bypass one or more crushing and
grinding operations. Fugitive dust usually is uncontrolled,
unless the amount being lost provides economic justification for
recovery equipment.
Liquid Waste Control—
Mine water generated from natural drainage is reused in
mining, leaching, and milling operations whenever possible. Some
large mines in arid regions produce no discharge because of
natural evaporation and percolation into the ground.
171
-------
Those mines that produce excess wastewater can recycle it as
makeup water in dump, heap, or in-place leaching. As a leach
solution, this effluent is acidified, percolated through the
waste dump, sent through an iron-precipitation facility, and
recycled to the dump.
At many facilities mine-water effluent also is used as mill
process makeup water. The mine water may pass through the pro-
cess first, or it may be conveyed to the tailing pond for use in
mill flotation with recycled process water.
Acid mine water that occurs in the copper mining industry is
usually neutralized by the addition of lime and limestone. Acid
mine water containing dissolved metals may be treated effectively
by combining the mine water with the mill tails in the tailings
pond. The wastewater may be further treated by lime clarifica-
tion and aeration. Lime precipitation is often used to facili-
tate the removal of heavy metals from wastewater by precipitation
as hydroxides. Application of this treatment technology yields
reductions approaching 100 percent of several heavy metals (29).
Process water from froth flotation is normally directed to a
large lagoon to settle out suspended solids. Effluent from the
lagoon is recycled to the flotation cell or to other facilities
as makeup water.
Effluent from vat leaching usually is completely recycled.
Similarly, the acid solutions from dump, heap, and in situ leach-
ing are usually completely recycled. At some mines the effluent
is recirculated through a tailings pond.
No special controls for effluent from solvent extraction are
indicated. The possible acid blowdown should be of a quality
that could be reused in leaching processes. Also, no special
controls are applicable to wastewater from the cementation and
electrowinning process.
Solid Waste Controls—
Tailings from the concentration process are discarded in a
tailings pond. Upstream construction of the tailings pond is
more common but downstream construction occurs occasionally. As
the ponds become full of solids, they are either abandoned or the
tailings are dredged or mechanically moved to form an embankment
and the pond raised via a peripheral discharge system. Tailings
from vat leaching also are discarded in the tailings pond. Low
sulfide tailings are sent to a dump for storage for possible
exploitation by future technologies.
Aside from site selection and stability control little
reclamation of solid wastes is practiced by the copper mining and
172
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beneficiating industry. Only a few companies control blowing
dust or attempt to reclaim or naturalize the dump areas. When
stabilization and revegetation practices are attempted, a variety
of problems can develop, particularly if excessive salinity or
acidity are encountered. Sometimes lime and sewage sludge are
applied to ameliorate acidity. In areas where water is avail-
able, soluble salts can be leached downwards by excessive irri-
gation prior to revegetating. Leaching, however, may complicate
the situation because the tailings may contain both salts and
pyrite. In arid climates, the pyrite is likely to be inactive
and have a high initial pH (43). The tailings generated by the
Utah Copper Division mill of the Kennecott Company has these
characteristics, and they are discarded in a semiarid environ-
ment. This material has a pH of 7.8 when fresh, a salinity
equivalent to 2.4 atmospheres osmotic concentration, and pyrite
content of approximately 1.3 percent (43). The salts in the
tailings produce an osmotic gradient that transfers fluid from
the plants. Thus, vegetation dies of dehydration as irrigation
of the plants leaches- away the salts, the pyrite oxidizes, and
the pH may drop from 7.8 to less than 3.0 within a month's time.
Conclusions and Recommendations
Fugitive dust generated by such sources as haul roads, ore
loading and dumping, and overburden removal, is a major pollution
problem at many copper mining operations. Dust control provided
by watering of haul roads and actively worked areas is of such a
temporary nature that chemical stabilizers furnish a more cost-
effective dust suppressant. More than 100 proprietary chemical
stabilizers are available, all reputed to be effective for con-
trolling dust on unpaved traffic areas. Some comparative studies
of these different stabilization chemicals would be valuable.
A major area of concern associated with copper mining and
beneficiation operations is the disposal of tailings. Mining and
milling operations generate large volumes of tailings annually,
and many of these wastes contain potentially hazardous materials
such as heavy metals. Most tailings are discarded into tailings
ponds, but because most of the ponds are not lined, the heavy
metals may leach into and cause contamination of the groundwater.
Therefore techniques for the removal of the heavy metals should
be evaluated and/or sealing ponds should be investigated. Seal-
ing existing ponds constitutes a major technolgical hurdle.
Another area for possible research is the development of
mechanical screening and filtering equipment to separate tailings
from concentrator water. Tailings are commonly removed from
flotation water by allowing them to settle in a pond. This solid
waste could be controlled more effectively if a mechanical device
that continuously separates tails from water could be developed
173
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to operate economically. The chance of developing an economic
alternative are remote at present.
The development of a reagent that can replace sodium cyanide
as a flotation depressant would constitute a contribution to
pollution control technology. Cyanide that enters a copper mill
tailings pond is stable in solution because the pond water pH is
above 9 (often as high as 10). Therefore the cyanide escapes
with any seepage that occurs. The development of an alternative
reagent would eliminate the risk associated with this pollutant.
Many projects are currently in progress to reclaim inactive
tailings by covering the surfaces with suitable soils and reveg-
etating them. Other copper tailings have been stabilized chem-
ically by encouraging encroachment of natural vegetation, or
stabilized physically by covering with smelter slag, gravel, wood
bark, or straw. Many times, however, pH .and associated para-
meters of copper tailings are such that they present detrimental
obstacles to revegetation and stabilization. Research and devel-
opment of mechanisms for overcoming this problem would be benefi-
cial.
GOLD
Industry Description
Gold is found in the* earth's crust in extremely low concen-
trations, perhaps 5 x 20" gram per gram in igneous rocks, 0.25 x
10~ gram per gram in the earth as a whole. It is also found in
seawater, which is estimated to contain about 4 x 10~ gram per
gram (46). Local concentrations of gold, sufficiently high to
mine economically, are produced by various geochemical processes
associated with quartz, sulfides, and tellurides. Natural erod-
ing of gold-bearing rocks combined with the current of flowing
streams often results in substantial local concentrations of gold
in placers (82). Some gold also is recovered during electrolytic
refining of copper, nickel, and other metals. Fifty to 60 per-
cent of domestic gold production comes from gold ores; the rest
is recovered as a coproduct of copper, zinc, or lead (14).
The gold industry is concentrated in eight states: Alaska,
Montana, New Mexico, Arizona, Utah, Colorado, Nevada, and South
Dakota (29). The total domestic output comes from an estimated
140 firms, and 75 percent of the 1974 total came from the four
largest firms (14).
Most of the gold used in industry is in the form of metal or
metal alloys. Industrial gold is shaped into bars, rods, sheets,
foils, wires, powder, granules, and shot. Gold used in high-
174
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quality jewelry is measured in karats and is an alloy of gold,
copper, and other metals such as silver, zinc, and platinum. For
example, 14-karat gold contains 58.3 percent gold; approximately
25 to 32 percent copper; and varying small percentages of the
other metals. Substantial amounts of gold also are used to
electroplate jewelry and decorative articles, and as rolled gold,
gold plate, and gold fill. A variety of organic gold compounds
also are produced for electroless gold plating. The jewelry and
aerospace industries use brazing alloys containing gold. The
dental profession uses gold extensively. Alloys containing 25 to
70 percent gold are used in wire form for orthodontic applica-
tions; other alloys (with 60 to 92.5 percent gold) are used in
cast form in inlays, crowns, and bridges. Gold alloys are also
produced for solders. The electronics industry produces bimetal-
lic strips in a variety of shapes and patterns, with gold applied
selectively to electrical contact areas. Tiny wires for transis-
tor connections are made of gold. Specialized gold compounds are
made for diverse uses, such as in medicines and glass (14).
Process Description
Gold is mined from two types of deposits: placers and lodes
or veins. About 1 percent of domestic gold comes from placer
deposits (46), approximately 33 percent from underground mines,
and the remainder from open-pit mines (14).
Processes for the recovery and beneficiation of gold and
gold-containing ores include cyanidation, amalgamation, flota-
tion, and gravity concentration. All of these have been used to
beneficiate ore mined from lode or vein deposits. Only gravity
methods (sometimes in conjunction with amalgamation) are used in
placer operations, however, in the past few years, the restric-
tion placed on the use of mercury has caused the use of amalgama-
tion to decrease while the use of cyanidation has increased (29).
Many mines use two or more processes, and the tailings from one
process, such as flotation or gravity separation, are further
processed by cyanidation to recover residual gold values. Figure
25 shows a flow sheet for mining and beneficiation of gold.
Placer mining consists of excavating gold-bearing gravel and
sand, now primarily by dredging. (In the past, hydraulic mining
and drift mining also were used.) The excavated gold-bearing
deposits are dumped into a feed hopper and conveyed to a washing
hommel screen. In the scrubbing section of the hommel screen,
the gravels are washed thoroughly to disintegrate all clay before
they are screened to reject the oversize. The undersize from the
screen passes to a jig for gravity separation, then the high
grade ore concentrate is discharged from the jig to a dewatering
screw classifier for removal of excess water.
175
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PLACER
MINING
W
OPEN-PIT
MINING
UNDERGROUND
MINING
WASHING/
SCREENING
CYANIDE
LEACHING
O
CRUSHING/
CLASSIFYING
GRAVITY
SEPARATION
FILTERATION
FLOTATION
ORE
GRINDING/
AMALGAMATION
ZINC
PRECIPITATION/
FILTRATION
CARBON
EXTRACTION
•GOLD CONCENTRATE
AMALGAM
GOLD CONTAINING
* PRECIPITATE
» CONCENTRATED
GOLD SOLUTION
AIR EMISSIONS
C\ LIQUID WASTES
O SOLID WASTES
Figure 25. Mining and beneficiating of gold ores
-------
Sometimes, placer mines use amalgamation to recover the lean
ore left from gravity separation. This process involves first
grinding the ore in a ball mill, then passing the pulp of crushed
ore and water over mercury-treated (amalgamated) copper plates,
to which the gold particles adhere. The amalgate of gold and
mercury is scraped off from time to time. Much of the mercury is
recovered and returned to the process.
Lode deposits of gold are recovered from open-pit and under-
ground mining by the conventional mining techniques described in
Section 2. The ore is transported to the mill house, where
recovery and beneficiation takes place by cyanidation, flotation,
or gravity separation.
Four basic methods of cyanidation currently are being used
in the United States: heap leaching, vat leaching, agitation
leaching, and a carbon-in-pulp process. Heap leaching is used
primarily to recover gold from low-grade ore or gold mine waste
dumps. Higher grade ores are crushed, ground, and vat-leached or
agitated-leached to recover the gold.
Vat leaching involves filling a vat with ground ore slurry,
allowing the water. to drain off, and leaching the sands from the
top with cyanide. This solubilizes the gold. Pregnant cyanide
solution is collected from the bottom of the vat and sent to a
holding tank. Agitation leaching involves adding a cyanide
solution to a ground ore pulp in thickeners, and agitating the
mixture until the gold becomes soluble. The cyanide solution is
collected from the thickeners by decanting (29).
Impurities and suspended solids are filtered from the gold-
bearing solution by passing the solution through a filtering
media (coated with diatomeceous earth) in a tank (83). Zinc dust
is used to precipitate the gold from the solution. The precip-
itate is collected in a filter press and sent to a smelter for
the production of bullion.
Cyanidation of slimes generated in the course of wet grind-
ing is currently accomplished by the carbon-in-pulp process. In
large tanks the slimes are mixed with a cyanide solution and the
solubilized gold cyanide is collected by adsorption to activated
charcoal. Gold is stripped from the charcoal by applying a small
amount of hot caustic. The concentrated gold solution is puri-
fied by electrowinning (29).
Gold that is finely disseminated in pyrites and some low
grade gold ores are recovered by flotation. The ore is crushed,
wet ground in a ball mill, and classified. After conditioning,
the pulp flows to a flotation tank of the cell-to-cell type.
Reagents for gold flotation are usually soda ash, a xanthate, and
177
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a frother. The gold-containing minerals that float to the top
are collected and sent to a disk filter for dewatering. The
resulting gold concentrate is further purified at a smelter.
Waste Streams
Table 29 presents a summary of multimedia wastes from the
mining and beneficiation of gold-bearing ores. The following
paragraphs explain in more detail the various air, liquid, and
solid wastes associated with the gold industry.
Air Emissions—
Mining and beneficiation of placer-mined gold do not gener-
ate air emissions because all the processes are carried out in
the presence of water.
Nothing is available on estimates and characteristics of
emissions from open-pit and underground gold mines or from the
crushing and grinding processes.
Liquid Wastes—
Placer mining and beneficiation processes uses large quan-
tities of water. Although no specific data are available on the
characteristics and concentrations of the effluent from washing,
screening, and gravity separation, the effluent is known to have
high suspended solids content and could be potentially hazardous
(46).
Effluent from grinding and amalgamation is also high in
suspended solids. Mercury is the prominent reagent used in this
process; therefore the effluent could be potentially toxic.
In open-pit mining, the only sources of possible discharge
are precipitation, runoff, and groundwater infiltration into the
pit. In underground mining, groundwater infiltration is the
primary source of water. Table 30 shows the chemical composition
of raw mine water from two underground gold mines.
As shown in Table 30, cyanide leaching results in high
levels of soluble metals. Cyanide and heavy metals are poten-
tially toxic and are of primary concern.
No specific data are available on the environmental impacts
associated with filtration operations. .Neither zinc precipita-
tion nor carbon extraction would generate much effluent because
of the extreme care that must be taken to minimize gold losses.
Solid Wastes—
No information has been reported on solid wastes generated
by placer mines.
178
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TABLE 29. SUMMARY OF MULTIMEDIA WASTES FROM MINING AND BENEFICIATING
OF GOLD ORES
V£>
Air
Source
Open-pit
raining
Underground
mining
Crushing/
grinding/
classifying
Pollutant
Fugitive
particulates
Fugitive
particulates.
gases
Particulates
Uncontrolled
emission rate
N.A.
N.A.
N.A.
Liquid
Source
Washing/ }
screening (
>
Gravity \
separation 3
Grinding/
amalgamation
Pollutant
SS
TSS
TOS
TOC
COO
Cu
As
Fe
Zn
Pb
Cd
Hg
Cn
S
Uncontrolled
discharge
High"
2.871 kg/Mg
of ore
0.930 kg/Mg
of ore
0.199 kg/Mg
of ore
0.066 kg/Mg
of ore
0.0002 kg/Mg
of ore
< 0.0004 kg/Mg
of ore
0.0087 kg/Mg
of ore
0.0075 kg/Mg
of ore
< 0.0006 kg/Mg
of ore
< 0.0001 kg/Mg
of ore
<0. 0000064
kg/Mg of ore
< 0.00006 kg/Mg
of ore
<0.0029 kg/Mg
of ore
Solid
Source
Placer mining
Washing/
screening
Gravity
separation
Grinding/
amalgamation
Open-pit
mining
Underground
Pollutant
Gangue
Tailings
Tailings
Tailings
Gangue
Gangue
Uncontrolled
quantity
N.A.
N.A.
N.A.
N.A.
N.A.
N.A.
(Continued)
-------
TABLE 20. (continued)
00
o
Air
Source
Pollutant
Uncontrolled
emission rate
Liquid
Source
Open-pit
mining
Underground
mining
Cyanide
leaching
Filtration
Flotation
Pollutant
c
PH
TSS
Turbidity
TDS
COD
Oil and
grease
Cn
As
Cd
Cr
Cu
Total Fe
Pb
Total Mn
Zn
N.A.
N.A.
Uncontrolled
discharge
N.A.
c
12.26a
545,000 rag/i
6.75 J.T.U.*
4.536 mg/ia
43 mg/la
<1 mg/ta
5.06 mg/ta
0.05 mg/*a
0.10 mg/la
0.06 mg/la
0.17 mg/ia
<0.5 mg/ia
<0.1 mg/ta
0.02 mg/la
3.1 mg/la
N.A.
N.A.
Solid
Source
Filtration
Carbon
extraction
Pollutant
Residue
Carbon
particles
Uncontrolled
quantity
N.A.
N.A.
Ref. 46.
b Ref. 67.
0 See Table 30.
N.A. - Not available.
-------
TABLE 30. CHEMICAL COMPOSITION OF RAW
MINE WATER FROM TWO UNDERGROUND GOLD MINES
Parameter
PHa
Alkalinity
Color
Turbidity (JTU)
TOS
TDS
TSS
Hardness
COD
TOC
Oil and grease
MBAS surfactants
Al
As
Be
Ba
B
Cd
Ca
Cr
Cu
Total Fe
Pb
Concentration, mg/i
Mine 1
-
275
34b
2.40
1,190
1.176
14
733
35.01
• 12.0
1
0.095
<0.2
0.03
<0.002
<0.5
0.18
<0.02
87.0
<0.02
<0.02
1.2
<0.1
Mine 2
6.14
-
-
-
535
530
5
-
27
-
<0.1
-
0.143
0.084
-
-
-
0.025
-
-
0.056
25.11
0.62
Parameter
Mg
Mn
Hg
Ni
Ti
V
K
Ag
Na
Sr
Te
Ti
Zn
Sb
Mo
Sulfate
Nitrate
Phosphate
Cyanide
Phenol
Chloride
fluoride
-
Concentration, mg/i
Mine 1
80.0
0.14
<0.0001
0.10
<0.05
<0.2
44.0
<0.02
80.0
0.78
0.10
-------
Open-pit mines generate considerably more waste material
than underground mines, but the characteristics of these wastes
are not known.
The filtration process generates residue that could be
potentially hazardous if cyanide or other noxious materials are
present. No information is available on the wastes generated by
carbon extraction.
Control Technology
The following paragraphs explain air, liquid, and solid
wastes control methods.
Air Emissions Control—
Dust from open-pit mining is minimized by water spraying.
Particulates generated by underground mining usually do not
require control because they are generally large and precipitate
in the vicinity of the mining activity. If crushing and grinding
are wet operations, they do not create a dust problem; however,
dry crushing and grinding operations require control by cyclones
or fabric filters.
Liquid Wastes Control—
Wastewater from placer mining operations (washing, screen-
ing, and gravity separation) is discharged into a tailings pond,
where suspended solids are allowed to settle out.
Mill water from grinding and amalgamation are also dis-
charged to a tailings pond. Decant from this pond may be dis-
charged into a stream, or may flow into a smaller polishing pond
prior to discharge into a stream. Data from one mill indicate
that, the use of two settling ponds (tailings and polishing
ponds) removes some additional selected metals, and achieves 99.9
percent total suspended solids removal.
One open-pit gold mine in Nevada has no discharge because of
the arid climate (76). Wastewater from underground gold mines is
either ponded or used as a source of process water in the mills.
Typically effluent from cyanide leaching operations is
discharged to a tailings pond to oxidize the cyanide and to
contain the heavy metals. In arid locations, the tailings pond
decant is recycled, and no discharge to a watercourse occurs.
Tailings from the flotation process of one beneficiating
facility are further processed by cyanidation/agitation, a leach
process to recover residual gold values (29).
182
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Solid Waste Control—
Most of the solid wastes generated by the beneficiation of
gold is discharged into an on-site tailings pond. When one pond
is filled up, a new one is worked. Although such ponds are built
around a dam, they are not lined. Rather, they are built on a
stratum of rocks, which prevents seepage into the groundwater.
At some mines, the tailings are sent back to the mine.
Conclusions and Recommendations
Insufficient data are not available to make a final assess-
ment of all the environmental impacts associated with mining and
beneficiation of gold.
Air pollution from gold mining and beneficiation is con-
trolled by conventional techniques and is not a major environ-
mental concern at this time.
Most of the wastewater is discharged into a tailings pond,
then either recycled to the mill or discharged into a water-
course. Solid waste is generally discarded into the same tail-
ings pond.
One possible area of research activity could concentrate on
the ultimate disposal or use of solids that settle out in the
tailings pond. These solids could contain gold or other recover-
able minerals. Another possible area of research involves the
development of economical methods of controlling or eliminating
wastewater that contains arsenic and cyanide.
LEAD AND ZINC
Although the lead and zinc industries each make a distinct
product, they have been considered a single economic unit for
many years because of the strong interrelation between the two
industries. Their products are marketed through many of the same
channels, using the same procedures. Since many of the ores
contain recoverable quantities of both lead and zinc, the indus-
tries regularly exchange material, and several companies produce
both metals, along with a variety of other coproducts/by-products
(copper, gold, silver, etc.). The two industries also share
similar production techniques and produce similar waste mater-
ials. Because of these interrelationships, lead and zinc are
discussed together in this section.
Industry Description
Lead--
Although most domestic lead is recovered from ores mined
primarily for their lead content, a sizable amount is recovered
183
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as a coproduct or by-product from complex ores containing zinc,
silver, gold, and often copper. Other materials recovered in
processing lead ores and concentrates include antimony, bismuth,
tellurium, arsenic, cadmium and sulfur (as sulfuric acid). The
economical extraction of lead at many operations depends on the
combined values of the associated materials recovered from the
ores.
Lead is most often found as galena (PbS2), the primary
sulfide of lead (77). These are rarely pure deposits. The
lead-bearing compound is usually mixed with pyrite, sphalerite,
and pyrrhotite. The deposits normally contain very little
copper, gold, or silver. Oxidized lead ores also are found.
They are composed primarily of anglesite and cerussite, which are
weathered products of galena.
In amount used, lead ranks fourth among nonferrous metals
(behind aluminum, copper, and zinc). As the world's leader in
lead consumption and production, the United States accounted for
27 percent of the consumption and about 17 percent of the total
mine production in 1974 (15). This country also has the largest
reserves of lead, estimated to be adequate to handle all primary
domestic requirements through the year 2000. Although reserves
are adequate, some dependence on imports and government stock-
piles to meet part of the domestic demand is likely to continue.
(See Section 1 for additional information on present and pro-
jected production statistics.)
The lead mining industry currently consists of 31 mines in
15 states (15). The output of these mines ranges from less than
1 megagram to 100,000 megagrams per year. Greater than 80 per-
cent of the domestic mine production comes from seven operations
in the newly discovered Lead Belt of southeastern Missouri.
Approximately 98 percent of the total mine production comes from
four states: 85 percent from Missouri; 8 percent from Idaho; 5
percent from Colorado; and 1 percent from Utah (15).
At most large and medium-sized mines ore is concentrated at
the mine site. At some smaller western mines it is trucked to
centrally located concentrating facilities. Ore concentrates are
then shipped to any one of the six smelters in the United States.
Four of these are fully integrated lead mining and smelting
operations.
Lead bullion, more than 99.9 percent pure, is the primary
product of this industry. Antimonial lead, a less ductile pro-
duct, is also produced. Whether the various by-products/
coproducts (mentioned earlier) are generated depends on ore
characteristics and market conditions. Lead is used primarily in
storage batteries for automobiles and battery-powered vehicles,
184
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as tetraethyl or tetramethyllead, an antiknock additive in gaso-
line, and in construction materials (roofing, piping, caulking,
etc.)- It is also used in ammunition, paints, and electrical
cable sheathing.
The market for many products of the lead industry is con-
tinually decreasing as the public becomes aware that lead and its
compounds are cumulative poisons. Lead pigments rarely are used
in paints anymore. Although tetraethyl lead for gasoline addi-
tives is still manufactured and continues to provide a major
market for lead, its use is being restricted. In recent years
other materials also have replaced lead as a joining material for
cast iron pipe, in plumbing, and in most other construction
applications. Although these traditional uses of lead are dimin-
ishing, factors such as the rapid growth in lead-acid batteries
and the development of new uses have more than offset this de-
cline and the demand for lead continues to grow.
Zinc—
Although most domestic zinc is recovered from ores mined
primarily for their lead content, a sizable amount comes from ore
containing zinc and varying amounts of other valuable and re-
coverable materials including lead, copper, cadmium, fluorspar,
gallium, germanium, gold, indium, manganese, silver, sulfur, and
thallium. Zinc may be recovered as the primary metal (as in the
zinc ores of Tennessee, Pennsylvania, and New Jersey deposits) or
as a by-product/coproduct as in the complex western ores or in
the lead ores of the Missouri Lead Belt. Zinc recovery at most
mining operations is dependent on the combined economic values of
the by-products/coproducts present in the ore.
In its natural state zinc is usually found as the sulfide
called sphalerite, which has a cubic lattice structure and is
commonly referred to as zinc blende, blende, or jack. Zinc
content can be as high as 67.1 percent in the pure phase.
Wurtzite, a polymorph of sphalerite, has a hexagonal structure
and is more stable at elevated temperatures. Almost all other
zinc minerals have been formed as oxidation products of these
sulfides. Most of these oxidized minerals are minor sources of
zinc, although franklinite and zincite are mined for their zinc
content at the New Jersey Zinc Co. mine (21).
Iron is the most common impurity or associated metal in zinc
ore because of its chemical similarities and the relative ease of
substitution in their respective lattices. Cadmium is the second
most abundant impurity. It is always associated with zinc, and
is usually present as greenockite (CdS). The commonly associated
nonzinc minerals in zinc ores are calcite (CaCO,), dolomite (Ca,
Mg)CO_, pyrite and marcasite (FeS5), quartz (SiO~), chalcopyrite
(CuFeS2), and barite (BaSO4). ^
185
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Among nonferrous metals of the world zinc ranks third in
annual consumption, behind copper and aluminum. A major consumer
of zinc, the United States used approximately 20 percent of the
total world supply in 1974 while it produced only 8 percent of
the primary zinc supply (78). In 1974 approximately 28 percent
of the U.S. zinc supply came from domestic mines and 45 percent
was imported. Of the remainder, 4 percent came from secondary
metal supplies; 16 percent from Government supplies and 7 percent
from industry stocks. In recent years the trend has been toward
less dependence on imported concentrates; however, since U.S.
resources are not expected to cover the domestic cumulative
demand through 2000, reliance on imports for a significant por-
tion of supply is expected to continue. (See Section 1 for
present and future production statistics for the zinc industry.)
In 1975, 18 states throughout the United States reported
zinc mining production. The major producing states were
Tennessee, 18 percent; Missouri and New York, 16 percent each;
Colorado, 10 percent; Idaho, 8 percent; and New Jersey, 7 percent
(77). Mining capacities of lead-zinc ore ranged from 10,000 to
10,000,000 megagrams per year. The 25 largest U.S. mines ac-
counted for over 90 percent of the zinc ore mined and, the 5
largest of these accounted for 40 percent (77). A total of 43
zinc mines operated in 1975 (84). Several large firms in the
domestic primary zinc industry are vertically integrated, with
mines, concentrators, smelters, and refineries. In 1974, five
integrated companies accounted for 89 percent of the slab zinc
production in the United States and 77 percent of the total
domestic mine output (15).
I
The major product of the primary zinc industry is metallic
zinc; other products include zinc oxide, sulfuric acid, cadmium,
and occasionally other chemicals such as zinc sulfate. Important
by-product compounds resulting from the primary zinc industry
include germanium, thallium, gallium, and indium. These by-
products often are not considered part of the industry because
they are not recovered at primary zinc smelters.
Uses for zinc products vary widely. Metallic zinc is used
for galvinizing, for making pigments and zinc compounds, for
alloying, and for grinding into zinc dust. Usage patterns in the
United States differ from those in the rest of the world in that
heavy emphasis is placed on zinc-based alloy castings, mainly for
the automotive industry. The primary product of most zinc com-
panies is slab zinc, which is produced in five grades and clas-
sified by its purity. Zinc oxide is used in rubber, emollients,
ceramics, and fluorescent pigments, and in the manufacture of
chemicals.
186
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Metallic cadmium is used in the production of alloys, in
corrosion-resistant plating for hardware, as a counter electrode
metal for selenium rectifiers, as neutron shielding rods in
nuclear reactors, in nickel-cadmium batteries, and in plastics
and cadmium compounds. Cadmium metal accounts for 60 to 70
percent of consumption, and cadmium sulfide used for pigments for
another 12 to 15 percent (22).
Process Description
Some mining operations recover ores containing lead but no
zinc, others recover ores containing zinc but no lead, and still
others recover ores containing both lead and zinc along with
other by-products/coproducts. The ores from which lead and/or
zinc are recovered are classified on the basis of the metal of
major value in the ore: zinc ores, zinc-lead ores, lead ores, and
all the other ores from which zinc and/or lead are obtained
(e.g., copper-lead-zinc ores). The mineralogy of the ores de-
termines the technology and economics of mining and processing
practices.
Specific factors that affect mining and processing methods
include size and interlocking of the mineral grains, association
with other metallic and nonmetallic minerals, and oxidation or
coating of mineral surfaces with soluble salts. Mining and
processing differ slightly throughout the lead and zinc indus-
tries; however, ore extraction and concentrating methods are
quite similar regardless of the ore type. The extraction and
beneficiation techniques associated with lead-zinc ores are
illustrated in Figure 26 and discussed in the following para-
graphs .
Ores containing lead and/or zinc are almost always extracted
by underground mining methods. A few zinc mines, particularly in
early stages of operation, use open-pit methods that closely
follow those of copper mining. Most lead ore is obtained by
normal stoping methods such as block caving, room-and-pillar
(with and without rock bolting), and cut-and-fill with timber
supports. Most zinc ore is mined using open shrinkage, cut-
and-fill, or square-set stoping methods. In most of the mines,
walls and pillars usually are left behind to support the over-
lying rock structure, unless the width of the ore body is such
that it can be left unsupported and the entire ore body ex-
tracted. The cycle of mining operations consists of drilling,
blasting, and removing the broken rock. The ore cut from the
deposit is hauled to the surface by rail tram, trackless shuttle
cars, or conveyor belts, then is transported to ore concentrating
facilities by rail car, truck, belt conveyor, or a combination
thereof.
187
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U«l tllHACIIM
MO IQAOIW
I«M«I.
HUM 1
IMJiiPUKI
SUMfACt
I1HIW
1
iwoisnjai 1
01 UKI 10
fUUCliSIHC
fkCRIII
CUINAIO
tHUSHING/
SCU1HINC
SUONUAkt
CRUSHING/
StBUNINC
MMIIIC
SCPAMIOt
rim ou 10 MIMIM
lUtCLt
KAO COMEIillAU 10
SIOMtt 01 iMllfl
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00
00
9 *ll IHI»IOM
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Figure 26. Mining and beneficiating of lead-zinc ores.
-------
Regardless of ore type and the number of recoverable mater-
ials in it, processing techniques in the industry share many
similarities and almost always involve some form of crushing,
grinding, concentrating, thickening, and dewatering. Lead and
zinc concentrates are recovered primarily by the flotation
method. Processing methods throughout the industry vary most in
the type and number of flotation cells used at an operation (most
facilities have two or more stages of flotation cells) and the
types of flotation reagents added to the process. It should be
noted that some facilities use gravity methods to preconcentrate
ores that contain relatively coarse minerals easily broken free
at an early stage in the crushing-grinding operations (84).
These gravity methods usually consist of jigs or heavy-media
(sink-float) systems placed ahead of the fine grinding part of
the circuit. By removing a portion of the waste material from
ores before the grinding and flotation steps, preconcentration
increases the capacity of the operation and decreases the cost of
flotation and grinding. The beneficiation operation illustrated
in Figure 26, and discussed in more detail in the following
paragraphs, applies to lead-zinc sulfide ores only. However, as
stated earlier, processing practices vary little throughout the
industry whether the ore type is lead, zinc, lead-zinc, or
copper-lead-zinc.
The first step in the processing of lead-zinc ores involves
size reduction or crushing. Primary and secondary crushing is
usually accomplished by a combination of jaw and gyratory crush-
ers with grizzly bars and screens. The ore then is conveyor-fed
into fine-ore storage bins (77). Tramp iron is removed by a
separator magnet operating on or under a conveyor belt between
the crushing and classifying operations. The crushed ore is
ground to a size that liberates the lead and zinc sulfide from
the gangue, usually by wet grinding in rod and ball mills. These
mills are equipped with classifiers that prepare the feed for
flotation.
At most facilities, classifier overflow is passed over a
vibrating screen to remove wood pulp, which is discarded. The
underflow is pumped to the first cell of the flotation circuit,
known as the lead conditioner cell, where a number of chemical
reagents are added. These reagents include sodium ethyl
xanthate, zinc sulfate, methyl isobutyl carbinol (MIBC), and
sodium cyanide (85). At some operations the sodium ethyl
xanthate and zinc sulfate are added earlier in the rod and ball
mills to provide more contact time. Sodium ethyl xanthate is a
collector, which coats the desired nonfloating mineral particles
and makes them more susceptible to flotation. Zinc sulfate and
sodium cyanide are depressants that inhibit the zinc sulfide
particles from floating with the lead sulfide. MIBC, a frother,
is added to coat and toughen the air bubbles that are introduced
189
-------
into the cell. The air bubbles carry the lead-laden frother to
the surface of the conditioner cell, and the mixture then over-
flows to a second series of flotation cells, known as the lead
roughers. Air bubbles are introduced at the bottom of the cell
and the lead-laden frother floats to the surface, flows over
weirs, and continues on to the remaining flotation cells. The
underflow material, consisting of zinc sulfide and gangue, is
collected at the bottom of the cell and sent to the beginning of
the zinc .flotation operation. The final lead flotation cells,
known as scavenger and cleaner cells, further separate lead
sulfide from zinc sulfide, and gangue and the residual material
from the cells are recycled back to the beginning of the lead
flotation circuit. The lead-laden overflow from the final flo-
tation cells (cleaner cells) is concentrated and thickened in
sedimentation tanks (86). The liquid overflow from the tanks is
recycled and the lead concentrate is vacuum-filtered, dried, and
stored or shipped by rail car to the smelter.
The underflow from the lead rougher cell is sent to the zinc
conditioner cell and mixed with a variety of chemical additives
such as Xanthate Z-ll, methyl isobutyl carbinol, copper sulfate,
quicklime and Separan (76). Copper sulfate activates the zinc
and must be added to the slurry first to neutralize the depres-
sion action of the zinc sulfate and sodium cyanide, which were
added to the lead conditioner cell. The zinc flotation circuit
is identical to the lead flotation circuit in that it consists of
conditioner, rougher, scavenger, and cleaner cells. Following
flotation, the zinc concentrate, like the lead concentrate, is
thickened, filtered, and either stored or shipped to the smelter.
The tailings from the rougher flotation cells are pumped to a
sand plant and passed through a cyclone. The fines from the
cyclone are disposed of in a tailings pond and the coarse mater-
ials are used for mine backfill. Backfilling is not practiced at
some operations and all the tailings is sent to the tailings
pond.
The operations illustrated on Figure 25 and just described
represent typical mining and beneficiating facilities for the
recovery of lead-zinc sulfide ores. Although mining and proces-
sing operations vary somewhat throughout the industry as a func-
tion of ore type and the number of recoverable materials in the
ore, such variations are small and usually involve only the type
and number of flotation cells employed and the chemical reagents
added to the process.
Waste Streams
Table 31 presents a summary of multimedia wastes from the
mining and beneficiating of ores containing recoverable amounts
of lead and/or zinc. The following paragraphs explain in more
detail the various atmospheric emissions, liquid wastes, and
solid wastes.
190
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TABLE 31. SUMMARY OF MULTIMEDIA WASTES FROM'MINING AND BENEFICIATING OF LEAD-ZINC ORES
Air
Source
Drl 1 ling
Blasting
Ore loading
Ore transport
Crushing/
grinding
Ore transport
and storage
Dried tal 1 Ings
Pol lutant
Fugitive
participates
Fugitive
participates
Fugitive
partlculates
Fug! tl ve
partlculates
Uncontrol led
emission rate
0. 1 kg/Mg of
ore mined3
0.9 kg/Mg of
ore processed
2. 3 kg/Mg of
ore processed
0. 1 kg/Mg of
ore mlnedc
Liquid
Source
Mine water
Flotation,
thickening,
dewaterlng
Pol lutant/
parameter
See Tables
j'2. jnd '<5
Wet tailings6
Unconlrol led
discharge
100-200,000
m3/dayd
1.000-16,000
m'/day
Solid
Source
Ore
extraction
Flotation,
th Icken 1 ng,
dewator Ing
Pol luta-it
Waste roc<
Dry tal 1 I igs
Uncontrol led
quantity
0.0-0.24 Mg/Mg
ore mined'
0.26-0.94 Mg/Mg
ore mined*
vo
Ref. bO.
b Re*. 20. B5, 89.
C Ref. B7.
d Ref. 20.
6 See Table 35 for characteristics.
f Re*. 77.
-------
Air Emissions—
The mining and beneficiating of lead and zinc ores produce
some fugitive particulate emissions. The major sources of fugi-
tive dust emissions at mining operations are drilling, blasting,
loading, and transport. Average fugitive dust emissions have
been estimated at 0.1 kilogram per megagram of ore mined, based
upon observations from several types of nonferrous metal mining
operations (79). Cadmium emissions also occur during the ex-
traction of zinc ore. Emissions due to wind loss from dried
tailings piles are estimated at 0.1 kilograms per megagram of ore
mined (87). Total emissions of cadmium to the atmosphere were
estimated to be 240 Mg in 1968 (87) and 220 megagrams in 1973
(88).
The major quantity of fugitive particulates generated by the
beneficiation of lead and zinc ores results from crushing and
grinding operations. Average particulate emissions from crushing
and grinding operations are 3.2 kilograms of ore processed; 0.9
kilograms is attributable to crushing and grinding operations and
2.3 kilograms to material transport and storage (29, 85, 89).
After water is added to form an ore-water slurry, particulate
emissions are negligible.
Liquid Wastes—
Mine wastewater can result from several sources including
groundwater, water pumped into the mine for utility purposes
(e.g., machinery cooling), hydraulic backfill operations, and
infiltration of surface water. The water is pumped from the mine
at a rate necessary to maintain mining operations. The required
pumping rate is not related to the ore output and it varies by
season. It also varies throughout the industry. Daily volume
may range from hundreds of cubic meters to as much as 200,000
cubic meters (29). The characteristics of mine wastewater are a
function of the ore mineralization and the local and regional
geology and hydrogeology encountered. The presence of dissolved
heavy metals in mine wastewater is a function of the solubiliza-
tion potential of the water, and solubilization is controlled by
the geologic conditions that prevail. In mines where limestone
and dolomitic limestone prevail and essentially no fracturing
takes place, the water has little or no solubilization potential.
Acid waters occurring under these conditions would require the
presence of pyrite or similar sulfur-containing materials, and
they would be quickly neutralized in situ before any heavy metals
are solubilized. The extent of heavy metals in solution there-
fore, would be minimal. Conditions associated with solubiliza-
tion include (1) the presence of acid-forming minerals (e.g.,
pyrite); (2) limited presence of minerals with neutralizing
capacity (e.g., limestone); and (3) heavily fissured ore body.
Wastewaters pumped from mines possessing these conditions can
contain substantial amounts of soluble salts. Other constituents
that may be present in mine wastewaters include the following:
192
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Suspended solids resulting from the blasting, crushing, and
transporting of the ore.
Oils and greases resulting from spills and leakages from
material-handling equipment utilized underground.
Hardness and alkalinity associated with the host rock and
ore.
Natural nutrients in the subterranean water.
Dissolved salts not present in surface water.
Small quantities of unburned or partially burned explosive
substances (fuel oil, ammonia nitrate, etc.).
These constituents are almost always present in mine waste-
water regardless of the solubility potential of the mine. Tables
32 and 33 show the chemical characteristics of wastewaters from
several mines with high solubilization potential and several with
low solubility potential.
Tailings resulting from the lead/zinc flotation cells are a
major source of liquid waste. These waste materials are pumped
to the tailings pond. The raw wastewater from lead/zinc flota-
tion mills is made up of the water used in the flotation circuit
and housecleaning water. The waste streams consist of tailings
streams (usually the. underflow of the zinc rougher flotation
cell), overflow from the concentrate thickeners, and filtrate
from concentrate dewatering. The liquid waste produced by flo-
tation processes varies in volume from 1000 to 16,000 cubic
meters per day. In terms of quantity of ore processed, liquid
waste streams from milling operations range from 330 to 1110
cubic meters per megagram (29).
The principal characteristics of the liquid wastes asso-
ciated with flotation operations are as follows:
(1) Solids loadings of 25 to 50 percent (tailings).
(2) Unseparated minerals associated with the tails.
(3) Fine particles of minerals—particularly if the thick-
ener overflow is not recirculated.
(4) Excess flotation reagents that are not associated with
the mineral concentrates.
(5) Any spills of reagents that occur in the mill.
193
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TABLE 32. RANGE OF CHEMICAL CHARACTERISTICS OF RAW MINE
WATERS FROM FOUR OPERATIONS INDICATING
HIGH SOLUBILIZATION POTENTIAL
Parameter
pH
Alkalinity
Hardness
TSS
TDS
COD
TOC
Oil and Grease
P
NH3
Hg
Pb
Zn
Cu
Cd
Cr
Mn
Fe
Sulfate
Chloride
Fluoride
Concentration in raw
mine water, mg/i
3.0
14.6
178
<2
260
15.9
1
0
0.020
<0.05
0.0001
<0.0001
0.1
1.38
<0.02
0.016
0.17
<0.02
0.12
48
<0.01
0.06
to 8.0a
to 167
to 967
to 58
to 1722
to 95.3
to 11
to 3
to 0.075
to 4.0
to 0.0013
to 0.0001
to 0.3
to 38.0
to 0.04
to 0.055
to 0.42
to 57.2
to 2.5
to 775
to 220
to 0.80
Value in pH units.
Source: Ref. 64.
194
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TABLE 33. RANGE OF CHEMICAL CHARACTERISTICS OF
SAMPLED RAW MINE WATER FROM THREE LEAD/ZINC
MINES SHOWING LOW SOLUBILIZATION
Parameter
pH
Alkalinity
Hardness
TSS
TDS
COD
TOC
Oil and Grease
P
NH3
Hg
Pb
Zn
Cu
Cd
Cr
Mn
Fe
Sulfate
Chloride
Fluoride
Concentration,
mg/1 /
7.4 to 8.ia
180 to 196
200 to 330
2 to 138
326 to 510
<10 to 631
<1 to 4
3 to 29
0.03 to 0.15
<0.05 to 1.0
<0.0001 to 0.0001
<0.2 to 4.9b
0.03 to 0.69
<0.02
<0.002 to 0.015
<0.02
<0.02 to 0.06
<0.02 to 0.90
37 to 63
3 to 57
0.03 to 1.2
Value in pH units.
Data may reflect influence of acid stabilization on sediment,
Source: Ref. 64.
195
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Table 34 shows the characteristics of the raw and treated
waste loads of five flotation mills. This summary does not
include information on a mill with total recycling or one where
mill wastes are mixed with metal refining wastes in the tailings
pond. Feed water for the mills is usually drawn from available
mine waters; however, one mill uses water from a nearby lake.
These data illustrate the wide variations caused by differences
in ore mineralogy, grinding practices, and reagents.
Solid Wastes—
The major sources of solid waste generated by the lead-zinc
mining industry are waste rock and tailings. Minor sources are
tramp iron and wood scraps. Of the more than 14 x 10 megagrams
of solid waste generated by the lead-zinc industry in 1974, 1.86
x 10 megagrams was waste rock and 12.43 x 10 megagrams concen-
trator tailings (77).
In 1974 the estimated average ratio of waste rock to ore
mined was 0.10 megagram per megagram (77). Depending on the age
of the mine, this ratio varied from 0 to 0.24 megagram per mega-
gram. Little waste rock is brought to the surface in older mines
because the rock is used underground for mine road construction,
but the waste rock is of no use in newer mines and must be hauled
to the surface. In 1974 the national average ratio of dry con-
centrator waste to ore mined in the lead-zinc industry was 0.69
megagram per megagram. This ratio varied from 0.26 to 0.94
megagram per megagram as a function of ore grade and percent of
lead, zinc, and other metals present in the ore (77). The dif-
ferences in recovery methods and disposal of by-product materials
had little impact.
Control Technology
Control technologies for air emissions, liquid waste, and
solid waste are covered in the following paragraphs.
Air Emissions Control—
Atmospheric emissions are not a major problem because almost
all lead and zinc ores are mined underground. Drilling crushing,
grinding, screening, and dried portions of tailings ponds,
however, are all sources of fugitive particulates. The amounts
of particulates resulting from processing operations are not
significant because moisture content of lead-zinc ores is fairly
high. When control is needed, manual water sprays are used to
minimize fugitive particulates resulting from ore processing.
The dried portions of tailings ponds are probably the great-
est source of fugitive dust. Wind contributes significantly to
the fugitive dust problem by eroding the exposed surfaces;
therefore reduction of surface wind speed across the source is a
196
-------
TABLE 34. RANGES OF CONSTITUENTS OF WASTEWATERS AND
RAW WASTE LOADS FROM FIVE SELECTED MILLS
to
Parameter
PH3
Alkalinity
Hardness
TSS
TDS
COD
TOC
Oil and grease
MBAS surfactants
P
Ammonia
Hg
Pb
Zn
Cu
Cd
Cr
Mn
Fe
Cyanide
Sulfate
Chloride
Fluoride
Range of
concentration in
wastewater, mg/4
lower limit
7.9
26
310
<2
670
71.4
11
0
0.18
0.042
<0.05
<0.0001
<0.1
0.12
<0.02
0.005
<0.02
<0.02
0.05
<0.01
295
21
0.13
upper limit
8.8
609
1760
108
2834
1535
35
8
3.7
0.150
14
0.1
1.9
0.46
0.36
0.011
0.67
0.08
0.53
0.03
1825
395
0.26
Range of raw waste load
Per unit ore milled,
kg/1000 Mg
lower limit
410
460
7
940
6
6.35
5
0.236
0.108
0.064
<0. 00013
<0.127
0.089
<0.026
0.008
<0.026
<0.026
0.064
<0.013
130
20
0.370
upper limit
1600
4700
285
8500
4800
130
21
13
0.876
26.4
0.0026
6.9
17.2
0.158
0.018
1.77
0.290
1.16
0.109
4800
870
0.944
Per unit
concentrate produced,
kg/1000 Mg
lower limit
1450
2290
30
4800
30
30
30
2.05
0.54
0.32
<0. 00168
<0.900
0.62
<0.18
<0.18
<0.18
<0.45
. 0.012
0.091
1260
210
230
upper limit
10,200
32,500
2000
50,900
50,000
580
130
60.7
2.54
185
0.130
32.2
86.0
1.96
8.85
1.36
10.0
0.198
0.509
33,700
4070
5.45
a Value in pH units.
Source: Ref. 6-9.
-------
logical means of reducing emissions. This can be achieved by
wind breaks, surface coverings, and planting of tall grasses or
grains on or adjacent to exposed surfaces. The vegetative tech-
nique is practiced most frequently, but this requires soil that
supports growth (contains nutrients and moisture and is of proper
texture and free of phytotoxicants). This type of soil is not
always present, and natural protection against wind erosion is
often insufficient.
Liquid Waste Control—
Mine pumpout water is reused in mining:and processing opera-
tions whenever possible. In the more arid regions some mines
produce no discharge because the water evaporates or percolates
into the ground.
At many facilities mine water is used as mill process makeup
water. The mine water may pass through the process first, or it
may be piped to the tailing pond for use in mill flotation with
recycled process water.
Acid mine water that occurs in the lead-zinc industry usu-
ally is neutralized by the addition of lime and limestone. Acid
mine water containing dissolved metals may be treated effectively
by combining mine water with mill tails in the tailings pond.
The wastewater may be treated further by lime clarification and
aeration. Lime precipitation often is used to facilitate the
removal of heavy metals from wastewater by precipitation as
hydroxides. This technology yields almost 100 percent reduction
of several heavy metals (29).
Process water from froth flotation is normally directed to a
large lagoon or pond to settle ,out suspended solids. Effluent
from the pond is recycled to the flotation cell or to the other
operations as makeup water.
Solid Waste Control—
Solid waste treatment practices in the lead-zinc industry
are similar to those of the underground copper mining industry
(76). Mine waste rock typically is disposed of in waste rock
piles, used for construction of tailings dams and mine roads,
disposed of in tailings ponds, or crushed and used as mine back-
fill. Tails from the concentration process are settled out in
tailings ponds. When the ponds become filled with solids, they
are either abandoned or the tailings are dredged or mechanically
moved to form an embankment and the pond raised via a peripheral
discharge of the solids.
Aside from selection of a suitable disposal site and stabil-
ity control, little reclamation of solid wastes is practiced by
the lead-zinc industry. Only a few companies control blowing
198
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dust or attempt to reclaim or naturalize the dump areas. When
stabilization or revegetation practices are attempted, a variety
of problems can develop, particularly if excessive salinity,
acidity, and/or phytotoxicants are encountered. (These problems
are discussed in more detail in this document in the solid waste
control section for copper.)
Conclusions and Recommendations
Fugitive dust generated from waste rock disposal areas and
dried tailings areas can be a major pollution problem at some
lead-zinc mining operations. Because the effectiveness of the
dust control provided by watering is so temporary, the use of
chemical stabilizers to control dust has proven to be more cost-
effective. Currently, more than 100 proprietary chemical stabil-
izers are available and all are reputed to control dust effec-
tively. A comparative study of these stabilizers would be valu-
able.
Vegetative stabilization of tailings areas has been attempt-
ed at some facilities, but the presence of extreme acidity,
salinity and/or pytotoxicants in the soil has rendered most of
these attempts unsuccessful. Further research is needed in the
area of soil amelioration to promote successful vegetative stabi-
lization. '
Disposal of concentrator tailings is a major area of concern
in the mining and processing of lead-zinc ores. Concentrating
operations generate large volumes of tailings, and scarcity of
land often makes disposal of these tailings a problem. The
tailings present the additional problem of often containing
potentially hazardous materials such as heavy metals. Tailings
usually are disposed of in tailings ponds, but most of these
ponds are not lined and heavy metals may leach into and contam-
inate the groundwater. For this reason, therefore, techniques
for the removal of heavy metals should be evaluated and/or seal-
ing of ponds should be investigated. (Sealing existing ponds
constitutes a major technological hurdle.)
Another area for possible research is the development of
mechanical screening and filtering equipment to separate tailings
from concentrator water. Tailings are removed from flotation
water by allowing them to settle in a pond. This solid waste
could be controlled more effectively if an economically feasible
mechanical device were developed to continuously separate tails
from the water.
The development of a reagent to replace sodium cyanide as a
flotation depressant would contribute to pollution control.
Cyanide can escape from tailings ponds via seepage and/or perco-
lation and can seriously degrade any surface of groundwaters it
might reach.
199
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MAGNESIUM
Industry Description
Magnesium is the eighth most plentiful element in the earth
and, in its many forms, makes up about 2.06 percent of the
earth's crust (16). Although it is found in 60 or more minerals,
only 4—dolomite [Ca,Mg(C03)], magnesite (MgC03), brucite
[Mg(OH)2] and olivine (Mg,Fe)2(Si04) are used commercially to
produce its compounds. Seawater and brines are also principal
sources of magnesium, which is the third most abundant element
dissolved in seawater (16).
In 1974, eight companies produced magnesium compounds from
seawater in California, Delaware, Florida, Mississippi, New
Jersey, and Texas; four companies from well brines in Michigan;
and two companies from brines of the Great Salt Lake in Utah.
One mine, located in Gabbs, Nevada, produces the only domestic
magnesite. Mines in North Carolina and Washington produce
olivine (16). Production statistics for magnesium appear in
Section 1 of this report.
The principal uses of magnesium compounds are outlined in
Table 35.
TABLE 35. USES FOR MAGNESIUM COMPOUNDS
Compound and grade
Uses
Magnesium oxide:
Refractory grades
Caustic - calcined
United States Pharmocopia
and technical grades
Precipitated magnesium
carbonate
Magnesium hydroxide
Magnesium chloride
Basic refractories
Cement, rayon, fertilizers
insulation, magnesium metal,
rubber, fluxes, refractories,
chemical process and manufac-
turing, uranium processing,
paper processing.
Rayon, rubber, (filler and
catalyst), refractories,
medicines, uranium processing,
fertilizer, electrical
insulation, neoprene compounds
and other chemicals, cement.
Insulation, rubber, pigments
and paint, glass, ink, ceramics,
chemicals, fertilizers.
Sugar refining, magnesium oxide,
Pharmaceuticals.
Magnesium metal, cement, ceramics,
textiles, paper, chemicals
200
-------
Potassium compounds, salt, and gypsum are extracted with
magnesium as coproducts from sediments of seawater evaporite
deposits. Sodium, lithium, iodine, and strontium compounds are
obtained from sediments and near-surface brines formed by inland
bodies of water. Bromine, iodine, calcium, and magnesium com-
pounds are generally extracted from seawater and well and lake
brines (16).
Process Description
In the United States, magnesium compounds are produced from
seawater, well brines, and lake brines, and by open-pit mining
magnesium-containing ores such as magnesite, dolomite, and
brucite. Figure 27 depicts a process flow sheet for the recovery
and beneficiation of magnesium.
In recovering magnesium from seawater, the seawater is
pumped through a series of screens (which remove floating
debris), chlorinated (to prevent growth of marine organisms) and
then pumped to a flocculator tank for pretreatment (90).
In the flocculator tank, the seawater is treated with an
excess of dilute caustic-lime solution. (The lime used in this
process is produced from oyster shells.)
The next process step involves precipitating the magnesium
hydroxide by agitation in a flocculator tank. Agitation is
promoted by the addition of lime, dolomite, or caustic soda.
Four sources of brines or liquors are used in this process:
0 Pretreated seawater
0 Bitterns from solar evaporation
0 Neutralized well brines
0 Untreated well brines
The insoluble magnesium hydroxide gradually settles to the
bottom of the tank and is pumped to rows of filters, which
dewater it so that it forms a cake of magnesium hydroxide.
Magnesium hydroxide is used either to recover magnesium metal or
to produce magnesium compounds.
In the solar evaporation process, seawater is pumped into
ponds, which may cover an area of hundreds of hectares to a depth
of 1 meter. As the seawater evaporates, moist crystals of crude
sodium chloride and a magnesium-rich mother liquor (bitterns) are
left behind. The mother liquor is sent to the flocculator tank,
where magnesium hydroxide is precipitated.
Well brines contain a mixture of magnesium, calcium and
sodium chlorides, and bromides; the actual magnesium content
201
-------
HlU« CAU
MAH«-
CinAuSI
IAU MlWi
iOi«»
{•AfOKAIIOd
HAPUKAIiUti/
CHISIAlLlMTIOn
10
o
to
WC COMIklMK
-------
averages about 0.8 percent (91). Magnesium hydroxide is re-
covered from these brines by acidifying the brine with hydro-
chloric acid. Enough chlorine also may be added to oxidize a
portion of the bromide to elemental bromine. The partially
chlorinated acidified brine is sent to a packed tower, through
which a counter-current flow of steam is passed. Gaseous chlorine
is injected into the tower at several points.
The bromine-stripped brine that flows from the bottom of the
tower then is neutralized by adding lime or caustic soda. The
solution is cooled in a heat exchanger before it is processed for
recovery of magnesium hydroxide.
Brines of Michigan contain mixed crystals of sodium chloride
(NaCl) and several double salts, including astrakanite
(MgSO. Na,SO.-4H,0), leonite (MgSO. -K^SO.^H-O), kainite
(KCl-HgSCn-3H2Or and possibly carnallitti *(KCIL-MgCl2-6H2O).
Magnesium is ^recovered from these brines by evaporating them in
solar ponds (92). The magnesium chloride bittern obtained from
solar evaporation then is sent to an evaporation/crystallization
process. The magnesium chloride bittern may pass through several
evaporation/crystallization process steps. Vacuum crystallizers
are probably utilized, although the specific crystallization
paths have not been disclosed. The product from this process is
a mother liquor rich in magnesium chloride.
A small percentage of the U.S. production of magnesium is
obtained from magnesite, dolomite, or brucite. Ore is recovered
by open-pit methods. Benches 3 meters high are advanced and
blasted with ammonium nitrate primed with dynamite (16).
Ore is delivered from the mines to gyratory or jaw crushers,
which reduce it to minus 12.7 centimeters in size, and then is
belt-conveyed to cone crushers, which further reduce it to 1.6 to
minus 1 centimeter. It is then screened and washed, passed
through rake classifiers to remove slimes and ground in ball
mills to 98 percent minus 100 mesh (16). From the ball mills,
the ore is conveyed to flotation cells for removal of lake and
serpentine impurities. The cleaned concentrate is dried in a
rotary dryer.
Waste Streams
Table 36 presents a summary of multimedia wastes from the
mining and beneficiating of magnesium. The following paragraphs
explain in more detail the various air, liquid, and solid waste
materials associated with this industry.
Air Emissions—
During chlorination of seawater, a sufficient quantity of
chlorine is released to the atmosphere to be detected in the
immediate vicinity by its odor (92).
203
-------
TABLE 36. SUMMARY OF MULTIMEDIA WASTES FROM MINING AND
BENEFICIATING OF MAGNESIUM
Air
Source
Screening/
chlorina-
te ion
Acidifica-
tion/
chlorina-
tion/strip-
ping
Overburden •>
removal
Ore
extraction
Ore
loading
Ore ->
transport
Crushers/
classifiers/
ball mills
Dryer
Pollutant
Chlorine
Chlorine
and
bromine
Particu-
lates
Particu-
lates
Particu-
lates
emission rate
N.A.
N.A.
N.A.
N.A.
N.A.
Liquid
Source
Pretreat-
ment
Settling/
filtration
Evaporation/
crystalliza-
tion
Overburden
removal
Ore extrac-
tion
Flotation
cell
Pollutant/
parameter
SS
Nad
Nad
N.A.
N.A.
N.A.
Uncontrolled
discharge
150,000 mg/l
N.A.
200-300 kg/Mg
MgCl2
n.A.
N.A.
N.A.
Solid
Source
Screening
Overburden)
removal /
(
(
Ore \
extraction)
^ /
•
Pollutant
Debris and
trash
Gangue
•
Uncontrolled
quantity
N.A.
N.A.
10
o
N.A. - Not available.
-------
Similarly, during the chlorination/stripping process for
recovery of magnesium from well brines, a gas stream containing
non-condensible gases is vented to the atmosphere. This stream
contains some chlorine and bromine (92).
Open-pit mining operations are a source of fugitive partic-
ulates. Other sources of participate emissions include the
crushers, ball mills, and dryers. Quantitative data on emissions
from these sources have not been reported.
Liquid Wastes—
The sole waste stream from the pretreatment process is a
slurry of calcium carbonate and clay particles suspended in
seawater, which typically carries 150 grams total suspended
solids per liter (92).
Two waste streams emanate from the settling/filtration
process — the supernatant spent brine from the settling tanks
and the filtrate. These streams, identical in composition,
together amount to 300 to 350 cubic meters per megagram of mag-
nesium hydroxide (92).
A slurry of NaCl is discharged as waste stream from the
evaporation/crystallization process for the recovery of magnesium
chloride from lake brines. The quantity of waste is reported to
range from 0.2 to 0.3 megagram per megagram of magnesium chloride
(92).
The only liquid waste sources from the mining of magnesite
are mine pumpout and tailings from the flotation cell.
Solid Wastes—
Floating debris and trash are collected by the screens as
the seawater passes through them. The only source of solid
wastes in the recovery of magnesite is the overburden removed
from the mine; the quantity is not known.
Control Technology
Control technologies applied to the magnesium industry are
explained in the following paragraphs.
Air Emissions Control—
Chlorine released from the chlorination process is dis-
charged to the atmosphere without control, as is the npncon-
densible gas stream from the chlorination/stripping operation.
205
-------
Fugitive dust emissions from the mining operation at the
sole open-pit mine (in Gabbs, Nevada) are not controlled.*
Neither are the emissions controlled from crushers and ball mills
at this mine. Particulate emissions from the dryer, however, are
controlled by a baghouse.
Liquid Waste Control—
Depending upon conditions, the waste stream from the pre-
treatment process may be (1) diluted with seawater and discharged
into the tidal system, (2) neutralized with dilute HC1 and then
discharged into tidewater, or (3) discharged into diked ponds for
further thickening, which qualifies the disposal as landfill
operation (92).
Effluent from the settling/filtration operation is usually
neutralized with waste hydrochloric acid prior to discharge. If
the effluent is from seawater, the waste stream is discharged
into tidewater. If it is from Michigan well brines, the stream
of spent brine either is used beneficially to recover sodium and
calcium chlorides or is sent to injection wells (92).
The sodium chloride slurry from evaporation/crystallization
is discharged to the Great Salt Lake (92).
Mine pumpout at the open-pit mine in Nevada is sent to a
tailings pond. Tailings from the flotation cell at this mining
operation is also sent to the tailings pond for treatment.
Solid Waste Control-^
Trash recovered from screening seawater is incinerated or
buried.
Overburden and waste rock from the open-pit mine are col-
lected and dumped on site.*
Conclusions and Recommendations
The magnesium mining and beneficiation industry causes fewer
environmental impacts than most other mining and processing
industries.
The following research and development programs could be
undertaken: (1) Unknown contaminants in the feed streams to
magnesia processing could be creating significant public health
impacts. Research efforts could characterize these feed streams
*Telephone conversation between Vijay Patel of PEDCo and
Mr. H. Ricci, Bureau of Environmental Health, State of
Nevada. Carson City, Nevada. April 1977.
206
-------
by assays of seawater and brines and analysis of ore concen-
trates. (2) Sufficient potentially hazardous chlorine is emitted
to the atmosphere from the chlorination process for the smell to
be detected in the immediate vicinity. Research efforts could be
focused on reducing or controlling the amount of chlorine emitted
to the atmosphere.
MERCURY
Industry Description
Although mercury is recovered almost exclusively from
cinnabar (Hgs), it also has been obtained from livingstonite,
metacinnabarite, and other mercury minerals. Pyrite, marcasite,
and small quantities of other sulfides such as arsenic and anti-
mony often are associated with cinnabar. A small amount of
mercury is recovered also as a coproduct of gold refining (17).
At the present time the primary mercury industry in the
United States is very small (93). Because of low prices and
slackened demand, this industry has been declining steadily in
recent years. During this same period the environmental hazards
and extremely toxic nature of mercury have come under public
scrutiny. (Production statistics for mercury are presented in
Section 1 of.this report.)
In 1974, only 12 mines were engaged in the mining of mercury
ore (17). California has historically been the leading producer,
followed by Nevada and Texas. Mercury has also been recovered
from ore in Arizona, Alaska, Idaho, Oregon, and Washington and is
recovered as a by-product from gold ore in Nevada and zinc ore in
New York (46).
Mercury is used primarily in the manufacture of alkalis and
chlorine and in electrical applications. Mercury and its com-
pounds are used also as preservatives in the paint industry; in
Pharmaceuticals, dental supplies, and instrumentation; and for
general laboratory purposes.
Process Description
Mercury ore is mined by both open-pit and underground
methods. In recent years underground methods have accounted for
about two-thirds of total mercury production (94). Ore grade has
varied greatly, ranging from 2.25 to 100 kilograms of mercury per
megagram of ore (46). The grade of ore currently mined averages
5 kilograms per megagram.*
*Telephone conversation between Vijay Patel of PEDCo and
Mr. Harold Drake, U.S. Bureau of Mines, Washington, D.C.
March 1977.
207
-------
As illustrated in Figure 28, the usual process of extracting
mercury from cinnabar essentially involves mining and sorting of
the ore, crushing, screening, and concentration.
Open-pit surface mining is accomplished by the normal drill-
ing, blasting, digging, and loading operations. Underground
mining is accomplished primarily by square-set stoping, but
shrinkage and sublevel stoping methods are also used. Ore is
broken by blasting, removed by scraper or mechanical loaders, and
hauled to the mill for processing (76). At the mill, the ore
first is crushed in a jaw crusher, then delivered by belt con-
veyor to the fine ore bin. The crushed ore is ground in a ball
or rod mill in closed circuit with a classifier to free cinnabar
from the gangue minerals.
The classified ore is sent to a flotation machine, where the
frothing action of the rising air bubbles causes the mineral
values to be freed from the gangue and rise to the surface of the
flotation cell. The mineral concentrate is scraped off the
surface and filtered through a disk filter. The dewatered con-
centrate is stored until needed for the retort plant.
Waste Streams
Table 37 presents a summary of multimedia wastes from mining
and beneficiating mercury. The following paragraphs explain in
more detail the various air, water, and solid wastes generated by
mining and beneficiating activities.
Air Emissions—
The major emissions from open-pit mines are fugitive dust
and mercury vapor. From open deposits of cinnabar ore, emissions
of mercury vapor through natural heat have been reported to be
0.005 kilogram per megagram of ore (76). Explosive gases are
encountered in some underground mines (75).
Estimates of dust emissions from crushing, grinding, and
classifying have not been reported.
Liquid Wastes—
Precipitation, runoff, and groundwater infiltration causes
wastewater discharge from open-pit mining. Most open-pit mercury
mines are in arid regions, however, so very little liquid waste
is discharged. Groundwater infiltration is the primary source of
water in underground mines. No specific information is available
concerning discharge from underground mines. It is expected,
however, that the particular metals present in underground mine
discharge and the extent of their dissolution depend on the
geology and mineralogy of the ore body and on the oxidation
potential and pH prevailing within the mine.
208
-------
tvj
O
O
OVtHBURUtN
REMOVAL
EXTRACTION
OP ORE
I
O
V
EXTRACTION
OF. ORE
r '
LOAD I NC
OP ORE
UNDERGROUND MINING
Figure 28 . Mining and beneficiating of mercury ores.
MERCURY
CONCENTRATE
9 *l" MISSIONS
^ LIQUID HASTES
J3 SOI 10 HASTES
-------
TABLE 37.
SUMMARY OF MULTIMEDIA WASTES FROM MINING AND
BENEFICIATING OF MERCURY
Air
Source
Overburden^
removal
Extraction
of ore
>
Loading of
ore
Transport
of ore
Underground
Dining
Crushing/
grinding/
classify-
ing
Pollutant
Fugitive
particulates
and mercury
vapor
Fugitive
particulates
Particulates
Uncontrolled
emission rate
Not available
for particu-
lates; 0.005
kg/Mg of ore
for mercury
vapora
N.A.
N.A.
Liquid
Source
Overburden)
remova 1 /
>
Extraction
of ore J
Under-
ground
mining
Flotation
concentra-
tion
Pollutant/
parameter
N.A.
N.A.
N.A.
Uncontrol led
discharge
N.A.
N.A.
N.A.
Solid
Source
Overburden ~)
removal /
>
Extraction \
of ore j
Underground
mining
Pollutant
Gangue
Gangue
Uncontrolled
quantity
N.A.
N.A.
" R«f. 76.
N.A. - Mot available.
-------
Wastewater emanating from mills employing froth flotation is
likely to be high in suspended solids loadings. Some of the
flotation reagents may also be washed out with the tailings.
Although -the total dissolved solids loading may not be extremely
high, a relatively high dissolved heavy-metal concentration may
result from the highly mineralized ore being processed. Also,
depending upon the process conditions, the waste stream may have
a high or low pH, which is of concern because of its effect on
the solubility of the waste constituents (29).
Solid Wastes—
The quantity of overburden and gangue removed from open-pit
and underground mines has not been reported. The predominant
minerals in the waste rock are silica and carbonate minerals, and
some deposits contain pyrite. Mercasite, stibnite, and orpiment
also occur, but rarely (76).
Control Technology
The following paragraphs contain explanations of the control
techniques as applied to air, liquid and solid waste.
Air Emissions Control—
Dust from open-pit and underground mines is controlled by
conventional techniques such as applying wet drilling methods and
treating haul roads with water. Mercury vapor emissions are not
controlled and may create a potential health hazard.
Control of emissions from crushing operations is achieved by
enclosing the crusher and venting emissions to a control device
such as a baghouse.* The efficiency of the baghouse has not been
reported.
Liquid Waste Control—
Since most open-pit mines are located in arid regions of the
country (Nevada and California), no discharge of liquid wastes
has been reported from these mines (29). At present no large-
scale underground mercury mines are operating in the United
States, so no data were available on effluents from this source.
One mill (which recently began operation) proposed to use a
recycle system in which the effluent from the flotation cell
first would be discharged into a tailings pond, then into a
clarification pond. The clarified effluent would be recycled to
the flotation cell, and no discharge was expected to result (29).
*Telephone conversation between Vijay Patel of PEDCo and
Mr. Harold Drake, U.S. Bureau of Mines, Washington, D.C.
March 1977.
211
-------
Solid Waste Control—
Currently, all solid wastes from open-pit mines are either
ploughed back into the mine site or are used for tailings pond
dam construction. The method of disposing of solid wastes from
underground mines is not known.*
Conclusions and Recommendations
The mercury industry in the United States is comparatively
'small in terms of production. Remote locations and arid climates
tend to minimize the environmental impacts of mercury mines.
The most significant environmental problem is the control of
hazardous mercury vapor from open deposits.
Most wastewater from mining and processing of the ore is
recycled; however, the potential is great for release of mercury
to the environment through impoundments. For this reason effi-
cient methods for the removal of mercury from water should be
developed.
RARE EARTH ELEMENTS
Industry Description
Rare earth elements, sometimes known as lanthanides, consist
of a series of 15 chemically similar elements with atomic numbers
57 through 71. Yttrium, atomic number 39, is also often included
in the group because of its similar properties and frequent
occurrence in association with lanthanides. The principal
mineral sources of the rare earth metals are bastnaesite (CeFCO-)
and monazite (Ce, La, Th, Y) P04 (29).
In 1974 only three U.S. companies mined rare earth oxides,
one each in California, Georgia, and Florida. The California
company mined more than 95 percent of the total output, whereas
the other two recovered monazite as a by-product while mining
pleistocene beach sands for titanium and zirconium minerals (18).
Table 38 lists many of the uses of the rare earths. Very
few of these consume significant quantities of rare earth.
*Telephone conversation between Vijay Patel of PEDCo and
Mr. Harold, U.S. Bureau of Mines, Washington, D.C.
March 1977.
212
-------
TABLE 38. USES OF RARE EARTH ELEMENTS
Metallurgy
Glass
Ceramics
Illumination
Electronic
Nuclear
Chemical
Other
As alloying agents in iron and steel, super-
alloys, and pyrophoric alloys; lighter
flints; pure metals for research.
In polishing, decolorizing, coloring; as
filters; in optical and photochromic glass
(camera lenses).
As colorants for enamels and glazes; in
coatings, refractories, and stabilizers.
In carbon arcs; lasers; fluorescent and
mercury vapor lamps; phosphors (X-ray in-
tensifiers, display, and color television).
In capacitors, cathodes, electrodes, semi-
conductors, thermistors, magnets, computer
components (garnets and ferrites) and
memories.
In control rods; as burnable poisons; as
dilutants; in shielding, radioactive heat and
power sources, detectors, and counters.
As catalysts; in pharmaceutical; water treat-
ment, chemical processing and analysis; as
shift reagents and tags in organic and bio-
logical chemistry.
In jewelry, photography, lubrication, ther-
mometers, paint and ink dryers, textiles.
Virtually all of the monazite from beach sands and river
gravel now is a by-product of mining ilmenite, rutile, tin, and
zircon. Other minerals often found in association with monazite
include xenotime, gold, staurolite, sillimanite, tourmaline,
garnet, kyanite, andalusite, spinel, and corundum (18).
Process Description
The California Mountain Pass Mine recovers the rare earth
mineral, bastnaesite, as a primary product. The ore, which is
recovered by open-pit mining, contains 7 to 10 percent rare earth
oxides. These oxides are upgraded during beneficiation to a
mineral concentrate containing more than 60 percent mineral.
Monazite in Georgia and Florida, on the other hand, is recovered
213
-------
predominantly as a by-product during the dredge-mining of sand
placers for their titanium mineral content. (For details on the
dredging of sand placers for their titanium mineral content refer
to Section 5.)
Very little overburden removal now takes place at -the
Mountain Pass Mine, but future stripping ratios may approach
5:1.* Ore is extracted by blasting, then loaded into trucks (by
power shovels) and hauled to the mill. At the mill the ore is
crushed, ground, and classified. Ore is concentrated at the mill
at a rate of 2721 megagrams per day (46). (See Figure 29.)
The crushing, grinding, and classifier operations consist of
a primary jaw crusher in series with a cone crusher, from which a
1.6 centimeter feed passes to a rod mill. The rod mill produces
a minus-0.3-centimeter material, which is then fed to a classi-
fier in closed circuit with a conical ball mill. The classifier
overflow is sent to a series of three heating agitators, which
heat the pulp by stages to 95°C, then to a fourth agitator, which
cools the slurry to 60°C before pumping it to rougher flotation.
Heating is necessary to condition the bastnasite for flotation
(46).
Flotation is initiated in four Fagergren and eight Agitair
rougher machines, which produce a tailing for discard. Barite is
depressed during flotation, and the froth is cleaned in five
stages of flotation cells. Froth from each cell advances to the
next stage, and tailings are recycled countercurrently to the
preceding cell. Concentrate from the final flotation cell con-
tains 63 percent rare earth oxides.
Leaching the concentrate with 10 percent hydrochloric acid
removes calcium and strontium carbonates and raises the grade of
the rare earth oxide to 72 percent (76). The concentrate is then
sent to a chemical refining facility for further concentration.
Waste Streams
Table 39 presents a summary of multimedia wastes from the
mining and beneficiation of rare earth minerals. The following
paragraphs explain in more detail the various air, liquid, and
solid wastes associated with this industry.
Air Emissions—
Fugitive dust is the primary particulate emission from
open-pit mining. Dust particles are also generated by the crush-
*Telephone conversation between Vijay Patel of PEDCo and
Mr. J. H. Jolly, Bureau of Mines, Washington, D.C.
March 1977.
214
-------
9O
OVERBURDEN
REMOVAL
o
ORE
EXTRACTION
•p
C)
NJ
M
Ul
9 AIR EMISSIONS
{\ LIQUID WASTES
1 SOI ID HASTES
ORE
LOADING
o
WATER
ORE
TRANSPORT
ORE CONCENTRATE
Figure 29 . Mining and beneficiating of rare earth elements,
-------
to
r-1
a\
TABLE 39. SUMMARY OF MULTIMEDIA WASTES FROM MINING AND
BENEFICIATING OF RARE-EARTH ORES
Air
Source
Overburden
removal
Ore
extraction
Ore loading
Ore
transport
Crushing/
g r i nd l nq/
classify-
Pollutant
Fugitive
particu-
lates
Particu-
lates
Uncontrol led
emission rate
N.A.
N.A.
Liquid
Source
Crushing/
grinding/
classifying
Flotation
concentra-
tion
Leaching
Pollutant/
parameter
N.A.
a
CaCOj
SrCOj
BaS04
Uncontrolled
discharge
N.A.
a
N.A.
N.A.
N.A.
54,000 mg/l
Solid
Source
Overburden
removal
Ore
extraction
Pollutant
Surface soil
and rock
Waste rock
Uncontrolled
quantity
N.A.
S«* Table 40.
N.A. - Hot available.
-------
ing operation. Quantities of particulate emissions from these
sources have not been reported.
Liquid Wastes—
No liquid wastes are discharged from the Mountain Pass
open-pit mining operation (76), and the only waste stream from
the grinding-classifying process results from spills. Raw wastes
are, however, discharged at a rate of 1.96 cubic meters per
minute from the flotation circuit. Table 40 shows the charac-
teristics of this waste stream.
TABLE 40. CHEMICAL COMPOSITION OF RAW
WASTEWATER FROM A FLOTATION MILL
Parameter
PH
TDS
TSS
TOC
Cr
Total Mn
V
Fluoride
Concentration (mg/£)
9.02a
14,476
360,000
3,100
0.35
0.5
<0.3
365
Value in pH units.
Source: Ref. 29.
The leaching process produces a waste stream that contains
dissolved calcite (CaC03), strontianite (SrCO-), and barite
(BaSO.) from the concentrates. Chlorides in solution are ex-
tremely high, 54,000 milligrams per liter. Leach waters are
impounded with wastewater from the flotation process (76).
Solid Wastes—
The only solid waste generated by the open-pit mining opera-
tion is waste rock. The quantity has not been reported.
As discussed previously in the liquid waste section, leach-
ing processes generate solid waste in the form of suspended
solids in a liquid (slurry).
217
-------
Control Technology
Control technology applied to the mining and beneficiation
of rare earth minerals is explained in the following paragraphs.
Air Emissions Control—
Water spraying is used to control dust from the open-pit
mining operation and also the crushing operation (75).
Liquid Waste Control—
Tailings from the flotation concentration process are dis-
charged to a tailings pond, and the clarified pond water is
recycled back into the flotation circuit. The treated recycle
water from the pond achieves the following removal efficiencies
(29): 96 percent total suspended solids, 35 percent total dis-
solved solids, 55 percent total organic carbon, 92 percent
chromium, and 85 percent fluoride.
Process wastes from the leach circuit are separately dis-
charged to an evaporation pond (29).
Solid Waste Control—
The amount of overburden at the Mountain Pass Mine is in-
significant. The comparatively small quantities of waste rock
are disposed of on the mine site.*
Conclusions and Recommendations
The rare earth mineral mining industry is not considered a
source of adverse environmental impacts.
One possible area of research involves the recycling or
disposal of the large quantities of overburden waste that rare
earth mining is expected to produce as the industry expands in
the future.
SILVER
Industry Description
The chief silver minerals of economic importance are native
silver (Ag), argentine (Ag^S), cerargyrite (AgC£), polybasite
(Ag^Sb-S^ ), prousite CAg_AsS_), pyrargyrite (Ag-SbS..),
stepRan!t^-L(Ag bS4), and tetrahidrite (Cu3 (Sb,Ag)S3). Silver°is
most commonly associated with lead and copper, but it is also
recovered as a by-product from some gold or zinc ores (19).
*Telephone conversation between Vijay Patel of PEDCo and
Mr. J. H. Jolly, Bureau of Mines, Washington, D.C.
March 1977.
218
-------
The supply-demand relationship of silver is more complicated
than that of other metals because of such factors as the use of
silver for monetary purposes and the sizable speculative and
investment market. Virtually all of the ore mined in the United
States is refined here, but only about half of the U.S. silver
refinery production comes from domestic ores. Secondary -re-
fining, changes in industry stocks, and treasury releases provide
a major portion of the silver supply (19).
In the United States, new silver is produced almost entirely
from low-grade, complex sulfide ores. About 25 percent is pro-
duced from ores in which silver is the chief value and lead,
zinc, and/or copper are by-products. The other 75 percent is
produced from ores in which lead, zinc, and copper are the
principal values and silver is a by-product (29).
The United States has about 25 percent of the estimated
704,000 megagrams of silver reserves in the world. These re-
serves are believed to be in the same ratio as current
production—25 percent in ores where silver is the main product,
75 percent in ores where silver is a by-product (19).
Almost 99 percent of the ores mined principally for silver
come from the Coeur d' Alene district in Idaho, and about 20
percent of the silver mined as a by-product also comes from this
area. This output makes the Coeur d'Alene district the source of
almost 40 percent of all silver produced in the United States.
Other silver by-product mines are located in Arizona, Nevada,
Montana, and Utah (95). Minor quantities of silver are also
mined in Alaska, California, Colorado, Michigan, Missouri, New
Mexico, and South Dakota (29).
Silver is used primarily in photography, silverware, and
electrical and electronic equipment. It is also used in jewelry,
arts and crafts, solders, brazing alloys, medicinal compounds,
and catalysts (95).
Silver mining yields many coproducts and by-products. For
example, most of the antimony produced in the United States is
mined as a by-product of silver. Other nonferrous metal Co-
products or by-products of silver include bismuth, copper, gold,
lead, platinum group metals, and zinc. Section 2 presents pro-
duction statistics for silver and associated metals.
Process Description
Silver is mined by open-pit methods and subsurface shafts
and drifts. The method varies from one ore body to another and
depends on such factors as steepness of the terrain, availability
of transportation, reserves, ore body or vein shape, depth of
219
-------
deposit, character of the host rock, and economic factors pecu-
liar to the individual mine. In the United States most silver is
mined underground. Figure 30 shows a composite flow diagram of
the mining and beneficiating of silver ores.
Only a small percentage of U.S. silver is mined from placer
deposits. These deposits are mined by excavating silver-bearing
gravel and sand, then washing and screening it to remove clay,
other soluable materials, and oversize gravel. The undersize
from the screening is sent to a jig for gravity separation.
Following gravity separation, the silver ore is chemically
separated by either amalgamation or flotation and cyanidation.
After these processes, it is still necessary to refine the silver
concentrate to a purity level generally exceeding 99.9 percent.
Less than 1 percent of the current domestic production of silver
is recovered by amalgamation or flotation/cyanidation processes
(29). A more complete discussion of these processes is contained
in Section 5, Gold.
Silver ores are recovered from open-pit mines in conjunction
with the mining of other metals. Overburden depth can be con-
siderable, and at one mine it exceeds 150 meters (76). After the
overburden is removed, mining operations consist of drilling
blasting holes, blasting of the ore, loading it into trucks or
rail cars, and transporting it to the concentrator. Occasional-
ly, blasting is not required, and the ore is merely "ripped" by
bulldozers, then loaded (76).
In underground mining, various techniques are used to remove
the ore from deep deposits, the choice depending on the charac-
teristics of the ore body. Caving and supported stoping are the
primary methods. The ore is hauled to the beneficiation site by
rail, truck, or belt conveyor.
The first beneficiation step involves crushing the complex
silver ore. This is a dry (natural moisture content) process,
but all additional beneficiation steps are performed wet. The
ore next undergoes wet grinding, followed by classification.
Oversize material from the classifier is returned for regrinding;
undersize ore is sent to a flotation unit for separation. Almost
all the ores require fine grinding to liberate the sulfide
minerals from one another and from the gangue.
Selective froth flotation is the most effective method of
beneficiating complex silver sulfide ores. Essentially, a com-
bination of various reagents is used to cause the desired sulfide
mineral to float and be collected in the froth while other
minerals and the gangue sink. This process or series of pro-
cesses is used to separate silver from copper, gold, lead, zinc,
and various other metals.
220
-------
UFINIHG
10
-------
Silver is recovered primarily from the mineral tetrahedrite,
(Cu, Fe, Zn, Ag)12Sb4S,2. The tetrahedrite concentrate from the
flotation unit will tisirally contain approximately 25 to 32 per-
cent copper, 2 to 4 percent silver, and up to 18 percent antimony
(which may or may not be extracted prior to shipment to the
smelter).
Although flotation is used to separate silver from complex
ores, recoverable silver still remains in the separated metal
concentrates (i.e., copper, lead, zinc). Also, the silver con-
centration in the complex ore often is not high enough to justify
flotation separation, in which case the silver is separated by
electrolytic refining of the base metal concentrate. In all
cases, further refining of the silver is necessary to attain the
marketable purity of 99.9 percent.
Waste Streams
Table 41 presents a summary of multimedia wastes from the
mining and beneficiating of silver ores. The following para-
graphs contain more detailed information on the various air,
liquid, and solid waste associated with this industry.
Air Emissions—
Mining and beneficiation of placer deposits do not generate
air emissions because all the processes are carried out in the
presence of water.
Air emissions from the mining and beneficiation of other
silver ores are mostly fugitive dust. Estimates and character-
istics of emissions from open-pit and underground silver mines
are not available. One reference did estimate the total silver
metal emissions from mining and beneficiating silver ores at less
than 2 megagrams per year nationally (96). No specific air
emission values are available for the crushing of silver ores.
The wide variety of ores containing silver would cause any es-
timates of emissions from ore crushing to vary greatly.
Liquid Wastes—
Placer mining and beneficiation processes use large quan-
tities of water. Although no specific data are available on the
characteristics of and concentrations in the effluent from wash-
ing, screening, and gravity separation, this effluent is known to
have a high suspended solids content.
Effluent from grinding and amalgamation is also high in
suspended solids. Mercury is the prominent agent used in this
process; therefore, the effluent is potentially toxic. Cyanide
leaching results in high levels of soluble metals. Both the
cyanide and heavy metals are potentially toxic; however, this
222
-------
TABLE 41. SUMMARY OF MULTIMEDIA WASTES FROM MINING
AND BENEFICIATING OF SILVER ORES
ro
K>
CJ
" ourct-
Open- pi t mining
Underground mi ninq
Tailings pond
Air
O U till
I'articulates
Part iculates
i'articulates
Uncontiol led
emi ss ion
i a c
Neglig ible
our e
Placer mining
Hashing
separation
Cyanidation
1'ulluunt/
1 urjnu i r
TDS, TSS
Sand, clay
CN . heavy
metals
1
Amalgamation Ma
j
Uncont rol Ic'J
i sc tiirqt.
' b
Flotation : CN
0.00019 kq/Mq oreb
ur
Placer mining
Washing
separation
Cyanidation
Solid
Ganque
Sand, clay
Heavy
metals
Amalgamation i HIJ,
tai lings
min i ng ganque
Underground Ganque
1 | -mini ng
Flotation
Flotation
Flotation
Flotation
Flotation
Underground
m i n i ng
Open-pit
mining
Ta i 1 i ng s
Tail ings
Cd I 0.00038 kq/Mq ore j Flotation
Cu 0.0016 kq/Mq oreb Ta.linqs
r
Uncontrol led
N.A.
N.A.
N.A.
N.A.
N.A.
Tailings • N.A.
Tai Lings i N.A.
Hq '0.00063 kq/Mq oreb |
Pb 0.0027 kq/Mq ore
1 K
Zn ; 0.00 2 4 kq/Mq ore
TSS
Cu
0.0085 kq/Hq orcC
0.00034 kq/Mq orec
I'b | 0.00069 kq/Mq orec
Zn : 0.0024 kq/Mq orcc
!
II.) JO.000014 kq/Mq ore0
TSS j 0.069 kq/Mq ored
Cu '. 0.00031-0.00017
kg/My oreu
Tailings Pb 1 0. 00065-0. 00034
Ta i 1 i ng s
Ta i 1 i ng s
| kq/Mq ored
Zn ,0.0021-0.0017
ki|/Mq ore"
M.| 1 0.000010-0.0000034
Jkq/Mt| ore1*
!'
|
. I
j
i
For mure complete information, see Section S.
Kef. 46. Hypothetical values.
C Ref. 46. Untreated (or hypothetical nine.
Ref. 46. Outflow from tailings - range from sett lint) to lime treatment.
N.A. - Not available.
-------
does not create a great problem because less than 1 percent of
domestic production of silver is currently recovered by amal-
gamation or cyanidation (46).
The leading silver producers (especially in Idaho) usually
recover the ore by underground mining. Some of the water from
mine pump-out is used in beneficiating operations; the rest is
sometimes discharged directly into streams (46).
Silver ores are recovered less frequently by open-pit min-
ing. The source of any pit discharge from open-pit mining,
results from precipitation, runoff, and groundwater infiltration
into the pit. No specific data are available on the pump-out
from open-pit silver mines.
Table 41 presents wastewater discharge rates for a hypo-
thetical silver mine. The figures are based on an arithmetic
average of five large silver mines (29). These figures represent
a combination of water from runoff, pumpout, and all processes
other than flotation. Discharge rates for mills using flotation
are shown separately. Froth flotation is the most common process
now used in beneficiation. The volumes of the waste streams
discharging from mills processing silver ore range from 1499 to
3161 cubic meters per day (29). The amount of solids contained
in these waste streams vary from 272 to 1542 megagrams per day.
Solid Wastes—
The quantity of solid waste rock from placer mining is
probably less than that generated by either open-pit or under-
ground mining (46). However, no specific solid waste data are
available for placer silver mining.
Washing to remove sand and clay and gravity separation do
generate solid waste, which is sent to tailings. Published data
have not estimated the exact makeup of this waste or quantity
generated.
Because of the small quantity of silver processed by either
cyanidation or amalgamation, no information has been published on
the quantity of solid waste produced by these beneficiating
processes.
Open-pit mining of silver ore can generate sizable solid
wastes. Because silver is such a valuable element, it is fea-
sible to remove large quantities of overburden to obtain rela-
tively small quantities of ore. For the same reason, large
quantities of gangue may also be generated once the ore body is
reached. No specific solid waste data are available, however, to
estimate the quantity of overburden and gangue generated by
open-pit silver ore mining.
224
-------
Typically, less solid waste is generated by underground
mining than open-pit mining. Little or no overburden is gener-
ated, and because the higher cost of underground mining limits
this means of silver recovery to only the richer deposits, less
gangue also is generated than with open-pit mining. Again, no
data are available on which to base estimates of the quantity of
waste generated by underground silver mining.
Most silver ore is beneficiated by the froth flotation
process. Selective froth flotation can effectively and effi-
ciently beneficiate almost any type and grade of sulfide ore.
The quantity of tailings generated by flotation of silver ores
depends, of course, on the concentration of silver and other
metals present in the ore. No composite figure is available to
estimate the quantity of tailings for a typical silver benefi-
ciation process.
Control Technology
Much the same control technology is used in the silver
mining industry as in other mining industries. The following
paragraphs explain these controls as applied to air, liquid, and
solid waste.
Air Emissions Control—
Overburden removal, ore extraction, and ore transport are
among the most variable fugitive dust sources in open-pit mining.
They are also among the largest particulate sources. Dust and
particulate emissions from these operations vary with the com-
position, texture, and moisture content of the material; excava-
tion procedures; equipment employed; etc. A literature search
yielded no controls that were specific to the open-pit mining of
silver ore.
Visits to two underground silver mines lead us to believe
that control of air emissions from mine ventilation is un-
necessary.
No information was found on specific emission controls for
the silver ore crushing process. Particulate emissions from this
source can be controlled by any of numerous conventional methods.
Air emissions from tailings occur only when the tailings
pond becomes dry (i.e., when the pond is no longer used).
Intentional or natural formation of a crust on the surface of the
pond can reduce emissions from this source by as much as 80
percent (65).
225
-------
Liquid Waste Control—
Wastewater from placer mining, washing, and gravity separa-
tion is discharged into a tailings pond, where suspended solids
are allowed to settle out. An alternative technology is to pump
the wastewater from the dredging operations to a tailings dis-
posal area for filtration through sands and gravels. It may be
necessary to enhance the settling of suspended solids by the
addition of settling aids when using this method (29).
Mill water from amalgamation and cyanidation is also dis-
charged into a tailings pond. Because of the small quantity of
silver beneficiated by cyanidation (less than 1%), no information
was found on controls used with these processes. Spillage of the
liquor containing cyanide is always a potential hazard, and
improper handling could have significant environmental impact
(46).
It is possible to eliminate discharge of liquid wastes from
cyanidation of silver by either recycling or total impoundment of
the process water. To implement this technology, recycling of
process reagents may be necessary both to achieve economy in
reagent use and to avoid high concentrations of cyanide in re-
cycled process water (29).
Only one operation now utilizes amalgamation to recover
silver. Two sedimentation ponds are now used to control waste-
water, but they are inadequate for proper metal removal.
Chemical precipitation of the metals would solve this control
problem (29).
Water from runoff, mine pumpout, and other processes (except
flotation) should be discharged into a tailings pond for settling
before it is released into a stream. According to one reference,
a typical silver mining operation has little or no effluent
treatment or control (29). Estimated control efficiencies for
treating an average silver mine effluent by sedimentation are as
follows: total suspended solids, 20 percent; copper, 10 percent;
lead, 5 percent; zinc, 14 percent; mercury, 25 percent. When
lime precipitation is used in conjunction with the settling,
control efficiencies are increased by the following additional
percentages: copper, 45 percent; zinc, 17 percent; and mercury,
33 percent. When sulfide precipitation and close control are
practiced in addition, both lead and mercury levels are reduced
an additional 40 percent (29).
Solid Waste Control— j
Because silver has such a high value, ore bodies containing
only small concentrations of silver are mined. The silver is
almost completely extracted, but this leaves huge quantities of
overburden, gangue, and tailings to be disposed of.
226
-------
TITANIUM
Industry Description
Rutile and ilmenite are the principal titanium-bearing
minerals. Rutile, or titanium dioxide, is the most desirable
source. It contains above 50 percent titanium after benefi-
ciation. This mineral is not abundant, however, and very little
is mined in the United States. Ilmenite, or iron titanium oxide,
is more abundant, but must be processed more to recover the
titanium oxide. Ilmenite deposits occur in sand and rock (97).
Economically recoverable titanium resources of the United
States are known to occur as 1) ilmenite rock deposits in New
York and Virginia; 2) ilmenite beach sands in Florida, New
Jersey, and Georgia; 3) rutile rock deposits in Virginia; and 4)
rutile sand deposits in Florida, South Carolina, Tennessee, and
Georgia. Additional, none economically recoverable ilmenite
resources are known to exist in California, Colorado, Minnesota,
Montana, New York, Rhode Island, Wyoming, Oregon, and Oklahoma
(95).
About 70 percent of the ilmenite produced in the United
States comes from three mines, two in Florida and one in New
York. The other 30 percent comes from two mines in New Jersey
and two more mines in Florida. Rutile associated with ilmenite
in Southeastern sand deposits is not shipped separately except
from one Florida mine. The rest of the world's output of
ilmenite comes mostly from Canada, Norway, Australia, and the
U.S.S.R. About 96 percent of the world's rutile comes from
Australia (20). The United States produced an estimated 580,480
megagrams of ilmenite in 1975 (98), and about 9070 megagrams of
rutile in 1974 (99).
Domestic ilmenite and rutile and imported ilmenite are used
to manufacture Ti02 pigment and other Ti02 products. Titanium
metal is either imported or produced from imported rutile.
Zirconium, hafnium, and rare earth elements (discussed in
separate sections of this report) are by-products and coproducts
of titanium processing.
Process Description
Titanium minerals of economic importance are contained in
rock and sand deposits. The ilmenite from rock deposits and some
sand deposits usually contains 35 to 55 percent TiO,. Some sand
deposits, however, yield altered ilmenite (leucoxene), which
contains 60 percent or more TiO-, as well as rutile, which con-
tains 90 percent or more TiO2 (99).
228
-------
The method of mining and beneficiating titanium minerals
depends on whether the ore is deposited in sand or rock.
Beach Sand Deposits—
Heavy mineral beach sand (placer) deposits occurring in
Florida, Georgia, and New Jersey, contain 1 to 5 percent TiO2.
These deposits are mined with floating suction or bucket-line
dredges that handle up to 1000 megagrams of material per hour.
The sand is treated by wet gravity methods that use spirals,
cones, sluices, or jigs to produce a mixed, heavy-mineral, bulk
concentrate. As many as five individual marketable minerals are
separated from the bulk concentrate by a combination of dry
separation techniques using magnetic and electrostatic (high-
tension) separators, sometimes in conjunction with dry and wet
gravity concentrating equipment (29). Figure 31 presents a
composite flow diagram for extracting and beneficiating placer
deposits containing rutile and ilmenite.
Ilmenite Rock (Lode) Deposits—
Ilmenite is being mined from a rock deposit in New York by
conventional open-pit methods. This ilmenite/magnetite ore,
which averages 18 percent TiO-, is crushed and ground to a small
particle size. The ilmenixe and magnetite fractions are
separated magnetically (the magnetite being more magnetic because
of its greater iron content). The ilmenite sands are further
upgraded in a flotation circuit. Figure 32 illustrates the
mining and beneficiation of titanium from an open pit.
Waste Streams
Table 42 presents a summary of multimedia wastes generated
by extraction and beneficiating of titanium ores. The following
paragraphs refer to this table in discussing the air, liquid, and
solid waste streams.
Air Emissions--
Fugitive dust emissions from the operations of an ilmenite
rock (lode) open-pit mine are the major air emissions associated
with titanium mining. The operations include overburden removal
and ore blasting, loading, transport (fugitive dust from haul
roads), and unloading. Although information is not available on
emission rates from individual operations, overall uncontrolled
fugitive emissions from open-pit mining are estimated to be 0.1
kilogram per megagram. Estimates indicate that hard rock mining
produces particles averaging 5 microns in diameter and ranging
from 0.5 to 10 micrometers (69). Of course, dredging of placer
sand deposits does not produce particulate emissions.
Uncontrolled air emissions from benefication operations at
open-pit mines are estimated to be 19 kilograms per megagram of
229
-------
..OVERFLOW TO
TAILINGS POND
DREDGING
(POND)
OP"
ROUGH SCREENING
GRAVITY
CONCENTRATION
SCRUBBING
DRYING
ELECTROSTATIC
CONCENTRATION
•••OVERSIZE-
•TAILINGS —J
STORAGE
9 AIR EMISSIONS
-, LIQUID WASTES
E SOLID WASTES
I I TAILINGS TO POND
NON- CONDUCTORS -1—CONDUCTORS "7
DISCHARGE
TO STREAM
•SOLIDS
T
GRAVITY CONCENTRATION
;WET-SP[SALS;
ORY-TABLES)
I
TAILINGS TO
MAGNETIC SEPARATION
OF
TITANIUM MINERALS
_ RUTILE
(NONMAGNETIC)
—"-ILMENITE
(MAGNETITE)
r
"AGNETIC SEPARATION
•ZIRCON (NONMAGNETIC)
•MONA:ITE (MAGNETIC)
DRY MILL
Figure 31. Mining and beneficiating of heavy-mineral
beach sand (placer) deposits.
230
-------
PRELIMINARY 1
PROCEDURES |
*&>
ORE EXTRACTION 1
],
9
; ?
ORE TRAN
I
i y
MAKE-UP
WATER ^
MAGNETIC
CRUSHING
P 1 "t
GRINDING
y AiK tniiblUli
\ LIQUID HASTES
SCREENING '
n cnr in uitTrc
MAGNETIC
SEPARATION
(WET)
5
j (MAGNETITE)
1' °IP
\ DEHATERING
* HATER RETURN
»TE ••
TAIL
NONMAGNETICS
(ILMENITE AND GANGUE)
THICKENING
PV n i. „ __.,-.._ ^
Y ?
INGS I , . . -.-j
-........_. umiBo 1
PONDS J
,..* ,, CONCENTRATED
SEASONAL . ILKNITE
DISCHARGE U«NITt
Figure 32. Mining and beneficiating of ilmenite
rock (lode) deposits.
231
-------
TABLE 42. SUMMARY OF MULTIMEDIA WASTES FROM MINING AND
BENEFICIATING OF TITANIUM ORES
N>
U)
N>
Source
Overburden removal3
Ore extraction3
Ore loading
Ore transporting3
Crushing3
A b
Drying '
Magnetic separa-
tionb
Dredging
Air
Pol lutant
Fugitive
particu-
lates
Particu-
lates anb
combus-
tion pro-
ducts
Pai ticu-
lates
Uncontrolled
emission
rate
0.1 kg/Mg
of ore
19 kg/Mg of
orec
4.75 kg/Mg
of orec
Source
Mine3
Mill3'6
(Con-
centra-
tions of
major
consti-
tuents)
Liquid
Pollutant
parameter
TSS
Oil und
grease
Fluo-
ride
Total
Kjeldahl
nitrogen
Nitrates
TSS
TOC
Ni
Ti
Fe
V
Cr
Uncontrolled
discharge
14 mg/£d
3.0 mq/td
3.2 mg/Hd
ri
2.24 mg/e
15.52 mg/lid
26,300 mg/td
9.0 mg/e
1.19 mg/td
2.08 mg/i
ft
500 mq/IT
2.0 mg/4d
0.58 mg/td
Source
Overburden
removal3
Ore ex-
traction
Magnetite
dewatering
I Imeni te
flotation
Rough .
screening
Gravity
concentra-
tionb (wet
mill)
Gravity
concentra-
tions^ (dry
mill)
Solid
Pollutant
Topsoil, subsoil
and other strata
Gangue
Tailings
Gangue
llardpan and
roots^
Tailings
Tailings
Uncontrolled
quantity
Total solid
waste gen-
erated at
mine is 1.25
Mg/Mg of ore
Approximately
97 percent of
total dredged
material is
returned to n
dredged area
(Continued)
-------
TABLE 42. (Continued)
Source
Air
Pollutant
Uncontrol led
emission
rate
Source
Raw mill
waste-
waterb, f
(Con-
centra-
tions of
major
consti-
tuents)
Liquid
Pol lutant
parameter
Oil and
grease
Cu
Zn
Fluo-
ride
Mn
TSS
TOC
COD
Oil and
grease
Ti
Fe
Cr
Phos-
phate
Total
Kjeldahl
nitroqen
Uncontrolled
di scharqe
2.0 mg/td
0.43 mg/td
7.6 mg/(d
32.5 mg/td
5.9 mq/t
209-11,000
mg/td
321-972
mg/td
362-133B
mg/' Id
40-400 mg/td
<0.2-0.40
0.93-4.9
mg/P.d
<0. 01-0. 03
0.35-0.40
mg/jd
0.65 mg/td
Source
Solid
Pollutant
Uncontrolled
quantity
1
N)
Ul
U)
llmenite rock (lode) open-pit operations. Represents the one facility jn U.S. (New York) which is currently operating.
Placer deposit operations.
Kef. 69. Order of magnitude estimation.
Ref. 29. Load rates in kg/Mg of concentrate available in this source for mill effluents.
This raw mill wastewater is treated at the New York facility by simple settling.
Combined wet mill and dredge pond discharge. Typically treated by flocciilation with sulfuric acid.
Ref. 69 and inspection of Humphrey's Mining Company's Orudginq operation (Boulogne, Florida) and dry mill (Folkston,
Georgia) by R. Amick and J. Greber of PEDCo. January 1977.
-------
material handled, whereas emissions from beneficiation of dredged
material are estimated to be 4.75 kilograms per megagram (69).
The primary sources of these emissions are the crushing operation
at open-pit mining facilities and the drying operations at each
type of mine. Particulate emissions from magnetic and electro-
static separation operations are insignificant compared with
these sources. Storage of the ore in open piles can be another
source of fugitive emissions.
Liquid Wastes—
Lode deposits—Considerable quantities; of water (2760 cubic
meters per day) are discharged from the open-pit ilmenite mine in
New York. The water contains high concentrations of oils and
greases, fluorides, Kjeldahl (organic) nitrogen, and nitrates
(from nitrate-based explosives) (76). Table 42 lists the concen-
trations .
Dewatering of magnetite concentrates and ilmenite flotation
also generates waste mill water at the New York open-pit facil-
ity. The raw wastewater stream from the flotation process
amounts to about 35,000 cubic meters per day and contains large
amounts of suspended solids and relatively high levels of iron,
titanium, oil and grease, zinc, nickel, vanadium, and chromium.
Table 42 lists the concentrations of the major constituents of
the raw mill wastewater. Reagents used in the flotation circuit
include tall oil, fuel oil, methyl amyl alcohol, sodium bi-
fluoride, and sulfuric acid (29).
Placer deposits—Water used for gravity separation in wet
mills at placer extraction facilities is discharged to a dredge
pond. The sands contain organic materials which form a highly
colored colloidal slime. In addition, high levels of phosphate
and organic nitrogen are present in the raw waste streams. Waste
lubricating oil from the dredge and wet mill and oversize from
the screens are also dumped into the dredge pond.
Wastewaters from the scrubbing operations of the dry mill
are a source of clay and other suspended solids. Tailings are
disposed of in the gravity concentration operation of the dry
mill, with subsequent discharge to a tailings pond or dredge
pond, depending on the location of the dry mill (77).
The organic colloidal slime (formed when the organic
materials in the placer bodies are disturbed) is comprised pri-
marily of humates and tannic acid, which are the principal waste
constituents of the dredge pond discharges. This is reflected in
the high chemical oxygen demand (COD) (362 to 1338 milligrams per
liter) and total organic carbon (TOC) (320 to 972 milligrams per
liter) detected in the raw waste streams before treatment. High
levels of phosphate and nitrogen are also present in the raw
waste streams (see Table 42).
234
-------
Solid Waste—
Considerable solid waste is generated at the New York open-
pit facility. Approximately 1.25 megagrams of waste must be
removed from the mine to obtain 1 megagram of ore (100). Tail-
ings generated by the magnetic separators still contain ilmenite
and are processed further by the flotation process. Gangue- is
routed from this process to the tailings pond. Similarly, the
filtrate from dewatering the magnetite is disposed of in the
tailings pond.
Overburden and gangue generated in the mining and wet mill-
ing of placer deposits goes directly back to the dredge pond.
Tailings from the dry mills scrubbing and gravity separation
operations are disposed of in the dredge pond or tailings pond,
depending on the location of the dry mill.
Control Technology
Waste streams generated by the mining and beneficiation of
titanium-bearing minerals are controlled by conventional methods.
Air Emissions Control--
Fugitive dust emissions from the New York open-pit mining
operations are best controlled by the methods described in
Section 3—wet suppresion, chemical suppression methods, and wind
breaks. Fugitive dust emissions from truck traffic on haul roads
is by far the most easily controlled via a conscientious
watering/chemical additive program. Control efficiencies of 50
percent are attainable by this method. Dusting of open storage
piles can also be controlled by wet suppression methods. Control
of particulate emissions from open-pit beneficiating sources,
trucking, and drying are best controlled by confinement, wet
suppression, or water sprays (for crushing only), and a high-
efficiency centrifugal collector. Control efficiencies of 90
percent are estimated for these sources, yielding a controlled
emission factor of 1.9 kilograms per megagram (69). '
Emission sources in the titanium ore dredging operations
(drying, electrostatic concentration, and magnetic concentration)
are controlled by methods similar to those applied to open-pit
beneficiating operation sources, i.e., confinement and use of a
fabric filter or high-efficiency centrifugal collector. Control
efficiencies of 90 percent are estimated, yielding a controlled
emission factor of 0.5 kilogram per megagram (69).
Liquid Waste Control—
Liquid wastes from the New York open-pit facility, generated
primarily in the flotation circuit, are discharged to a formerly
used open-pit quarry that serves as a tailings pond. Clarified
overflow from this pit is recycled back into the mill circuit at
235
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the rate of 34,900 cubic meters per day with a makeup rate of 978
cubic meters per day (total mill water requirement is 35,772
cubic meters per day). The process water has an alkaline pH
(69).
Discharges from the settling pond at a quarry pit occur
seasonally when rain and resulting surface runoff exceed mill
water makeup requirements. Before it is finally discharged, this
water is briefly retained in a small pond. Treatment of mill
effluent could be improved by diverting surface runoff away from
the quarry pit (which results in almost no discharge) and in-
creasing the retention time in the small secondary pond. Treat-
ment with lime or some other precipitating agent also would
ensure optimum metal and fluoride removal (69).
Concentrations of major constituents in treated recycle
water from the settling pond (discharged to a stream during heavy
rains) include iron (<0.03 milligram per liter—99+ percent
removal), titanium (<0.2 milligram per liter—90 percent re-
moval), oil and grease (2 milligrams per liter—no removal), zinc
(<0.002 milligram per liter—99+ percent removal), nickel (<0.01
milligram per liter—90+ percent removal), vanadium (<0.5 milli-
gram per liter—>75 percent removal)^ and chromium (0.02 milli-
gram per liter—97 percent removal).
Liquid wastes from placer deposit milling operations are
typically discharged to a dredge, pond. If the dry mill is not
located adjacent to the dredging wet mill, a separate tailings
pond also is necessary. Discharge of wet mill effluent can be
significant, i.e. as much as 12,000 cubic meters per day from one
operation (69). Dredge pond effluent, which contains colloidal
organic material of high coloring capacity, is treated in a
series of three or four settling ponds. Sulfuric acid is added
as a flocculant to reduce the pH to 3.5. Both acid and lime are
fed automatically. Reagents are added to the waste streams in
flumes designed to create turbulent mixing.
Two of the major constituents of settling pond effluent are
concentrations of COD (13.5 milligrams per liter--96 percent
removal) and TOC (5.5 milligrams per liter—97 percent removal).
Solid Waste Control—
Overburden from open-pit mining of titanium rock deposits is
disposed of by filling in exhausted quarry areas, then grading.
Provisions should also be made to landscape the exhausted mine
site.
As discussed in the solid waste section, overburden and
gangue generated in the mining and milling of placer deposits are
236
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typically disposed of in the dredge pond. If this dredging
operation is improperly managed, it can devastate a large area of
land. Reportedly some companies are carefully restoring land
traversed- by their dredges. Such restoration practices were
observed at the Humphrey's Mining Company operations in Boulogne,
Florida (dredging and wet milling) and Folkston, Georgia (dry
milling).* These facilities stockpile the topsoil during site
preparation operations and revegetate the area after it has been
dredged and backfilled. Colloidal slimes from three settling
ponds that treat discharge from the dredge pond are dried out in
designated areas. These colloidal slimes, which contain 20
percent solids, are spread in 30-centimeter layers over areas of
dried-up dredge pond tailings. After it dries to a 8-centimeter
solid layer, it is dug up and plowed into an adjacent sandy area.
The first two settling ponds are cleaned out every 30 to 60 days.
Average flow rate through these treatment ponds is 2 to 4 cubic
meters per minute and average retention time is about 5 days per
pond.*
Conclusions and Recommendations
Waste streams generated by mining activities associated with
hard rock (lode) and tracer deposits appear to be sufficiently
controlled (or at least controllable) by conventional techniques,
e.g., placer deposit operations typically return solid and con-
ventionally treated liquid wastes to their point of origin, the
dredge pond. Solid and liquid wastes generated by beneficiation
also appear to be adequately controlled/controllable by conven-
tional techniques. Beneficiating operations, particularly in
open-pit mines, are a potential source of appreciable air emis-
sions (TiO,), even though they are 90 percent controlled;
however, tnis control efficiency could easily be upgraded by
applying such conventional methods as fabric filters.
Based on the above conclusions and the fact that the United
States has less than 10 producers of titantium ore, research and
development programs for this industry appear to be unnecessary.
Sufficient solutions are available to handle any pollutant con-
trol problems that are likely to develop in titanium ore facili-
ties.
Inspection of Humphrey's Mining Company's Dredging Operation
(Boulogne, Florida) and dry mill (Folkstan, Georgia) by R. Amick
and J. Greber of PEDCo.
237
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SECTION 6
NONFERROUS METALS (REFINERY/SMELTER BY-PRODUCTS)
This section deals with several nonferrous metals that are
not mined for their own economic value, but are recovered as
smelter or refining by-products of ores that are mined for more
economically attractive metals.
BISMUTH (95, 101)
Nearly all domestic bismuth is recovered as a by-product of
lead smelting. Most bismuth resources are associated with
copper, lead, and zinc ores in Arizona, California, Colorado,
Idaho, Montana, Nevada, New Mexico, and Utah. Other sources
include electrolytic sludges and other metallurgical products
from copper and zinc refineries, which are sent to lead re-
fineries for separation and refining of other associated metals
such as gold, silver, selenium, and platinum. Approximately
one-half of the domestic requirement for refined bismuth is
imported, primarily from Japan.
CADMIUM (95, 102)
Cadmium is recovered in the United States as a by-product of
zinc ore smelting and refining. In 1974, however, more than
one-half of U.S. demand was imported.
GALLIUM (95, 103)
Gallium is recovered as a by-product from processing alum-
inum and zinc ores. Although domestic resources are large,
demand outstrips production and gallium must be imported, mostly
frbm Canada and Switzerland. Recent increases in national demand
are expected to result in expanded domestic operations and in the
development of gallium as a by-product of other raw material
sources.
238
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GERMANIUM (95, 104)
U.S. production of primary germanium comes from the pro-
cessing o_f domestic and foreign zinc smelter concentrates and
from the reprocessing of scrap and foreign material. Imported
germanium-containing zinc concentrates come primarily from Canada
and West Germany.
HAFNIUM (95, 105)
Hafnium is found in association with the zirconium in zircon
ore, which is recovered from titanium-bearing minerals as a
coproduct or by-product. Although domestic resources of zircon
are quite large, hafnium production depends on the demand for
reactor-grade, hafnium-free zirconium. Zircon ore is contained
in sand deposits in Florida, New York, and New Jersey, and is
recovered by dredging.
INDIUM (95, 106)
U.S. indium is recovered as a by-product of smelting and
refining zinc and lead ore. It is obtained by refining the
residue and flue dusts from these smelters. About 75 percent of
the national demand is met by imports of the metal or unprocessed
concentrates, mostly from Canada.
SELENIUM (95, 107)
Domestic selenium is recovered principally from the anode
slimes obtained from the electrolytic refining of copper. In
1974, about 55 percent of the selenium used in the United States
was imported.
TELLURIUM (95, 108)
Tellurium also is recovered from the anode slimes obtained
from the electrolytic refining of copper. In recent years, about
75 percent of U.S. tellurium has come from domestic production.
The remaining 25 percent has been imported, chiefly from Peru and
Canada.
THALLIUM (95, 109)
All thallium recovered in the United States occurs as a
by-product of the base metals mining industry, primarily zinc
239
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smelting. Since supply exceeds demand, collected zinc residues
are now being stockpiled.
ZIRCONIUM"(95, 105)
Zirconium is produced from zircon, which is a mineral re-
covered only as a coproduct or by-product of titanium mining.
Zircon is used primarily as facing for foundry molds, particu-
larly in the iron and steel industry, and a very small amount is
used for the production of zirconium metal. If zirconium is to
be used for nuclear purposes, hafnium must be removed (hafnium
occurs in association with zirconium in zircon in varying ratios,
averaging 1:50) to provide a reactor-grade product. In 1975
zirconium metal in the United States was produced largely from
imported zircon ore.
240
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SECTION 7
NONFERROUS METALS (NONDOMESTIC)
Section 7 deals with those nonferrous metals that are not
presently recovered from domestic ores. Because these metals are
imported either in a finished or semifinished form or are pro-
duced from imported raw ores, their extraction does not pose an
environmental hazard within the United States.
ARSENIC (95, 110)
Arsenic is an undesirable minor by-product associated.with
ores mined chiefly for copper, gold, and lead, and it must be
removed to minimum levels when refining these metals. Arsenic
recovery depends on the efficiency of base-metal smelter flue
dust treatment. The U.S. demand for arsenic is met largely by
the processing of imported base metal ores.
The disposal of arsenical materials at base metal smelters
presents a solid waste disposal problem, particularly in relation
to soil and water pollution. Environmental problems related to
underground mining of arsenic-bearing ores are similar to those
related to base metal mining. Also, arsenic in sulfide minerals
that are exposed to the atmosphere may form soluble arsenates,
which can cause surface and groundwater pollution.
CESIUM (95, 111)
No cesium is mined in the United States; therefore, all
cesium raw material is imported, primarily from Canada. Although
cesium ore was once mined in Maine and South Dakota, future
extraction of significant quantities in the United States is
unlikely.
PLATINUM-GROUP METALS (95, 112)
Platinum, palladium, iridium, rhodium, ruthenium, and opmium
makeup the platinum-group metals. About 9 percent of total
domestic demand is produced in the United States, principally as
a by-product of copper smelting. Platinum group metals have also
been obtained by dredging placer deposits of the Salmon River in
241
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the Alaskan Goodnews Bay District, but this source was closed
indefinitely in early 1976. Production had been declining for
years (in 1974 only 0.3 percent of the total U.S. demand came
from this- source). More than 90 percent of the domestic demand
is met by imports. South Africa, Russia, and Canada supply the
greater portion.
Since most U.S. mine production of platinum-group metals is
recovered as a by-product of copper mining and refining, environ-
mental problems are incidental to copper production.
RADIUM (95, 113)
Radium is present in small amounts in uranium ore and the
geology of radium and uranium are the same. Radium-226 is the
commercial radioactive decay product of uranium-238, the most
abundant uranium isotope. The United States has not mined radium
since 1950.* At one time radium was recovered from high-grade
uranium deposits in Colorado.
RUBIDIUM (95, 114)
Rubidium is not mined in the United States. Domestic
rubidium and its compounds are obtained from the residues re-
maining from the processing of lepidolite for lithium compounds.
Commercially productive residues containing rubidium are likely
to be exhausted in the near future, and future domestic recovery
will probably come from residues resulting from the processing of
imported pollucite for cesium.
SCANDIUM (95, 115)
The supply of scandium in the United States has come from
sporadic domestic production, reprocessed uranium residues, and
irregular imports. Data on these sources are not available.
TIN (95, 116)
The United States has no commercially significant tin mines;
however, a very small amount of tin is recovered from placer
deposits in Alaska and New Mexico and as a by-product of molyb-
denum at the Climax Mine in Colorado. These sources are expected
to remain negligible in the foreseeable future, and virtually all
primary tin requirements will be met by imports.
*Telephone conversation between R. Amick of PEDCo and
Ms. M. Kahn, Bureau of Mines, Pittsburgh, Pennsylvania.
April 1977.
242
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APPENDIX A
EXPLANATION OF GUIDANCE CRITERIA FOR
ESTABLISHING R&D PRIORITIES
As stated in the Summary, criteria that may be used to
establish R&D priorities are arranged in Table 1 according to
their relative importance in defining possible research and
development efforts. The generation of hazardous waste by any
industry is assumed to be the criterion of prime importance
because of the environmental threat (lethal or sublethal) posed
if such wastes are not controlled. Control of nonhazardous
atmospheric emissions and liquid and solid wastes is considered
necessary in the mining industry; however, the environmental
threat of these wastes is not of the magnitude as that from
hazardous wastes. Thus, values applied to hazardous waste are
higher than those applied to nonhazardous waste.
The quantity of ore mined by a particular industry is also a
criterion because the amount of ore mined is directly related to
the amount of waste generated by that industry. A review of the
industries covered in this study reveals that there are three
distinct size classes of ore production. (See Table 1.)
The* future of each industry is also important in determining
research and development needs. If projections indicate that an
industry is to decline in the future, the need for research and
development is less; whereas projected increases in an industry
indicate more waste materials will be generated and improved
control of the waste materials will be required.
The number of domestic mines, principal producing states,
and the total number of producing states are important criteria
in that the wider the geographic distribution of an industry, the
more widespread will be the pollution problems associated with
that industry and the greater need for control.
The degree of information available on each industry is a
necessary criterion for several reasons. Lack of understanding
regarding an industry's process means a lack of knowledge about
its waste streams, and the less that is known about the waste
streams, the greater the possibility that hazardous and non-
hazardous waste streams are either inadequately controlled or
completely uncontrolled. ... - • . .
243
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