ENVIRONMENTAL ASSESSMENT OF ,
DOMESTIC PRIMARY COPPER, LEAD
AND ZINC INDUSTRIES
EXECUTIVE SUMMARY
PEDCo ENVIRONMENTAL
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PEDCo - ENVI RON M ENTAL
SUITE13 • ATKINSON SQUARE
CINCINNATI. OHIO 45246
513 /771-4330
ENVIRONMENTAL ASSESSMENT OF THE
DOMESTIC PRIMARY COPPER, LEAD
AND ZINC INDUSTRIES
EXECUTIVE SUMMARY
Prepared by
PEDCo-Environmental Specialists, Inc.
Suite 13, Atkinson Square
Cincinnati, Ohio 45246
Contract No. 68-02-1321
Task No. 38
EPA Project Officer
Margaret J. Stasikowski
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Industrial Environmental Research Laboratory
5555 Ridge Avenue
Cincinnati, Ohio 45268
November, 1976
BRANCH OFFICES
Suite 110, Crown Center Suite 107-B Professional Village
Kansas City, Mo. 64108 Chapel Hill, N.C. 27514
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EXECUTIVE SUMMARY
INTRODUCTION
This report presents the results of a multi-media (air, water, and
solid waste) study of the environmental impacts of the primary produc-
tion of copper, lead, and zinc in the United States. The open litera-
ture was surveyed to identify all processes employed by the primary
copper, lead, and zinc industries having a significant environmental
impact. All pollutant effluent streams were characterized and described
as far as possible through engineering analyses of available data.
Special attention was given to the identification of potentially hazard-
ous process outputs. Toxic materials released to the environment were
identified and health effects data were assessed. Although limitations
on the amount of information available leave some important environ-
mental questions unanswered, the report presents a multi-media environ-
mental overview and identifies information gaps as well as R&D efforts
needed for more effective pollution control.
The primary copper, lead, and zinc industries are defined as the
facilities that extend from the mining of the ores through the produc-
tion of the purified metals as marketable castings. The three indus-
tries are closely interrelated. Many of the same companies are active
in more than one field, and many ores yield recoverable amounts of more
than one of the metals.
In addition to copper, lead and zinc, these industries also extract
many by-products from the ores including precious and rare metals and
raw materials for semiconductor electronic manufacturing.
Thirteen companies operate the 35 smelters and refineries in the
United States, providing employment for approximately 50,000 people.
Many other companies, some very small, are engaged primarily in mining
and concentrating. This industry makes commodity products that must
meet international specifications and that are sold to an international
market. Foreign competition is very strong.
The demand for copper is expected to continue to increase. Fore-
casts for the year 2000 range from 3 to 5 times present consumption.
The demand for lead and zinc, on the other hand, is not expected to
increase, at least for the short term, since markets are being lost to
other materials.
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London metal market prices for the three metals on October 27, 1976
were: copper, $1.21/kg; lead, $0.43/kg; zinc, $0.60/kg. Copper is the
least available metal, and copper ore containing as little as 0.4 per-
cent copper is being processed. Lead and zinc are still being mined at
concentrations of 8 percent in the ore. This country uses much more
zinc than it produces, while it is almost self-sufficient in the produc-
tion of lead and copper.
An important factor in the international competition in this
industry is that many U.S. producers have never established major
markets for the sulfur contained in the ores they process. In contrast
with other countries, the United States has large deposits of elemental
sulfur that have offered too much competition for sulfur obtained as a
by-product. Most of the largest smelters are located far from the major
sulfur acid markets, and many are located close together, producing a
local oversupply of sulfur.
Also in contrast with most of the international competition, the
domestic industries consist largely of old plants, especially in the
copper industry, many of them dating back to the turn of the century.
Plant owners frequently claim that they cannot justify the costs of
rebuilding or modernization. Several plants have closed in recent years
and a few newer ones are now operating. One copper smelter is being
constructed and one zinc smelter is being converted to an electrolytic
plant.
PRIMARY COPPER INDUSTRY
The processes by which copper is produced in the United States are
now undergoing change. Whether new pyrometallurgical techniques or the
new field of hydrometallurgy will be the dominant technology is not yet
clear, but the industry is searching for improved methods. Most of the
U.S. copper is being made by the "conventional" pyrometallurgical pro-
cessing methods, little changed for almost 75 years. Now a nev. flash
smelter process has been imported, fluidized bed roasters are operating,
a continuous smelter is being constructed, and at least one new hydro-
metallurgical process has progressed as far as semi commercial operation.
This country has sixteen copper smelters and seven electrolytic re-
fineries, most of which are located in western states. They process
domestic ores of copper, also mined mostly in the west, and they also
import concentrates and partially smelted copper from several other
countries. These plants produce a variety of products, of which the
principal one is electrolytic copper, over 99.9 percent pure, repre-
senting over 90 pecent of the copper consumed in this country. The
primary copper industry produces at least eight other metals and semi-
metals, including all the arsenic, selenium, and rhenium this country
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consumes. In 1975, domestic copper smelters produced about 1.3 million
metric tons of copper.
Eight companies own and operate the smelters and refineries. They
also directly own 20 of the 25 largest domestic copper mines, and they
provide employment for approximately 40,000 persons. Many other com-
panies are engaged primarily in mining and concentrating operations.
Environmental Impacts, Copper
For assessment of the environmental effects of this industry, the
technology is broken into 43 separate sections, or processes. These are
shown in Table 1, along with the waste products that each process
generates. Each waste stream is further discussed in the main body of
the report. Each major section of the industry produces a distinct
environmental impact. The mining and concentrating section produces
thousands of tons of metalliferous solid wastes each day and large
volumes of contaminated water. The electrolytic refinery concentrates
many of the less-common elements into a highly acidic solution (black
acid), for which there is no easy method of disposal. Treatment and
disposal methods should be developed. Hydrometallurgical processes may
produce a tailings rich in elemental sulfur that may not be stable on
extended weathering. The copper smelter produces atmospheric pollution,
consisting of hazardous particulates, both from the process stack and as
fugitive emissions, mixed with large quantities of S02 gas.
Each main processing section of the industry is examined, sepa-
rately, as summarized in the following paragraphs.
Copper Ore Mining and Concentrating
In the United States, more than 95 percent of mined copper ore is
produced from about 25 large mines. The remainder is largely by-product
concentrate from other mining industries. Each of the copper mines is
directly associated with a concentration plant that uses froth flotation
methods to produce a copper concentrate containing 20 to 30 percent
copper from the raw ore of less than 1 percent copper. The remaining
waste rock is discarded, a solid waste produced by the industry at a
rate of about a half million tons per day.
Stockpiles of ore are probable sources of water pollution through
solution of heavy metals in run off water. There have been no reports
to indicate the degree to which ore materials exposed to the weather in
the normal operation of a mine of concentrator plant contribute to water
pollution.
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Table 1. COPPER INDUSTRY SUMMARY OF PROCESS WASTE STREAMS
No. Process
Mine Processes
1 Mining
2 Concentrating
Smelter Processes
3 Multiple-hearth roasting
4 Fluldization roasting
5 Dryi ng
6 Reverberatory smelting
7 Electric smelting
8 Flash smelting
9 Pelrce-Smith converting
10 Hoboken converting
1 1 Noranda
.12 Slag treatment
13 Contact su If uric acid plant
14 DMA SOg absorption
15 Elemental sulfur production
16 Arsenic recovery
17 F1re refining or anode casting
Refinery Processes
18 Electrolytic refining
19 Electrolyte purification
20 Melting and casting cathode
copper
21 Slime acid lead
22 CaS04 precipitation
23 Slimes roasting
24 Slime water lead
25 Dore furnace
26 Scrubber
27 Soda slag leach
28 Selenium and tellurium recovery
29 Dore metal separation
Hydrometallurgy
30 Heap and vat leaching
1 31 Cementation
32 Solvent extraction
33 Electrowinning
34 Sulfation roasting
35 Sponge iron plant
36 Clear reduction
37 Clear regeneration-purge
38 Clear oxidation
39 Cymet leaching
40 Cymet crystallization
41 Cymet reduction
42 Cymet solvent regeneration
X - Large or important waste
V - Smaller waste
? - Possible waste
Process
X
X
V
X
X
X
X
X
X
X
V
V
V
X
X
V
V
V
V
?
?
V
?
?
V
V
V
V
?
V
V
V
?
Fugitive
X
X
V
V
V
V
?
?
V
X
V
V
X
V
V
V
V
V
Solid
X
X
X
X
X
?
?
X
V
V
V
X
X
?
Liquid
X
X
V
V
V
V
X
V
V
X
V
?
•
?
•>
X
V
V
V
?
V
?
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Production of the concentrate requires a water usage of about 7.5
million cubic meters each day. Much of this is reused after the tail-
ings settle, but much is discarded as a highly mineralized wastewater.
The industry provides little control of either the solid or liquid
wastes. Little is done to naturalize the tailings deposits, and water
treatment usually consists only of pH adjustment and simple settling,
occasionally assisted by coagulation.
Fugitive dusts created by the blasting and handling of these
massive quantities of material are likewise little controlled, except
for local water sprays, but fugitive dust is rarely an important waste
from this part of the industry.
The operations take place on large tracts of land, occupied by
people who are dependent on the industry. The total environmental
impact of this section of the industry is difficult to assess.
Copper Smelting
In a copper smelter, production of copper from the ore concentrate
is accomplished in four steps, each with several operating variations.
First the concentrate is either roasted or dried to remove water and
usually to remove a portion of the sulfur as S02 gas. Two types of
roasters are currently in use - the older multiple-hearth roaster and
the fluidization roaster. Several types of mechanical dryers may be
substituted.
The second step is the smelting process which forms a copper matte,
a mixture of copper compounds containing considerable impurities but
with much-reduced iron and sulfur content. Three types of smelters are
either in use or about to be used in the United States. The older
reverberatory furnace is still the dominant type and will continue to
be, at least for the near future. Electric smelting is used at two
installations, flash smelting at one, and a continuous process, Noranda,
is under construction. The reverberatory furnace is an energy-ineffi-
cient device, using several times the theoretical amount of energy.
Copper metal is produced in the third step, the converter. Air is
blown through the molten matte to remove practically all the remaining
sulfur and to form a slag containing most of the remaining iron. Crude
blister copper is withdrawn.
A continuous smelter of the Noranda design is soon to be opera-
tional, which performs on a continuous basis, the functions of both
smelting and converting.
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The final step of smelter treatment is fire refining and anode
casting, in which some of the impurities are reduced. The anode copper
is cast into special shapes for shipment to the electrolytic refinery.
The copper smelter, therefore, must eliminate all the sulfur from
the ore, and pyrometallurgical processing converts all of it into S02-
Unlike the smelting of zinc and lead, this is not all removed at once,
but a little at a time in at least two, and usually three, of the four
main processing steps. Almost all of the 15 processes used in the U.S.
that constitute a copper smelter emits S02 as a waste stream. S02
concentrations in those streams range from less than 1 percent up to 20
percent, depending on the process. Most smelters do not produce con-
tinuous streams since all of the older processes are batch operations;
thus both the quantity and the S02 concentration will vary from minute
to minute.
S02 gas represents one of the major environmental pollutants from
the primary copper industry. Control is difficult because of the dilu-
tion and intermittent production from the old, conventional processing
units. The best control is to reclaim most of this S02 for the manu-
facture of liquified S02, elemental sulfur, or sulfuric acid. Three
methods are used in this country to recover strong gas streams in this
way. In all U.S. smelters, however, weak gas streams are uncontrolled
in regard to SC>2 removal. The process descriptions do not discuss
inorganic chemical scrubbing techniques, although they are listed as
acceptable methods of control, and are used abroad. The reason for this
omission is that none are in use in any U.S. copper smelter.
Sulfuric acid plants require extensive upstream gas cleaning facil-
ities to produce a low temperature, dry, particulate-free gas for the
catalytic converter. Conventionally a water scrubber is used, resulting
in the addition of moisture to the gas stream that has to be removed by
cooling. It has been suggested that the use of a stable, high-boiling
liquid instead of water in the scrubber could eliminate this musture
and reduce the cost of acid manufacture. This idea requires consider-
able further development, but may be a suitable field for research
activity in the interest of environmental protection and energy con-
servation.
DMA absorption of SC"2 produces a small but concentrated liquid
waste stream for which there is no simple method of disposal. The
stream is a solution of sodium sulfate, sulfite, and bisulfite, con-
taining solid particles and a small amount of organic material. Further
study to establish the best disposition of this stream is indicated.
Pyrometallurgical processing also generates large quantities of
participates. Dusts and fumes that leave with the S02 in the exit gases
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are toxic and highly metalliferous often containing copper, lead, zinc,
arsenic, and cadmium. Most smelters include equipment to collect and
recycle part of these dusts, since their copper content justifies such
collection. Fugitive losses of these materials, however, occur often.
In one plant that treats these dusts to manufacture arsenic as a by-
product, the plant washdown water analyzed 0.310 milligrams of arsenic
per liter. This is a measure of the fugitive emissions typical of most
copper smelters. The fugitive losses are not well characterized in
published literature. Most smelters generate many fugitive losses in
the batch handling of bulk materials. None of these emissions is con-
trolled in U.S. smelters.
A detailed process balance characterizing the mass flow behavior of
all chemical species would be valuable in identifying feasible emission
controls and the effects of process changes. A similar energy balance,
likewise, could be used to identify areas where energy utilization
improvement is possible. It appears that further development work in
these areas is justified at the present time.
A copper smelter produces large quantities of solid waste in the
form of slag discharged from the smelting furnace. This waste is some-
times granulated and sometimes dumped on the ground and allowed to
solidify. This material contains up to 0.6 percent copper and measur-
able quantities of many other heavy metals. The long-term stability of
this material is unreported. There is apparently no established method
of control for this waste.
Electric slag cleaning furnaces are being installed to accompany
newer pyrometallurgical copper smelting processes. These furnaces will
produce a gaseous stream, probably low in volume, very hot, containing
trace element fumes, carbon monoxide and hydrogen gas. The control
being exercised of this stream has not been reported, and best control
technology is not established.
Water pollution from U.S. copper smelters is largely uncontrolled.
Not much pollution from this source has been reported, since a smelter
uses little direct contact water and produces only a small amount of
direct process wastes. The principal threat to water resources is in
rainfall and natural runoff from the smelter property. Location of the
smelters, usually in arid regions, has minimized observable incidents of
water pollution.
The use of soluble sulfides for wastewater treatment has been
proposed as a means of reducing the concentrations of hazardous metals
in the effluent. The technique has several disadvantages, however,
including sulfide poisoning of the effluent, secondary resolution of
precipitated metals, formation of hazardous sludge, and possible air
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contamination with poisonous hydrogen sulfide gas. This treatment,
however, may provide very low concentrations in the effluent. Develop-
ment of techniques to handle these secondary side-effects and evaluation
of the effectiveness of metals removal are indicated.
Copper Electrolytic Refinery
Operations of an electrolytic refinery are defined by twelve
processes, but only two of these are concerned with production of cop-
per. Anodes from the smelter, containing about 1 percent impurities,
are placed in an electrolytic cell where, under the influence of elec-
tric current, the copper dissolves from the anode and re-forms at the
cathode. Then the cathodes are melted and cast into marketable shapes
containing less than 0.1 percent imputities.
The other processes, and the major environmental impact of the
electrolytic refinery, are concerned with the missing 0.9 percent im-
purities that were removed from the copper. At this stage, these im-
purities are other elements which become heavily concentrated, either
dissolved in the electrolyte, or formed into a slime that falls to the
bottom of the electrolytic cells.
The electrolyte must be routinely purged to remove some of these
impurities; otherwise, concentrations will build up and begin to con-
taminate the copper product. This electrolyte is a strongly acidic
solution containing copper, nickel, arsenic, antimony, bismuth, iron,
cobalt, and zinc, and probably some lead, selenium, and tellurium. Most
refineries salvage the copper from this "black acid" purge stream, and
three reclaim the nickel. Disposition of the rest of these materials is
not consistently reported in published literature and is a subject
appropriate for further investigation.
Arsine, a toxic gaseous arsenic compound is formed under specific
conditions in the electrolytic process. An investigation to determine
whether this poses a significant hazard to the environment is suggested.
The slimes contain gold, silver, copper, selenium, tellurium, the
platinum group metals, iron, lead, arsenic, antimony, and bismuth. Most
refineries separate as valuable by-products the selenium, tellurium, and
precious metals. At one point a "sharp slag" is formed, which may be
sent to a lead smelter for recovery of the lead, simultaneously trans-
ferring to the lead smelter some iron, arsenic, and antimony. At one
plant a wet scrubber forms a sludge that is reprocessed.
Compared to the volume of copper being processed, the quantity of
these impurities is very small; they are cumulative, however, repre-
senting the end of the line for the trace elements found in the ore.
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Any losses, either planned or unplanned, are potentially hazardous
because of possibly high concentrations of less-common elements.
Copper Hydrometallurgical Processes
In this group of sixteen processes are operations that range from
simple heap leaching to complex chemical operations. Only processes
that have reached the stage of semi commercial plant construction are
included.
The simplest form of acid leach is in fairly wide use to extract
copper from ores and spoil that are not economically suitable for con-
ventional processing. These are unsophisticated operations using open
ditches or trenches, or open concrete vats. Scrap iron is used to form
a slime or precipitate of "cement copper" that is added into a smelting
furnace for purification. If they were located anywhere other than in
the arid or desert regions, these leaching operations would be poten-
tially severe sources of water pollution.
One of the most potentially hazardous aspects of hydrometallurgy is
the eventual disposal of leach solutions after desired metals have been
recovered. S02 control requirements may make large quantities of un-
marketable sulfuric acid available, inducing expansion of ore leaching
activity. This may produce significant adverse effects on terrestrial
and aquatic environments. These effects should be investigated.
The principle of cementation has been applied to acidic streams to
remove copper and other heavy metals from solution by reaction with
metallic iron. Studies have demonstrated the applicability of this
technique to waste treatment under optimum laboratory conditions. There
has been no development of guidelines, however, to indicate effective-
ness in practical applications where conditions are less than optimum.
Studies are indicated to establish the effects of pH, aeration, settle-
able solids and other practical factors on the effectiveness of cementa-
tion in waste treatment applications.
Solvent extraction is sometimes used in connection with the leach-
ing operations, a technology that may be expected to continue. This
offers'^ direct although expensive method of bypassing pyrometallurgical
treatment of some ores. It is difficult to assess the environmental
effect of this system, since its use is limited and potential applica-
tions are not thoroughly explored.
One hybrid process is examined, in which the concentrate is roasted
in a pyrometallurgical process and then leached for recovery of the
copper. It produces a strong and steady S02 stream suitable for sul-
furic acid manufacture, while discharging waste rock and impurity
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elements as an unconsolidated tailing. This process also could generate
serious water pollution in well-watered regions. Little is now known
about the fate of the trace elements in such processes.
Finally, three complex hydrometallurgical systems are examined,
although data are sparse. "Arbiter" uses an ammonia leach system;
"Cymet" and "Clear" use chlorides. These systems do not oxidize the
sulfur to S02 and thus eliminate a troublesome environmental effect of
conventional smelting. The sulfur may still present environmental
problems, since it remains intimately mixed with the tailings as ele-
mental sulfur. A study to evaluate the long-term stability of these
tailings and to devise effective methods of control is recommended.
Many copper concentrates yield leach residues that contain signif-
icant quantities of iron and other marketable metals, warranting an
investigation of the use of these residues as raw materials for the iron
and other metal industries. Such uses may reduce the environmental
problems associated with disposal of these leach residues.
PRIMARY LEAD INDUSTRY
Lead is currently produced in the United States by pyrometallur-
gical methods that have changed little in 75 years. New technology has
not been applied in the industry.
Of six major lead smelters in this country, three are located in
Missouri and three in the western states. These smelters process
primarily domestic ores, together with relatively small amounts of
concentrates from several foreign sources. The large majority of
domestic ore processed is from Missouri. The principal smelter products
are refined lead of 99.9 percent purity and antimonial lead; metallic
by-products such as gold, silver, bismuth, cadmium, zinc oxide, and
arsenic trioxide are also produced. About two-thirds of the lead pro-
duced is used in storage batteries and tetraetheyl lead gasoline.
Six companies account for more than 90 percent of lead production
in the United States from mines they own and operate. These companies
employ about 7,000 people, with two-thirds in mining and concentration.
Environmental Impacts, Lead
The environmental effects of this industry are assessed in terms of
individual processes, are presented in Table 2 with a list of the waste
products. As with the copper industry, each major section of the lead
industry entails a different impact. Mining and concentration generate
multithousand-ton quantities of metal-bearing solid wastes and contami-
nated water. Smelting emits sulfur dioxide and hazardous particulates.
Those effects are summarized in the following paragraphs.
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Table 2. LEAD INDUSTRY SUMMARY OF PROCESS WASTE STREAMS
No. Process
Mine Processes
1 Mining
2 Concentrating
3 Sintering
4 Acid plant
5 Blast furnace
6 Blast fuming
7 Dressing
8 Dross reverberating
9 Cadmium recovery
Smelter Processes
15 Reverberatory softening
16 Kettle softening
17 Harris softening
18 Antimony recovery
19 Desilverizing
20 Retorting
21 Cupelling
22 Vacuum dezincing
23 Chlorine dezincing
24 Harris dezincing
25 Debismuthizing
26 Bismuth refining
27 Final refining and casting
X - Large or important waste
V - Smaller waste
? - Possible waste
Process
X
V
X
X
X
X
X
X
X
V
V
?
?
Fugitive
V
X
?
?
?
?
?
Solid
X
X
X
X
V
X
Liquid
X
X
V
X
.
V
11
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Lead Ore Mining and Concentration
Lead ore is secured chiefly from underground mines in the United
States, 80 to 85 percent from the southern part of Missouri. The re-
mainder comes from mines in the western states. An ore concentration
plant is located near each mine to produce smelter feed material. Dense
medium and froth flotation processes are used for concentration.
Western mines yield a concentrate containing 45 to 60 weight percent
lead, derived from raw ore analyzing 3 to 8 percent; Missouri mines
yield concentrates containing more than 70 weight percent lead. Re-
sidual waste rock is discarded at a rate of about 2,000 metric tons per
day. The water requirement for ore concentration is estimated to be 4
cubic meters (1,060 gallons) per metric ton of processed ore. Although
the water is reused, it is eventually discharged in a highly mineralized
condition. The quality of these discharge waters should be assessed in
order to determine whether additional effort is justified in order to
remove heavy metals and other contaminants from these waters.
As in the copper industry, there is little control of the solid or
liquid wastes in the western states. In the Missouri area, flotation
agents contained in wastewater are biotically degraded before water is
discharged to neighboring streams. Solid waste is used for road build-
ing as backfill or is dewatered and impounded. The leaching properties
of these spoil banks may be a subject worthy of further investigation.
Fugitive dusts generated by ore crushing and handling are estimated as
3.2 kilograms (7 Ib) per metric ton of ore processed. Aside from the
use of local water sprays, these emissions are not controlled.
Lead mining and concentrating facilities are located in remote
areas populated by those dependent on the mine; in Missouri they are
populated also by farming communities. Since the mines are underground,
surface land requirements are relatively small. In comparison with
other lead production processes segments, the mining and concentrating
processes impose only a slight environmental impact.
Lead Smelting
The production of high-purity lead from ore concentrates is accom-
plished in three sequential steps: roasting or sintering, smelting, and
refining or impurity removal. Each of these steps is subject to opera-
ting variations caused by feed or product requirements.
Sintering agglomerates the feed and alters it chemically to render
the material suitable for blast furnace use. The step is characterized
by the evolution of large amounts of sulfur dioxide and particulate
matter. About 85 percent of the sulfur in the concentrate is liberated
as SOp from the sintering operation. At least part of the gas stream is
12
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strong enough that S02 can be recovered as sulfuric acid. Further
research is necessary to further improve S02 concentration so that all
the gas can be used to make acid.
Smelting of the sinter is done batchwise in a vertical blast
furnace. The sintered feed is reduced to crude lead bullion, which is
subjected to purification, and slag, which is cooled and granulated
after defuming. The blast furnace operation emits large quantities of
hot gases containing particulates and weak concentrations of S02- The
feasibility and necessity to control these SC>2 emissions should be
investigated. The emissions are an order of magnitude lower than from
the sintering machine.
The crude lead bullion is purified stepwise by refining. In each
step, the molten lead is treated in a furnace to remove one or more of
the impurities. Metallic by-products are derived from the removed
impurities. Many of the processes generate fumes or particulate emis-
sions as well as slag material. There is little or no S02 evolution.
In summary, conventional lead smelting produces one strong S02
stream that is reclaimable, large quantities of exhaust gases containing
particulates, and a large amount of slag.
Half of the smelters in this country recover sulfur from the S02
stream from sintering, but none attempt control of the weak S02 streams
from other processes.
All smelters control emissions of particulate matter from the major
smelting operations by means of electrostatic precipitators or filter
baghouses, which may operate at a high degree of efficiency, but no data
are published which document the effectiveness of these control devices.
The emissions of metallic particulates should be quantified. Uncon-
trolled fugitive losses occur at many points. The literature does not
characterize these losses either by composition or quan-tity. The par-
ticulate matter contains compounds of copper, lead, zinc, antimony,
arsenic, and cadmium, all of which are relatively toxic.
Slag is generated at a rate of 2 tons per ton of lead produced by
the blast furnace. This slag is granulated by water cooling before it
is discarded in a dump. The material contains lead, zinc, and copper,
and measureable amounts of antimony, arsenic and cadmium. In addition,
unknown amounts of slag are discarded from kettle softening and bismuth
recovery processes. Some plants recover zinc from slags via a fuming
process. Potential carbon monoxide and metallic emissions from these
fuming plants should be investigated. Kettle-softening slag contains
13
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water soluble salts of arsenic, antimony, and tin; bismuth-recovery slag
contains water-soluble chlorides of magnesium, calcium, and lead. These
slags are discarded in open dumps. Better disposal technologies should
be developed.
Waste slags constitute a cumbersome disposal problem for all base-
metal smelters. The potential use of these slags as raw materials for
other industries such as cement, aggregate, or steel should be investi-
gated, since such use would help to eliminate disposal problems and
would maximize resource utilization.
Water for granulation of blast furnace slag and for cooling of lead
castings constitutes the major streams that are in direct contact with
the process. The streams are normally neutralized, clarified, and
recycled at the smelter. A controlled waste stream is bled off, in
which concentrations of zinc, mercury, lead, and cadmium are monitored
against established maximum allowable concentrations. Five of the six
operating smelters meet the effluent water standards.
Hydrometallurgical production of lead has been investigated for
environmental advantages, but the processes are not yet economical.
Further development of these processes should be encouraged.
Various processes in the lead smelter produce relatively small
effluent quantities, but may be worthy of additional investigation
because the contents of the exhaust stream are not fully documented.
Cadmium recovery roasters may emit cadmium and other volatile metallic
pollutants. Some metal fume emissions from lead softening operations,
cupelling operations, and dore retorting processes may occur. Arsenates
in residues from Harris softening processes may require special disposal
techniques. Chlorine and fume emissions from bismuth refining may
require treatment, and slag from the process may require special dis-
posal because of chloride content.
ZINC INDUSTRY
The primary zinc industry produces zinc metal as its primary prod-
uct, and also produces zinc oxide, cadmium metal, and small amounts of
other by-product metals. These are produced in six zinc smelters and
one zinc oxide plant, located in several sections of the country, in-
cluding Pennsylvania, Texas, and Idaho. One smelter in Pennsylvania
produces more than a third of all the domestic 'zinc.
Zinc is almost always mined as a co-product with other metals,
usually lead, and zinc ores are produced from about 40 mines in 18
states, widely scattered across the country. About a third of the ore
1:4
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is mined and concentrated by independent companies. Total employment in
mining of lead and zinc ores is estimated at 6700 persons.
Each zinc smelter is owned and operated by a different company,
four of which also operate lead smelters. These companies employ about
4,000 people. Currently the smallest U.S. smelter is being replaced by
an electrolytic facility of smaller capacity. No plant expansions are
expected in this industry segment, since demand for the product has
decreased since 1969 and foreign competition is very strong.
Environmental Impact, Zinc
Zinc smelters were once among the worst industrial operations in
terms of environmental impact. This is no longer true, since most zinc
smelters are located in populated regions and are subject to local
pressures. Newer processes are used for zinc manufacture than for
copper or lead, and all U.S. zinc smelters manufacture sulfuric acid
from their S0£ streams. Many of the solid wastes are shipped to other
plants for further processing.
The technology of primary zinc production is divided into 17 sec-
tions, or processes, as shown in Table 3. They are summarized in the
following paragraphs.
Zinc Ore Mining and Concentrating
All mines in the United States being worked primarily for zinc or
for lead and zinc are underground mines, producing considerably less
than half a million tons a year each. Most of the larger mines operate
a concentrator plant nearby. Some ores range up to 10 percent zinc and
also contain appreciable lead. Ores may be preconcentrated by heavy
medium separation and are generally concentrated by froth flotation.
Concentrates up to 55 to 60 percent zinc are produced; thus less than
half the ore is discarded as tailings. This proportion is smaller than
with most other mining operations. Occasionally a combination lead-zinc
concentrate is produced, which further reduces the quantity of tailings
and also reduces the complexity and water usage of the concentrator
plant.
Although quantities are smaller than, for example, in the copper
industry, solid waste disposal and water pollution are problems in this
industry. Efficiency of control is variable. No published survey
includes all the smaller mining operations.
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Table 3. ZINC INDUSTRY SUMMARY OF PROCESS WASTE STREAMS
No. Process
Mine Processes
1 Mining
2 Concentrating
Smelter Processes
3 Multiple hearth roasting
4 Suspension roasting
5 Fluidized bed roasting
6 Sintering
7 Horizontal retorting
8 Vertical retorting
9 Electric retorting
10 Oxidizing furnace
11 Leaching
12 Purifying
13 Electrolysis
14 Melting and casting
15 Cadmium leaching
16 Cadmium precipitation
17 Cadmium purification and cast-
ing
X - Large or important waste
V - Smaller waste
? - Possible waste
Process
X
X
X
X
V
V
V
X
V
V
V
Fugitive
X
X
V
V
V
V
V
V
V
V
V
V
Solid
X
X
X
X
X
X
X
?
?
V
Liquid
X
X
?
?
X
V
?
X
V
.
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Zinc Smelter
The zinc sulfide concentrates are first burned in a roaster to
produce impure zinc oxide and to eliminate about 90 percent of the
sulfur in the concentrate as S02- Three types of roasters are in use.
The oldest, the multiple-hearth, is used now only as part of a more
complex roasting system. Newer types are the flash roaster and the
fluidized bed roaster. The intent in zinc roasting is to burn off as
much of the sulfur as possible; the gas effluent is high in S02 and
suitable for sulfuric acid manufacture.
After roasting, zinc metal is produced either by a pyrometallur-
gical or an electrolytic technique. In the pyrometallurgical method,
the roasted concentrate is sintered, heating the material to a high
temperature, driving off most of the remaining sulfur, and vaporizing
lead and cadmium for downstream recovery. The zinc forms a hard oxi-
dized material, or sinter, suitable for the next process step. Sinter
machines evolve a gas stream weak in S02, which cannot be effectively
treated except by wet scrubbing. None of the existing smelters remove
SOz from this stream. Sinter crushing and screening operations produce
fugitive dust emissions that should be controlled.
Sinter is briquetted and fed into a retort furnace, where it
reacts with coke to produce zinc metal. Temperatures are high enough
that the zinc vaporizes, to be condensed downstream to form the product.
Three variations of the retort furnace are in use, although one is being
phased out. Vertical and electrothermic retorting will continue. A
fourth variation re-oxidizes the vaporized zinc with air to form puri-
fied zinc oxide as a product. The retorting processes are indirectly
heated; although there is no intentional loss of product at this stage,
some fumes of zinc or zinc oxide may escape through the condenser,
forming the "blue powder" occasionally observed in the air near a zinc
smelter. It appears that hazardous particulates such as metal carbonyls
may also be potentially formed. This possibility should be investigated
in order to determine if additional particulate controls are required.
About 42 percent of domestic zinc production is from electrolytic
plants, in which the roasted concentrate, instead of being sintered, is
leached with sulfuric acid. This process is frequently used with lead-
zinc ores, since the leach residue can then be sent to a lead smelter
for further processing. Leaching dissolves the zinc from the mixture.
The resulting solution is purified by precipitating and filtering out
metallic impurities. Zinc is then recovered in electrolytic cells.
Pollution from the production of electrolytic zinc is primarily minor
chemical fumes, fugitive dusts from materials handling, accidental
losses of the acidic and concentrated liquors and residues, and spent
electrolyte requiring disposal.
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All zinc smelters also recover cadmium. Flue dusts and electro-
lytic slimes are leached to dissolve the cadmium, which is then precipi-
tated by the addition of powdered zinc metal. Leach liquors contain
several unusual trace elements and may constitute the most hazardous
waste of this industry segment.
Published literature does not indicate the disposition of most of
the trace elements that enter a zinc smelter along with the concentrate.
Cadmium, mercury, arsenic, and other metals liberated in the roasting
process are probably captured by the acid plant gas cleaning equipment
and recovered as a sludge or residue. These elements cannot be recycled
indefinitely. Methods for the safe disposal of these materials should
be developed.
AIR MANAGEMENT
Smelter air pollution emissions from the primary copper, lead, and
zinc industry are readily noticeable. All of these emissions contain
inorganic particulates, toxic fumes, and S02 gas; the emissions usually
include various products of fuel combustion.
A potential area for research and development effort may be the
treatment of ores or concentrates to isolate and remove undesirable
materials before they enter the various smelting processes, thus pre-
venting the escape of those materials as air or water pollutants.
Usually gases from all the major processes are mixed to form one
principal stream. This creates an air management problem, since it is
possible to overload the control devices. Most metallurgical operations
have a non-uniform rate of waste gas production, and control equipment
cannot usually handle simultaneously peak flows from several processes.
Treatment of the waste gas stream is a multi-step process Gas is
cooled and the velocity is reduced to allow the larger particulates to
settle. Most smelters are designed to allow large amounts of cool air
to mix with the hot gases, thus reducing the gas temperature, allowing
the gas to be handled in steel ductwork. The larger particulates are
recycled to minimize loss of product.
Fine particles are usually removed by an electrostatic precipitator
(ESP), sometimes aided by water sprays to further cool the gas and
improve collection efficiency. Baghouses may also be used for fine
particulate removal. Dust from the ESP or baghouse is usually recycled,
but it may be discarded.
The gas is then treated for S02 removal. The best economic tech-
nology to remove S02 from a waste gas stream converts the SC>2 into
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sulfuric acid. Most smelters have made changes 1n their operations to
make acid production possible. Changes that increase S02 concentration
have most often been applied, such as adoption of newer processes that
minimize the quantity of combustion gases that are mixed into the
stream. The principal change, however, has been to minimize air infil-
tration and to substitute other methods for cooling the gas. Other
changes, to produce a waste stream at a constant rate and composition,
have also been necessary, since sulfuric acid plants cannot operate
efficiently with a variable feed stream.
For removal of S02 from waste gases that have a low S02 content,
wet scrubbing with a chemical solution is the only proven method. In
other countries, smelter gas is treated by the scrubbing techniques now
used for coal-fired boilers in this country. None of the domestic
smelters now include wet S02 scrubbing facilities.
Fugitive losses of dusty materials occur in smelters. One toxic
material is the flue dust, which may contain significant amounts of ar-
senic and other trace elements. Careful handling of this material is
recommended to minimize fugitive losses of toxic elements.
Many smelters have been designed to use the infiltration of air
into the waste gas streams not only to cool the waste gas, but also to
ventilate the working area and capture fugitive losses of S02 and par-
ticulates. If air infiltration is minimized to improve S02 control by
acid production, ventilation fans must be installed to capture the
fugitive materials. For proper air management, additional air control
devices will be necessary to remove the particulates, fumes, and S02
from the ventilation air in order to avoid release of these pollutants
to the surroundings.
WATER MANAGEMENT
Sulfide Ore Mining and Concentrating
The mining and concentrating of copper, lead, and zinc minerals
involve common problems of water management. Most ores produce recover-
able quantities of more than one of the metals; in all of them, the
metals are chemically combined as sulfides, and all contain iron sulfide
as an impurity.
Sulfides are strongly reduced substances that are not stable when
exposed to the oxygenated and wet environment of the earth's surface.
Mining and concentrating introduce these materials into this environment
in four main areas of activity:
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1. Water enters a mine and contacts the mineral in place.
2. Spoil, containing sulfide minerals, is discarded near the mine
where it is exposed to weather.
3. Stockpiles of ore or concentrate are also exposed to weather.
4. In a major process, the ore is mixed with large volumes of
water, and the tailings, still containing sulfide minerals,
are discarded on the surface of the ground.
All four of these sources contain soluble .substances. Water that
flows from them is highly acidic and highly mineralized and contains
hazardous metals in solution.
Laboratory and pilot plant tests have suggested guidelines that
show the practical extent to which copper, lead and zinc can be removed
from wastewater by pond treatment, chemical coagulation, and filtration.
Similar estimates have not been reported for other hazardous elements
such as cadmium and molybdenum. There has also been neither practical
nor theoretical evaluation of the effectiveness of those waste treatment
methods in removing elements of periodic classification VA and VIA such
as arsenic and selenium.
The largest volume of water used in the copper, lead and zinc
industry is in the concentration of ores. Although some of the water is
reused, the overflow is discharged and contains heavy metals and other
minerals in solution. It also contains organic and inorganic flotation
and decomposition chemicals and a heavy loading of suspended solids. A
complete characterization of these wastes should be made to assess their
environmental significance.
Organic flotation chemicals in the wastewater produce adverse
stream effects such as algae blooms. Additional research in ti.e field
of flotation separation may produce substitute chemicals that are less
detrimental to the environment. Consequently, such research should be
encouraged.
All wastewaters from mining and concentrating sources are mixed
into a common stream, usually the tailings pond. The pond may also
receive water from other sources: rainfall, surface run-off, other
wastes from the industry, and frequently sewage from plant facilities.
Combining these wastes may limit the reuse of the wastewater or hinder
effective treatment of the water prior to its discharge into public
waters. This is not a matter of temporary treatment. Once sulfide
minerals are exposed to the surface of the earth, they will in time
become oxidized, and most of the metals they contain will wash away to
20
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the ocean. The mechanisms by which this occurs have been extensively
studied; at present the best control is to contain the harmful con-
stituents, minimize the rate of sulfide oxidation, and avoid gross
pollution.
The possibility of using a mechanical device to separate and remove
tailings from flotation water should be investigated. Elimination of a
tailings pond would minimize the time that the tailings are in contact
with water and would reduce land area requirements for waste disposal.
The report examines techniques for reducing the rate of sulfide
weathering. Rapid pump-out of mining operations, various methods for
sealing of spoil dumps and tailings, and chemical treatments to scavenge
oxygen from such deposits are all effective.
If heavy metals do become converted into soluble materials, how-
ever, they must be contained. The practice of indiscriminate mixing of
all wastes is examined. The principal effects of this practice are that
it makes some concentrated streams more difficult to treat effectively
and that it limits the practical degree of recycle of the water. Such
wastes as boiler blowdown, domestic sewage, and strongly acidic and
metalliferous streams are best controlled if they are not mixed with the
bulk of industry wastewaters.
Containment of the harmful substances in the main waste stream
requires treatment. If properly managed, the tailings pond can provide
one stage of treatment. If the water is made alkaline, many of the
harmful constituents will recombine into relatively stable inorganic
materials, and the quantity of soluble heavy metals in the effluent will
be substantially reduced. This apparently simple process, if carefully
operated, can be effective. Pond treatment has a disadvantage, however,
in that if effluent quality is inadequate, there is no way to know what
should be done, and no way to do anything about it.
Further control is therefore examined. Use of ponds in series,
though frequently employed, provides no assurance of improved water
quality. Further treatment by coagulation and clarification is sug-
gested, with the assumption that this treatment would follow a tailings
pond. The technology is well known and is in constant use in clarifica-
tion of both public and industrial water supplies. Pilot plant studies
on clarification of wastes from sulfide ore mining and concentrating
have demonstrated effective removal of hazardous metals. The problem of
disposition of the sludge from these operations, however, is not solved.
Techniques to dispose of the highly metalliferous sludge should be
evaluated. Proposed techniques include chemical fixation and recycling
to pyrometallurgical operations.
21
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Filtration is considered to back up the clarification operation,
providing greater effectiveness in removal of heavy-metals.
Post-treatment to reacidify the water and adjust the pH to within
environmentally acceptable limits is also examined; the full effect of
neutralizing the water with sulfuric acid should be investigated. Some
evidence indicates that downstream oxidation of certain species in the
discharge water tends to partially self-neutralize the effluent.
Finally, although other treatments of water are possible, none has
proved feasible for direct application to large volumes of dirty, heav-
ily mineralized wastes containing lesser quantities of hazardous metals.
The use of chelating agents to form metal complexes that are amenable to
inert solvent extraction may be a suitable area for further research and
development. Chelating chemicals that are specific to copper have been
used for copper recovery. It is possible that less specific chelating
agents could be developed to remove several metals from wastewater
simultaneously. The possibility of developing magnesium-based ion
exchange resins is suggested, and also the possibility that certain
plant species that naturally accumulate selenium in their tissues could
be useful in the control of this element.
EMERGING TECHNOLOGY
For the near future at least, the greatest changes in technology
are likely to occur in the copper industry. The lead and zinc indus-
tries have largely preceded the copper industry in adopting new proc-
esses and updating plant and equipment. However, recent economic
developments, as well as environmental concerns, have emphasized the
need for changes in copper production.
One line of current research is into continuous pyrometallurgical
designs, which have the advantages of improved process economics and the
production of an off-gas high in S02 content suitable for direct appli-
cation to sulfuric acid production. The Australian WORCRA process both
smelts and converts in a single furnace, and is at the pilot plant
stage. Mitsubishi of Japan has a continuous design which is starting
commercial operation. A Soviet process, the Kivcet, which can use
varying combinations of copper and zinc concentrates, is operating in a
pilot plant as is an American design, the Q-S Oxygen process, which uses
pure oxygen. Japan's Momoda furnace is already in commercial operation,
and may be economical for smaller decentralized Installations.
Hydrometallurgical processing, which recovers metals without the
use of high temperature reduction, is likely to find wider use as a
22
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result of current research. Hybrid processes, which follow roasting by
leaching and electrolysis, include the American Treadwell design.
France's Minemet is scheduled to begin pilot plant testing in 1977.
Among the most promising hybrid process at the laboratory scale is one
using fused-salt electrolysis developed by the U.S. Bureau of Nines. A
number of completely hydrometallurgical designs, which use no pyrometal-
lurgical steps, are in the pilot or demonstration plant stage. These
include a ferric chloride leach process developed by Sherritt-Gordon and
Cominco, a nitric-sulfuric acid leach process of DuPont and Kennecott,
and a high-pressure leaching design of Lurgi-Mittenburg.
There are several other areas of emerging technology. New electro-
lytic techniques are being developed, including processes for the elec-
trolytic refining of lead, .purification of the leach liquor at zinc
smelters, and increased production rates at copper refineries. An
American company is studying the Torco process in use at some foreign
smelters, because it allows'the extraction of copper silicates by flota-
tion from gangue rock. The TBRC process of Cana'da, which is scheduled
to begin commercial operation in 1977, is said to produce copper that
can be directly cast as anodes, thus eliminating fire-refining. The use
of oxygen or oxygen-enriched air to increase production capacity is
finding wider application. There is also research into processes for
treating the slags produced by the new continuous pyrometallurgical
copper designs.
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APPENDIX A
HEALTH EFFECTS
A study was performed to determine what environmental nonoccupa-
tional diseases are resulting from primary copper, lead, and zinc
smelting; the most probable causes of these diseases; and possible
solutions for any health problems identified. Toward this end, a
comprehensive literature search and an epidemiological analysis of
published mortality data were undertaken. Earlier work indicated that
metals are the key etiological agents in smelter induced mortality and
morbidity. Accordingly, the study focused on the health effects of
metals.
The results of this study strongly indicate that counties contain-
ing primary copper, lead, or zinc smelters are exposed to a significant
public health hazard. Elevated rates of cancer of the trachea, lung,
and bronchus and all cancers combined have been found in association
with the majority of these smelters. Excess mortality from cancer of
the kidney and bladder was linked with the majority of lead and zinc
smelters, while elevated rates of cancer of the liver and biliary
passages were associated with the majority of lead and copper smelters.
Excess mortality from small vessel disease other than arteriosclerosis
was associated with most lead smelters, and excess mortality from hy-
pertension, with most zinc smelters.
The two elements contained in smelter ore concentrates that were
most strongly linked with excess mortality in this study are arsenic and
lead. Smelting zinc ore concentrates with high levels of arsenic was
clearly associated with significantly elevated rates of cancer of the
trachea, lung, and bronchus. Numerous earlier epidemiological studies
have suggested the relationship between excessive cadmium exposure and
hypertension. The results of this study strongly show that a relatively
narrow range of lead exposure must also be present before excess hyper-
tension mortality is observed. Excess hypertension mortality was noted
only in association with facilities which processes ore concentrates
with medium levels of lead. The smelting of ore concentrates with
either low or high levels of lead was not associated with excess hyper-
tension mortality, regardless of the levels of cadmium present.
Three other elements present in copper ore concentrates and two
specific smelting unit processes were linked with excess mortality by
24
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this assessment. All copper smelters with associated excess mortality
from ischeroic heart disease had medium levels of both antimony and
selenium in the ore concentrates. In addition, excess mortality from
cancer of the kidney around copper smelters was always accompanied by
ore concentrates high in nickel. The use of slag fuming furnaces by
lead smelters was strongly associated with elevated rates of cancer of
the kidney, thyroid, and liver and biliary passages. Less strongly
associated was the use of fluidized bed roasters by zinc smelters and
excess mortality from hypertensive heart disease.
25
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APPENDIX B
ECOLOGICAL EFFECTS
Several sources of pollution from the copper, lead, and zinc in-
dustry can be expected to have an impact on the ecology of a region.
The sources are mine and mill waters, solid wastes, and atmospheric
emissions.
Field studies on surface waters in Canada and Great Britain have
shown that aquatic life is severely depleted by heavy-metals that enter
public waters from operations of this industry. Copper and nickel are
toxic to algae and therefore the food base for animals is depleted.
Bioassays in this country have shown that copper, lead, and zinc may be
toxic to aquatic life in the concentrations reached in streams near the
industry's operations. Low pH acts to increase the toxicity of the
metals, and in soft waters, concentrations of lead and zinc, as low as
0.1 milligram per liter have been shown to be toxic to aquatic life.
Terrestrial vegetation is also affected by metallic emissions from
smelters. An Australian field study has shown a correlation between the
distance from a smelter and the concentration of heavy metals in plant
tissues. In this country, bioassays have shown toxic effects by heavy-
metals on vegetation, and field studies have shown that plants in an
area have evolved metal-resistant strains near operations of this in-
dustry.
Sulfur dioxide from smelters can cause severe damage to local
vegetation, especially broad-leaf plants. S0£ destroys the capacity of
the plants to hold water, and damages the chlorophyll in the leaves.
Damage is heaviest during weather conditions which favor plant growth,
when the plants are absorbing gases at a high rate from the atmosphere.
A study in Montana and Washington showed a high mortality of tree
seedlings, therefore very little natural regeneration of the forest.
Apparently, however, there is little residual damage once S02 fumigation
is discontinued.
The greatest need is for full-scale long-range field documentation
in this country into the effects of the copper, lead, and zinc industry
on the ecology. Most knowledge of the environmental impacts are now in
the form of bioassays, with very little actual confirmation of the
findings.
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