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Environmenttl Protection
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
H. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL
PROTECTION TECHNOLOGY series. This series
describes research performed to develop and
demonstrate instrumentation, equipment and
methodology to repair or prevent environmental
degradation from point and non-point sources of
pollution. This work provides the new or improved
technology required for the control and treatment
of pollution sources to meet environmental quality
standards.
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EPA-R2-73-247b
September 1973
WATER-POLLUTION CONTROL IN THE
PRIMARY NONFERROUS-METALS INDUSTRY
VOLUME II. ALUMINUM, MERCURY, GOLD, SILVER,
MOLYBDENUM, AND TUNGSTEN
By
J. B. Hallowell
J. F. Shea
G. R. Smithson, Jr.
A. B. Tripler
B. W. Gonser
Contract No. 14-12-870
Project 12010 FPK
Project Officer:
John Ciancia
Edison Water Quality Research Laboratory, NERC
Edison, New Jersey 08817
Prepared for:
OFFICE OF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price $1.45
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EPA Review Notice
This report has been reviewed by the Environmental
Protection Agency and approved for publication.
Approval does not signify that the contents neces-
sarily reflect the views and policies of the
Environmental Protection Agency, nor does mention
of trade names or commercial products constitute
endorsement or recommendation for use.
ii
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ABSTRACT
Volume II of this study deals with the processes and water practices in
the aluminum, mercury, gold, silver, molybdenum, and tungsten indus-
tries. Data obtained from the producers of these metals showed the
patterns and amounts of water usage for different purposes within these
types of plants and the degrees and types of waste water either con-
trolled, treated, or discharged to various receiving waters. Water us-
age and recirculation were found to be highly variable among the indi-
vidual plants, with some practices being associated with climate and
water costs.
The trends in waste-water control varied with the individual industries.
Alumina refineries and aluminum smelters apparently are moving toward
zero or decreased discharge despite installation of increased produc-
tion capacity. Water practices in the primary mercury industry re-
flected the remote location and arid climates associated with these
operations. The need for air-pollution control in the mercury industry
possibly may require new equipment or processes, with associated needs
for water-pollution-control measures. The balance of the operations
studied showed individual characteristics varying as much as their loca-
tions, which ranged from remote desert to municipal locations.
This report was submitted in fulfillment of Contract No. 14-12-870 under
the sponsorship of the Office of Research and Monitoring, Environmental
Protection Agency.
iii
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CONTENTS
Section Page
I Conclusions 1
II Recommendations 3
III Introduction 5
IV Procedures 7
V The Primary Aluminum Industry 9
VI The Primary Mercury Industry 43
VII The Primary Gold and Silver Industries 55
VIII The Primary Molybdenum and Tungsten Industries 69
IX Discussion 101
X Acknowledgment 109
XI References 111
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FIGURES
Page
1 Location of Alumina Refining Plants in the U.S. 10
2 Locations of Aluminum Reduction Plants 14
3 Primary Aluminum Production and Mill Product Shipments 18
for Selected Spans of Years
4 Flowsheet of Major Processes in Aluminum Production 23
5 Generalized Diagram of Common Features of Water Circuits 28
of Alumina Refineries
6 Generalized Diagram of Common Features of Water Circuits 30
of Aluminum Smelters
7 Locations of Mercury Mines 45
8 Pyrometallurgical Process for Producing Mercury 47
9 Generalized Diagram of Common Features of Water Circuits 49
of Mercury Mines and Plants
10 Processes for Recovering Silver 65
11 Diagram of Processes and Products in the Molybdenum 73
Industry
12 Flowsheet for Processing of Tungsten Ore to Concentrates 84
13 Diagram of Processes and Products in the Tungsten Industry 86
14 Flowsheet for the Production of Synthetic Scheelite 88
15 Flowsheet for the Purification of Tungsten Trioxide 90
16 Characteristics of Water Circuits of Molybdenum and 96
Tungsten Processing Plants
VI
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TABLES
No. Page
1 Operating Companies, Locations, and Capacities of U.S. 9
Alumina Refining Plants
2 Ownership, Location, and Production Capacity of U.S. 12
Primary Aluminum Plants
3 Estimated World Ore Reserves of Bauxite 20
4 Sources of Bauxite and Locations of Alumina Plants 21
Supplying the U.S. Aluminum Industry
5 Comparative Figures Showing Imports and Domestic 21
Production of Bauxite and Alumina for the U.S. Aluminum
Industry
6 Water Data for Alumina Refineries and Aluminum Smelters 31
7 Water Uses and Recirculation Practice in Aluminum Smelters 33
8 Water Analyses, PPM, Associated With Alumina-Refinery 35
Operations
9 Published Data on Aluminum Smelter Waste Waters 37
10 Water Analyses, PPM, Associated With Aluminum-Smelting 36
Operations
11 Past Waste-Water-Treatment Practice in the Primary Aluminum 39
Industry
12 Water Costs in the Aluminum Industry 41
13 Mercury-Producing Mines in the United States in 1969 44
14 Forms and Amounts of Consumption of Primary Mercury 44
15 Production of Gold in the United States in 1969, by States, 56
Types of Mines, and Classes of Ore Yielding Gold, in Terms
of Recoverable Metal
16 Twenty-Five Leading Gold-Producing Mines in the United 57
States in 1969, in Order of Output
17 Twenty-Five Leading Silver-Producing Mines in the United 62
States in 1969, In Order of Output
vii
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TABLES (continued)
No, Page
18 Mine Production of Recoverable Silver by States in 1969 63
19 Principal Producers of Molybdenum Concentrates in the 70
United States
20 Amounts, Forms, and End Uses of Molybdenum Consumed (1969) 71
21 Salient Tungsten Statistics 76
22 Major Producers and Processors of Tungsten Concentrates 78
23 Tungsten Mines and Mills (Past and/or Possible Producers) 79
24 Producers and Processors of Tungsten Materials 80
25 Tungsten Minerals 82
26 Reagents Used in Flotation of Molybdenite 93
27 Analysis of Water Samples 94
28 Water Data for Refractory-Metal-Processing Plants 97
29 Water Uses and Recirculation Practice in Refractory Metal 98
Processing Plants
30 Assessment of Information Obtained in Terms of Unit 102
Processes and Future Needs
viii
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SECTION I
CONCLUSIONS
1. The trend in the primary aluminum industry is toward reduced or
zero discharge of waste water from both alumina refineries and aluminum
smelters.
2. The principal treatment needs of the aluminum industry relate to
common types of industrial waste water such as cooling tower blow-down
and neutralization products, and the specialized need to remove or re-
cover fluoride ion components from fume scrubbers at smelters.
3. The primary mercury industry, by virtue of a current air pollution
control problem, may require increased measures of water pollution con-
trol associated with air emission control equipment or new processing
methods.
4. The primary molybdenum industry, consisting of a small number of
operations other than those associated with the copper industry, has
taken or is designing effective methods of water pollution control
ranging from isolated water systems to changes in flotation reagent
concentrations.
5. Plants processing refractory metal concentrates to end products
generally are associated with municipal water systems and show high
materials recoveries with concurrent close control and careful segrega-
tion of waste water streams. Neutralization with filtration of acid
wastes is a common practice of the plants surveyed.
6. The small amount of information available for the primary gold and
silver industries shows greatly differing practices, ranging from zero
discharge in arid climates to problems with mercury and cyanide con-
tents in waste waters.
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SECTION II
RECOMMENDATIONS
Based on the findings of this study, it is recommended that:
1. Studies be carried out dn the removal and reclamation of fluoride
components from the wet-gas-scrubber liquors used in aluminum smelters.
2. Current and future developments in the primary mercury industry be
monitored and evaluated to allow timely development of water pollution
control practices applicable either to wet methods of air emissions
control, or to waste waters generated by new hydrometallurgical pro-
cesses .
3. Further insight be obtained into tungsten ore concentrating opera-
tions to identify specific needs in terms of geographical location,
intermittent operation, and the disposal or treatment of waste leaching
liquors.
4. A more intensive study be conducted directed at obtaining data on
individual unit process waste sources, and that such a study include
some provision for sampling and analysis. This work should be aimed
at defining point sources, characteristics, volumes, unit waste loads
and the effectiveness of treatment practice in more detail than this
study has shown to be presently available.
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SECTION III
INTRODUCTION
The purposes of this study are to assess current water-pollution-con-
trol practices and problems and to provide a basis for recommending
specific directions to develop water-pollution-control methods in the
nonferrous-metals industry. The approach used in this study has been
to deal with specific practices and problems rather than with generali-
ties or overall considerations. This study, in attempting to be speci-
fic, thus has dealt with the variegated and individualistic nature of
the metal-producing operations which constitute the total industry.
This report is organized to present the data obtained in groupings
which are determined by the relationships between production operations.
Thus, Volume I dealt with the production processes and water-use prac-
tices of the copper, lead, and zinc industries. These major metal-
plant operations include the manufacture of the following by-products:
cadmium, "by-product" gold, silver, platinum, palladium, and rhodium;
arsenic, bismuth, thallium, indium, selenium, tellurium, and molybdenum
concentrates or oxides; antimony; and the metal compounds arsenic tri-
oxide, copper sulfate, nickel sulfate, zinc oxide, zinc sulfate, and
sulfuric acid. This volume (Volume II) deals with operations producing
alumina and aluminum, mercury, primary gold and silver, and molybdenum
and tungsten.
In preparing this report, it was found necessary to deal with manufac-
turing processes in a somewhat intensive manner in order to identify
the process steps which produce characteristic components of waste
water; i.e., in some cases the primary metal product is so efficiently
extracted that little waste is generated, whereas marginal discharges
of by-product operations or nominally minor components of raw materials
appear in waste streams.
The method used in the study was to assemble the often fragmentary in-
formation available in the literature and, more importantly, to obtain
information directly from the industry. The letters of inquiry sent to
selected companies requested information on current practices of water
usage, and the sources, characteristics, and amounts of waste water,
and the industry's own statements of problem areas and treatment needs.
Two constraints were applied to the data supplied by industry: that
such information be supplied voluntarily and at the expense of industry,
and that the specific sources of each lot of information remain anonymous,
In reporting the results of this study, separate sections have been de-
voted to each metal or metal grouping. The size and distribution of the
particular industry, its economic characteristics, the technology em-
ployed, its water-usage characteristics, its waste-collection, treatment,
-------
and disposal practices, and anticipated future treatment requirements
are discussed in each section.
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SECTION IV
PROCEDURES
The sequence of tasks in this program consisted of:
1. Compilation of a list of the companies and plant facilities in the
United States which produce nonferrous metals
2. Contacting the identified companies by telephone, letter, or per-
sonal visits to obtain the desired information
3. Compilation and analysis of the data obtained to prepare this
report
4. Use of documentary sources wherever available to obtain required
associated information such as industry structure, overall economic
aspects, process technology, prior studies on water usage, and other
supplementary information.
The open literature was found to contain little specific information on
water problems or treatment in the nonferrous industry. This study,
therefore, placed its main reliance for specific details on the volun-
tary contributions of unpublished data from industry. Further, it was
found that the degree of precise knowledge of plant water usage is still
highly variable from plant to plant.
Out of 56 companies approached, about 50 percent responded by submitt-
ing data in varying degrees of detail. Their replies covered 78 facili-
ties ranging from single mine operations to complexes of mines, mills,
smelters, refineries, etc. The responses received provided information
on 35 mines, 33 concentrators, 8 copper leach-precipitation operations,
27 copper, lead, and zinc smelters, 20 refineries, 8 sulfuric acid
plants, and 8 power plants. This group of operations is reported on in
Volume I.
Also, responses were obtained on 3 alumina refineries, 11 aluminum
smelters, 3 primary mercury mining and furnace operations, 2 mines pro-
ducing gold and/or silver, and 4 refractory-metal processing plants.
These processes and associated water use and treatment practices are
discussed in Volume II.
In view of the extreme complexity of the nonferrous-metals industry and
recognizing that many who use this report may be unfamiliar with the in-
dustry, it was decided that each section should include a more or less
detailed description of the industrial segment, its structure, and
technology, as an aid to understanding and interpreting its water and
waste-treatment problems and practices.
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SECTION V
THE PRIMARY ALUMINUM INDUSTRY
Characteristics and Geographical Distribution
The major characteristics of the primary aluminum industry of the
United States and its processing operations may be briefly indicated as:
1. The importation of most of its principal raw material, bauxite ore,
from overseas sources
2. The refining of bauxite ore to an intermediate product, anhydrous
alumina, at the points of entry on the coastline
3. The location of metal-reduction plants near sources of low-priced
electrical power.
The primary aluminum industry in the United States may be considered to
consist of two segments, the alumina-refining plants and the aluminum-
reduction works.
The alumina-refining plants operated by the various United States alumi-
num producers, their capacities, and their locations are indicated in
Table 1 and Figure 1. These plants process raw bauxite ore to the
TABLE 1. OPERATING COMPANIES, LOCATIONS, AND CAPACITIES
OF U.S. ALUMINA REFINING PLANTS
(T)
Company
Plant Location
Capacity,
thousands
short tons/year
Aluminum Company
of America
Kaiser Aluminum &
Chemical Corp.
Reynolds Metals
Company
Ormet Corporation
Mobile, Alabama
Bauxite, Arkansas
Point Comfort, Texas
Baton Rouge, Louisiana
Gramercy, Louisiana
Hurricane Creek, Arkansas
La Quinta, Texas
Burnside, Louisiana
950
400
900
985
620
840
1,185
550
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a
O
2
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10
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intermediate product form of refined alumina. In 1966, these plants
accounted for the refining of 2,000,000 short tons of domestic bauxite
and 12,700,000 short tons of imported bauxite. The dollar value of
these ores is difficult to express because in many cases the bauxite
mine, shipping means, and alumina refinery are related either by common
ownership or trading arrangements between operations. By 1968, these
plants were refining about the same amount of domestic ores and approxi-
mately 12,000,000 short tons of imported bauxite, and, in addition, 1.8
million tons of alumina were imported. The recent trend has been to re-
duce the volume of material shipped by refining the bauxite ore to
alumina overseas (a 2 to 1 reduction in shipping weight), at, for exam-
ple, the Harvey Aluminum Company's refinery in the Virgin Islands
(350,000 tons per year) or the refinery at Queensland, Australia.
The ownership, location, and size of current and future aluminum-reduc-
tion plants are shown in Table 2. (2, 3) xhe locations of these plants
are indicated on the map in Figure 2.
The reasons for the geographical distribution of the aluminum reduction
plants may be illustrated by the following values of delivered cost of
alumina and electrical
Geographical Shipping Cost Power Cost,
_ Area _ per Ton of Alumina, $ mils/kwhr
Pacific Northwest
By ocean 5.00 2. 1
By rail 12.26 2.1
Ohio Valley 8.95 3.5
Tennessee Valley 5.35 4.2
These figures serve to explain the trend toward the opening of new
plants in the Tennessee Valley and Pacific Northwest areas. The in-
creasing rate of expansion of the Australian ore reserves and alumina
refineries, which would supply the Northwest area, is another factor to
be considered in future trends in aluminum-plant location.
That is, the availability of cheap electrical power, usually from hydro-
electric generators, or, alternatively, from natural-gas-fueled gener-
ators as in the Gulf Coast area, must be balanced against the shipping
cost of the refined alumina and other raw materials to the smelter, and
the shipping cost of the aluminum ingots to markets.
Contribution to United States Economy
The contribution of the primary aluminum industry to the economy may be
expressed in two ways: dollar values and product usefulness. According
to statistics for 1967, the primary aluminum industry was described in
the following economic terms.
11
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TABLE 2. OWNERSHIP, LOCATION, AND PRODUCTION CAPACITY
OF U.S. PRIMARY ALUMINUM PLANTS (2>3)
Capacity, short tons/yr
Installed, Planned,
1969 1973
Aluminum Company of America
Alcoa, Tennessee
Badin, North Carolina
Massena, New York
Point Comfort, Texas
Rockdale, Texas
Vancouver, Washington
Warrick, Indiana
Wenatchee, Washington
Totals
American Metals Climax
Warrenton, Oregon
Anaconda Aluminum Company
Columbia Falls, Montana
Sebree, Kentucky
Consolidated Aluminum Corporation
New Johnsonville, Tennessee
Eastalco Aluminum Company
Frederick, Maryland
Gulf Coast Aluminum Company
Lake Charles, Louisiana
Harvey Aluminun (Inc.)
The Dalles, Oregon
Cliffs, Washington
Intalco Aluminum Corporation
Bellingham, Washington
Kaiser Aluminum & Chemical Corporation
Chalmette, Louisiana
Mead, Washington
Ravenswood, West Virginia
Tacoma, Washington
Totals
National-Southwire Aluminum Company
Hawesville, Kentucky
200,000
100,000
125,000
175,000
225,000
100,000
175,000
175,000
1,275,000
175,000
140,000
87,000
265,000
260,000
206,000
163,000
81,000
710,000
275,000
100,000
125,000
175,000
275,000
100,000
275,000
175,000
1,500,000
150,000
175,000
295,000
140,000
255,000
35,000
87,000
191,000
265,000
260,000
206,000
163,000
81,000
710,000
180,000
Continued on following page.
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TABLE 2. (continued)
Noranda
New Madrid, Missouri
Northwestern Aluminum Company
Warrenton, Oregon
Ormet Corporation
Hannibal, Ohio
Revere
Scottsboro, Alabama
Reynolds
Arkadelphia, Arkansas
Jones Mills, Arkansas
Listerhill, Alabama
Longview, Washington
Massena, New York
San Patricio, Texas
Troutdale, Oregon
Unidentified by Plant
Totals
U.S. Totals
240,000
Capacity, short tons/yr
Installed, Planned,
1969 1973
75,000
135,000
240,000
112,000
63,000
122,000
221,000
190,000
128,000
111,000
100,000
40,000
975,000
5,520,000
63,000
122,000
221,000
190,000
128,000
111,000
100,000
935,000
3,827,000
13
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w
Hi
g
14
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Number of Establishments 25
Number of Employees 23,800
Payroll $190,900,000
Value of Shipments $1,608,700,000
Materials Consumed
Alumina 5,692,500 short tons
Alumina $365,600,000
Other $271,800,000
Purchased Electrical Energy
Million kwhr 41,956.0
Million dollars 143.6
Primary Aluminum Produced 6.54 billion pounds
Total Consumption 8.3 billion pounds
Per-Capita Consumption 42 pounds
In this listing the difference between primary production and total
consumption is due to secondary metal recovery and imports.
The primary aluminum industry produces only a raw material for other
manufacturers. The distribution of aluminum in its final product forms
may be indicated as follows:(")
Shipments, Share of
Major Market Area millions of pounds Market
Transportation 1,915 21.4
Building and Construction 1,866 20.8
Electrical 1,249 13.9
Containers and Packaging 866 9.7
Consumer Durables 844 9.4
Machinery and Equipment 625 7.0
Exports 657 7.3
Others 940 10.5
8,962
It is estimated that there are about 4000 end-use forms for aluminum.
Only an indication can be given of these final uses in this report.
The commercial forms of aluminum and aluminum alloys include
Castings Structural shapes
Sheet and plate Tube and pipe
Foil Forgings
Wire, rod, and bar Impact extrusions
Extrusions Particles, powder, and paste
The final applications of aluminum include and far exceed those indi-
cated in the following listing'"/:
Building Construction -- siding, gutters and downspouts,
awnings, doors, windows, insulation, curtain walls, orna-
mental metalwork, railings, roofing
15
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High Products -- bridges and railings, guard rails, signs,
light standards, fencing, culvert
Electrical Structures -- towers, crossarms, switchyard
support and sheltering structures
Petroleum Industry -- drill rigs, offshore structures, drill
pipe, storage tanks, pipelines
Chemical, Food, Drug, and Beverage Industry -- corrosion-
resistant tanks, bins, pipe, stills, condensers, trays, heat
exchangers, tank cars, valves, fittings, rolls, buckets,
spools
Structures and Equipment for Refrigeration and Cryogenic
Applications
Automotive and Engine Applications -- cylinder blocks, heads,
bearings, engine covers, connecting rods, pistons, super-
chargers, transmission cases, wheels, housings, trim, hard-
ware, fuel tanks, truck chasis, frames, and bodies, panels,
tank trucks
Railroad Equipment -- tank cars, hopper cars, buildings, car
panels, signs, signals
Marine Applications -- protective anodes, buoys, hydrofoils,
small craft, gun boars, canoes, barges, engine blocks
Aircraft and Aerospace Applications -- aircraft, airframes,
skins, panels, forgings, engine components, honeycomb panels,
castings, helicopter rotor blades, propellers, missile skins,
frames, and fuel tanks, space vehicles, ground support and
test equipment
Military Vehicles and Equipment -- armor plate, wheeled
vehicles, mobile equipment, wheels, amphibious vehicles,
portable bridges, rocket and grenade launcher tubes
Machinery, Tooling and Instrument Applications -- bearing
alloys, pumps, tire molds, patterns, tooling plate, assembly
jigs, irrigation pipe, business-machine covers, nonmagnetic
instrument cases and components, materials-handling equipment,
mining equipment, textile machinery, printing machinery
Electrical and Electronic Equipment -- wire, cable, bus bar,
power transmission and distribution equipment, towers, capa-
citors, conduit, antenna, lighting reflectors
Household Goods -- appliances, furniture, etc.
16
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Packaging Applications -- cans, foil packages, collapsible
tubes, bottle caps
Pigment and Paint Applications.
Projected Growth of the Industry
The history of the output of the primary aluminum industry is indicated
in Figure 3.(6,7) Shown for comparison are the data for mill-product
shipments for the years 1960 to 1970. Various analyses have found
growth rates for the aluminum industry to be a compounded annual growth
rate of 5.8 percent over the last 20 years for primary production and a
10 percent annual growth rate for the total consumption of aluminum
mill products and other forms. At the end of 1969, one projected growth
rate was estimated at 7 percent a year, or nearly 16 billion pounds of
mill products by 1975.''' Unless patterns change, this would call for
9.9 billion pounds of primary production in 1973, and 12 billion pounds
in 1975. Currently planned expansions in primary production (Table 2)
also agree with the forecasts of 7 to 10 percent annual expansion rate.
It appears that estimates of future growth fall within the range of 5.8
percent (based on the past 20 years) to 10 percent (based on the past
10 years).(7,8)
Raw
Materials and Process' '
The raw materials used in the production of 1 pound of aluminum metal
are:
Input to Alumina Plant
4 pounds bauxite ore
0.2 pound soda
0.2 pound limestone
0.5 pound coal
0.25 pound fuel oil
Input to Aluminum Plant
2 pounds alumina
0.25 pound pitch
0.5 pound petroleum coke
0.1 pound cryolite
0.04 pound aluminum fluoride
0.6 pound baked carbon
10 kilowatt hours of electrical energy.
The following discussion deals briefly with the most important of
these raw materials and where they are used in the production processes.
17
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12.0
11.0
Mill Product
Shipments
Primary Aluminum
Production
1930
1940 1950
1960 1970 1980 1990
Year
FIGURE 3. PRIMARY ALUMINUM PRODUCTION AND MILL PRODUCT SHIPMENTS
FOR SELECTED SPANS OF YEARS (6) (7)
18
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Types and Sources of Bauxite Ores
Bauxite ores vary in characteristics from stony materials to soft clays.
In general, the term bauxite applies to weathered deposits from which
substances other than alumina have been leached to leave a high enough
alumina content to make the deposit profitably workable. The composi-
tions of bauxite ores usually fall within the following ranges:
Content,
_ Material _ weight percent
40 to 60
free and combined 1 to 5
H20 combined 12 to 30
Fe203 7 to 30
Ti02 3 to 4
F, P20s, V205, other 0.05 to 0.20
The principal determinants characterizing a bauxite ore are the form of
hydrate in which the alumina occurs and the form in which the silica
occurs. The alumina may be present as a monohydrate, indicated by the
formula A1203-H20, and, as such, may take either of two mineralogical
forms, identified as boehmite or diaspore, or may be present as the tri-
hydrate indicated by Al203'3H20, taking forms known as gibbsite or hydra-
gillite. The principal distinction between the two hydrated forms is
that the trihydrate forms are more soluble than the monohydrate in the
solvent (sodium hydroxide or sodium carbonate solution) used in the re-
fining process.
The silica content and the form in which it is present are important
factors in the yield of a bauxite ore. On a weight basis, one part of
silica ties up one part of alumina in the form of the mineral kaolinite
Al203> 2S102' 2^0, and, additionally, results in the consumption of one
part of the caustic solution in the formation of insoluble sodium
aluminum silicate. The use of high-silica bauxites involves either the
above losses or the use of a two-step, "combination" process to recover
the losses in the initial processing.
Deposits of bauxite ores are found worldwide, as shown by the listing
of estimated ore reserves in Table 3. Of more specific interest is the
listing of Table 4 which shows the sources of ore used by the United
States aluminum industry and the specific alumina-refining plants pro-
cessing the ores. The geographical locations of the alumina refineries
were shown in Figure 1. It should be noted that the United States
aluminum industry obtains two types of raw materials from overseas:
bauxite ore and refined alumina. Some comparative figures showing the
domestic production of bauxite and imports of bauxite and alumina for
related years are given in Table 5.
Thus, in brief, the sources of bauxite ores are overseas except for a
19
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TABLE 3. ESTIMATED WORLD ORE RESERVES OF BAUXITE
(4)
Region
Country
Estimated
Ore Reserves,
millions of tons
Present Status
of Utilization
Europe France
Spain
Italy
Yugoslavia
Austria
Hungary
Rumania
Greece
Turkey
Americas United States
British Guiana
Dutch Guiana Surinam
French Guiana
Caribbean Islands
Haiti and Dominican
Republic
Jamaica
Brazil
U.S.S.R. U.S.S.R.
Africa Guinea
Mali
Ghana
Cameroons
Congo Republic
Asia India
Malaysia and Indonesia
Tonkin
China
Australia
100
Some
Some
100
Some
HOO
10-20
50-100
HO-50
^50
Several hundred
Several hundred
40
300
5-10
200-300
-vLOO-150
4-5
200-100
200
500-1000
10-50
100-200
10-50
Small
Information
uncertain
1000
Used in France
Unexploited
Used in Italy (with
imports)
Exported to Germany
and Italy
Exported to U.S.S.R.
Unexploited
Exported to Western
Germany and U.S.S.R.
Unexploited
Supplies 207» of U.S.
consumption
Exported to U.S.
Exported to U.S.
Unexploited
Exported to U.S. and
Canada
Exported to U.S. and
Canada
Exported to U.S. and
Canada
Little information
available
Lacks bauxite; uses
nepheline
Current production
exported to U.S.
and Europe
Large deposits found
Exported to Britain
and Germany
Unexploited
Exported to Japan
Exported worldwide
20
-------
TABLE 4. SOURCES OF BAUXITE AND LOCATIONS OF ALUMINA
PLANTS SUPPLYING THE U.S. ALUMINUM INDUSTRY
Source of Bauxite
Locations of Alumina Refining Plants
Arkansas
Australia
Dominican Republic
Guinea
Haiti
Jamaica
Surinam
Bauxite, Arkansas
Hurricane Creek, Arkansas
Queensland, Australia
Point Comfort, Texas
St. Croix, Virgin Islands
Corpus Christi, Texas
Point Comfort, Texas
Baton Rouge, Louisiana
Gramercy, Louisiana
Corpus Christi, Texas
Mobile, Alabama
Point Comfort, Texas
Burnside, Louisiana
TABLE 5. COMPARATIVE FIGURES SHOWING IMPORTS AND DOMESTIC
PRODUCTION OF BAUXITE AND ALUMINA FOR THE U.S.
ALUMINUM INDUSTRY
Year
1960
1968
1969
Source
U.S.
Imports
U.S.
Imports
U.S.
Imports
Jamaica
Surinam
Dominican
Haiti
Guyana
Bauxite ,
millions of
short tons
2.24
9.75
1.86
12.32
2.20
13.45
^8.06
^2.69
Republic 1
V balance
Alumina ,
millions of
short tons
0.089
--
1.345
--
1.8
Australia ^1 . 2
Surinam ^0.45
Other I
sources V balance
21
-------
single deposit within the United States, in Arkansas, which is mined at
a rate of about 2 million short tons per year. The balance of the
bauxite requirements are supplied from overseas. A recent trend in
this pattern is the establishment of alumina-refining plants at over-
seas sites (Jamaica and Queensland) and the importation of the refined
alumina. The relatively recent development and exploitation of bauxite
reserves in Australia and the construction of refining plants there
will continue to have an increased effect on the import pattern in the
near future.
The sources of bauxite and alumina have been discussed above. Of the
other required raw materials, most are obtained from conventional com-
mercial sources. Two of the materials cryolite and aluminum fluoride--
are especially noteworthy because removal of their fluoride contents
accounts for the major use of water in gas scrubbers in aluminum-reduc-
tion plants. Cryolite and aluminum fluoride are the major materials
used to form a fused-salt electrolyte in which alumina is dissolved and
electrolyzed to produce aluminum metal.
Cryolite is a white crystalline material with the chemical formula
AlF3'3NaF. Natural cryolite has been found in only one location,
Greenland, and exhibits major constituents as follows:
Fluorine, F 51 weight percent
Sodium, Na 30 weight percent
Alumina, Al2C>3 12.5 weight percent.
The output of natural cryolite is limited and it is used only during
the starting period in the operation of the electrolytic cell because
it is apparently more stable than the synthetic form. Synthetic cryo-
lite is used during the operating period of the cell and is produced by
chemical processes having as the principal reaction:
AlnO,-3H^O + 12HF + 6NaOH 2 NaJUF. + 12H.O.
/ _) 2 j o Z
Aluminum Trifluoride, A1F3, also is a product of chemical processing
and is used in great quantities by the aluminum industry.
Major Processes in the Production of Aluminum '
The major processing operations discussed in the following sections are
shown on the flowsheet in Figure A.
The refining of alumina from bauxite is accomplished by either of two
processes: one called the Bayer process, the other the combination
process.
In the Bayer process, the bauxite ore is dried and ground prior to
chemical treatment. The hydrated alumina in the bauxite is converted
22
-------
KaAlO
Brown Mud
Dissolving
Heat & Pressure
CaCO.,
NaCO:
Waste <- Redl Mud
Petroleum
Coke
Paste Mixing ,
Pressing
NaAlO, Solution
1
Anthrz
1
Paste
Mixer
" f
Soft
cite
Baking 1
A1203
t
Cryolite (Na,AlF,)- *- Cell
J P ..,, ^
1
Aluminum
Pitch
^Fluorine
Containing
Gases
Waste
Water
FIGURE A. FLOWSHEET OF MAJOR PROCESSES IN ALUMINUM PRODUCTION
23
-------
to a soluble salt, sodium aluminate, by reaction with either sodium
hydroxide or a combination of lime and sodium carbonate to accomplish
the following net reaction:
(monohydrate) AlO-OH + NaOH > NaAlCl 4- HO
(trihydrate) A1(OH)3+ NaOH + NaAl02 + 2H20.
In practice this reaction is accomplished by mixing the ground ore with
caustic solution in large iron mixing tanks. The mixture is fed into
pressure vessels or autoclaves and heat and pressure developed by either
steam heating of jacketed autoclaves or direct injection of live steam.
Conditions must be varied to suit the bauxite ore composition but may
be indicated as follows:
Trihydrate forms - a solution containing 100 to 150 g/1 of Na 0 and
temperatures of 120 to 170 C at 50 to 70 psi
pressure
Monohydrate forms - a solution containing 200 to 300 g/1 of Na20 and
temperatures of 200 to 250 C at pressures as high
as 500 psi.
Most bauxite ores contain different proportions of the monohydrate and
trihydrate ores and operating conditions are adjusted to obtain optimum
processing. The greater portion of bauxites processed in the United
States is predominantly of the monohydrate form, which permits the use
of the lower concentrations, temperatures, and pressures.
The product of the above digestion process is a slurry containing
NaAl02 in aqueous solution and undissolved solids consisting of parti-
cles (in the micron size range) of sodium aluminosilicate, metal oxides,
and residues of the reagent materials. These products are discharged
from the digesters (usually through heat exchangers to liberate heat to
ingoing mix), put through thickeners (typically with four stages), and
finally separated by decantation of the clear sodium aluminate solution
from the slurry product. The wastes-so lids product is the well-known
red mud of the aluminum industry. The red mud is washed with water to
remove the final traces of soluble sodium aluminate and recover any
residual caustic. The wash waters are recirculated to the beginning of
the process and combined with the input to the mixers. From here, the
red mud may be moved as a waterborne slurry to a waste area, known as
the red-mud lake, and not further processed. In the combination pro-
cess, applied to high-silica bauxites, the red mud is treated to ex-
tract additional amounts of the alumina.
This additional extraction step is accomplished by mixing the red mud
with limestone (effectively CaCO-j) and sodium carbonate, and the mix-
ture is sintered at 1100 to 1200 C. The important reactions are the
conversion of silica to calcium silicate and of the residual alumina to
sodium aluminate. The sintered products are leached in a caustic
24
-------
solution to produce additional sodium aluminate solution which is fil-
tered and added to the main stream operation. The residual solids
(brown muds) are slurried to a waste lake.
From either of the alternative processes, purified sodium aluminate
solution is passed through heat exchangers and cooled to 50 to 60 C
prior to being discharged into large precipitation vessels. By the
addition of seed material and by careful control of composition and
controlled agitation, alumina trihydrate is precipitated in a controlled
form, amenable to easy separation and washing. Precipitation may take
2 to 4 days.
The precipitated trihydrate is dewatered and fed to calcining furnaces.
Calcining at 1200 C drives off the excess water, breaks down the trihy-
drate alumina to simple alumina, and transforms the alumina to a cry-
stalline form (alpha) most suitable for later use in the electrolytic
reduction to aluminum metal.
The clarified liquor obtained after precipitation is a mixture of sod-
ium hydroxide and soluble salts of impurities and is reclaimed by pro-
cessing in multiple-effect, steam-heated evaporators to drive off ex-
cess water, bring the NaOH concentration upward toward that desired for
reuse, and eliminate the impurity salts. The reclaimed NaOH solution
from the evaporators is refortified with new caustic additions and re-
used in the process.
In general, the purified alumina is transported a considerable distance
from the refinery for the smelting or electrolytic reduction to alumi-
num metal.
The heart of the aluminum plant is the electrolytic cell, or pot,
which consists of a steel container lined with refractory brick with
an inner liner of carbon. The outside dimensions of the pot may vary
from 12 by 15 to 8 by 20 feet or larger. Most cells are around 3 feet
in height. The cells are arranged in rows, in an operating unit called
a potline, which may contain 100 to 250 cells electrically connected in
series. The electrical supply is direct current, on the order of sev-
eral hundred volts and 60,000 to 100,000 amperes. The carbon liner on
the bottom of the furnace is electrically active and constitutes the
cathode of the cell when covered with molten aluminum. The anode of
the cell is formed of baked carbon blocks supported from above. The
electrolyte consists of a mixture of
Percent
Cryolite 80-85
Calcium fluoride 5-7
Aluminum fluoride 5-7
Alumina 2-8
The fused-salt bath usually is operated at a temperature of 950 C.
25
-------
Cells presently in use operate with current on the order of 100,000
amperes with a voltage drop across the cell of about 4.5 volts. The
reaction in the aluminum reduction cell is not completely understood,
but results in the reduction of the aluminum from the apparent Al+^
state, assuming ionization in the molten salt, to the Al° state at the
carbon cathode at the bottom of the furnace, where the metal collects
as electrolysis proceeds. Oxygen, assumed present in the bath as 0" ,
appears at the carbon anode and immediately reacts with the anode and
surrounding constituents to form a mixture of 75 percent carbon dioxide
and 25 percent carbon monoxide, which results in the consumption of the
carbon anode.
Thus, the operation of the electrolytic aluminum reduction cell results
in the continuous consumption of alumina and the carbon anode, and the
evolution of gaseous reaction products. The alumina content of the
cell is replenished intermittently. The aluminum is withdrawn from the
bottom of the molten bath by a vacuum siphon device, at a rate of about
500 to 1800 pounds every 24 hours, although practice may vary. The
molten aluminum is collected in ladles and cast into ingots or pigs as
the final product of the smelting process.
The continuous consumption of the carbon anode gives rise to the exis-
tence of an anode-preparation plant associated with every aluminum
plant. The thermal stability and electrical properties of the anodes
are of importance to the proper operation of the cell. Two methods of
anode preparation are used at present. One method is the prebaked
anode practice and the other the continuous anode, or Soderberg process.
The anode raw materials are hard pitch and petroleum coke--these are
purchased in large quantities to the desired specifications. The prep-
aration of these materials includes crushing and classifying into frac-
tions with particle sizes ranging from 0.2 to 15 mm and blending in
carefully controlled proportions. Classifying may be accomplished by
various combinations of screens and cyclones handling the different
size fractions. The mixtures are preheated to 200 to 300 F to soften
the pitch and mixed warm to achieve uniformity of mix and density.
This mix is called "anode paste".
In the prebaked anode method, the warm paste is formed into anode
blocks in a hydraulic press and the anodes are baked and graphitized by
a heating cycle that may, for example, last 15 days with a maximum
temperature of 2000 F.
The continuous anode or Soderberg process consists of the continuous
supply of anode paste within a consumable aluminum sleeve to the cell.
This system relies on the approach of the anode materials to the bath
surface to achieve the baking operation immediately before the anode
enters the bath.
In either case, the facilities for preparation of anode materials, re-
ferred to as the paste plant, include extensive equipment and facili-
ties for dust control and particle classification.
26
-------
The continuous evolution of the gaseous reaction products from the
aluminum-reduction cell yields a large volume of fume which consists
chiefly of carbon dioxide and carbon monoxide but also includes signi-
ficant amounts of volatile fluoride compounds and fine dust evolved
from the cryolite, aluminum fluoride, alumina, and carbonaceous materi-
als used in the cell. The removal of this fume from the working area
involves extensive air-flow control which may extend to the design of
the plant building and hoods, ducts, dust collectors, cyclones, and gas
scrubbers. These dust- and air-pollution control measures are the out-
standing characteristics of an aluminum plant and account for the major
use of water at an aluminum plant.
Water Usage in the Aluminum Industry
Water usage in the primary aluminum industry includes that of the two
major divisions of processes in the industry: the alumina refining
operations and the aluminum reduction or smelting operations.
The alumina-refining operations (discussed in detail in a prior section
of this report) show the major process characteristics of the leaching
of the desired A1203 constituent from bauxite ores by a hot, pressur-
ized, caustic leach with precipitation and drying of the pure A^C^ and
the discard of the residue from the original bauxite ore. The general
pattern of water usage (Figure 5) includes the uses of water for leach-
ing solution, washing of precipitates and other steps of the chemical
extraction process, considerable use for heat-exchange purposes in con-
nection with the control of temperatures in the reaction, i.e., steam
heating, flash evaporation, or multiple-effect evaporators, etc. From
the viewpoint of water recirculation or discharge, however, the major
feature of the water circuit is the red- or brown-mud lakes operated at
all alumina refineries. This is analogous to a tailings pond in a flo-
tation concentrator operation, i.e., the mud lake serves as a receiver
of solid residues, a receiver and reservoir of process water, a point
of evaporation and seepage losses, and a collector of rainfall. It may
be noted that water serves as the medium in the transport of the waste
portion of the ore to the lake, i.e., some minimum amount of water is
required by the mechanics of flushing the material to the disposal
plant.
In general, the Bayer process in either of its versionsthe standard
or the combined process has no demand for water for use in air-pollu-
tion control. The processes used essentially are carried out in closed
vessels, with little potential of emissions to the atmosphere. As with
any plant, a sanitary water circuit is part of the operation, requiring
a source of potable water. Disposal may be to a municipal sewer system,
a plant sewer system, or the red-mud lake, with or without any form(s)
of treatment.
The general pattern of water use at aluminum smelters would include
27
-------
Wells or River
Treatment
1
Processes
Digestion
Precipitation
Evaporation
T
Condensates
to Plant
Use or
Discharge
Process
Liquor
To
Receiver
or
Red-mud
Lake
Red-mud
Slurry
FIGURE 5. GENERALIZED DIAGRAM OF COMMON FEATURES
OF WATER CIRCUITS OF ALUMINA REFINERIES
28
-------
(Figure 6) features of sanitary and boiler uses, and usually cooling
circuits applied to d-c power equipment, metal-casting operations, fur-
nace cooling in the anode plant, and miscellaneous equipment cooling.
Cooling waters may be recirculated through a cooling tower, used in
series or used on a once-through basis, with various discharge practice.
The major use of water is in the fume scrubbing operations (if wet
systems are used) associated with the anode plant, casting operations,
and the aluminum-reduction cells. Here practice varies from once-
through methods to a closed circuit with recycle and reclamation.
In the present study, information of varying detail was obtained on
3 alumina refineries with an aggregate capacity of 1.9 million tons of
alumina, and on 1J smelters with an aggregate "nominal" capacity of 2.2
million tons of aluminum per year. These data are summarized in Table
6.
The reports on alumina refineries were of two types: generalized re-
ports on groups of plants owned by a single company and specific reports
on individual operations. The patterns of water use in alumina refin-
eries showed total plant intakes varying from approximately 10 to 900
million gallons per year with unit intakes ranging from 60 to 1560 gal-
lons per ton of metal.
A breakdown on the distribution of water use within those refineries
reporting specific uses was as follows:
Percent
Cooling 77.3
Sanitary 11.1
Process 9.4
Other 2.2
100.0
Process uses include both direct addition to the process stream or
makeup water to the red mud lake, which may be used in either process
or other uses, depending on recirculation. The breakdown shows no use
of intake for boiler feed, as this is derived from process condensates.
The "other" category includes uses such as treatment of incoming water,
uses in instruments, and numerous small uses about the plants. The
plants all show high recirculation rates, where such ratios could be
defined, i.e., the ratios of actual flows to intakes of new water were
8.6 for process water and 15.6 for cooling, while boiler feed and some
cooling water supply was being derived from process condensates. Total
consumption ranged from 60 to 259 gallons of water per ton of alumina
produced, i.e., 0.03 to 0.12 gallon per pound.
Discharges ranged from 0 to 1,370 gallons per ton of alumina, with the
minimum intake corresponding to minimum consumption, i.e., 60 gallons
per ton for both values, and these were associated with zero discharge.
29
-------
Wells or River
To Municipal
System
or
Receiver
i
FIGURE 6. GENERALIZED DIAGRAM OF COMMON FEATURES OF WATER
CIRCUITS OF ALUMINUM SMELTERS
30
-------
The pattern of water use at aluminum smelters is indicated by the data
in Tables 6 and 7. Here plant intakes are shown to vary from 89 to
7,000 million gallons per year, with the plant with lowest total intake
showing greatest unit intake, again reflecting the range of variations
in individual plants.
The two most significant factors in water use and discharge pattern have
been related to the scrubbing of potroom fumes. The approaches to this
have varied over the years to include
1. No scrubbing
2. Wet scrubbing using once-through water (discharged with or without
treatment)
3. Wet scrubbing with recirculation of water and reclamation of con-
tained fluorides, alumina, etc.
4. The use of dry scrubbing systems, using no water, which allow
reclamation of fume components.
Current economic and other pressures have brought almost all the indus-
try to States (3) and (4). The dry fume-scrubbing method is being in-
stalled in some of the plants, currently under construction, and has been
or is being installed to replace wet scrubbers in some of the older
plants. The dry fume-scrubbing' system reduces plant water requirements
to sanitary, boiler feed, and heating needs. Thus, the potential ex-
ists for the elimination of air pollution, a large decrease (i.e., =75
percent) of water intake, the elimination of all discharges of process-
contaminated waste water, and the reclamation and recycle of formerly
wasted materials. This classic engineering feat is currently the pro-
perty of the originating company, but its potential spread through in-
dustry makes predictions of future water usage largely useless, as the
presence or absence of this system changes the water use at any plant
almost by the entire amount of water which would be predicted for any
other system.
Nevertheless, some aluminum-smelt ing plants will probably continue to
exhibit the variegated water usage and discharge patterns indicated in
Table 7.
These patterns are determined by the interrelationships of water costs,
local water availability, individual plant design, and climate.
Waste-Water Characteristics and Amounts
Alumina Refineries
The waste-water characteristics associated with alumina refineries
31
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have previously been labeled "not a pollution problem". However, these
waste waters or their components as found by this survey were reviewed
because they contain components or impurities common to many industrial
plant operations. The specific components of the total waste water may
include
Sanitary wastes
Cooling water
Intake water treatment plant effluents
Pump bearing cooling
Boiler blowdown
Demineralizer resin regeneration waste water.
The reported compositions of such waters are given in Table 8. It may
be seen that none of these waste waters reflect the characteristics of
the process, i.e., a hot caustic leach. The number of analyses related
to intake water treatment is occasioned by the fact that some alumina
refineries are located on the lower reaches of rivers and use them as
sources. The waste waters from intake water treatments include:
1. A sludge containing Fe(OH)3 and CaSO/ which is flushed away using
enough river water to transport the solids
2. The stream from the neutralization of the regenerating reagents
used on a resin demineralizer.
In the latter case, NaOH and t^SO^ solutions are used to regenerate the
resin and are then combined to neutralize each other, the supernatant
(i.e., the given analysis) is waste to receiving xvaters, and the settled
sludge is otherwise disposed of.
Two other examples of common industrial-waste-water types are given in
Table 8. The analysis of cooling-tower water shows relatively high
values of total hardness, dissolved solids, and chlorides, and the
presence of chromates used to inhibit corrosion of and deposits on
tubes and pipes. The composition of boiler blowdown also is shown in
terms of its major constituents, phosphates and sulfites. These also
originate from chemicals added to prevent corrosion and caking.
Aluminum Smelters
A thorough study of aluminum-smelter waste waters has been published as
the result of a program connected with the planning, design, construc-
tion, and initial operation of a new plant using a wet-scrubber system
located on the northwestern coast of the United States.(12) The program
included the early determination of effluent characteristics using sam-
ples from existing plants, preoperation surveys of the environmental
conditions in the planned area of discharge, studies of the interaction
of effluent samples with the receiving seawater, and monitoring of the
34
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<<-< 60
4-J i-j
td
J-* ,C
-------
conditions around the discharge point after plant start-up.
The published results of the study included the listing of characteris-
tics of samples of smelter waste waters, shown in Table 9. Studies of
the settling characteristics in seawater of the materials contained in
the waste water proved that the coarser fractions of particulates
settled while the finer particles rose to the surface. These and other
studies showed that the effluent would be dispersed so effectively from
its point of outfall (1800 feet offshore) that no effect on the environ-
ment was expected.
Examples of water analyses reported by aluminum-smeIter operators dur-
ing this study are given in Table 10. Anode plant scrubber waters were
characterized as being contaminated with tars, oxides of carbon and sul-
fur, and hydrofluoric acid, as indicated in the table. In the plant re-
porting this analysis, these waters are settled and skimmed to remove
solids and oils, and diluted with cooling water before release.
TABLE 10. WATER ANALYSES, PPM, ASSOCIATED WITH ALUMINUM-
SMELTING OPERATIONS
pH
so4
F"
Oils
s(b)
Hardness
Chloi ides
BOD
Anode
Plant
Scrubber
Water
3.4-3.6
20-30
13-23
4-14
70-150
--
Potline
Scrubber
Waters
3.0-3.1
120-150
--
200-500
--
4
30-50 50-90
__
30
_ _
__
Cast(a)
House
Discharge
8.2
230.
--
--
230.
70.
Treated
Sanitary
Wastes
7.0
0
--
^30
__
--
50-62
(a) Treated with commercial additives to allow recirculation.
(b) Suspended solids.
The potline scrubber waters exampled show the characteristic influence
of HF fumes: low pH and fluoride-ion content varying from 50 to 150 pprn,
with some variation in suspended-solids contents. These particular
waters were variously recycled or discharged without treatment.
ne example of cast house cooling water exhibits characteristics due to
additions of a commercial additive permitting recirculation and reuse
before discharge, while the analysis of sanitary wastes shows charac-
teristics of treatment in a system referred to as a "package plant".
36
-------
01
00
CO
i-i
o>
CN
CN
PQ
CN
Pi
W
H
W
H
P-i
X
CO
6
6
CO
CM
CM
CO
in
CM
Pi
fd
H
W
s
CO
0)
oo
CO
o>
Pi
i i
cfl
4J
O
H
CX
CX
O)
d
13
H
cn
01
Pi
01
i i
o
CO
Ol
4-J
i 1
i-l
P-I
01
TJ
H
yj
Q>
Pi
0>
, I
42
CO
^_l
01
4-1
i 1
i-l
(4.4
C
O
SZ
e
CX
a,
*
&
C
H
e
d
-------
The information supplied concerning water quality during use in the
fume-scrubbing operation indicated that scrubber water immediately after
use will contain up to 1/2 percent hydrofluoric acid, but that this
level must be reduced to permit recirculation, i.e., the vapor pressure
of the dissolved HF markedly affects the collector efficiency.
A prior (1952) study of water requirements, use, and disposal in the
aluminum industry dealt with the then existing six alumina refineries.^ '
In this prior study, the following uses of water were listed for alumina
refineries:
Sanitary and washhouse
Cooling water
Hydrate wash
Red-mud-lake makeup
Total
Intake per Day,
thousands of
gal Ions
984
3,591
550
6,676
Percent of
Total Intake
8.4
30.4
4.7
56.5
11,801
100.0
Intake per
YearW,
millions of
gallons
344.4
1,256.9
192.5
2,336.6
4,130.4
(a) Assuming 350 operating days per year.
A ratio of water intake to product of 0.66 gallon per pound of alumina
(or 1320 gallons per ton) was reported. However, the variation among
individual plants ranged from 0.28 gallon to 1.10 gallons per pound of
alumina. Moreover, at that time, a modification was planned at one
plant which would increase the average water intake from 0.66 to 3.48
gallons per pound of alumina and widen the range for individual plants
to 0.28 to 26.0 gallons per pound.
The same prior study included water use at 14 aluminum smelters and
gave the following breakdown of uses:
Intake per
Intake per Day,
thousands of
gallons
Engine cooling
Compressor cooling
Sanitary
Boiler feed
Electrode plant
Rectifiers and transformers
Gas scrubbers
Metal-casting cooling
Total
1,168
714
8,682
416
1,420
13,524
78,599
1,357
104,523
Percent of
Total Intake
1.1
0.7
8.3
0.4
1.4
13.0
75.1
1.3
100.0
millions of
gallons
408.8
249.9
3,038.7
145.6
497.
4,733.4
27,509.7
475.0
36,583.18
(a) Assuming 350 operating days per year.
38
-------
The data show that the largest single use of water by the smelters was
for gas scrubbing (75 percent). The average water use for the entire
industry at that time was given as 14.62 gallons per pound or 29,240
gallons per ton of aluminum. Again, intake varied widely for individual
plants, from 1.24 to 36.33 gallons per pound of aluminum.
The treatment and disposal practices at the time of the prior survey
are reported in Table 11. The alumina plants showed a strong emphasis
on recirculation, with two-thirds of the refineries recirculating pro-
cess water and one-third discharging to a river. On the other hand,
waste-water-disposal practices at the smelters were divided between
discharging the process water and recirculating it.
TABLE 11. PAST WASTE-WATER-TREATMENT PRACTICE IN THE
PRIMARY ALUMINUM INDUSTRY^10)
Treated
Type of Waste Water
Receiver
Sanitary
Process
Alumina Refineries (6 Plants)
Yes
Yes
No
No
No
Yes
Yes
Yes
No
Red-mud lake
Stream
Red-mud lake
Stream
Estuary
Aluminum Smelters
Stream
Estuary
Septic tank
Recirculated
Stream
1
1
2
1
1
(14 Plants)
8
2
1
0
3
0
0
4
2
0
1
1
0
5
7
Note: Numbers indicate number of plants using indicated practice.
The discharges of waste water from alumina refineries were character-
ized as involving no pollution problems. These discharges consisted
chiefly of cooling water, cooling-tower blowdown, or condensate from
the evaporator after-condenser in the processing sequence.
The waste waters discharged by the smelters were characterized as being
acid by virtue of their fluoride content. The two (of fourteen) plants
then treating water before discharge were using a practice of liming in
settling ponds, with the sludge disposed of in landfill.
39
-------
The data from the 1952 survey may be compared with the data obtained in
this survey in the following terms:
1952 1970
Number of Refineries Surveyed 6 3
Gallons Intake per Ton of Al2C>3 Product 560-2,200 60-1,560
Number of Plants With Untreated Discharge 2 0
Number of Smelters Surveyed 14 11
Gallons Intake per Ton of Aluminum 2,480-72,660 6,090-104,500
Product
Number of Plants With Untreated Discharge 7 1
The apparent changes are decreased water intake with better control of
discharges at alumina refineries, and increased intake and increased
control of discharges at aluminum smelters.
Water Costs
The water costs were reported in various terms and showed a wide range
in terms of costs, designs, practices, and treatments. The terms and
items reported were reduced to common terms of capital investment and
running (operating and maintenance) costs in terms of capacity of the
individual water operation. The results are given in Table 12. Total
water costs varied from less than 1 to 10 cents per thousand gallons
for the three plants reporting in these terms. Of the various water
treatments reported, the standard treatments, i.e., chlorination, sew-
erage treatment, and boiler feed (chemical softening), fell in the usual
brackets of costs assignable to them. The cooling-tower operation re-
ported served a smelter circuit including rectifiers and cast house
cooling functions with water treated for recirculation. The anode-
plant fume-scrubber water treatment reported consisted of settling and
skimming operations to remove, respectively, suspended solids (75 per-
cent removal) and oils (80 percent removal). One plant reported potline
scrubber water treatment with reclamation of contained materials and re-
cycle of the water, which could be related only to total production, as
costing $0.26 per ton of aluminum produced. The only other cost infor-
mation supplied was that a change in a potline scrubber water circuit
from once-through to reclaim and recycle was expected to cost about
1.4 million dollars and would treat an estimated 16 billion gallons per
year in the recirculating system. On the basis of the data reported,
total water costs were calculated to be on the order of 0.05 to 0.1 per-
cent of the product value, using a value of $0.30 per pound of aluminum.
However, none of the operators included all costs such as depreciation,
etc., in their reports.
40
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TABLE 12. WATER COSTS IN THE ALUMINUM INDUSTRY
Operating and
Capital Investment, Maintenance Costt,,
Category or Operation $,-'1000 gal/yr capacity $/1000 gal
Total plant water
Ditto
n
Intake system
Ditto
Sewerage treatment
Boiler feed treatment
Chlorination
Cooling tower
Anode-plant fume-scrubber
water treatment
1.32
1.27
2.46
0.50
2.43
0.34
0.04
0.25
0.07
0.074
0.10
0.0065
0.07
0.04
0.54
0.35
0.01
0.007
0.008
Waste-Water-Treatment Practices, Plans, and Needs
For the three refineries and eleven smelters contributing information
to this study, current waste-water treatment practices were identified
as:
Two Refineries Zero discharge
One Refinery Discharges consisting of treated
sewerage and untreated cooling
water.
Of the total of 2.2 million tons of smelter capacity surveyed here, the
breakdown of fume-treatment practice was as follows:
Aluminum
Production Capacity,
percent
Dry fume scrubbing 22
Wet fume scrubbing with recycle 60
Wet fume scrubbing water treated 6-1/2
Water partially treated 11-1/2
In the first category, no "process" water would be discharged: dis-
charges would thus consist of sanitary, cooling waste waters, and minor
amounts of boiler blowdown. The last group included two plants, one of
which treated anode plant scrubber water but not that from potline
scrubbers. Both the latter plants currently are planning to convert to
41
-------
recycling systems to reduce water requirements and discharges.
With these plans announced by the responding plants and indications
from announcements in current journals, it would appear that almost all
existing smelters will be refitted, and all new construction will use
either the recycle system of wet scrubbing or the new dry fume-scrubbing
system. Thus water intakes and discharges by the industry will follow
a new and greatly reduced rate of increase relative to expansion of pro-
duction capacity.
The only problem expressed by two respondents was the need for better
ways to remove or recover fluoride ions from waters also containing
sodium, aluminum, and sulfate ions. This need is applicable to both
the recovery system which is considered adequate now but not completely
efficient, and the treatment of the necessary small bleed-off of some
recovery systems.
42
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SECTION VI
THE PRIMARY MERCURY INDUSTRY
Size and Characteristics of the Industry
The current (1971) conditions in the mercury industry preclude anything
but a historical treatment of mercury production and operations. Under
the effects of a number of factors affecting price, consumption, and
operation, the mercury industry is in the midst of a drastic slowdown.
The domestic production for 1970 may be estimated at about 28,000 flasks,
while that predicted for 1971--on the basis of first-quarter production
(4,488 flasks)--may be 18,000 flasks.
The latest year for which complete statistics have been published is
]^969<(13) In 1969, 109 mines produced 29,860 flasks of primary mer-
cury. The major producing mines for that year are listed in Table 13
and their locations are shown in Figure 7. Mines in California and
Nevada produced 26,645 flasks (91 percent of the total) and the balance
was produced by mines in Idaho, Alaska, Arizona, Texas, and Oregon.
The maior uses of mercury are indicated by the 1969 consumption pattern
published by the Bureau of Mines. These are listed in Table 14 in order
of decreasing amounts. The difference in the figures for production
and consumption is due to imports and government stockpile inputs. How-
ever, this list is of only historical interest, as the consumption of
chloralkali plants (for amalgam electrodes) and by agriculture (for
pesticides) is rapidly changing because of efforts to curtail mercury
emissions to the environment.
The primary mercury consumption shown in Table 14 is supplemented by
products known as redistilled and secondary mercury, so that total con-
sumption of all three forms amounted to 79,104 flasks (a flask is equal
to 76 pounds of mercury).
Raw Materials and Processes
Although there are 25 known mercury-bearing minerals, the primary source
of this metal is cinnabar (mercury sulfide). Other economically impor-
tant mineralogical species of mercury include native metallic minerals
of iron, arsenic, and antimony.
The gangue associated with cinnabar deposits includes carbonate and
silicate minerals such as calcite, chalcedony, dolomite, opalite, quartz,
and serpentine. The deposits usually are shallow, extending downward to
43
-------
TABLE 13. MERCURY-PRODUCING MINES IN THE UNITED STATES IN 1969
(13)
Production Categories
State
1000 Flasks or More 500 to 1000 Flasks 100 to 500 Flasks
California
Nevada
Idaho
Texas
Alaska
Buena Vista
Gambonini
Gibraltar
Abbott
Culver-Baer
B&B
Quinn River
Runa
Idaho-Almaden
Brewster
Goldbank
Altoona
Chileno Valley
Corona
El Capital
Juniper
Klau
Knoxville
New Almaden
Oat Hill
Petray
Cahill
Horton's Mercury
Cinnabar Creek
White Mountain
TABLE 14. FORMS AND AMOUNTS OF CONSUMPTION OF PRIMARY MERCURY
(13)
Consumer
Number of Flasks
Chloralkali plants
Electrical apparatus
Paint
Miscellaneous
Instruments
Agriculture
Catalysts
Laboratory use
Pulp and paper making
Pharmaceuticals
Dental preparations
Amalgamation
Unknown
Total
19,263
13,260
9,730
8,427
2,832
2,689
2,235
1,232
558
360
214
194
134
61,128
44
-------
o
to
2;
O
H
H
<
U
o
1-1
r^
W
Cd
t5
O
M
fn
45
-------
depths of slightly less than 2500 feet. Almost all of the deposits are
in areas of tertiary or quaternary volcanic activity. The most impor-
tant deposits occur in Italy, Spain, the U.S.S.R., Yugoslavia, China,
the United States, Canada, Mexico, and the Philippines.
Both surface and underground methods are used in mining mercury ore.
To be economically attractive, the ore produced in underground opera-
tions must contain significantly more mercury than that produced in
open-pit operations. Ores produced in open-pit mining, which contain
2 to 3 pounds of mercury per ton, have been processed economically.
Mercury contents two to three times greater are needed for economically
attractive underground operations.
Ore Preparation
The mine-run ore is transported to the crusher bins from which it is
conveyed to a screen where the minus-3-inch material is removed and the
oversized fraction is reduced to about minus 3 inches with a jaw crusher.
Both the undersized material from this screen and the crushed ore then
are conveyed to a fine-ore bin from which the raw ore is fed into the
furnace.
Conventionally, the mined ore is subjected to pyrometallurgical treat-
ment without preliminary concentration. On the basis of differences in
the physical properties of the mineral species, e.g., density, methods
of concentration have been used in specific instances. These include
hand, rotary, jigging, tabling, and flotation. The last is the most
effective of these techniques, yielding mercury recoveries of approxi-
mately 90 percent and concentrates containing 500 to 1000 pounds of mer-
cury per ton. Flotation necessitates grinding the ore to the relatively
fine size of the concentrate, however, and yields a feed more amenable
to retorting than to continuous mechanical furnace operation.
Pyrometallurgical Processing
The pyrometallurgical processing of mercury ores involves heating the
ore in the presence of air to volatilize the mercury in the elemental
form. All of the current domestic production of mercury is based on
this technique. The mercury vapor from the furnace is condensed and
treated with lime to produce relatively pure metallic mercury. The
pyrometallurgical treatment may be conducted in a batchwise manner in
indirectly heated retorts or in continuous mechanical furnaces such as
multiple-hearth roasters or rotary kilns. The latter type of mechani-
cal furnace is most commonly used in the larger plants currently oper-
ating in the United States. Figure 8 is a schematic flow diagram of a
typical rotary-kiln installation for processing mercury ore. In the
process, the crushed ore is fed into the kiln against a countercurrent
46
-------
1C
(LJ
47
-------
flow of hot combustion gases with a shotgun feeder. The temperature of
the gases being exhausted at the feed end of the kiln ranges from 600
to 650 F. The temperature of the barren solids being discharged at the
firing end of the kiln usually ranges from 1000 to 1500 F. These solids
may be cooled to as low as 200 to 300 F by direct contact with the in-
coming air, either in an auxiliary cooler, or as they leave the dis-
charge end of the kiln. To avoid leakage of mercury vapor, the kilns
are operated at less than atmospheric pressure.
The mercury-laden gases from the kiln pass through one or more cyclone
separators to remove the finely divided particulates. The dust collec-
tors are operated at 450 to 500 F to avoid condensation of the mercury
vapor. The dust products from the cyclone and the calcined ore are
transported to the waste-disposal area.
After the mercury-laden gases pass through the cyclone and the hot fan
which follows, they usually are divided into two streams and injected
into two banks of air-cooled, vertical U-tube condensers. These con-
densers are about 16 inches in diameter and from 20 to 40 feet in
height. The individual pipes are connected at their tops and bottoms
with U-turns. At the bottom these U-turns have openings which are
sealed with water through which the condensed mercury flows and is re-
covered. The condensers are constructed of cast iron, mild steel, tile,
stainless steel, or Monel, depending largely upon the sulfur and/or
chloride content of the ore and the subsequent corrosiveness of the
gases. The total length of the condenser depends on the tonnage of
material being processed in a particular kiln and the resultant flow of
combustion gases. The condenser system normally is designed to provide
a temperature of less than 110 F at the exhaust end. Although the con-
densers normally depend on natural air circulation for cooling, it is
common practice to spray water on the outside of the hottest pipes in
the condensing system, particularly during the summer months. The
major portion of the mercury condenses in the initial four or five
pipes in the condenser.
After the gases leave the condenser, they are expanded into one or two
large baffled redwood tanks for further cooling and the subsequent re-
moval of some of the remaining mercury. From these tanks, the waste
gases pass into the bottom of the stack, from which they are emitted in-
to the atmosphere at temperatures of 60 to 90 F. Sometimes water is
sprayed into the bottom of the redwood expansion chambers and the stack
to effect additional cooling of the gases prior to their release into
the atmosphere, in order to decrease mercury emissions and to increase
yield.
The metallic mercury, dust, and soot collected in the condenser system
are removed periodically and transported to either a manual or a mech-
anical hoe table where the impure product is mixed with lime to recover
the mercury. During this operation, the mercury coalesces and flows
into a sump at a low point in the table, where it is collected and
bottled in flasks. The residue from the hot table either is returned
48
-------
Intake
L
"I
Mine
Chlorination
Mine
Drill
Cooling
T
Compressor
Cooling
Cooling
Tower
Condenser
Seals
and Washdown
Sanitary
Uses
To
ground
Pond
or
Slag Dump
I
I
FIGURE 9. GENERALIZED DIAGRAM OF COMMON FEATURES OF WATER
CIRCUITS OF MERCURY MINES AND PLANTS
49
-------
to the rotary kiln for processing or is mixed with other mercury-con-
taining materials and processed in an indirect-fired retort in order to
increase yield.
In some mercury-producing operations involving the processing of rela-
tively small tonnages of raw materials either raw ore or concentrates--
retorts may be used as the primary processing furnaces. Since the re-
tort is an indirectly fired unit, the volume of mercury-laden gases is
much less than that produced in a direct-fired rotary kiln. This
diminished volume of exhaust gases decreases the overall loss of mer-
cury to the atmosphere and improves the mercury recovery efficiency by
a few percent.
Water-Usage Patterns, Practices, and Problems
Representatives of three mercury-producing companies responded to this
survey program. Responses were sparse because of numerous closings and
current pressures on more salient problems. However, most mercury fur-
nacing operations are similar and these few responses will be discussed
for the insight which they contain.
The water-usage patterns reported contained the elements indicated in
Figure 9. The only process-type water consists of the water pool which
forms the seals at the bottoms of the condenser U-tubes, and any wash
water used in periodic cleaning of the inside of the condenser tubes for
maintenance purposes. One instance was reported of the use of a closed-
circuit cooling system for associated air compressors.
Remote locations and'an arid climate are characteristics of most of the
mercury operations. Thus, one mine operation reported the use of
bottled drinking water and chemical toilets, but did have a discharge
of mine water. No furnacing operation was associated with this mine.
The three operations had capacities to mine and process about 200,000
tons of ore a year and showed the following discharges of water.
Intake, Discharge, Type of Discharge
MGY MGY or Receiver
5 0 Evaporation pond
250 250 Untreated; to surface
water
60 46 Mixed mine and process
water
In the last example, waste waters were percolated through the slag or
tailings dump and the effluent from the heap was diluted with fresh
water. The diluted effluent which constituted the discharge to the re-
ceiving water had the following analysis:
50
-------
mg/1
Nitrate 2.4
Chloride 63.8
Sulfate 2382.6
Bicarbonate 12.2
Carbonate 0
Sodium 186
Potassium 23.0
Calcium 289.6
Magnesium 294.4
Fluorides 1.7
Silica 18.0
Iron 0.02
Manganese 2.4
Boron 3.7
Cyanide 0.03
Lead 0.000
Arsenic 0.000
Copper 0.08
Mercury 0.02
Total Hardness 1950.0
pH 4.8-5.7
Considerable elevation of the contents of dissolved salts and some
metals are apparent in this analysis.
The information obtained on the primary mercury industry is so scant as
to serve only as an isolated example. However, even among the various
aspects of the present state of the industry, there is the long-range
possibility of one process modification to overcome the problem of mer-
cury emissions to the atmosphere which would affect water usage by the
industry. One of the possible alternatives to the present processes is
hydrometallurgical processing.
Potential Hydrometallurgical Processes
Over 90 years ago, Volhard reported that an aqueous solution of sodium
sulfide can be used for dissolving cinnabar. Until recently, however,
the only hydrometallurgical technique used was developed in 1915, for
the recovery of mercury from amalgamation. In the late 1950's the U.S.
Bureau of Mines conducted considerable research on the use of sodium
sulfide and sodium sulfide-sodium hydroxide solution for leaching mer-
cury ores and concentrates.*- '
The great variations in composition of ores, the cost of grinding ores
finely enough for effective leaching, the simplicity and efficiency of
pyrometallurgical processing, and the cost of reagents generally have
51
-------
precluded the consideration of hydrometallurgical processes for the re-
covery of mercury. However, if flotation is used to concentrate the ore,
the cost of alkaline sulfide leaching followed by electrolytic precipi-
tation of the mercury has been estimated to be about the same as the
cost of pyrometallurgical treatment. This teaching-electrolytic tech-
nique has been evaluated at least to the pilot scale at the Hermes plant
in Idaho.(14)
Other hydrometallurgical processes which have been developed for the
recovery of mercury include hypochlorite leaching and electrolytic oxi-
dation .
In 1964, U.S. Bureau of Mines investigators^- ' estimated the costs in-
volved in the mining and hydrometallurgical treatment of ores from both
open-pit and underground mining operations. The grade of the ore from
the open-pit operations was assumed to be 4 pounds of mercury per ton;
that from the underground mining was assumed to be 20 pounds of mercury
per ton. At ore-treatment levels of 250 tons per day for the lower
grade and 50 tons per day for the higher grade, the treatment costs
were estimated to be $5.29 and $33.33 per ton, respectively. Costs for
mining and treating the ores from open-pit and underground mining oper-
ations by conventional pyrometallurgical techniques were estimated to
be $3.95 and $33.10 per ton, respectively.
The literature indicates that
1. Hydrometallurgical processes for treating mercury ores have been
developedat least to the pilot-plant scale
2. Estimated costs of treating some mercury ores by hydrometallurgical
and pyrometallurgical techniques are similar.
Nevertheless, the literature does not indicate any extensive utiliza-
tion of hydrometallurgy for recovering mercury from domestic ores or
concentrates. This may be due to the relative simplicity of both
processing and processing equipment involved in the pyrometallurgical
technique.
Treatment of finely ground ore through flotation and chemical process-
ing should not lead to significant emissions of mercury to the atmos-
phere. However, it is probable that soluble mercury compounds would
be left in the tailings from the leaching operations, even with careful
countercurrent washing. This would create a water-pollution problem
which might require considerable effort to eliminate.
Since no data are available on the potential losses of mercury in the
solid residues and waste waters from sizable hydrometallurgical opera-
tions, it would be very difficult to estimate either the magnitude of
the water-pollution problem or the cost of alleviating it. Lack of
such information precludes further consideration of hydrometallurgical
processing as a possible means of air-pollution control at this time.
52
-------
If further consideration is believed desirable, old records from pre-
vious research and development on this technique should be reviewed to
acquire information specific to the water-pollution potential of this
technique.
53
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-------
SECTION VII
THE PRIMARY GOLD AND SILVER INDUSTRIES
Size and Characteristics of the Gold Industry
In 1969, the United States gold industry produced about 1.7 million
ounces of gold from sources of ore shown in the following tabulation:
Gold Ore, Gold Recovered,
short tons troy ounces
Placer Mines -- 25,418
Gold Mines 3,392,503 1,031,050
Gold-Silver Mines 208,105 1,883
Silver Mines 654,674 2,900
Copper Mines 189,279,503 579,171
Lead Mines 369,355 3,069
Zinc Mines 760,057 1,057
Copper-Lead-Zinc, 3,725,190 84,742
etc. Mines
Miscellaneous 149,935 3,886
Total 198,539,322 1,733,176
These mines were located in 14 states with production being distributed
as shown in Table 15. The 25 leading primary gold-producing mines in
the United States which account for more than 97 percent of the gold
production are listed in Table 16.
A breakdown of the data shown in the prior tabulation indicates the
relative importance of the various sources of gold to the industry.
Troy Ounces
Recovered Percent of Total
Placer Mines 25,418
Gold Mines 1,031,050
Gold-Silver Mines 1,883
Silver Mines 2,900
Copper Mines 579,171
Lead Mines 3,069
Zinc Mines 1,057
Copper-Lead-Zinc Mines 84,742
Miscellaneous 3,886
Total 1,733,176
The gold industry is a relatively minor direct contributor to the
55
'
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TABLE 15. PRODUCTION OF GOLD IN THE UNITED STATES IN 1969, BY
STATES, TYPES OF MINES, AND CLASSES OF ORE YIELDING
GOLD, IN TERMS OF RECOVERABLE METAL
Lode
Placer
Gold ore
Gold-silver ore
Sliver ore
Alauk n
Idaho
Utah
Other States
Total . .
Percent of total
gold
(iroy
ounces of
gold)
21 146
5
2,650
1,056
1^
2
1
W
W
25,418
1
Short tons
/j\
612
«6,263
100
1 '68
"7,086
1 380,771
854
1 , 934 , 622
62,237
3,392.503
Troy
ounces
of gold
75
500
4,739
70
'75
'7,479
378,934
875
1 593,146
45,708
1,031,050
69
Short tons
63 , 665
616
(')
1,287
142,738
208,105
Trey
ounces
of gold
139
86
(')
502
1,156
1,883
Short tons
75,487
126
3,5X3
531,313
36,242
5,081
2,842
654,674
Troy
ounc'-H
of gold
153
3
63
887
9K6
264
544
2,900
Lode
Copper ore
Lead ore
Zinc ore
Short tons
Troy ounce* Troy ounces Troy ounces
of gold Short tons of gold Short tons of gold
Alaska
Arizona _.
California
Colorado
Idaho
Montana.,
Nevada,
New Mexico -__
Oregon
Utah
Other States
Total
Percent of total
gold
107,774,696
642
16,016,901
14,345,225
12,491,450
38,650,300
389
189,279,503
108,718
6
15,420
76,212
8,163
370,632
21
679,171
33
50
218
104,388
982
'255,785
'2,879
4,519
534
369,355
6
106
391
97
'1,555
'267
615
32
3,069
(')
277 ,350
(')
(')
221 , 563
261,144
760,057
873
(')
(')
182
2
1,057
P)
Lode
Copper-lead, lead-zinc
copper-zinc, and
copper-lead-zinc ores
Idaho
Utah
Other States
Total
Percent of total
gold
W Withheld to avoid
ores as noted.
Short tons
106,783
741,484
677,039
1,068
2,749
54,413
1,574,140
567,514
3,725,190
Troy
ounces
of gold
30
"23,532
875
9
28
102
126
60.040
84,742
6
Old tailings, etc.
Short tons
91,744
417
600
5,435
14,844
76
36,786
33
149,935
Troy
ounces
of gold
1,227
121
3
24
239
2
981
"1,289
3,886
0)
disclosing individual company confidential
Total p
Short tons
50
108,113,005
111,194
1,024,014
1,465,337
16,069,611
15,753.189
12,768,789
854
1,934,622
1,574,140
39,400,714
323,803
198,539,322
data; included in
Troy
ounces
of gold
21.227
110, 87i
7,904
25,777
3,403
24.189
456,294
8,952
875
693,146
126
433, 3S5
47,020
1,733,176
100
placer total
Refinery
reduction "
(troy
ounces
of gold)
18,900
114,900
7,250
26,200
3,400
20,000
452 , 500
10,000
350
593,200
no
425,000
" 45,010
1,716,850
and in lode
1 Less'than \j unit.
1 Gold and gold-silver ores combined to avoid disclosing individual company confidential data.
1 Placer combined with gold and ^old-silver ores to avoid disclosing indi\idual company confidential data.
4 Placer combined with pold ore to avoid disclosing individual company confidential data.
* Excludes Oregon and South Dakota placer production; included in placer total.
Lead and lead-zinc ore11* combined to avoid fliiclosinn individual company confidential data.
1 Lead and zinc ores combined to avoid disclosing individual company confidential data.
1 Includes byproduct gold recovered from uranium ore.
Includes byproduct gold recovered from tungsten ore.
0 Includes byproduct gold recovered from fluorspar ore.
» Includes byproduct gold recovered from magnet! te-py rite ore.
" Source: U.S. Bureau of the Mint.
» Washington only.
56
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economy. It has been estimated that gold-mining operations per se em-
ploy about 3000 to 3500 people, and, in addition, about 700 to 800
people are employed in the base-metal industries to recover and refine
the by-product gold from copper, lead, etc., ores.
Raw Materials and Processes
Ores
Gold is widely distributed in nature in both native and combined form.
The principal ore mineral is "native" or metallic gold, which occurs in
association with quartz and other rocks. Native gold, almost invari-
ably containing minor quantities of silver, may occur as perceptible
grains, flakes, sheet, or wire in veins of quartz and other minerals or
in a finely divided state disseminated in the ores of copper, lead, and
occasionally zinc.
When rocks or deposits containing gold are dissolved and disintegrated
by "weathering" (i.e., rain, freezing, erosion, etc.), the gold parti-
cles resistant to these forces are liberated and washed into waterways.
Owing to the high specific gravity of the gold, it tends to settle and
becomes concentrated by hydraulic action in stream beds, in layers.
Often, over the ages, such forces have produced concentrations of "free
gold" that can be profitably recovered. This is the so-called "placer"
gold ore and is distinguished from "lode" ore in which the gold is still
associated, encapsulated, etc., in other rocks.
Mining
Gold-mining methods vary widely, depending on the size, shape, and
depth of a deposit, the associated minerals, economic considerations,
etc.
Two broad types of mining must be distinguished. These are "placer"
mining and "lode" mining.
Placer mining, which accounts for a relatively small but still signifi-
cant amount of gold production, is applied to "placer" deposits. These
may be described as unconsolidated deposits of detrital material result-5
ing from the weathering of rock containing gold in economically impor-
tant concentration, together with sand, gravel, and other minerals,
resulting from the degradation of the original rock. They may exist in
currently running water or they may be the dried out relics of a stream
that changed its course or ceased to exist ages ago.
Gold placer deposits were mined originally in this country by the 49'ers,
58
-------
in California, employing small-scale hand methods, such as pans, sluice
boxes, rockers, etc. Some small-scale placer mining by individuals is
still practiced. Large-scale placer mining, employing draglines, bucket
dredges, hydraulic dredges, etc., accounts for most of the gold recovery
by this mining method.
The objectives of both large and small-scale placering is the same--to
eliminate the worthless waste rock and to collect gold in a high-grade
concentrate. The principle employed is the same in both cases. The
ore is removed from the deposit by the most convenient and economic
means available. This includes excavation with shovels or draglines,
by hydraulic methods (i.e., by breaking up the poorly consolidated mat-
erial with high-pressure streams), by bucket dredging, or by suction
dredging. The ore is then transported to a washing plant by bucket
elevators, through sluices, prepared channels, or through lines to a
screening and washing plant.
Washing plants may be placed on land or may be afloat, often on the
dredges themselves. The objectives of screening and washing are to
clean and remove from the circuit the larger rocks and boulders. The
screening and washing is commonly done in trommels, which are rotating
horizontal cylinders, with perforations of a size and frequency selected
to permit the immediate rejection of barren rock oversize. The smaller
rocks, sand, heavy minerals, and gold pass through these apertures and
are treated by methods which take advantage of the high specific gravity
of gold. These include sluice boxes, tables, jigs, etc. In some cases
mercury may be employed to increase gold recovery by amalgamating with
fine gold particles which might escape the concentrating operation.
Placer mining produces a still impure gold concentrate which may first
be treated by amalgamation, melting, fluxing, etc., to produce high-
purity gold bars, or which may be sent to gold refineries.
Placer gold in arid locations is, in some cases, concentrated by dry
methods, using air instead of water to wash away lighter materials.
These are small operations.
The mining of lode ores of gold is done through shafts and adits by
many of the conventional methods of underground mining. The major U.S.
gold mine, which produces about 60 percent of the country's gold, em-
ploys cut and fill stoping methods in which mined out stopes are filled
with mill tailings. In recent times, open-pit mining of gold ore has
been practiced in Nevada. As mentioned previously, about one-third of
the gold produced in the United States is as a by-product from copper,
lead, and zinc mines. Mining practices have been discussed elsewhere.
Recovery
The recovery of gold from lode gold mines is done by any one or
59
-------
combination of several methods selected and designed to yield maximum
economic recovery.
Unlike placer gold, however, lode gold has not been preconcentrated by
the forces of nature and has not been liberated from its host rock.
Accordingly, all lode gold mines preface recovery processes by crushing
and grinding to liberate gold physically or make it accessible to chemi-
cal solutions.
After crushing and grinding, roasting may be necessary. Treatment may
be by any one or a combination of three methods. These are:
1. Gravity methods such as riffling or jigging as is applied to placer
gold deposits. It is believed that very few of the lode gold operations
now employ this procedure.
2. Amalgamation. Gold with clean surfaces dissolves rapidly in mer-
cury to form an amalgam. Amalgamation is generally carried out by feed-
ing mercury into the grinding circuit to form an amalgam with the gold
as it is liberated. The slurry of crushed ore in water is then passed
over large copper plates previously coated with mercury. Amalgam from
the ore collects and builds up on these plates. They are then period-
ically scraped by hand with rubber scrapers to remove the accumulated
gold-mercury amalgam. This amalgam is then placed in retorts and the
mercury vaporized and condensed and recovered for reuse. The residue
from retorting is crude gold and is sent to a furnace refining operation.
3. Cyanidation. Gold ore, as mined, or the residue containing gold
which escaped amalgamation from the amalgamation process is subjected
to a leaching process in which dilute aqueous sodium cyanide solution
(about 0.02 to 0.05 percent) is the solvent. This form of leaching,
called cyanidation, is done in tanks. Agitation and the necessary oxy-
gen is supplied by bubbling air through the slurry. The reaction occur-
ring during leaching is
4Au + SNaCN + 2H20 ^4Na Au(CN)2 + 4NaOH.
The cyanide leach liquor is filtered from the residue and the filtrate
is treated with zinc dust to precipitate the gold as metallic particles
according to the reaction:
NaAuCN2 + 2NaCN + Zn + 2H 0 ^ NaZnCN^ + Au + H + 2NaOH.
The gold particles are recovered by filtering and the clear solution re-
turned to the leaching operation.
Refining
The impure gold recovered from either the amalgamation or cyanidation
60
-------
is refined by treatment in the so-called Dore' furnace. In this opera-
tion the material is melted with appropriate fluxes (soda ash, borax,
silica, etc.) under oxidizing conditions to produce a gold-base alloy
which may still contain silver and tiie platinum group metals and a slag
which will contain impurities such as copper, zinc, etc.
If platinum-group metals ara absent or virtually so, the Dore' metal is
purified while still molten by the Miller process, in which chlorine is
bubbled through the charge. This treatment volatilizes base metals
which may be present and converts silver to molten silver chloride salt
which rises to the top of the melt and can be poured or skimmed from
the gold. Refined gold made by this process generally contains about
99.6 percent gold, and is suitable for many purposes.
If platinum metals are present or if higher purity is desired, the Dore
metal is cast into small anodes and electrolyzed in chloride solution
by a miniaturized method analogous to the refining of copper by elec-
trolysis. In tliis, the Wohlwill process, gold is e lectrolyti cal ly oxi-
dized as the anode passes into solution and is deposited in pure form
on the cathode. The resulting cathode is melted and cast into bars of
99.9+ percent purity. In the Wohlwill process, silver is also electro-
lytically oxidized at the anode, but is quickly and almost completely
converted to insoluble silver chloride.
Gold by-products obtained from the processing of lead, zinc, and copper
ores are generally given special pretreatments to eliminate base-metal
impurities. Eventually in these processes a Dore''alloy is formed which
is then treated by refining techniques for gold as described above, or,
if significant silver is present, by the processes of electrolysis de-
scribed in the section of this report on silver.
Size and Characteristics of the Silver Industry
About two-thirds of domestic silver produced in 1969 was a by-product
of copper, lead, and zinc ores. Most of the remainder came from mines
worked principally for their silver values. Gold-silver ores, accounted
for about 1 to 2 percent of silver production.'~^'
Twenty-five leading silver producers contributed 80 percent of the total
domestic output. These are listed in Table 17. Production data by
states for 1969 are shown in Table 18.
It has been estimated by the Bureau of Mines that the mining and milling
segment of the silver industry employs less than 2000 people. No esti-
mate has been advanced for employment in the metal-recovery and refining
segment of the industry owing to its complex interrelationship with
base-metal smelting and refining practice.
Forecasts indicate that primary silver demand in the United States in
61
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62
-------
TABLE 18. MINE PRODUCTION OF RECOVERABLE SILVER BY
STATES IN 1969
States
Troy Ounces
Alaska
Arizona
California
Colorado
Idaho
Maine
Michigan
Missouri
Montana
Nevada
New Mexico
New York
Oklahoma
Oregon
Pennsylvania
South Dakota
Tennessee
Utah
Wyoming
Washington
2,030
6,141,022
491,927
2,598, 63
18,929,697
319,718(a)
1,009,022
1,442,090
3,429,314
884,155
465,591
31,755
Combined with Maine
4,749
Combined with Maine
124,497
78,614
5,953,567
Combined with Maine
Combined with Maine
Total
41,906,311
(a) Production of Maine, Oklahoma, Pennsylvania,
Washington, and Wyoming (1969) combined to avoid
disclosing individual company confidential data.
63
-------
the year 2000 will range from 280 to 560 million troy ounces with a
median of 420 million troy ounces. Present demand (1969) is about 160
million troy ounces.
Raw Materials and Processes
Minerals of silver are shown in the following tabulation:
Argentite
Polybasite
Proustite
Slephanite
Pynargyrite
Cerargynite AgCl
Native silver Ag
Silver- bearing tetrahedrite (Cu-Ag) Sb2S7 .
The major ore mineral in the United States is silver-bearing tetrahe-
drite associated with sulfides of copper, lead, and zinc. Silver-
bearing ores vary in silver content from the extremely low levels found
in major copper deposits to grades in which silver is the main component.
As mentioned previously, much of the primary silver produced in the
United States is as a by-product of copper, lead, and zinc mining. The
mining of ores in which the principal value is silver is generally done
by underground methods.
Recovery of Silver From Copper Ores
Figure 10 outlines routes for the recovery of silver and gold. Silver
and gold follow copper through all stages of concentration, smelting,
and fire refining (1). When copper is refined electrically, however,
these metals, together with selenium, tellurium, etc., collect as finely
divided solids in the electrolytic tank. These are called slimes (2)
(see section on copper). Slimes, as produced, contain high percentages
of fine copper and are first leached in hot dilute sulfuric acid (3), to
dissolve excess copper, and some tellurium and selenium, away from the
silver and gold (4). Typically, such leached slimes will contain about
10,000 ounces of silver per ton, with varying proportions of gold, lead,
selenium, arsenic, antimony, etc., depending on the characteristics of
the original ore (5). The treated slimes are then smelted in a small
reverberatory furnace, called a Dore furnace (6) with various fluxes
such as limestone, borax, fluorite, silica, etc., selected to produce a
fluid slag of the base metals so that they may be separated from the
bulk of the molten silver and gold. This slag (7) normally contains
significant amounts of gold and silver and to recover these values it
is usually returned to the copper smelter. The gold and silver alloy,
64
-------
as
3e
rt r
B rH O^
I/U
w /
65
-------
now rid of most of its base metal and metalloid impurities, is called
Dore metal (8). Typically such an alloy will contain 90 or more per-
cent of silver, gold, platinum, and a small amount of copper. The mol-
ten Dore'metal is cast into small anodes (10). These are electrolyzed
in small specialized cells in nitrate solution (11). Two main types of
electrolytic cells are used. In one type, the Thum cell, carbon
cathodes constitute the floor of the cell, and the impure silver anodes
are suspended in a shallow receptacle with a cloth bottom. On electro-
lysis in this type of cell, the silver dissolves anodically and is de-
posited in small crystals on the bottom cathode. These crystals are
raked either manually or mechanically from the cell, washed, and dried
(13). During the electrolysis, gold and platinum do not dissolve but
collect as slimes on the cloth bottom of the anode receptacle (12).
These are sent to further processing for the recovery of these metals.
The electrolytically refined silver crystals (13)--which will exceed
99.9 percent puritysubsequently are melted and cast into bars weigh-
ing about 100 pounds. Another type cell called the Moebius cell is
also used in silver refining. In this cell the anodes are enclosed in
cloth bags and suspended alternately between cathodes. During electro-
lysis in the nitrate solution, the silver is anodically dissolved and
deposits as loosely adherent crystals on the cathodes. These are per-
iodically scraped off mechanically into a basket on the bottom of the
cell. The gold and platinum slimes in the Moebius cell are retained in
the anode bags.
Recovery of Silver From Lead Concentrates
The recovery of silver from ores in which lead and zinc are the major
components by weight is less straightforward than the recovery from
copper ores. Silver follows copper through to the electrolytic refin-
ing step in copper metallurgy. In lead metallurgy, however, silver may
follow several routes. After lead concentrates are sintered (15) and
smelted in the blast furnace (16), a portion of the silver will accom-
pany the copper matte that is normally formed. This matte (17) is re-
turned to copper smelters for the recovery of both silver and copper as
outlined in Column I of Figure 10. Much of the silver, however, accom-
panies lead in a bullion (18). Bullion from most ores contains enough
gold and silver to make their extraction profitable. In addition, it
contains undesirable impurities such as copper, zinc, tin, antimony,
and arsenic which must be removed by refining. The processing steps for
refining lead will vary with the composition of the impure bullion and
the end product desired. The steps shown in Column II from the dross-
ing step on are typical.
Dressing (19) consists in holding the molten bullion at a temperature
just above the melting point, during which operation copper rises to
the top and is skimmed off. The last traces of copper are removed by
adding sulfur. The copper dross is returned to a copper smelter for
66
-------
copper recovery and the recovery of whatever silver may have accompanied
the copper dross. Arsenic, antimony, and tin are subsequently oxidized
and are volatilized or skimmed from the surface of the lead.
After dressing, two routes are available for the production of refined
lead. One, essentially fire refining, includes a silver and gold re-
covery procedure involving the addition of zinc metal to the molten
lead (21, 22, 23, 25, 26). When zinc is added in trie desilvering step,
the precious metals alloy with the zinc and rise to the surface. The
last traces of zinc in the lead are removed either hv vacuum distilla-
tion or by fluxing with caustic soda (23). The ;H nc fraction or zinc
crusts (25) removed from the lead are dezinced by distillation or
vacuum, then "cupelled" (26) in a small reverberatorv furnace under
strongly oxidizing conditions to convert the lead to molten lead oxide
which carries off other materials besides some silver and gold. Lead
oxide with its burden of impurities such as zinc, arsenic, antimony,
etc., is returned to the lead blast furnace. The molten gold and sil-
ver remains in the cupel furnace as Dore metal, and is cast into anodes
for treatment as shown in Column I of Figure 10 (10-11).
Another path for producing refined lead after the dressing operation is
by electrolytic refining (29). This technique has been described in the
section of Volume I of this report dealing xvith lead. Electrolytic re-
fining generally is employed when undesirably high concentrations of
bismuth are present. During the electrolysis of lead, silver and gold,
as in copper electrolysis, separate as slimes. These are collected and
subjected to cupellation (26) and electrolysis (27) as described previ-
ously.
Recovery of Silver From "Silver Ores"
As explained previously, some ores have predominant silver values, but
in all cases, the quantity of silver involved is much less than that of
base metals, such as lead. Such ores are first concentrated by flota-
tion processes (34) as described elsewhere in this report. Concentrates
then are treated by the processes outlined in Columns I and II (Figure
10) to recover silver.
Waste Water in the Gold and Silver Industries
Responses to this survey were provided by only two gold mines. One
mine took in 66 million gallons per year and discharged no water. This
type of situation is analogous to the numerous examples of "tailings-
pond"-type operations in desert climates, whose characteristics are dis-
cussed in greater detail in Volume I of this report dealing with copper,
lead, and zinc. Briefly, however, the water-usage pattern involves the
use of major portions of the water in the ore-concentrating process,
67
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with all water from all other uses (boiler, sanitary, dust control,
etc.) being discharged to the common receiver of the tailings pond from
which xvater is recycled to the ore-processing operation. In desert
climates, evaporation from the large surface area of the pond and seep-
age into the ground result in zero discharge.
The other gold-producing operation contributing to this program ran a
uniquely identifiable operation and so cannot be treated within the
constraints of this report.
A recent journal article described the current situation of the Home-
stake mine with regard to water-pollution problems.(21) The mine and
concentrator were designed to use the dual amalgamation-cyanidation
process on an ore with gold content of 0.3 ounce per ton, achieving a
reported 95 percent efficient recovery rate, with 62 percent recovered
by mercury amalgamation and 33 percent by cyanide leaching.
The tailings slurry, using the dual process, was reportedly discharged
untreated at a rate of 1700 gpm, and containing 5,600 tons of solids
per day and 10 to 40 pounds of mercury. At the end of 1970, the plant
suspended the use of the amalgamation process and used only cyanidation,
with a reported loss of 75 pounds (3 percent) of the 2500-pound daily
use, about 50 pounds as cyanide and 25 pounds ad cyanate. The analyses
of waste waters reported mercury and cyanide as follows:
Free
Mercury, Cyanide,
Location
Jan., 1971 Whitewood Creek below discharge -- 2.6
Leach Process (3 25 to 30 miles below discharge -- 0.05
Dual Process Whitewood Creek at Deadwood 96.0
Whitewood Creek 25 to 30 miles 67.0
below
Belle Fourche River 12.0
At Bridger on Cheyenne River 1.1-1.8
(estimated 100 to 150 miles
downstream)
The current leach practice is achieving a recovery of less than 94 per-
cent .
A considerable portion of the article was devoted to the varying assess-
ments of the effects of the discharges. It would appear that, through
process modification, the mercury content of the effluent has been re-
~^uced to zero. The development of a treatment process to control the
ported discharge of free cyanide is under way. The estimated pollu-
tion-control cost of $3 million is about 15 percent of the nominal value
of annual production, i.e., $20,265,000.
68
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SECTION VIII
THE PRIMARY MOLYBDENUM AND TUNGSTEN INDUSTRIES
Size and Characteristics of the Molybdenum Industry
The raw ore concentrates from which molybdenum is extracted may be con-
sidered to arise from two sources: those mining and concentrating oper-
ations producing molybdenum as the principal product and those opera-
tions producing molybdenum as a by-product. The former category con-
sists of two operations, while by-product molybdenum concentrates are
produced chiefly in association with copper production from porphyry
ore deposits and to lesser extents with uranium and tungsten operations.
The principal producers of molybdenum concentrates are listed in Table
19. The first two entries in the table are operations where molybdenum
is the principal product; the balance of the operations produce molyb-
denum as a by-product of copper. Total production in 1969 amounted to
100 million pounds or 50,000 tons of contained molybdenum. The molyb-
denum in these concentrates is converted to various compounds, alloys,
and the pure metal. The amounts, forms, and end uses listed by the
Bureau of Mines for 1969 are listed in Table 20. This breakdown of con-
sumption shows that the greatest usage of molybdenum is in the oxide
form and in the form of ferromolybdenum, both for use in the steelmaking
industry. A relatively small portion of the total molybdenum production
is reduced to the form of pure molybdenum metal or molybdenum-base
alloys. In any event, metallic molybdenum is produced from the oxide
form, one step removed from the naturally occurring sulfide form.
(23)
Raw Materials and Processes
The two most important mineral forms of molybdenum are molybdenite,
MoS2, or wulfenite, PbMoO^. An example of a commercially important de-
posit of molybdenite is the Climax Mine in Colorado where the ore con-
tains 0.6 percent molybdenite. The other major operation in the United
States is that at Questa, New Mexico, where the important mineral is
wulfenite. Molybdenite (sulfide) is the form associated with the con-
centrating-grade copper sulfide ores and is the form of the by-product
concentrate produced by differential flotation at many copper-producing
operations.
Molybdenum disulfide mineral concentrates produced as by-products from
porphyry copper operations constitute the sole source at present of the
metal rhenium. Rhenium is recovered from the flue dust during the
roasting of the molybdenum sulfide to the oxide form. Rhenium is not
recovered from the minerals of the principal molybdenum mines, i.e.,
69
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its recovery has been limited to copper ores.
The general route followed from mineral to product consists of the con-
version of the sulfide to a crude (but salable) oxide, by roasting, the
purification of the oxide by sublimation to produce yet another product
form, and for a small portion of total production, the conversion of
the pure oxide to metal or to ammonium molybdate, which may then be con-
verted to metal.
The production of molybdenum from ore deposit to oxide or metal product
follows the general sequence of mining, crushing, grinding, flotation
concentration, and furnacing of concentrates to produce oxide and even-
tually the metal.
Mining and Concentrating
Molybdenum ores are mined by both open pit and underground methods.
Generally standard mining methods, discussed in more detail in the por-
tion of this report dealing with copper, lead, and zinc, are used in
molybdenum operations. The most recent entries into the molybdenum-
producing field may serve as examples of methods.
The Sierrita Property of the Duval Corporation in Arizona is a large
open-pit mining operation mining an ore containing 0.35 percent copper
and 0.036 percent molybdenum. Ore-mining and -concentrating capacities
are to process 85,000 tons of throughput per day. The ore is blasted
loose, loaded with power shovels, trucked to a primary crusher which
discharges to a conveyer belt, and conveyed 2-1/2 miles to the mill.
The ore is then processed through secondary and tertiary crushers and
wet ground in ball mills. The ground ore is floated to produce a
rougher concentrate which is reground and floated again to produce a
concentrate containing both copper and molybdenum minerals. This con-
centrate is then conditioned and subjected to another flotation opera-
tion in which the molybdenum mineral is floated and the copper mineral
depressed. Both concentrates are dewatered by thickeners and filters
and shipped. The molybdenum sulfide concentrate is either sold as is
for use as the sulfide or sold for roasting to the oxide.
Processing of Concentrates
The various product forms of molybdenum and the processes used to pro-
duce them are indicated in Figure 11.
The conversion of molybdenum sulfide concentrates to crude molybdenum
oxide is achieved in a manner similar to that for almost all other sul-
fide ores by roasting in circular hearth furnaces. In the case of
molybdenum roasting, the desired reaction is the complete oxidation of
72
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all sulfur and production of the higher oxide, MoOo. The oxidation re-
action is self-sustaining, but the significant volatility of the oxide
at about 1300 F requires that the temperature be controlled by limit
losses. An example of a molybdenum sulfide roasting operation would
thus include a Nichols-Herreschoff 12-hearth circular roasting furnace.
The molybdenum sulfide concentrate is introduced to the upper hearth,
and mixed by rotating rakes to successive lower hearths. The furnace
is operated at a slight vacuum (<0.1 inch of water) so that air is
drawn in at the lower hearth and is withdrawn from several of the middle
hearths where the major heat of reaction is generated. The off-gas con-
tains the products of combustion and SCU. The upper hearths operate at
800 to 900 F as the concentrate is preheated and volatiles are driven
off, the center hearths operate at 900 to 1100 F where the major reac-
tion occurs, and the lower hearths are maintained at 500 to 900 F by
supplementary gas heating to ensure that sulfur is reduced to about
0.05 to 0.25 percent. The product, withdrawn from the bottom hearth of
the roaster, is known as technical-grade molybdic oxide. This form of
oxide usually contains most of the impurities present in the original
concentrate and is thus defined only by a specification requiring a
minimum of 60 percent molybdenum, with maximum impurity levels speci-
fied for copper (0.50 percent), lead (0.15 percent), phosphorus (0.05
percent), and sulfur (0.25 percent).
Purified molybdic oxide, containing on the order of 99.5 to 99.975 per-
cent MoC>3, is produced by heating of technical-grade oxide in a furnace
to temperatures of 1800 to 2150 F, which results in the sublimation or
vaporization of the oxide. The vapors are carried in a stream of forced
air from the furnace, through ducts and cooling flues to a fabric fil-
ter collector, e.g., a wool fabric baghouse. The sublimation is usually
accomplished in a muffle-type furnace with a controlled, forced-air
draft system, and in the case of one large producer, a circular furnace
with a rotating hearth, so that crude oxide and residue may be continu-
ously charged and withdrawn, respectively. The sublimation process used
to produce purified molybdic oxide may be iterated to increase purity to
high levels.
An alternative method of achieving high-purity forms of molybdenum is
to dissolve purified (once-sublimed) molybdic oxide in ammonium hydrox-
ide solution. The solution is filtered and evaporated to crystallize
pure ammonium molybdate (Nlfy)6Mo7C>24'4H20. This process is character-
ized as producing the purest form of commercially available molybdenum.
Either the trioxide or ammonium molybdate may be reduced to elemental
metal by heating to a temperature of 1800 to 2000 F in a hydrogen atmos-
phere. The specific choice of starting materials and reduction condi-
tions (e.g., single or two-stage reduction) depends on such conditions
as initial purity of the starting materials.
The hydrogen reduction of oxide particles or ammonium molybdate crystals
is the most common method used to produce molybdenum metal. The product
of reduction is metal powder. The processing of the powder to ordinary
74
-------
metal forms of sheet, bar, etc., can be accomplished bv two routes.
One, the powder metallurgy route, involves the compaction of the pow-
ders into appropriate sized blocks, cylinders, or other preforms, fol-
lowed by high-temperature heat treatment to accomplish the sintering or
bonding of the particles. Subsequent steps of processing apply heat
and pressure either separately as in the compacting and sintering
stages, or simultaneously as in a hot forging or other hot-working pro-
cess to consolidate the powder, eliminate any porosity, and eventually
produce a completely solid, wrought product form.
The alternative route involves the initial hot or cold compaction and
sintering of the powder into long bars, which serve as consumable elec-
trodes in an arc-melting process. In an appropriate furnace, consist-
ing chiefly of a water-cooled copper crucible, the preformed bars serve
as one electrode for striking a high-current, low-voltage arc between
the bar, and a starting pad of molybdenum metal. As the bar is pro-
gressively melted by the arc, the molten metal falls through the arc
and forms an ingot, which progressively freezes into solid form. The
ingot may be remelted to improve purity or quality and then fabricated
to product form.
Calcium molybdate no longer is made in the strict sense of chemical
terminology. The current form of product to which the term calcium
molybdate is attached is a mixture of roasted concentrate (i.e., tech-
nical-grade oxide) and ground limestone, and is used for molybdenum
additions to molten steel.
Size and Characteristics of the Tungsten Industry
The tungsten-producing and -processing industry is small, diffuse, and
rather specialized compared with the major nonferrous metals industries.
The net domestic production figure published for 1969 was 6,500 tons of
contained metal. Tungsten concentrates are produced by about 42 mines,
but as coproducts of other minerals or concentrates or on an intermit-
tent basis. The end-product forms of tungsten include the metal, the
oxides, carbides, chemical forms, and ferrotungsten. The tungsten
values may be transferred between plants in varying stages of refine-
ment or form, or may be processed from mineral form to final product in
a single plant.
The release of 19,000 tons of tungsten by the U.S. Government in 1969
was an unusual event in a rather diffuse industry structure, where pro-
duction is erratic owing to both market conditions and the geographical
and climatic (high altitude and heavy snows) conditions ruling most-
mine sites. No detailed analysis or prediction of future production is
included in this discussion beyond the listing of recent past domestic
mine production, roughly 3,500 to 5,000 tons per year. The statistics
for the tungsten industry as published by the Bureau of Mines for 1965
to 1969 are given in Table 21.
75
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The most noteworthy of current tungsten mining and processing opera-
tions are listed in Table 22. In addition to the major operations
shown in Table 22, intermittent tungsten production was reported for
1969 only in terms of the states of Arizona, California, Colorado,
Idaho, Montana, Nevada, and Utah. No complete, carrent listing of
tungsten-producing mines and mills is available in the literature. A
survev of tungsten technology listed 21 tungsten mills in California
and '11 mills in Nevada in 1959 (Table 23). The current status of pro-
duction of these operations is a matter of circumstance and not readily
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TABLE 23. TUNGSTEN MINES AND MILLS (PAST AND/OR POSSIBLE PRODUCERS)(26)
State
County
Operations
California Fresno
Inyo
Nevada
Madera
Tulare
11
Mono
Kern
San Bernadino
Ditto
Humbolt
it
Pershing
it
it
Churchill
M
Douglas
Lander
I!
White Pine
Ditto
H
Elho
Mineral
Esmeralda
Nye
Lincoln
Clark
New Idria Mining and Chemical Co.
Round Valley Tungsten Co.
El Diablo Mining Co.
Red Hill Custom Mill
Molybdenum Corporation of America (Beware Mill)
Union Carbide Corp.
Ajax Tungsten Corp.
Rossi Mill
Miller and Warken Mill
Piute Mining and Milling Co.
June Bee Mill
Tulare County Tungsten Mining Co.
Sherman Peak Mining Co.
Wah-Chang Mining Corp. (Benton Mill)
McKee Mill
Rand Mining and Milling Co.
Butte Lode Mill
Surcease Mining Co.
Parker Bros. Mining and Milling Co.
Minerals Material Co.
Section 9 Tungsten Mine and Mill
Getchell Mine, Inc.
Winnemucca Mountain Mining Co.
Nevada-Massachusetts Co.
Wolfram Company-Toulon Mill
Trojan Mill
White Cap Metals Mill
Churchill Tungsten Mining Company
Metallurgical Development Co.
Conquest Mine and Mill
Linka Mine and Mill
Minerva Custom Mill
Baltimore Camas Mill
Strategic Metals - Tungstonia Mill
White Star Tungsten Mill
Nevada Scheelite Corp.
Dead Horse Wells Mill
Kinkhead Mill
Florey Mill
Gun Metal Mill
Minada Corp.
Commadore Mill
Gabbs Exploration Co.
El Capitan Mill
Baxter Mill
Yaney Custom Mill
Wah Chang Corporation (Lincoln Mill)
Tri-State Metals Mill
79
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81
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Raw Materials and Processes(25,26,28)
Ores and Concentrating Processes
The mineral forms from which tungsten and tungsten compounds are pro-
duced are complex metal oxide forms. The mineral names and chemical
nomenclature and formulas are listed in Table 25. Of the many mineral
forms, only the first four are of practical significance.
TABLE 25. TUNGSTEN MINERALS
Mineral
Name
Scheelite
Feberite
Wolframite
Hubnerite
Powellite
Chillagite
Stolzite
Raspite
Cuprotungstite
Tungstite
Tungstenite
Ferritungs tite
Chemical
Formula
CaWC>4
FeW04
(Fe, Mn)W04
MnW04
(Ca, Mo)W04
3PbW04-5PbM04
PbW04
PbW04
CuW04'2H20
W03-H20
WS2
Fe203-W03- 6H2O
Chemical
Nomenclature
Calcium tungstate
Iron tungstate
Iron-manganese tungstate
Manganese tungstate
Ca Ic i urn- mo lybdo tungstate
Lead tungstate- lead molybdate
Lead tungstate
Lead tungstate
Hydrous copper tungstate
Hydrous tungsten trioxide
Tungsten sulfide
Hydrous iron- tungsten oxide
The occurrence of these minerals in workable deposits is limited to the
western states mentioned previously and to isolated deposits such as
the one currently worked in North Carolina and an obsolete operation in
the New England area. The grades of ore currently producing tungsten
are described as containing between 0.3 and 0.5 percent W03, This
metal content is generally associated with one or more coproducts, usu-
ally molybdenum. The multiple-product nature of the ores is the feature
that makes them economically practical. Tungsten concentrates generally
are sold, traded, and treated at a level of 60 percent WCs. Thus, con-
centration processes accomplish about the same tenfold concentration as
is performed on copper ores, although the scale of operations is much
smaller. The yields obtained in concentrating tungsten ores range from
60 to 90 percent, owing to the nature of the mineral particle behavior.
The concentrating or milling of tung~sten ores involves the use of gra-
vity separation methods, flotation, magnetic separation, and leaching
techniques in various combinations or sometimes in series to achieve
82
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the desired concentrate composition. The leaching and flotation opera-
tions are sometimes indirect, i.e., materials other than the tungsten
compound are removed, to leave a residue with an increased proportion
or percentage of tungsten.
The determinants of the design of a tungsten-concentrating operation
are the minerals associated with the tungsten. The popular flotation
concentration process was developed principally for sulfide ores which
may be naturally or readily conditioned to be aerophilic or floatable.
The common minerals of tungsten are oxide forms and are floatable only
under special conditions, which may result in the simultaneous flotation
of other mineral or gangue components in the ore. Each ore requires an
individual process but some unique or generally common features of tung-
sten-concentrating processes may be identified here.
The principal considerations are that the tungstate minerals have high
densities and commonly occur as coproducts with floatable sulfide min-
erals of other metals. The concepts of flotation are discussed in
Volume I of this report and so only the broad considerations of the
process are included here. Tungsten-concentration processes thus may
include the usual liberation steps of crushing, grinding, classifying,
and sizing which assure uniform feed of desired size to the subsequent
process. If, for example, copper and/or molybdenum sulfides or iron
sulfides are present in the ore, they are amenable to separation by flo-
tation wherein the tungstate would appear in the tailing or discard por-
tion of the flotation separation. The tungstate minerals, by virtue of
a relatively high density, can be separated by gravity methods, such as
table classifiers or jigs, from any lighter associated minerals. An-
other separation technique possible depends on the nonmagnetic nature of
tungstates as opposed to the magnetic iron oxide. If the iron sulfide
mineral, pyrite, or the complex iron-aluminum (or other) silicate, gar-
net, are present, they may be converted by roasting to forms which are
magnetically separable from nonmagnetic tungstates. If the minerals
apatite [Ca5F(P04)3] or calcite (CaCOo) are present with the tungstate,
they may be removed by controlled leaching with hydrochloric acid. Con-
siderable care is necessary in leaching so that any calcium tungstate-
type minerals present are not also dissolved.
Some of the elements of tungsten-concentration processes are shown in
the simplified and generalized flowsheet in Figure 12. The operation of
ore crushing and sizing usually involves such unit operations as primary
crushing, fine crushing, and ball or rod mill grinding with associated
screening, cyclones or other classifiers which pass acceptable sizes,
and recycle oversize to the appropriate crushing operation. The output
size of the initial sizing operation is controlled to be amenable to
the subsequent operation. In the example given in the figure, the ore
is conditioned initially with suitable reagents and floated to separate
sulfide minerals. In the cases of many tungsten ores, an initial separ-
ation of slimes (particles less than 20 microns, for example) would be
necessary. Because of the usual brittle and friable nature of tungsten
minerals, slimes generation is a common occurrence during comminution
83
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Sulfide
Concentrates
Ore Crushing
and Sizing
Feed
S1 irae s
(Fine)
Sulfide
Flotation
Tailings
Rougher
F lot fit ion
Ce 1 ] s
Cleaner
Flotation
Cells
Concent rates
Scavenger
Flotation
Cells
-Tail ings-
-Waste Acid Leach
Calcium Tungstat_e_
Concentrates
To
Market
Sulfide
Concentrates
Tailings
Sands
(Coarse)
Gravity I
Separation j
Fines
Roaster
Magnetic
Separation
Irony Product
Garnet
Calcium
Tungstate
FIGURE 12. FLOWSHEET FOR PROCESSING OF TUNGSTEN
ORE TO CONCENTRATES
84
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to any size. Slimes may or may not interfere with a flotation opera-
tion but are generally detrimental to efficient separations. The indi-
cated initial sulfide flotation could, for example, separate the copro-
duct sulfides of copper, molybdenum, or iron either singly by their
single occurrence, or by differential flotation, or in combination, in
which case the product would be treated by differential flotation for
further separation. In the example, the flotation tailings are classi-
fied into fine and coarse and treated by two alternative routes. The
fines are reconditioned, reagents added, and the fines refloated to
achieve additional separation of suifide minerals. After reconditioning
and addition of new reagents, the fines are refloated through rougher
and cleaner flotation cells, with the flotation product being in this
stage the tungsten mineral and some associated gangue minerals. Compo-
nents of the gangue in this example are calcite and apatite. A first-
stage leach with hydrochloric acid (HC1) removes the calcite (CaCCO as
a calcium chloride (CaCl2) solution which is discarded. A second stage
leach is used to dissolve the apatite [CaF(PO^)3], which is not dis-
solved in the presence of calcium chloride.
The sand fraction is further classified into two size ranges and treated
with the gravity-separation technique of a reciprocating table. The
large particles are returned to the beginning of the process and are
subsequently and eventually processed as fines. The concentrates from
the tables are dried, roasted, and subjected to magnetic separation.
The magnetic separation results in a three-way split of product: a
strongly magnetic high-iron-content product; a weakly magnetic product,
garnet; and a nonmagnetic product, calcium tungstate. The intriguing
and individual features of this particular example are that an initial
crushing and grinding operation produces a product which allows the sep-
aration of sulfides by flotation and a split of the tailings into two
fractions, each with a characteristic combination of gangue minerals,
allowing each pair of gangue minerals to be removed, with the gravity-
roast-magnetic leg screening out some of the material from the fines
circuit. Acid consumption is minimized.
Treatment of Concentrates
The processing and products derived from concentrates are indicated in
the chart in Figure 13. As previously discussed, the end products in
the primary industry include the major categories of ferrotungsten, and
scheelite, both used as additions to alloy steels, and the other cate-
gories of metallic tungsten in the forms of powder, consolidated metal,
tungsten-base alloy mill products, alloying additions in superalloys,
or as tungsten carbides or chemicals.
The production of ferrotungsten may use any of the types of tungsten
concentrates or a mixture of them. The predominant practice in this
country is the use of the electric furnace process in which the concen-
trates, ferrosilicon, and basic flux material (e.g., limestone) are fed
85
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Concentrates
Carbothermic
and
hcUHothcrralc
Processes
Scheelite Type
(Fe,Fe-Mn,Mn)WO.
HC1
Process
Ferrolungsten
Alloy
Steels
Synthetic
Scheelite
"1
Wolframite Type
CaWO,
Sodium
Tungstate
Tungstic
Acid
Ammonium
Hydroxide
Process
Ammonium
Paratungstate
I
Ignition.
Tungstic
Oxide
Tungsten Powder
Super Electrical
Alloys Contact
Materials
Consolidation
Processes
Carburizing
and Coating
Chemicals
and Dyes
Mill Products
and Shapes
Carbides
FIGURE U. DIAGRAM OF PROCESSES AND PRODUCTS IN THE TUNGSTEN INDUSTRY
86
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into an electric arc furnace. The mixture is smelted into a slag and a
ferrotungsten product. The solid ferrotungsten may be retrieved from a
demountable furnace and crushed and sold as chunks for addition to alloy
steel melts.
The alternative methods of production use carbon, aluminum, or a combi-
nation of silicon and aluminum. The silicon-aluminum reaction is self-
sustaining after an initial ignition, whereas the other methods of re-
duction are usually carried out in electric furnaces. All accomplish
the reaction of a reducing agent with the oxide of tungsten in the pre-
sence of iron (either in the form of scrap steel or a ferroalloy) with
the oxide products fluxed and removed as a molten slag.
Another method of adding tungsten to steels is in the form of calcium
tungstate, CaW04, usually as a product called synthetic scheelite.
Here the calcium tungstate reacts with the molten-steel bath so that
the calcium enters the slag and the tungsten enters the molten steel
as reduced metal.
The production of synthetic scheelite may utilize low-grade tungsten
concentrates of the scheelite type to produce a required high-grade
material usually containing about 70 percent W03 instead of the usual
60 percent WC>3 encountered in most concentrates. The synthetic schee-
lite process, indicated in simplified form in the diagram in Figure 14,
consists of the selective leaching of the tungsten, followed by its
precipitation and agglomeration into nodular form for addition to steel
me 11 s.
The feed material for the process consists of concentrates ranging down
to about 15 percent or less W03- The feed is blended, ball-milled,
etc., and fed as a water slurry, with the addition of sodium carbonate,
to a heated, pressurized digester vessel. Heat (as steam) and pressure
are applied and controlled to conditions to maximize the leaching of
the tungstate as soluble sodium tungstate and to minimize the leaching
of other components. The liquor from the digester is cooled in a heat
exchanger and pressure filtered, including washing operations, to ob-
tain all the solubilized tungstate. Wash waters are routed either to
the subsequent process or back to the grinding circuit. The liquor is
treated with various reagents to achieve the precipitation of calcium
tungstate as a solid, which is filtered from the liquor and the fil-
trate discarded. The filter cake is dried and agglomerated in a kiln
to give the final product.
The treatment of concentrates for the production of other forms of
tungsten is usually started by reacting the concentrate with sodium
carbonate at 800 C to achieve a fused-salt mixture, which when cooled,
crushed, and water leached yields a solution of sodium tungstate. The
addition of hydrochloric acid to this leach solution causes the preci-
pitation of a solid, tungstic acid (^WO^) . By heating (to 1000 C) the
acid is decomposed to tungsten trioxide. The preparation of a pure
form of the oxide is highly desirable if pure metal powder is to be
87
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Feed
(Ores or Concentrates)
Sodium Carbonate
Sulfuric Acid
Sodium Hydroxide
Sodium Sulfohydrate
Calcium Chloride
Hot, Pressurized
Digestion Reaction
Agglomerating
Kiln
Wash Waters
Solids
Liquor
Fume
_Scrubber
Liquor
Synthetic Scheelite
(Calcium Tungstate)
FIGURE 14. FLOWSHEET FOR THE PRODUCTION OF SYNTHETIC SCHEELITE
88
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produced. The pure oxide may be obtained by repeated dissolving and
precipitation of the tungstates as indicated in the diagram in Figure
15. Here the sodium tungstate leach liquor is treated with calcium to
precipitate calcium tungstate, and the solid is filtered from the liquor,
The solid is leached with HC1 to produce a calcium ciloride liquor and
a residual solid of tungstic acid, H3W04. After wasiing and separation,
the solid tungstic acid is redissolved in ammonium hydroxide, the solu-
tion filtered, and solid impurities discarded. The clarified solution
(ammonium paratungstate) is treated with hydrochloric acid to reprecipi-
tate tungstic acid, with the liquor being discarded after the separation
of the solid. The solids are redissolved in ammonium hydroxide and re-
precipitated with additional impurities remaining in the discarded
liquor. The solid tungstic acid, t^WO^., is dried and heated or ignited
to decompose to the trioxide (WOo) and water vapor.
The point of the above purification steps is to achieve high-purity
oxide and remove a number of impurities usually found in the ores: iron,
manganese, calcium, molybdenum, alumina, silica, lead, copper, titanium,
sulfur, phosphorus, arsenic, antimony, bismuth, and tin.
Pure tungstic oxide is used for the production of tungsten-metal powder.
Most commonly the process consists of charging the oxide in ceramic con-
tainers, or "boats", into a furnace and heating under a circulating
hydrogen atmosphere. Furnace temperatures usually are about 1200 C,
where the overall reaction proceeds.
W03 + 3H2 -> W + 3H20.
Because of its high melting point, and rapid oxidation rate, tungsten-
metal powders are treated by powder-metallurgy techniques with protec-
tive or inert atmospheres or in vacuum furnaces. The production of
metal parts or shapes proceeds through the steps of hot or cold compac-
tion of powders, sintering, and hot or cold deformation to accomplish
the consolidation and shaping of the metal. The consolidation of tung-
sten is also achieved by the cold-crucible, arc-melting techniques de-
scribed in the section of this report describing the processing of
molybdenum. Tungsten metal end products include sintered, porous elec-
trical contacts, sintered electrical contacts in which the porous tung-
sten skeleton is filled or infiltrated with copper or silver, and con-
solidated tungsten mill products such as plate, bar, rod, wire, foil,
etc. The classical application of tungsten wire is, of course, in lamp
filaments. The applications of tungsten and tungsten-base alloys are
determined by its density, high-temperature strength, and high oxidation
rate, the last requiring that its high-temperature service be in nonoxi-
dizing (i.e., inert gas or vacuum) environments.
The production of tungsten carbide involves the heating of oxide or
metal powder mixed with powdered carbon. If the oxide is used, the car-
bon reduces the oxide to the metal. The carbon and tungsten interact
at high temperatures by solid-state diffusion to form the carbide com-
pounds WC and W2C. Cemented carbides are produced by ball milling a
89
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Concentrates
Sodium Carbonate ^, Fusion
Solids
Leach Liquor
(Sodium Tungstate Solution)
Lime
Solids Separation Liquor
Calcium Tungstate (solids)
Hydrochloric Acid
Leach Calcium Chloride Liquor
Tungstic Acid (solid)
Ammonium Hydroxide
Hydrochloric Acid
Solids Separation Liquor
Ammonium Hydroxide M Dissolving Ta
nks
Ammonium Tungstate Liquor
Hydrochloric Acid
Solids Separation Liquor
Pure Tungsten Trioxide Product
FIGURE 15. FLOWSHEET FOR THE PURIFICATION OF TUNGSTEN TRIOXIDE
90
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mixture of carbide powders and metal (usually cobalt) powder to coat
each carbide particle with the metal, after which hot- or cold-pressing
and sintering operations produce a bonding of the particles by means of
the adhering metal. With the technique of the modern arc furnace, car-
bides may be fused and cast into simple shapes. Carbides are used for
applications such as cutting and grinding tools, engine components such
as valves, and abrasion-resistant parts in sand-blasting machines or
rocket engines.
Water Practices in the Molybdenum and Tungsten Industries
Water usage in the molybdenum- and tungsten-producing industries shows
a considerable number of components in view of the great number of vari-
ous unit processes. Water-use data were obtained from only four opera-
tions in this segment of industry. However, the data are reviewed here
to serve as examples of what may be expected as regards waste water
from such plant operations.
The refractory-metal industry may be considered from the viewpoint of
plant operation and water usage to consist of two segments: mining and
milling, and the chemical-type plant in which concentrates are pro-
cessed to chemical or metal end products.
Mining and milling of the metal ores represents a somewhat complex sit-
uation in the case of molybdenum and tungsten. Because of the coproduct
status of molybdenum minerals, a considerable portion of water usage
attributable to the mining and milling of molybdenum is initially dis-
cussed in Volume I of this report, under the discussion of the mining
and concentration of copper ores.
In the case of the major molybdenum producers, the published literature
serves as a source of information on individual problems and water-pol-
lution-control practices associated with specific molybdenum mining
operations.
In 1966, work on the effects and control of tailings-pond effluent from
a flotation-concentrating operation included cooperative studies by in-
dustry and state officials. J' A molybdenum mining and concentrating
operation was found, by virtue of breakdown of some elements of the
plant, to be leaking concentrator effluents from points other than the
originally designed tailings-pond discharge point, resulting in fish
kills in the receiving river. The breakdowns consisted of breaks in
pipe lines carrying the slurry from the concentrator to the tailings
pond and in a break in conduit under the tailings pond.
The breaks in the pipe line were traced to the abrasive wear of the
steel pipe by the crushed rock waste in the tailings slurry, and were
found most often at curves or bendc in the pipe line.
91
-------
This aspect of the problem has been minimized by constant patrol and
inspection of the pipe line, using test devices to check the thickness
of the pipe. The break in the underground conduit was attributed to
the shifting of the fill on which the conduit was originally laid. The
conduit was lined with steel pipe to overcome the leakage problem.
One of the major parts of this work was the examination of the disposi-
tion of the reagents used in the concentration process, and some modifi-
cation of reagent use, involving the use of minimum quantities of
reagents so that no excess is discharged in the effluent. Some of the
most interesting information generated by this study is given in the
following tables. The first (Table 26) gives information on the nature
and disposition of the flotation reagents, while the second (Table 27)
shows the published data on waste analyses.
The conclusions of the article were that with proper control of reagent
additions, a tailings-pond effluent has been achieved which is of suffi-
cient quality that fingerling trout survive indefinitely in the undiluted
effluent.
Still other published information has indicated the approach to water-
pollution-control practice in a new molybdenum mining and concentrating
operation.^ '^ ^ This operation, relatively recent in being started,
has had the benefit of advance consideration of effects on the environ-
ment. While complete details of the operation of the metallurgical pro-
cesses have not yet been published, some of the major considerations for
control of water pollution have been identified. Most simply stated,
the plant and associated natural and new drainage and water systems
have been designed to isolate the plant water system from the surround-
ings in case of equipment failure or floods up to a level of the largest
expectable flood in a period of 100 years. The concentrator and tail-
ings disposal area were placed within the features of the local terrain
to allow for natural drainage of spills or leaks into the tailings pond,
with the only possible discharge being completely controlled. To pre-
vent storm runoff entering and overloading the controlled system, cut-
off drainage measures were installed to route any such natural drainage
around the operation to be discharged to local streams without entering
the mill system.
Included in this design are collection systems to control mine drainage
water and basins and dams below the tailings pond to serve the purpose
of collecting any potential underground seepage escaping from the tail-
ings storage area and moving down the local geological system. This
system also allows for extensive recirculation and reuse of water in
the concentrating operation.
Water Usage in Metal-Processing Plants
The water-usage patterns exhibited by metal-processing plants exhibited
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general characteristics apparently governed by two general conditions:
municipal locations and the relatively high price of the materials
being processed. These factors corresponded to generally good knowledge
and control of water systems and the use of processes and waste-water
treatments to control material losses. The major common features of
the refractory-metal-processing plants, as reported during this study,
are indicated by the generalized water-use diagram in Figure 16. The
sources for these plants were municipal water systems, and with the ex-
ception of one plant's boiler feed water, no treatment was applied to
incoming water. The uses of the water included the usual common cate-
gories of sanitation, cooling, boiler feed, and in the cases of two of
the four plants, air-pollution control. The process-water category
included uses in acid leaching and other chemical operations, the wash-
ing and rinsing of the metal products, and use in open coolant and lub-
ricant circuits in metals fabrication, machining, and grinding opera-
tions. In addition, one plant reported use and control of water in a
cyanide equipment washing operation.
The receivers of discharge waters of these plants included sanitary
sewers, storm sewers, and surface waters. The discharge patterns gen-
erally showed segregation of waste-water streams, with neutralization
or other treatment before release of waste water from specific opera-
tions.
The water-usage data reported by these plants is given in Table 28.
Total intakes for the plants vary considerably and merely reflect that
plant size and operations are considerably diverse. However, the fig-
ures show considerable use of water in these complex processing plants.
The percentages of water used for the various categories within the
plant (Table 29) show that the two categories of process and cooling
are the major ones in these plants.
Waste-Water Sources, Treatment, Practices, and Costs
Of the four plants submitting data, the quantities of discharge water
fell into the following categories:
Million Gal/Yr
Total Discharge 305.7
Sanitary Waste Water 18.6
Industrial Waste Water
Treated 105.8
Untreated 181.3
All of the sanitary waste waters of these plants were discharged to
municipal sanitary sewers. The industrial waste waters were discharged
to sanitary sewers, storm sewers, or surface waters. Only one of the
plants indicated any problem with discharge-wa.?te-water quality and
95
-------
Municipal System
Sanitary
Use
Air
Pollution
Control
Cooling
Process
Boiler
Feed
Water
~!
Sanitary Sewers'
Storm Sewers
Surface Waters
Solids
Recovered
Solids
Lr
Acid
Equi p-
trent
Washing;
etc.
Neutrali-
zation,
Filtering
FIGURE 16. CHARACTERISTICS OF WATER CIRCUITS OF MOLYBDENUM
AND TUNGSTEN PROCESSING PLANTS
96
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identified heavy metals content as the problem, with the receiver bein*1;
surface water. The water treated by these plants was all of the type
identified as waste water from acid-leaching operations and was all
treated by neutralization and filtration. Lime and sodium carbonate
were used as neutralizing reagents.
Within the category of untreated water reported above, the respondents
induced washing, rinsing, and machining coolants, which were actual Iv
treated by simple settling. By the definition used in this report,
the water is classified as process water since it contacts the product,
However, the respondents stated that none of the processed refractory
metals entered this type of water. The settling out of the inert metal
particles was classed as a materials-recovery measure by these plants,
as was the recycling of some of the neutralization sludges. One plant
reported better than 99 percent yield of processed material, which
would be understandable in view of the value of refractory metals re-
lative to other metals.
One characteristic of these plants is indicated in the water-use diagram
in Figure 16. In three of the four plants, water use was segregated
and waste-water streams were directed to specific receivers. Examples
of this included the splitting of streams of used cooling and process
water, partly to sanitary sewers and partly to storm sewers.
Only two types of water costs were reported in this segment of industry.
A cost of $0.43 per 1000 gallons was given for the neutralization and
vacuum filtration of acid-leaching waste water. Total water costs for
both municipal supply and sewer rates were reported as $0.37 and $0.57
per 1000 gallons of intake, although sewer rates were included in the
charges. In the plant with the lower rate, some recirculation was prac-
ticed, but not to a large extent. In the plant with the higher rate of
water cost, extensive evaporation was practiced (with associated mater-
ials recovery), and one extensive cooling-water circuit was segregated
with its own reservoir and a discharge of carefully monitored wate> to
natural surface water.
99
-------
-------
SECTION IX
DISCUSSION
A number of nonferrous metals producing industries, processes and
associated water usage and water pollution control practices have been
discussed in this report.
The content of this volume has been reviewed and assessed in terms of
unit processes and associated waste waters. The numerous unit processes
covered have led to a tabular arrangement in presenting this assessment,
which is given in the form of Table 30.
The approach has been to review each metal in terms of all unit pro-
cesses, indicate whether water is used and follow with waste water char-
acteristic and control status, wherever such information was obtained
in the program. Also included are recommendations for the next action
appropriate for each process step indicated.
The data presented in Table 30 indicate that there are many specialized
problems but a brief discussion may aid in the understanding of the
table entries. The recommendations are in terms of double objectives:
(1) identifying needs for research development, or demonstration to lend
impetus to water quality improvement, and (2) assessing the approach of
the study to the point where unit process waste loads and effluent standards
standards could be set. There follow some generalizations which may be
drawn from the table.
The hot caustic leaching process by which bauxite ore is treated to
produce refined alumina, and the fused salt electrolysis process by
which alumina is smelted to aluminum metal were discussed in the review
of the aluminum industry. Alumina refineries show no discharge of pro-
cess (i.e., caustic) liquors, the process being characterized by closed
vessels and extensive evaporation processes which conserve the process
materials. Rather, the alumina refineries were characterized by a
closed water circuit (i.e., zero discharge), with the major feature
being the recirculation of water from a red-mud lake where ore residue
is accumulated. The waste waters identified by this study for a small
fraction of the alumina refineries surveyed were of the types common
to many industries: cooling tower blowdown, boiler water bleed-off,
sanitary wastes, and miscellaneous water treatment waste streams. The
overall trend in the information obtained was toward decreased or zero
discharge.
Aluminum smelters show the same trend. At smelters, the classical
major use of water has been for air pollution control devices to con-
trol the fluoride and carbonaceous fume from the electrolytic cells.
The overall trend in smelters is influenced by two factors: materials
101
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recovery from the wet scrubbing operation and the advent of a new dry
scrubbing system which also recovers fume components. The major trends
identified were decreasing discharges of waste water associated with a
rapid expansion of smelting capacity. The only research and development
needs identified in the aluminum industry were process development for
the removal or recovery of fluoride type components in wet scrubbing
liquors.
The current situation and processes of the primary mercury industry re-
flected considerable uncertainty regarding future needs. The primary
mercury industry shows continued contraction due to simultaneous
pressures of market economics and air pollution controls. Water pollu-
tion control practices of a very small sample of producers were mostly
indicative of remote locations and arduous climates. The waste water
characteristics reported showed only elevated values of salts and some
metals. No specific needs were identified at this time. The future of
primary mercury producers will most likely contain some increased con-
trol of air emissions. It can only be speculated that one approach to
the air emissions problem would be the initiation of hydrometallurgical
operations (e.g., leaching with sodium sulfide or hypochlorite solu-
tions). If such processes, whose feasibility remain to be demonstrated,
were to be initiated, the requisite water pollution control measures
could be designed into the new installations.
The review of the primary gold and silver industries indicated a simi-
lar current decrease in the number of operations. The information
available indicated that operations in desert areas showed zero dis-
charge and high recirculation of water similar to the circumstances of
mining and concentrating operations discussed in Volume I of this report,
In contrast, the largest gold mine in the United States has reduced
mercury in its discharge water to zero by suspending the use of the
classic amalgamation process and is currently dealing with the remain-
ing problem of cyanide in waste waters.
The primary molybdenum industry has published documentation of two
approaches to water pollution control: one included the initiation of
special surveillance and water control measures to prevent accidental
discharges of tailings slurry and modification of reagent concentration
in a flotation process; the other demonstrated approach was the design
of water pollution control measures into an extensive mine and concen-
trator operation. The design approach was to isolate the entire opera-
tion from incoming drainage and to allow for complete fail-safe type
control of all process water, accidental spills, mine drainage, and
underground seepage.
The primary tungsten industry, which utilizes both flotation and acid
leaching processes for the concentration of ores, remains largely
unknown in terms of this study. Plants processing the tungsten concen-
trates to various end products were associated with municipal water
systems and showed high materials recovery (i.e., close control of pro-
cessing water) and generally showed careful segregation of waste water
106
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streams. One such plant indicated a need for control of heavy metals
content in process waste water and indicated a desire to achieve
associated materials recovery.
107
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SECTION X
ACKNOWLEDGMENT
L'he sections of this report dealing with waste-water sources, charac-
teristics, amounts, and treatment practices are based largely on the
contributions of data and information of producers of nonferrous metals.
These contributions were made on a purely voluntary basis and at no
cost to the project. The constraint of confidentiality does not allow
the recognition of the contributors to this study on an individual or
corporate basis, thus due acknowledgment must be given to the nonferrous
metals industry in general.
Acknowledgment can be given to the American Mining Congress Ad Hoc
Committee on Wastewater Treatment Practice Survey. This committee
served to establish policies, supply information, and contribute expert
technical, review and comment on various sections of this report.
The program covered by this report was conducted by Battelle-Columbus
during the period of June, 1970, through June, 1971. Battelle staff
and consultants participating in this program were J. B. Hallowell,
A. B. Tripler, Jr., R. H. Cherry, Jr., G. R. Smithson, Jr., B. W.
Gonser, and J. F. Shea.
The support of this program by the Water Quality Office, Environmental
Protection Agency, and the help provided by Messrs. R. L. Feder,
E. L. Dulaney, and John Ciancia of that office is acknowledged with
sincere thanks.
109
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SECTION XI
REFERENCES
1. Minerals Yearbook, Bureau of Mines, U. S. Department of the Inter-
tor, U. S. Government Printing Office, Washington, D. C. (1968).
2. "1969 Aluminum Supplement", American Metal Market, Wednesday,
November 19, 1969, Section II.
3. " 'Statesmanship' and Shutdowns Save the Day for Aluminum",
Chemical Week, pp 17-18 (December 2, 1970).
4. "Aluminum, Profile of an Industry; 6, The Economics and the Out-
look", Metal Week, J39 (51), 193A-236A (December 16, 1968).
5. 1967 Census of Manufactures, "Smelting and Refining of Nonferrous
Metals and Alloys", U. S. Department of Commerce (September, 1970).
6. Aluminum, Volume II Design and Applications, Ed K. VanHorn, ASM,
Metal Park (1967).
7. U. S. Industrial Outlook, 1970, U. S. Department of Commerce, U. S.
Government Printing Office, Washington, D. C. (1969).
8. "Guideposts for the Future", Metals Week, pp 16-18 (January 4, 1971)
9. Kirk-Othmer Encyclopedia of Chemical Technology, Second Edition,
"Aluminum and Aluminum Alloys", Volume I, pp 929-990, Wiley and
Sons (1963).
10. Conklin, H. I., "Water Requirements of the Aluminum Industry",
Geological Survey Water Supply Paper 1330 C, U. S. Government
Printing Office, Washington, D. C. (1956).
11. Mayers, David, "New Techniques in Aluminum Production", Chemical
Engineering, pp 102-104 (June 5, 1967).
12. Sylvester, R. 0., Oglesly, R. T., Carlson, D. A., and Christman,
R. F., "Factors Involved in the Location and Operation of an
Aluminum Reduction Plant", pp 441-454 in Proceedings of the 22nd
Industrial Waste Conference, May 2, 3, and 4, 1967, Park One,
Engineering Extension Series No. 129, Purdue University, Lafayette,
Indiana.
13. West, J. M., "Mercury", pp 685-695 in Minerals Yearbook, 1969,
Volume I-1I, Bureau of Mines, U. S, Government Printing Office,
Washington, D. C. (1971).
Ill
-------
14. Pennington, James, "Mercury--A Material Survey", U. S. Burean of
Mines Information Circular 7941 (1959).
15. Erspamer, E. G. , and Wells, R. R. , "Selective Extraction of Mer-
cury and Antimony From Cinnabar-Stibnite Ore", U. S. Bureau of
Mines Report of Investigations 5243 (1956).
16. Town, J. W., et al., "Caustic Sulfide Leaching of Mercury Products",
U. S. Bureau of Mines Report of Investigations 5748 (1961).
17. Stickney, W. A., and Town, J. W., "Hydrometallurgical Treatment of
Mercury Ores", paper presented at the Annual Meeting of AIME
(March, 1961).
18. Town, J. W., and Stickney, W. A., "Cost Estimates and Optimum Con-
ditions for Continuous Circuit Leaching of Mercury", U. S. Bureau
of Mines Report of Investigations 6459 (1964).
19. Hoyt, C. D. , "Gold", pp 521-538 in Minerals Yearbook, 1969, Volume
II, Metals, Minerals and Fuels, Bureau of Mines, U. S. Government
Printing Office, Washington, D. C. (1971).
20. Hoyt, C. D., "Silver", pp 997-1010 in Minerals Yearbook, 1969,
Volume II, Metals, Minerals and Fuels, Bureau of Mines, U. S.
Government Printing Office, Washington, D. C. (1971).
21. Hacker, D. W., "Gold Means Dead Water in Deadwood", The National
Observer, JLO (12), pp 1 and 16 (March 22, 1971).
22. Morning, J. L., "Molybdenum", Minerals Yearbook, 1969, Volume II,
Metals, Minerals and Fuels, Bureau of Mines, U. S. Government
Printing Office, Washington, D. C. (1971).
23. Harwood, J. J., "The Metal Molybdenum", in Proceedings of a
Symposium, September 18-19, 1956, American Society for Metals,
Cleveland (1958).
24. Staff, Bureau of Mines, Mineral Facts and Problems, 1965 Edition,
Bureau of Mines Bulletin 630, U. S. Department of the Interior,
Washington, D. C. (1965), pp 595-606.
25. Stevens, R. F., Jr., "Tungsten", pp 1091-1107 in Minerals Yearbook,
1969, Volume II, Metals, Minerals and Fuels, Bureau of Mines, U. S.
Government Printing Office, Washington, D. C. (1971).
26. Zadra, J. B. , "Milling and Processing Tungsten", Bureau of Mines
Information Circular 7912, U. S. Government Printing Office,
Washington, D. C. (1959).
27. "Tungsten Report", American Metal Market, February 5, 1971, Sec-
tion II.
112
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28. Staff, Bureau of Mines, Mineral Facts and Problems, 1965 Edition
Bureau of Mines Bulletin 630, U. S. Department of the Interior,
Washington, D. C. (1965).
29. Bhappu, R. B., Fair, J. H., and Wright, J. R. , "Waste Problems
Relative to Mining and Milling of Molybdenum", pp 575-592 in
Proceedings of the 22nd Industrial Waste Conference, May 2, 3, and
4, 1967, Part Two, Engineering Extension Series No. 129, Purdue
University, Lafayette, Indiana.
30. Shriver, W. W.,"Design Considerations for the Henderson Project
Tailing and Mill Process Water System", paper presented at the
AIME World Symposium on the Mining and Metallurgy of Lead and Zinc,
St. Louis, Missouri (October 21-23, 1970).
31. "Climax Mine Awarded Citation for Preventing Water Pollution",
American Metal Market, p 7 (July 24, 1971).
113
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1
Accession Number
w
2
Subject Fiold & Group
05G
SELECTED WATER RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
_LJ
Organization
Batte.lle Columbus Laboratories, Columbus, Ohio
Title
Water-Pollution Control in the Primary Nonferrous-Metals Industry Volume II.
Aluminum, Mercury, Gold, Silver, Molybdenum, and Tungsten
10
Autl>0r(g)
Hnllowell, J. B.
Shea, J. F.
Sm:thson, G. R., Jr.
Tripler, A. B.
Gonser, B. W.
16
Pro/act Designation
EPA, OR&M Contract No. 14-12-870
.23
Note
22
Citation
Environmental Protection Agency report number,
EPA-R2-73-247b, September 1973.
93 I Desc'riptota (Started First)
.i i.-, *
Heavy Metals Water Pollution Control, Mining, Smelting, Refining
Waste Water Treatment Costs, Cu, Pb, Zn, Al, Hg, Au, Ag, Mo, W, Cd, Bi, Sb
25
27
Identifiers (Starred First)
Mining, Nonferrous Metals, Smelting
tie aw Metals
Abstract
The purpose of the program was to identify specific research needs in the area of
water pollution in the primary nonferrous metals industries. This program consisted
ot a survey of literature and the acquisition of data from industrial operations.
The contents 01 the final reports (2 volumes) include: the identification of process
^teps uuing water and/or generating wastewater, the amounts of water used for various
purposes, T'ecirculation rates, amounts of wastewaters, specific or characteristic
substances in wa&tewaters, the prevalance of wastewater treatment practice, methods,
and costs; current treatment problems, and plans for future practices of recirculation
or w.nteviter treatment.
!'he metals reported on included copper, lead, zinc, and associated byproducts (arsenic,
cadmium, silver, gold, selenium, tellurium, sulfuric acid, salts and compounds),
mercury, (primary) gold and silver, aluminum, molybdenum, and tungsten.
ihe information presented includes detailed processing descriptions and flowsheets,
tabulations of quantities of water intake, quantities used by category, recirculated
,-;ater, cischarge water quantities and analyses, water treatment costs. Representative
water flowsheets are given. (HallowellBattelle-Columbus).
Abstractor
J . B. Hallowell
Battelle-Columbus Laboratories
SCND, rtMH COPY OF OOCUMTMT, TO: VYAlf.R RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
-»SHINCTON. D. C. 20240
CPO: 1070 - «07 -881
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