United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Cincinnati OH 45268
EPA-600/2-80-170
July 1980
Research and Development
Industrial Process
Profiles for
Environmental Use
Chapter 29
Primary
Copper Industry
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental 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.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-80-170
July 1980
INDUSTRIAL PROCESS PROFILES
FOR ENVIRONMENTAL USE:
CHAPTER 29
PRIMARY COPPER INDUSTRY
by
PEDCo Environmental, Inc.
11499 Chester Road
Cincinnati, Ohio 45246
Contract No. 68-03-2577
Project Officer
John 0. Burckle
Energy Pollution Control Division
Industrial Environmental Research Laboratory
Cincinnati, Ohio 45268
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
US Environmenta. Protection Agenc*
Region V, Library
So south Dearborn^eet
-------
DISCLAIMER
This report has been reviewed by the Industrial Environmental Research
Laboratory-Cincinnati, U.S. Environmental Protection Agency, and approved
for publication. Approval does not signify that the contents necessarily
reflect the views and policies of the U.S. Environmental Protection Agency,
nor does mention of trade names or corrmerical products constitute endorse-
ment or recommendation for use.
U.S Env,ronmenta, Protection Agency
n
-------
TABLE OF CONTENTS
INDUSTRY DESCRIPTION
Raw Materials
Products
Companies
Environmental Impact
References
INDUSTRY ANALYSIS
Process No. 1,
Process No. 2,
Process No. 3,
Process No. 4,
Process No. 5,
Process No. 6,
Process No. 7,
Process No. 8,
Process No. 9,
Process No. 10,
Process No. 11,
Process No. 12,
Process No. 13,
Process No. 14,
Process No. 15,
Process No. 16,
Process No. 17,
Process No. 18,
Process No. 19,
Process No. 20,
Process No. 21,
Process No. 22,
Process No. 23,
Process No. 24,
Process No. 25,
Process No. 26,
Process No. 27,
Process No. 28,
Process No. 29,
Process No. 30,
Process No. 31,
Mining
Concentrating
Multiple-Hearth Roasting
Fluidization Roasting
Drying
Reverberatory Smelting
Electric Smelting
Flash Smelting
Peirce-Smith Converting
Hoboken Converting
Noranda
Electric Furnace Slag Treatment
Flotation Slag Treatment
Contact Sulfuric Acid Plant
DMA S02 Absorption
Elemental Sulfur Production
Arsenic Recovery
Fire Refining and Anode Casting
Electrolytic Refining
Electrolyte Purification
Melting and Casting Cathode Copper
Slime Acid Leach
CuS04 Precipitation
Slimes Roasting
Slime Water Leach
Dore" Furnace
Scrubber
Soda Slag Leach
Selenium and Tellurium Recovery
Dore" Metal Separation
Vat Leaching
Page
1
1
3
5
12
12
15
20
24
31
38
41
43
52
54
57
64
66
68
70
72
79
82
84
87
94
98
102
105
107
109
111
113
115
117
119
121
123
iii
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TABLE OF CONTENTS (Continued)
Process No. 32, Sulfide Ore Leaching
Process No. 33, Cementation
Process No. 34, Solvent Extraction
Process No. 35, Electrowinning
Process No. 36, Sulfation Roasting
Process No. 37, Sponge Iron Plant
Process No. 38, CLEAR Reduction
Process No. 39, CLEAR Regeneration - Purge
Process No. 40, CLEAR Oxidation
125
128
130
132
134
136
138
140
142
IV
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14 Concentration and Weight Analysis of Particulate
Effluents from a Multiple-Hearth Copper Roaster
LIST OF TABLES
Table
2
1 Copper Minerals Important in U.S. Production
2 Typical Analysis of Copper Ore Used at White Pine Copper
Company, Michigan
t 6
3 Consumption of Refined Copper in 1976
4 Statistical Data for the Primary Copper Industry in the
United States in 1976
5 Principal By-Product Sulfuric Acid Producers - 1974
6 U.S. Primary Copper Producers (Conventional Smelting/
Refining Operations)
7 Twenty-Five Leading Copper Mines in the United States
in 1974 IU
8 Annual Generation of Hazardous Pollutants from U.S.
Primary Copper Industry - 1978 (metric tons)
9 Raw Waste Load in Water Pumped from Selected Copper Mines 22
?fi
10 Analysis of Copper Concentrate
27
11 Typical Flotation Collectors
?Q
12 Metallic Elements in Concentrator Wastewater "
13 Typical Size Profile of Multiple-Hearth Copper Roaster '•
Effluents •"
34
15 Typical Levels of Volatile Metals in Domestic Copper
Ore Concentrations
16 Composition of Charge to a Reverberatory Furnace 44
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LIST OF TABLES (Continued)
Tab1e Page
17 Analysis of Participates Emitted from a Reverberatory
Furnace 45
18 Composition of Reverberatory Furnace Exhaust Gases 46
19 Effluents from Slag Granulation (mg/1) 47
20 General Range of Reverberatory Furnace Slag Composition 49
21 Material Balance on Converters - Smelters in Arizona
(percent) 58
22 Composition of Converter Dust 59
23 Particle Size Distribution in Converter Dust 60
24 Particulate Emissions Analysis at Stack Outlet for
Reverberatory Furnace and Converter 60
25 Converter Off-Gas Composition 62
26 Estimated Maximum Impurity Limits for Metallurgical
Off-Gases Used to Manufacture Sulfur Acid (Approximate 73
limit, mg/Nm3)
27 Raw Waste Characterization: Acid Plant Slowdown 75
28 Acid Plant Slowdown Control and Treatment Practices 77
29 Analysis of Arsenic Plant Washdown Water 85
30 General Range Analysis of Anode Copper 88
31 Water Requirements for Copper Refineries 91
32 Waste Effluents from Anode Cooling Water 91
33 Contact Cooling Water Control and Treatment Practices 92
34 General Range Analysis of Electrolyte, Refined Copper
and Anode Slime 96
35 Waste Effluents from NiS04 Barometric Condenser 100
36 Analysis of Water Used to Cool Refinery Shapes
(Concentrations in mg/1) 103
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LIST OF TABLES (Continued)
Table
37 Dore* Metal Analysis 113
38 Analysis of Tailings Effluent from a Precipitation Plant 129
LIST OF FIGURES
Figure
1 U.S. Primary Copper Smelting and Refining Locations
2 Copper Industry Flow Sheet
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COPPER INDUSTRY
INDUSTRY DESCRIPTION
Many changes have recently been taking place in the primary copper indus-
try. There is much speculation as to the direction these changes will or
should take. Whether the trend is toward improved pyrometallurgical proces-
sing or toward adoption of hydrometallurgy, most experts agree that some basic
changes are imminent.
At six smelters, copper has been or is now routinely produced by technol-
ogies newly introduced into U.S. production practice. One new smelter now
uses a continuous flash smelting process and a continuous smelting process is
being used to produce copper in Utah. One installation has produced copper
with a roast-leach-electrowinning technique. Three advanced hydrometallurgical
processes are approaching -semicommercial production. The following^descrip-
tion of the industry does not concentrate on these installations, since they
do not now account for a sizable percentage of copper being produced.
Most copper production is now being accomplished with the "conventional"
pyrometallurgical methods that center on the energy-inefficient reverberatory
furnace. Matte from the reverberatory furnace is converted to blister copper,
and the blister copper is reduced, cast into anodes, and refined in electro-
lytic cells. These operations occur in about 25 locations, all but five of
which were operating before World War II. In twelve of these locations,
copper has been produced since before World War I. Although new equipment was
provided during the intervening years, in most of the plants, new technology
was not. Most domestic copper is being made now by the same procedures used
50 years ago.
Raw Materials
The principal raw materials for copper production are the domestic ores,
which consist of copper minerals embedded in gangue rock. Throughout the
world, copper in minerals is most often chemically combined with sulfur,
frequently with iron or arsenic, and sometimes with other elements. Table 1
shows five of these sulfide minerals; the first three listed are most abundant
in the ores of this country.
When sulfide minerals are exposed to air and water, they oxidize to form
sulfuric acid and metal ions. The metal ion may, in turn, react with rock
minerals to form metal oxides, or they may move with ground or surface waters
-------
Table 1. COPPER MINERALS IMPORTANT IN U.S. PRODUCTION (1)
Mineral
Sulfide Ores
Chal copy rite
Chalcocite
Bo mite
Covellite
Enargite
Oxide Ores
Malachite
Azurite
Cuprite
Chrysocolla
Native Copper
Composition
CuFeS2
Cu2S
Cu,-FeS,
b 4
CuS
Cu3AsS4
CuC03-Cu(OH)2
2 CuC03-Cu(OH)2
Cu20
CuSi03.2H20
Cu
Copper content,
percent weight
35
80
63
66
48
57
55
89
36
100
Occurrence9
SW, NW, NC
SW, NW, NC
SW, NW
SW, NW
NW
SW, NW
SW, NW
SW
SW
NC, SW
NW - Montana and surrounding area.
NC - Michigan and surrounding area.
SW - Arizona and surrounding area.
-------
and subsequently precipitate to form secondary metal deposits. Weathering may
therefore create deposits of oxidized copper minerals. The table shows four
of these, the highly colored azurite and malachite being most abundant in
domestic ores.
The ore deposits of northern Michigan are a unique occurrence of primary
origin, and native copper mixed with sulfide minerals is mined in this area.
Table 2 gives an analysis of the ore from this deposit. Except for the pres-
ence of elemental copper and the low-sulfur content, this analysis is similar
to that of most domestic ores, since it shows iron present in much higher con-
centration than copper in a gangue rock of silica and alumina minerals.
The first step in the processing of an ore is to form a copper concen-
trate, which consists of the copper minerals separated from most of the gangue.
These concentrates are an article of commerce, and represent another raw
material of this industry. Ores mined primarily for other metals may be the
origin of concentrates rich in copper, which are sold to copper producers.
This may constitute 5 to 10 percent of all the primary copper that is mined in
this country. Also concentrates are regularly imported from other countries;
domestic smelters frequently process concentrates from Canada, South America,
Australia, and the Philippines.
The industry also imports copper from other countries at several interme-
diate stages of processing. These imports include partially smelted matte and
crude anode or blister copper. Although they do not represent a large frac-
tion of the copper consumed in this country, most copper imports are in the
form of these intermediate products. A small amount of unprocessed high-grade
ore is also imported.
The industry consumes other materials in various processing steps, but
not in large quantities. Mining and concentrating entail use of explosives
and small amounts of organic chemicals, and smelting requires limestone and
silica rock as fluxing materials.
Primary copper smelting and refining, together with the primary aluminum
industry, accounts for 3 percent of all energy consumed by manufacturing in-
dustries in the U.S. (2). Currently, natural gas is the fuel most heavily
relied upon by copper smelters, with oil also being widely used. Energy con-
sumption in 1974 for all copper refining and smelting operations in the U.S.
was: natural gas - 1.52 x 1013 kilocalories, oil - 4.13 x 1012 kilocalories,
and electricity - 6.82 x 1C8 kilowatt-hours (2). Coal was originally the only
fuel source in the domestic copper industry, but its use was largely discon-
tinued in favor of oil, natural gas, or electricity because of material han-
dling problems. However, the rapidly increasing costs of these forms of
energy is leading to new consideration of reconversion to coal.
Products
Commerce recognizes a number of different grades of copper, classified
into two main groups. Relatively impure grades are directly produced in a
copper smelter. These are sold for use in alloys or for other special pur-
poses, or they may be exported to be refined elsewhere. More than 90 percent
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TABLE 2. TYPICAL ANALYSIS OF COPPER ORE USED AT COPPER RANGE
COMPANY, WHITE PINE, MICHIGAN
Element
Cu
Ag
Au
A1203
Si02
CaO
Fe
MgO
Ni
S
Pb
As
Mo
Bi
Mn
Zn
Na
K
Co
Se
Percentage (Weight)
1.0
0.0006
Trace
15.0
61.5
7.4
6.6
3.7
0.005
0.35
0.001
0.0005
0.002
0.0001
0.05
0.001
1.5
1.0
0.003
0.0005
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of the copper produced is refined in this country into one of the electrolytic
grades. Table 3 shows the distribution of consumption of electrolytic copper
in 1978. More than two-thirds of it is used directly to manufacture wire and
tubing. More than half the electrolytic copper is cast at the refinery into
wirebars for direct use on wire and tubing forming machines.
Several byproduct elements are isolated from copper ores. In 1978 the
copper industry produced all the arsenic, selenium, and tellurium manufactured
in this country, almost all the platinum and palladium, and almost half the
gold, silver, and molybdenum. Except for molybdenum, all of these were pro-
duced as purified metals or compounds. Molybdenum was sold as concentrate,
and most copper producers also reclaim zinc and lead as a concentrate.
Several copper smelters recover tellurium, and one company situated near steel
mills makes a high-grade iron sinter from the iron pyrite in its ore. This
same company manufactures sulfuric acid as a major product, and most others
have facilities to manufacture it as a byproduct. Three companies produce
copper sulfate, and two manufacture chemicals of a specialized nature in the
same plant with their copper operations.
Table 4 provides the basic 1978 statistics of this industry, and Table 5
lists major sulfuric acid producers.
Companies
The United States is the world's largest copper producer, accounting for
about 18 percent of the total world mine production in 1978. Domestic mine
output that year was estimated at 1.36 million metric tons and valued at $1.97
billion (4).
In 1978 nine companies operated 16 primary smelters and 19 companies
operated 23 refineries and electrowinning plants (4). The locations of
domestic primary copper smelters and refineries are indicated in Figure 1.
Table 6 lists some of these companies, with applicable data. The three largest
domestic producers are Kennecott Copper Corporation, Phelps-Dodge Corporation,
and ASARCO, Inc.
Most of these companies own or control domestic mines that supply at
least part of their own needs. Table 7 lists the 25 largest copper mines
operating in 1976. Most of these were directly owned by a producing company.
At least three other large companies own mines or leaching operations intended
primarily for production of copper, as do several smaller companies. The 25
listed mines produced more than 95 percent of the domestic copper in 1974.
The remaining five percent of domestic copper was produced from a few smaller
mines, or as byproducts of other mining industries.
Projected changes through 1985 include addition of new capacity and
improvement of pollution control. Technology should not change radically due
to the lead time required, the lack of recent innovations, and the capital
intensive nature of the industry (2).
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TABLE 3. CONSUMPTION OF REFINED COPPER
IN 1978 (3)
Consumer
Quantity,
metric tons
Wire mills
Brass mills
Secondary smelters
Chemical plants,
foundries, and
miscellaneous plants
1,514,489
619,278
3,546
32,659a
Estimated.
TABLE 4. STATISTICAL DATA FOR THE PRIMARY COPPER INDUSTRY
IN THE UNITED STATES IN 1978 (3)
Primary copper produced, metric tons
Mines, from domestic ores
Smelters, from domestic ores
Refineries, from domestic ores
Refineries, from foreign ore, matte, etc.
Exports, metric tons
Unmanufactured
Refined
Imports, metric tons
Unmanufactured
Refined
1,351,956
1,270,002
1,278,129
112,720
177,847
91,924
546,401
414,703
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TABLE 5. PRINCIPAL BY-PRODUCT
SULFURIC ACID PRODUCERS - 1974 (5)
Producer
Capacity,
metric ton/year
The Anaconda Co.
Anaconda, Montana
ASARCO, Inc.
Corpus Christi, Texas
El Paso, Texas
Hayden, Arizona
Tacoma, Washington
Cities Service Co.
Copperhill, Tennessee
Inspiration Consolidated Copper Co.
Inspiration, Arizona
Kennecott Copper Corp.
Hurley, New Mexico
Hayden, Arizona
Garfield, Utah
Magma Copper Co.
San Manuel, Arizona
Phelps Dodge Corp.
Ajo, Arizona
Hidalgo, New Mexico
Morenci, Arizona
210,000
104,000a
145,000
163,000
49,000
l,143,000b
397,000
181,000
249,000
544,000
803,000
91,000
524,000
544,000
ASARCO - Corpus Christi smelter is no longer operating.
Approximate composition is 5% smelter gases; 95% gases from pyrites.
-------
c»
• COPPER SMELTER
* COPPER REFINERY
* COPPER SMELTER/REFINERY
Figure 1. Primary U.S. copper smelting and refining locations.
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TABLE 6. U.S. PRIMARY COPPER PRODUCERS (6,7)
Company
AMAX, Inc.
The Anaconda Company (ARCO)
ASARCO, Inc.
Cerro Corporation
Cities Service Company
Copper Range Company
(Louisiana Land)
Inspiration Consolidated
Copper Company
Kennecott Copper
Corporation
Magma Copper Company
(Newmont Mining)
Phelps Dodge Corporation
Southwire Company
Location
Cateret, New Jersey
Anaconda, Montana
Great Falls, Montana
Tacoma, Washington
El Paso, Texas
Hayden, Arizona
Amarillo, Texas
St, Louis, Missouri
Copperhill, Tennessee
White Pine, Michigan
Miami , Arizona
Garfield, Utah
Hurley, New Mexico
Hayden, Arizona
McGill, Nevada
Baltimore, Maryland
Magna, Utah
San Manuel, Arizona
Morenci , Arizona
Douglas, Arizona
Hidalgo, New Mexico
Ajo, Arizona
El Paso, Texas
Laurel Hill, New York
Carroll ton, Georgia
Description
Refinery
Smelter
Ref i nery
Smelter/refinery
Smelter
Smel ter
Refinery
Ref i nery
Smelter
Smel ter/ refinery
Smel ter/ refinery
Smelter
Smelter/refinery
Smelter
Smelter
Refinery
Ref i nery
Smelter/refinery
Smelter
Smelter
Smel ter
Smelter
Refinery
Refinery
Refinery
Capacity,
metric ton/year
(Cu content)
236,000
180,000
229,000
91,000/142,000
104,000
163,000
381 ,000
236,000
20,000
82 ,000/82 ,000
64,000/136,000
245,000
73,000/93,000
73,000
45,000
250,000
169,000
181,000/181,000
161,000
n's.ooo
91 ,000
64,000
404,000
83,000
65,000
Note: Refineries typically produce copper from both blister and scrap in varying proportions, and for this reason the
U.S. Bureau of Mines does not categorize refineries as either "primary" or "secondary." In general, refineries
located in Western states or adjacent to primary smelters process chiefly a blister feed, while those refineries
in the East produce a higher proportion of copper from scrap.
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TABLE 7. TWENTY-FIVE LEADING COPPER-PRODUCING MINES IN THE UNITED STATES
IN 1976, IN ORDER OF OUTPUT (8)
Rank
1
2
3
4
5
6
7
8
9
10
11
12
13
Mine
Utah Copper
Morenci
San Manuel
Sierrita
Twin Buttes
Tyrone
Berkeley Pit
Ray Pit
Pima
Metcalf
Pinto Valley
Chi no
New Cornelia
County and State
Salt Lake, Utah
Greenlee, Arizona
Final, Arizona
Pima, Arizona
do
Grant, New Mexico
Silver Bow, Montana
Pinal, Arizona
Pima, Arizona
Greenlee, Arizona
Gila, Arizona
Grant, New Mexico
Pima, Arizona
Operator
Kennecott Copper Corporation
Phelps Dodge Corporation
Magma Copper Company
Duval Sierrita Corporation
Anamax Mining Company
Phelps Dodge Corporation
The Anaconda Company
Kennecott Copper Corporation
Cyprus Pima Mining Company
Phelps Dodge Corporation
Cities Service Company
Kennecott Copper Corporation
Phelps Dodge Corporation
Source of Copper
Copper ore, copper
precipitates
Copper ore, copper
precipitates, copper
tailings
Copper ore
Do.
Do.
Copper ore, copper
precipitates
Do.
Do.
Copper ore
Copper ore, copper
tailings
Copper ore, copper
precipitates
Do.
Copper ore
(continued)
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TABLE 7 (continued)
Rank
14
15
16
17
18
19
20
21
22
23
24
25
Mine
White Pine
Magma
Inspiration
Mission
Yerrington
Continental
Silver Bell
Sacatoti Unit
Bagdad
Lakeshore
Eaperanza
Copper Canyon
County and State
Ontonagon, Michigan
P1nal , Arizona
Gila, Arizona
Pima, Arizona
Lyon, Nevada
Grant, New Mexico
Pima, Arizona
Final , Arizona
Yavapai, Arizona
Pinal , Arizona
Pima, Arizona
Lander, Nevada
Operator
White Pine Copper Company
Magma Copper Company
Inspiration Consolidated Copper Company
ASARCO Inc.
The Anaconda Company
UV Industries, Inc.
ASARCO, Inc.
do.
Cyprus Bagdad Copper Company
Heel a Mining Company
Duval Corporation
do.
Source of Copper
Do.
Do.
Copper ore, copper
precipitates
Copper ore
Copper ore, copper
precipitates
Do.
Do.
Copper ore
Do.
Do.
Copper ore, copper
precipitates
Do.
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An estimated 40,000 persons are employed by the primary copper industry.
Most are engaged in mining and concentrating. In 1974, industry employment
was reported as 33,942 persons, of which 14,861 were in open-pit mines, 9,545
in underground mines, and 4,536 in ore concentrating mills. The copper in-
dustry is the largest single employer in Arizona, Montana, Nevada, and Utah.
Environmental Impacts
Smelting is the most important source of environmental problems in the
copper industry.
Emissions of air pollutants from copper processing are of concern,
especially those that are potentially hazardous to human health. Among the
known trace elements of concern are arsenic and cadmium. The copper industry
is a primary source of arsenic emissions, producing about 30 percent of total
arsenic emissions in the United States.
Copper smelters are a major source of sulfur dioxide, emitting 80 percent
of the total amount of S02 emitted from the copper, lead, and zinc industries.
The industry is implementing control methods to recover some of the S02 as a
marketable product. Fifteen percent of the S02 generated by the industry is
fugitive emissions.
The industry makes use of water recycle techniques, but the extent has not
been quantified. Mine wastewater may contain acid and dissolved metals. Mill
tailings may also contain heavy metals. Smelter and refining wastes often
contribute a heavy load of dissolved metals to the tailings pond. These wastes
can affect the quality of the decant water as well as effluent volumes. Slag
from the industry, which is dumped, contains many elements. Table 8 presents
approximate quantities of selected pollutants from the U.S. primary copper
industry (9). Primary copper smelting and fire refining produce approximately
3 metric tons of wastes containing slag, sludge, and dust (including acid plant
sludge) per metric ton of product. Smelting followed by electrolytic refining
produces about 2.4 kilograms of wastes per metric ton of product.
In 1974 the copper ore mining and concentrating industry produced about
651 million metric tons of solid waste, or about 85 percent of the national
total for metals mining and concentrating. Of this figure, 56 percent was
waste rock, 7 percent was overburden, and 36 percent was concentrator tailings
\ 11 •
References
1. Mining Informational Services of the McGraw-Hill Mining Publications.
1975 E/MJ International Directory of Mining and Mineral Processing
Operations. McGraw-Hill, Inc., 1975.
12
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TABLE 8. ANNUAL GENERATION OF SELECTED POLLUTANTS FROM U.S. PRIMARY COPPER INDUSTRY - 1978 (9)
(metric tons)
Ore crushing
Roasting
Smelting
Converting
Refining
Total
Production
269,000,000
2,781,000
5,562,000
5,562,000
5,562,000
-
Parti cul ate emissions
Before control
269,400
75,400
122,400
124,000
29,200
620,400
After control
269,400
14,300
17,100
18,600
4,100
323,500
Sulfur oxide emissions
Before control
-
634,000
962,100
1,957,800
-
3,553,900
After control
-
N.A.
N.A.
N.A.
-
1,930,400
N.A. - Not available.
-------
2. Energy Penalty Study of the Nonferrous Metals Industry. Arthur D.
Little, Inc. Draft Final Report to Policy Planning Division. U.S.
Environmental Protection Agency. Washington, D.C. August 1977.
3. U.S. Department of the Interior. Bureau of Mines. Mineral Industry
Surveys, Copper in 1978. Washington, D.C. April 3, 1979.
4. U.S. Department of the Interior. Bureau of Mines. Commodity Data
Summaries 1979. Washington, D.C. 1979.
5. Stanford Research Institute. 1977 Directory of Chemical Producers,
United States of America. Menlo Park, California.
6. U.S. Department of the Interior. Bureau of Mines. Copper - 1977.
MCP-3. Washington, D.C. June 1977.
7. Development Document for Interim Final Effluent Limitations Guidelines
and Proposed New Source Performance Standards for the Copper Segment of
the Nonferrous Metals Manufacturing Point Source Category. EPA
440/1-75/032b. U.S. Environmental Protection Agency. Washington, D.C.
November 1974.
8. U.S. Department of Interior. Bureau of Mines. Minerals Yearbook 1976.
Washington, D.C. 1978.
9. Data provided by Mr. Charles Mann, Monitoring and Data Analysis Division,
Office of Air Quality Planning and Standards, U.S. Environmental Protec-
tion Agency.
14
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INDUSTRY ANALYSIS
The environmental impacts of many industries, including the primary
copper industry, have received wide attention and have been the subject of
many industrial and governmental studies. Emissions of S02 and their impacts
on the atmosphere are considered especially important.
This industry analysis examines each individual production operation,
called here a process, to examine in detail its purpose and its actual or
potential effect on the environment. Each process is examined in the fol-
lowing aspects:
1. Function
2. Input materials
3. Operating conditions
4. Utilities
5. Waste streams
6. Control technology
7. EPA classification code
8. References
The only processes included in this section are those that are either
operating in the United States, are under construction, or are currently
being demonstrated on a large scale at a U.S. facility. Figure 2 is a flow-
sheet showing these processes, their interrelationships, and their major
waste streams.
15
-------
OTHER COPPER
BEARING MATERIALS f
BLASTING
AGENTS
BY-
SULFIDE ~\l PRODUCT
CONCENTRATED I CONCEN-
TRATES
TO
HYDROMETALLUGICAL
PROCESSES
A WATER
O AIR
D SOLID
TO SULFUR
UTILIZATION
PROCESSES
Figure 2. Copper industry flow sheet.
-------
FROM
SMELTING
COPPER
RECYCLE
TO
SMELTING
it.
FLUX
|
r
KHP
1
.
fc
!
^-
L-*
— >
C
PEIRCE-
SMITH
1
C
HOBOKEN
CONVERTING
10
)
j>
J
J
i
1
i
r'
*A
1 A
H
FROM
FLASH
SMELTING
"FLASH*
FURNACE
SLAG
FROM
NORANDA
1
p
C
FURNACE
SLAG
TRFflTMFNT 1 ?
i
F
— >
FROM ROASTING
AND SMELTING
RECLAIMED^
COPPER
i
f
1
FLOTATION
SLAG
TREATMENT
13
RECYCLE TO
CONCENTRATE
DRYER
CONVERTER
OFF-GAS
FIRE
REFINING
AND ANODE
CASTING
COLLECTED FLUE
DUSTS AT ONE
SMELTER
WATER
O AIR
O SOLID
CHARCOAL
Figure 2 (continued)
-------
CO
RECYCLE TO ELECTROLYTIC
REFINING OR ELECTROLYTE
PURIFICATION
Figure 2 (continued)
-------
FROM
MINING
WATER
O AIR
D SOLID
37
COAL-
/
i
\ "
h- *
E
ION
Y
1
>
r
^
SOLVENT
—*• tXIRAlllON
34
ORGANIC | |
MATERIALS—1
SULFURIC —1
ACID
(
SPONGE IRON
^/PIIRTFTFnX^
"VSOLUTION,/
r
_^/ SPONGE \_w
""*
CEMENTATION
33
SCRAP >f
IRON
-J
ELECTROWUtt
— 1
GLUE -
jrf .J
TO
SMELTING
FURNACE
CLEAR
REGENERATION
PURGE
Figure 2 (continued)
-------
PRIMARY COPPER PRODUCTION PROCESS NO. 1
Mining
1. Function - Rock containing enough copper to justify its recovery is
removed from the ground and transported to a concentrator plant. Mining
methods are determined by the size, depth, and configuration of the ore body,
as these are adaptable for underground or open pit mining. The capability
for high productivity in large-scale open pit operations has made possible
the development of large deposits of relatively low-grade porphyry ores; in
1973, 83 percent of all the ore mined in the United States came from open
pits (1).
In an open pit mine, holes for placement of explosives are drilled be-
hind the face of a near-vertical bank. Other explosives are placed in
secondary drill holes. The explosives reduce the rock to sizes that can be
handled by power shovels or other mechanical equipment. Shovels load the ore
into trucks or railroad cars or onto belt conveyors for transportation to the
concentrator plant.
2. Input Materials - Important copper ore minerals are listed in Table 1.
Chalcopyrite, bornite, and enargite are considered the primary minerals that
were formed deep underground by igneous processes. The other sulfide minerals
were formed by the leaching action of underground water in the absence of
oxygen. When oxygen was present, the sulfur was oxidized, and minerals such
as chrysocolla, azurite, and malachite were formed. Native copper is some-
times found in these oxidized deposits.
Porphyry deposits are now the major source of the world's copper.
Porphyry is the term applied to the type of deposit in which the copper
minerals are uniformly distributed throughout a rock composed of other
minerals. The copper content is between 0.6 and 2 percent (2). The copper
ores of southwestern United States are from porphyry deposits.
Explosives used in copper mining are almost always a mixture of ammonium
nitrite and fuel oil (AN-FO). Some mines add sodium nitrate to make the
explosive slightly more powerful (3). No values are available for the con-
sumption of these explosives.
3. Operating Conditions - Most copper ores are mined in the arid regions of
the West or Southwest where open pit operations continue through both hot and
cold weather. Other mining operations in Michigan and Tennessee are under-
ground mines where more constant temperatures prevail.
4. Utilities - In most mines, electrically operated power equipment is used
for drilling, loading, and hauling. In 1973, 1.02 kilowatt-hours of elec-
tricity was consumed by the mining process per kilogram of copper produced
(4).
A small amount of water is needed for equipment cooling, drill lubrica-
tion, dust control spraying, equipment washing, and sanitary facilities.
Occasionally the water sent to the mine is reused water from the concentrator
plant or tailings pond.
20
-------
5. Waste Streams - Mining operations generate fairly large amounts of dust
from drilling, blasting, loading, and transporting operations. One estimate
of 110 grams of fugitive dust per metric ton of ore mined is given as the
average for several types of nonferrous mining (5). The dust composition is
dependent on the character of the ore being mined, and there is a large
variation in particle size.
Wastewater from copper mining comes from seepage or runoff from the mine
or spoil dumps, and from the water sent into the mine for utility uses.
Improper backfill operations may result in acid drainage. The amount of
wastewater from open pit copper mines ranges from zero to 0.3 cubic meter of
water per metric ton of ore mined. From underground mines, the amount ranges
from 0.008 to 4.0 cubic meter per metric ton of ore (6). Chemical charac-
teristics are typical of those from any sulfide mine. Table 9 gives analyses
of waters from two copper mines.
Large amounts of solid wastes are generated in a mining operation.
Overburden stripped to uncover an ore body, shaft and tunnel developmental
wastes, and low-grade ore (less than 0.4% copper) found within the mine are
disposed of near the mine. The amount varies widely, from as little as 0.004
metric ton per metric ton of ore up to 15 metric tons per metric ton of ore
mined. Average quantities in 1973 were reported as 2.65 metric tons per
metric ton for open pit mines, and 0.13 metric ton per metric ton for under-
ground mines (7). These wastes contain small and varying amounts of copper
minerals, sometimes minerals of other metals, and large amounts of the native
rock of the region. Concentrations of most materials do not exceed background
levels (8).
6. Control Technology - The only control provided for fugitive dust is the
manual use of water sprays, to be used when needed. Dust from blasting can be
controlled by proper blast design. Most open pit copper mines are very large,
with sufficient natural ventilation that dust conditions are not unbearable.
Mining companies attempt to locate waste dumps where natural seepage will
not contaminate a stream or underground aquifer. Otherwise there is little
control of these solid wastes in the copper industry (9).
Mine water wastes and seepage from the spoil dumps are major potential
sources of water pollution from the primary copper industry. Two character-
istics of copper mines differ from those in the lead and zinc industries.
First, their location greatly simplifies control of water discharges. Most
large open pit mines are in regions of deficient rainfall, and some are in
desert areas. Natural evaporation within the pit greatly reduces the volume
of wastes that must be pumped out, and seepage from spoil dumps rarely enters
a stream. The water that accumulates is in many cases disposed of merely by
pumping it onto a nearby flat area, where it either seeps into the alkaline
soil or evaporates. It is thought that most of the dissolved metals are con-
verted to insoluble compounds by this process, and officials of several
mining companies state that they have shown that none of these waters has
21
-------
TABLE 9. RAW WASTE LOAD IN WATER PUMPED FROM SELECTED COPPER MINES (7)
rv>
ro
Parameter
Flow
PH
IDS
TSS
Oil & grease
TOC
COO
B
Cu
Co
Se
Te
As
Zn
Sb
Fe
Mn
Cd
N1
Mo
Sr
Hg
Pb
Underground mine
Concentration
(mq/X.)
3,815.3m3/day
7.37a
29,250
69
<1.0
<4.5
819
2.19
0.87
<0.04
<0.077
0.60
<0.07
2.8
<0.5
<0.1
2.22
<0.02
<0.05
<0.5
119
<0.0001
<0.1
Raw waste load per unit ore mined
kq/1000 metric tons
17.28 m3/1000 metric tons
7.37a
5,053.9
11.9
<0.173
<0.778
141.5
0.378
0.150
<0.007
<0.013
0.104
<0.012
0.484
<0.086
<0.017
0.384
<0.003
<0.009
<0.086
20.6
<0. 00002
<0.017
Open-pit mine
Concentration
(mg/Jl)
409 nfVday
6.96a
1,350
2
7
10
4
0.07
-1.05
<0.06
0.096
<0.2
<0.01
0.1
<0.5
<0.1
0.9
<0.03
<0.05
<0.2
0.8
<0.0001
<0.5
Raw waste load per unit ore mined
kg/1000 metric tons
75 m3/1000 metric tons
6.96a
101
0.2
0.5
0.75
0.3
0.005
0.08
<0.005
0.007
<0.02
<0.0008
0.008
<0.04
<0.008
0.07
<0.002
<0.004
<0.02
0.06
<0. 000008
<0.04
aValue In pH units
-------
entered underground supplies. In the vicinity of some of these mines, copper,
zinc, selenium, and arsenic are detected in analysis of water from springs and
wells, in concentrations usually less than 0.1 milligrams per liter; it is
not clear whether this amount exceeds the natural concentrations in a highly
mineralized region (1). These alkali waters naturally have total dissolved
solids that can be several thousand milligrams per liter.
Near some copper mines, the practice of leaching low-grade ore is being
practiced. This practice and its effect in the control of mining wastewaters
is described in the section outlining Process No. 32, Sulfide Ore Leaching.
7. EPA Source Classification Code - None
8. References -
1. Mineral Facts and Problems, Washington, D.C. U.S. Department of the
Interior, Bureau of Mines, 1970.
2. Hallowell, J.B. et al. Water Pollution Control in the Primary
Nonferrous Metals Industry - Volume I. Copper, Zinc, and Lead
Industries. EPA-R2-73-274a. U.S. Environmental Protection Agency,
Washington, D.C. September 1973.
3. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc., New York. 1967.
4. Energy Consumption in Domestic Primary Copper Production, U.S.
Bureau of Mines.
5. Davis, W.E. National Inventory of Sources and Emissions: Copper,
Selenium, and Zinc. PB-210 679, PB-210 478, and PB-210 677. U.S.
Environmental Protection Agency. Research Traingle Park, North
Carolina. May 1972.
6. Development Document for Interim Final and Proposed Effluent Limita-
tions Guidelines and New Source Performance Standards for the Ore
Mining and Dressing Industry. Point Source Category Volumes I and
II. EPA/1-75/032-6. Environmental Protection Agency, Washington,
D.C. February 1975.
7. Minerals Yearbook. U.S. Department of the Interior, Bureau of
Mines., Washington, D.C. 1973.
8. A Study of Waste Generation, Treatment and Disposal in the Metals
Mining Industry. PB 261-052. Midwest Research Institute for
Environmental Protection Agency. Washington, D.C. October 1976.
9. Dayton, S. The Quiet Revolution in the Wide World of Mineral
Processing. Engineering and Mining Journal. June 1975.
23
-------
PRIMARY COPPER PRODUCTION PROCESS NO. 2
Concentrating
1. Function - Sulfide ore from the mine is separated by the concentration
process into two or more fractions. The fractions rich in valuable minerals
are called concentrates, and the waste rock, low in metals content, is called
the gangue. With this process, ore that usually contains less than 1 percent
copper is concentrated into a fraction analyzing from 20 to 30 percent
copper. At least 85 percent of the ore copper content is recovered in the
concentrate.
Concentrating consists of milling the ore, crushing and grinding it to
a fine powder, and then separating the minerals by froth flotation. In
milling, the ore is sent through crushers and then through fine grinders.
Between stages, the ore is classified (screened), and the final milled
product is a mixture of particles between 65 and 200 mesh.
In the last stages of milling, water is added along with chemicals to
condition the ore for froth flotation.
Flotation is a continuous process that uses compressed air and various
flotation chemicals to separate the ore into fractions. By proper selection
of additives, certain minerals are caused to float to the surface and are
removed in a foam of air bubbles, while others sink and are carried out with
the slurry. The ore passes through many flotation stages in order to accom-
plish this separation. The chemicals that are added are classified as
"frothers", which create the foam; "collectors", which cause certain minerals
to float; and "depressants", which cause certain minerals to sink.
In the flotation of copper ores, the frothers most often used are
reportedly pine oils, cresylic acid, or long-chain alcohols (1). Lime is
usually added in the final stages of grinding, both to adjust the pH of the
slurry to an optimum level and to act as a depressant for iron pyrite. In
this application it is often used in conjunction with cyanide (1). Various
xanthates or dithiophosphates act as collectors for the valuable sulfide
minerals, and the copper and other recoverable minerals come off with the
froth (2). The gangue does not float and is discarded as "tailings".
After initial separation, the valuable minerals are sent through
stages that further separate them by selective or differential flotation.
By use of proper collectors or depressants, the concentrates may be up-
graded to remove more iron pyrite. In some cases, other fractions high in
lead and zinc, or molybdenum and rhenium, may be produced. These are
usually sold to processors in the industries handling those metals. The
copper ores of the west are a prime source for molybdenum; to separate
this fraction, the concentrate must be steam stripped to remove the
collector originally added (3).
Occasionally, a concentrator will batch-treat a copper concentrate with
cyanide to dissolve its silver and gold content. After separating the leached
24
-------
solution from the concentrate, zinc metal is added to reprecipitate the
precious metals.
Concentrates are dewatered by clarification and filtration. They may
be partially dried to simplify handling and shipment, or may be more com-
pletely dried for direct "green" feed to a smelting furnace (see Process No.
5). Ten of the sixteen conventional smelters in this country have concen-
trator plants onsite or nearby (4).
Table 10 shows typical composition of copper concentrates; compositions
vary with the character of the ore and the amount of processing employed.
2. Input Materials - Only sulfide ores of copper can be successfully
separated by the flotation process. Oxidized ores are treated by hydro-
metallurgical processes (see Process No. 31).
Lime is used for pH adjustment and as a pyrite depressant. Quantities
added vary between 0.9 and 18.0 kilograms per metric ton of ore processed (5),
Pine oil frothers are usually consumed at a rate of about 0.09 kilogram per
metric ton of ore (5). No data are available on the quantities of long-
chain alcohols or cresylic acid required if they are substituted for pine oil,
Table 11 lists some of the chemicals that are used as collectors in
the flotation process. The use and quantity of any one of these materials
depends on the mineral assemblage particular to each ore type. Alkyl-based
organic molecules are more commonly used than aryl compounds.
Miscellaneous compounds such as cyanides, zinc dust, various filter
aids, and inorganic salts are occasionally used in small quantities.
3. Operating Conditions - Most portions of this process are carried out at
ambient temperatures in closed buildings. At few points temperatures may
approach 100°C (i.e., steam stripping for molybdenite concentration). Occa-
sionally circulating streams are heated slightly to retain efficiency during
cold weather.
4- Utilities - In 1973, usage of water at 21 copper concentrators ranged
from about 100 to 500 cubic meters of water per metric ton of concentrate
produced, the amount depending on the complexity of the process employed (4).
In the same year, concentrators consumed about 6630 million kilowatt-hours
of electricity, which is about 400 kilowatt-hours per metric ton of
primary refined copper (2,6). The greater part of this electricity was used
to operate the crushing and grinding equipment, with a smaller amount for
production of compressed air.
5. Waste Streams - The handling and milling of dry ore is the principal
source of air pollutants in this process. Items of equipment are always
enclosed, but transitions between pieces of equipment are difficult to seal
tightly. Ore classifiers are not always completely sealed. Dust quantity
is reported as about 1 kilogram per metric ton of ore (3).
25
-------
TABLE 10. ANALYSIS OF COPPER CONCENTRATE (7)
Element
Cu
S
Pb
Fe
Zn
Ag
Au
Pt etc.
Pd
As
Sb
Bi
Se
Te
Re
Ni
Co
Cd
In
Ge
Sn
Cl
F
Al
Si
Ca
Mg
Mo
Mn
Flotation reagents
Composition,
% weight
20 - 50
30 - 38
tr. - 0.67
20 - 30
0.2 - 4.0
0.13
31.53
tr.
tr.
tr. - 4.0
tr. - 0.36
tr. - 0.05
tr. - 0.03
tr.
tr.
tr. - 0.1
tr. - 0.02
tr. - 0.01
tr.
tr.
tr.
0.05
0.05
Varies
Varies
Varies
tr.
tr.
tr.
tr.
Value for Au in grams/metric ton.
tr. = trace
26
-------
TABLE 11. TYPICAL FLOTATION COLLECTORS (2)
Type
Formula'
Xanthate
Dithiophosphate
Dithiocarbamate
Thiol (mercaptan)
Thlocarbanilide
Fatty acid soaps
Arenesulfonate or
alkylarenesulfonate
Alkyl sulfate
Primary amine
Quaternary ammonium salt
Alkylpyridinium salt
ROCSSNa
(RO)2PSSNa
R2NCSSNa
RSH
RCOONa
RS03NA
ROSOgNa
RN(CH3)3C1
RCCH.N-HC1
o *\
3 R is the abbreviation for an alkyl group
such as CH3(CH2)n. Although alkyl com-
pounds are common, alkyl aryl compounds
may also be used, as in alkylarenesul-
fonates.
27
-------
This process produces the largest amount of wastewater in the industry.
The ore flotation water is used to sluice the tailings into a pond, and
suspended solids are the most critical pollutant in concentrator effluent (8).
Although part of the water is recycled to the plant, the remainder is dis-
carded. Excluding the amount lost by evaporation in the tailings pond, the
volume of wastewater from this process will equal the water consumption,
ranging from 100 to 500 cubic meters per metric ton of concentrate (3). In
many cases in the Southwest, evaporation may equal consumption.
Reported analyses indicate that the water from the concentrator may
contain up to 3500 milligrams per liter of dissolved solids, from 0.01 to
0.1 milligram per liter of cyanides, and ranges of metallic elements indi-
cated in Table 12 (3).
The water may also contain thiosulfates and thionates, and the materials,
both inorganic and organic, used as flotation additives.
More than 95 percent of all the ore brought from the mine is discharged
from this process as tailings; this quantity totals approximately 241 million
metric tons of waste material each year from the industry (2,6,9). Tailings
are composed primarily of the common rock-forming minerals, but they also
contain around 15 percent of the heavy metals originally found in the ore,
and usually much of the iron pyrite. Production of higher-grade concentrates
to minimize air pollution has increased the proportion of pyrites in the
tailings. In this solid waste, the minerals have been pulverized and inti-
mately mixed, and are therefore subject to weathering much more rapidly than
rock masses of similar composition. They form a soil that is usually highly
acidic and that contains no plant nutrients.
6. Control Technology - Dust from the milling operations is generally
reduced by drawing air through the equipment and collecting the dust with
cyclone separators. This is both a dust control and an integral part of the
process since it allows these small particles to bypass one or more crushing
and grinding operations. Fugitive dust is usually uncontrolled unless the
amount being lost economically justifies the installation of equipment for
its recovery. Dust control at the tailings pond may be accomplished through
use of Coherex or a similar product.
Control of wastewater is discussed in more detail in following sections.
This waste, although it is the major one, is rarely controlled independently,
since waters from many sources find their way into the tailings pond.
Occasionally this source is kept separate; the pond itself represents one
stage of treatment.
Disposal of the tailings is a major problem in this industry. There is
no universal solution for disposal of such vast quantities of solid materials;
each concentrator plant requires separate study.
28
-------
TABLE 12. METALLIC ELEMENTS IN CONCENTRATOR WASTEWATER (3)
Element
Arsenic
Antimony
Cadmium
Copper
Cobalt
Iron
Manganese
Mercury
Molybdenum
Nickel
Lead
Selenium
Silver
Strontium
Zinc
Concentration, mg/1
0.07 approximately
0.2 to 1.0
0.02 to 0.05
0.08 to very high
0.04 to 1.68
0.1 to 2.0
0.05 to 4.8
0.001 to 0.05
0.2 to 20
0.05 to 3
0.01 to 3
0.003 to 0.02
0.1 approximately
0.03 to 2.5
0.05 to 8.50
29
-------
7. EPA Source Classification Code - None
8. References -
1. Hawley, John R. The Use, Characteristics and Toxicity of Mine-Mill
Reagents in the Province of Ontario. Ontario Ministry of the
Environment. Toronto, Ontario. 1977.
2. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc., New York. 1967.
3. Hallowell, J.B. et al. Water Pollution Control in the Primary
Nonferrous Metals Industry - Volume I. Copper, Zinc, and Lead
Industries. EPA-R2-73-274a. Environmental Protection Agency,
Washington, D.C. September 1973.
4. Development Document for Interim Final and Proposed Effluent
Limitations Guidelines and New Source Performance Standards for the
Ore Mining and Dressing Industry. Point Source Category Volumes I
and II. EPA/1-75/032-6. U.S. Environmental Protection Agency,
Washington, D.C. February 1975.
5. Development Document for Interim Final Effluent Limitations,
Guidelines and Proposed New Source Performance Standards for the
Lead Segment of the Nonferrous Metals Manufacturing Point Source
Category. EPA 440/1-75/032a. U,S. Environmental Protection
Agency, Washington, D.C. February 1975.
6. Dayton, J. The Quiet Revolution in the Wide World of Mineral
Processing. Engineering and Mining Journal. June 1975.
7. Little, A.D. Economic Impact of New Source Performance Standards
on the Primary Copper Industry: An Assessment. C-76072-20. U.S.
Environmental Protection Agency, Washington, D.C. October 1974.
8. Williams, Roy E. Waste Production and Disposal in Mining, Milling,
and Metallurgical Industries. Miller Freeman Publications, Inc.
San Francisco. 1975.
9. Minerals Yearbook. Washington, D.C. U.S. Department of the
Interior, Bureau of Mines, 1973.
30
-------
PRIMARY COPPER PRODUCTION PROCESS NO. 3
Multiple-Hearth Roasting
1. Function - Roasting is frequently the first of the pyrometallurgical
processes applied to the copper ore concentrate at the copper smelter. The
purpose of roasting is to reduce the sulfur content so that subsequent pro-
cesses operate efficiently. Roasting also removes the water from the con-
centrate, volatilizes some of the arsenic and antimony, and preheats the ore
before it is charged as calcined feed to the reverberatory furnace.
Roasting is accomplished either with a multiple-hearth or fluidization
process (See Process No. 4). In the multiple-hearth roaster, concentrate is
introduced at the top of a cylindrical vessel fitted with a series of round
horizontal trays, or hearths. The ore is raked across each hearth in turn
until it is discharged from the bottom of the cylinder. Air is admitted into
the roaster, along with a fuel if necessary to maintain adequately high
temperature.
Most of the chemical reactions that occur in the roaster are with the
pyrite in the concentrate rather than with the copper minerals. Copper has a
higher affinity for sulfur, whereas iron combines preferentially with oxygen.
Admitting a limited amount of air, therefore, causes the pyrite to oxidize,
producing iron oxide and sulfur dioxide gas (1).
The heat of the roasting process generally vaporizes much of the arsenic
and some of the antimony and other elements in the ore, and these "fumes"
leave the roaster with the S02 gas.
Multiple-hearth roasting is currently in use at four domestic copper
smelters. The roasters are built to handle from 125 to 650 metric tons of
concentrate per day (2). There appears to be a trend away from their use
except in "custom" smelters since with higher-grade concentrates the cost of
operation frequently outweighs the benefits realized (1). Custom smelters may
require multiple-hearth roasters, as the longer residence time and more
moderate rate of temperature change may be advantageous in the separation of
certain impurities, such as arsenic.
2. Input Materials - Copper concentrate, as received from the copper concen-
trator, is generally the only input. Composition is shown in Table 10 (Process
No. 2). At some smelters, fluxes such as limestone and silica are placed on
the lower hearths for premixing and preheating prior to the charging of the
roasted calcine to the smelting furnace.
3. Operating Conditions - Multiple-hearth roasters generally operate at
temperatures from 760°C on the bottom hearth down to around 200°C on the top
hearth (3). The roaster operates under negative draft near atmospheric pres-
sure.
4- Utilities - With the concentrates now being used, some fuel in the form
of oil or natural gas is always required. If concentrates are especially high
in sulfur content (24 percent or more), sufficient heat is released by
the burning sulfur and supplemental fuel is required only to preheat the
31
-------
roaster at startup (autogenous roasting). A reported energy requirement is
280,000 kilocalories per metric ton of copper produced (4).
.Cooling air is circulated through a hollow shaft that drives the rake
arms to prevent damage to mechanical'bearings and seals.
Electricity is used to drive the roaster rakes and for auxiliary mate-
rials handling equipment. Approximately 5700 kilowatt-hours is required for
a plant of 100,000 metric tons of copper per year capacity (5).
5. Waste Streams- Gases leaving most multiple-hearth roasters are too weak
in SOp gas for direct use by a sulfuric acid plant unless the inlet air can
be enriched in oxygen or unless air infiltration is reduced. The S0? con-
centration is variable, being dependent upon the required degree of sulfur
removal and the amount of fuel necessary to maintain roasting temperatures.
With lower-grade concentrates, 20 to 50 percent of the total SCL generated by
smelter facilities once came from the roaster. Since fuel gas was not re-
quired, the emissions contained from 5 to 10 percent S02 (6). Published
data on current operations are inconsistent and contradictory; recent re-
ports give S02 concentrations in emissions from roasters at 0.5 to 2 per-
cent (2,7,8,9,10,11,12). Gas from roasting is a steady stream, however, and
if sufficiently concentrated in S0? is otherwise suitable for sulfuric acid
manufacture.
Emissions of particulate matter from most multiple-hearth roasters are
little affected by operational changes. About 75 kilograms of particulates
are produced per metric ton of copper produced (5,9,10,11,13). Fifteen per-
cent is present in sizes below 10 microns (14). Table 13 presents typical
particle-size profiles. Although composition is dependent on the ore,
particulates may be expected to contain the more volatile elements, such
as arsenic, antimony, selenium, zinc, mercury, bismuth, rhenium, and lead.
These will leave the roaster as vaporized materials. Some copper and iron
will be physically carried over by the gas stream. Table 14 gives a
weight analysis of particulate and fume emissions from a multiple-hearth
roaster. Table 15 lists the typical levels of volatile metals found in
copper ore concentrates. These metals apparently appear in these dusts as
sulfates, sulfides, oxides, chlorides, and fluorides, but it is not known
which of the metals is combined with each negative radical. There are
significant fugitive emissions of dust and fume at some multiple-hearth
roasters.
The multiple-hearth roaster produces no liquid wastes.
Any organic materials that enter the roaster with the copper concentrates
are vaporized or decomposed in the roaster.
6. Control Technology - At present, none of the operating multiple-hearth
roasters is equipped with controls for S02 emissions. The only suitable
controls are the various scrubbing systems, as outlined for reverberatory
furnace gases (Process No. 6).
32
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TABLE 13. TYPICAL SIZE PROFILE OF MULTIPLE-HEARTH
COPPER ROASTER EMISSIONS (15)
Size, microns
Percent by weight
Entrained particles, carried from the
roaster as solids.
230 - 218
149 - 230
100 - 149
74 - 100
44 - 74
28 - 44
20 - 28
10 - 20
< 10
4.6
4.0
5.3
7.4
10.6
12.8
6.8
8.0
10.5
Sublimed particles, condensed from
metallic vapor.
0.5 - 10
30.0
33
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TABLE 14. CONCENTRATION AND WEIGHT ANALYSIS OF PARTICULATE
EMISSIONS FROM A MULTIPLE-HEARTH COPPER ROASTER (15)
Concentration
Entrained participates
1.4 g/Nm3
Sublimed participates
0.6 g/Nm3
Emission
Chemical
Cu
Fe
S
As
Sb
Pb
Zn
Sn
Cd
Ni
Mn
Se
Si02, CaO
CaSO.
Op (oxides)
inerts
As2°3
Sb2o3
inerts
% Weight
23.8 - 34.5
21.2 - 30.7
1.7 - 2.5
tr.
tr.
tr.
tr.
tr.
tr.
tr.
tr.
tr.
10 - 15
13 - 19
0.8
tr. - 17
tr. - 13
tr.
34
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TABLE 15. TYPICAL LEVELS OF VOLATILE METALS IN
DOMESTIC COPPER ORE CONCENTRATES (6)
Lead
Zinc
Arsenic
Cadmi um
Beryl 1 i um
Vanadium
Antimony
Tin
Concentration
1 eve!
<5000 ppm
5000 ppm-<2%
>2%
<1%
1 -<4%
200-1000 ppm
1000 ppm-1%
<1000 ppm
<10 ppm
<100 ppm
<200 ppm
>200- 500 ppm
>5000 ppm
<1000 ppm
Percent of
concentrates
surveyed
96
2
2
67
1
88
10
2
100
100
100
97
3
1/2
100
35
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The proposal has been made that enrichment of the air to a roaster with
oxygen would increase its S02 content to a level where it could be used as
feed to a sulfuric acid plant. This proposal has been rejected on several
grounds by smelter operators. Most multiple-hearth roasters cannot mechani-
cally withstand the high temperatures caused by oxygen enrichment. One
company that recovers arsenic from flue dusts maintains that oxygen enrich-
ment causes the arsenic to oxidize to AS205 and prevents its removal by
current techniques (16).
A variety of devices are used in various combinations for control of
particulate emissions. Larger particulates are occasionally separated with
cyclone collectors or with "balloon flues." The latter are oversized ducts
in which flue gas velocity is reduced enough that the particles settle by
gravity. Removal efficiency is 30 to 60 percent (16). Cyclones can remove
80 to 85 percent of the solids, but require an addition of energy to compen-
sate for pressure drop. Smaller particles in the gas stream are separated
by hot gas electrostatic precipitators, or the gas may be cooled with water
sprays before entering an ESP unit or a baghouse. Control is not complete,
especially in regard to sublimed particles and fugitive losses.
The collected dusts are returned to the metallurgical processing,
usually to the smelting furnace. One smelter extracts arsenic trioxide be-
fore returning the dusts to the furnace. Excessive accumulation of im-
purities causes dusts to be discarded, but the means of disposal have not been
reported.
7. EPA Source Classification Code - 3-03-005-02
8. References -
1. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc., New York. 1967.
2. Compilation and Analysis of Design and Operation Parameters for
Emission Control Studies. Pacific Environmental Services, Inc.
(Individual draft reports.).
3. Control of Sulfur Oxide Emissions in Copper, Lead, and Zinc Smelt-
ing. Bureau of Mines Information Circular 9527. 1971.
4. Fejer, M.E., and D.H. Larson. Study of Industrial Uses of Energy
Relative to Environmental Effects. U.S. Environmental Protection
Agency. Research Triangel Park, North Carolina. July 1974.
5. Jones, H.R. Pollution Control in the Nonferrous Metals Industry.
Noyes Data Corporation. Park Ridge, New Jersey. 1972.
6. Background Information for New Source Performance Standards:
Primary Copper, Zinc, and Lead Smelters. Volume I, Proposed
Standards. EPA-450/2-74-002a. U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina. October 1974.
36
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7. Copper Smelters. In: Compilation of Air Pollutant Emission Fac-
tors, Second Edition. AP-42. U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina. April 1973.
8. Donovan, J.R. and P.J. Stuber. Sulfuric Acid Production from Ore
Roaster Gases. Journal of Metals. November 1967.
9. Exhaust Gases from Combustion and Industrial Processes, Engineering
Science, Inc., Washington, D.C. October 2, 1971.
10. High, M.D., and M.E. Lukey. Exhaust Gases from Combustion and
Industrial Processes. PB-204 861. U.S. Environmental Protection
Agency, Durham, North Carolina. October 1971.
11. Measurement of Sulfur Dioxide, Particulate and Trace Elements in
Copper Smelter Converter and Roaster/Reverberatory Gas Streams.
EPA 650/2-74-111. U.S. Environmental Protection Agency, Washington,
D.C. October 1974.
12. Systems Study for Control of Emissions Primary Nonferrous Smelting
Industry. Arthur G. McKee & Co. for U.S. DHEW. June 1969.
13. Vandegrift, A.E., L.J. Shannon, P.G. Gorman, E.W. Lawless, E.E.
Salless, and M. Reichel. Particulate Pollutant System Study - Mass
Emissions, Volumes 1, 2, and 3. PB-203 128, PB-203 522, and PB-
203 521. U.S. Environmental Protection Agency, Durham, North
Carolina. May 1971.
14. Goldeberg, A.J. A Survey of Emissions and Controls for Hazardous
and Other Pollutants. EPA-R4-73-021. U.S. Environmental Protec-
tion Agency, Washington, D.C. February 1973.
15. Duncan, L.J., and E.L. Keitz. Hazardous Particulate Pollution from
Typical Operations in the Primary Nonferrous Smelting Industry.
Presented at the 67th Annual Meeting of the Air Pollution Control
Association. Denver, Colorado. June 9-13, 1974.
16. Personal communication, A.D. Little Company.
37
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PRIMARY COPPER PRODUCTION . PROCESS NO. 4
Fluidization Roasting
1. Function - The function of fluidization roasting is the same as for
multiple-hearth roasting (Process No. 3): to reduce the sulfur content of
the concentrate and to oxidize some of the iron, so that the matte produced
in the smelting process can be treated most efficiently in the copper con-
verter. Roasting also volatilizes some impurities and preheats the rever-
beratory feed. The roasted concentrate to be smelted is called calcined
feed.
The fluidization roaster is the pyrometallurgical application of the
fluidized-bed principle that has revolutionized so many operations in other
industries over the past 30 years. It is based on the discovery that par-
ticles of a solrid added to a gas stream moving vertically upward at just the
right velocity take on many of the characteristics of an agitated liquid.
Each particle of the solid is in constant agitated motion, separated from all
other particles, and is in intimate contact with the gas stream. Any chemical
reaction that takes place between the solid and the gas happens very quickly,
with no cold pockets or hot spots.
In the fluidization roaster, the gas is a recycled stream of flue gas,
into which regulated streams of air and fuel gas are introduced. The solid
is copper concentrate, continuously being fed and overflowing the fluidiza-
tion vessel. Both the fuel and the oxygen are completely consumed; by
elimination of excess air, the S02 content of the flue gas stream is greatly
increased, to a concentration great enough for feed to a sulfuric acid plant.
If the sulfur content of the concentrate is high enough, fuel is needed
only at startup. With 20 percent sulfur in the feed, sufficient heat is
released by the sulfur to make additional fuel unnecessary. Operators of
fluidization roasters, therefore, find it best not to process the ore into
super-quality concentrates, but to tailor the quality of the concentrate to
match the requirements of the roaster. Fluidization roasters may not pro-
vide sufficient residence time for volatilization of certain substances such
as arsenopyrites (1).
Four domestic copper smelters have adopted fluidization roasting.
Being complex and highly instrumented units, they must be capable of large
throughput to justify the investment. Units with capacities from 700 to 1500
metric tons per day are in use (2).
2. Input Materials - Copper concentrate is the only input, usually blended
or produced to a quality that the roaster can most economically process.
The concentrate may be pelletized or granulated before being fed to the
roaster.
3. Operating Conditions - Because of the thorough mixing in the fluid bed,
temperature is held constant in all portions of the bed in the range of 650°
to 760°C. The pressure in the bed is slightly above atmospheric, and in
portions of the recycle stream the pressure may be 1 kilogram per square
centimeter or more.
38
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4. Utilities - The major utility used is electricity to compress the
recycled gas, to inject air, and to operate auxiliary devices. No estimates
of power consumption are published.
Fuel gas is the usual source of heat for starting the charge, although
some plants have fuel oil facilities for standby. Quantity consumed is
small.
Oxygen enrichment facilities are being considered for some of these
units in order to provide more operating flexibility.
5. Waste Streams - Fluidization roasters are always fitted with cyclone
separators that catch the large amounts of dust that rise from the bed. The
dust is returned to the bed. Dust quantities can be as much as 75 percent of
the feed (2,3). The cyclones are most properly considered as part of the
process, and the waste stream considered the outlet of the cyclones. This
waste stream contains particulates and fumes of the same chemical character
as those from a multiple-hearth roaster (Process No. 3); they are rich in
volatile elements such as arsenic and contain considerable copper. Data on
total quantities of dust are not available; they are likely to be greater
than emissions from a multiple-hearth roaster because of the more complete
separation of smaller particles from the body of the charge.
Sulfur dioxide concentrations in the gas from the fluidization roaster
are reported to be from 12 to 16 percent (2,4,5).
The roasting operation produces no liquid or solid wastes.
6. Control Technology - All the smelters that operate fluidization roasters
use the S02 for production of sulfuric acid. Except for other processing to
recover liquid S02 or elemental sulfur, this is the only known technology
with which to dispose of such a concentrated gas stream.
Almost complete removal of particulates is required before the gas is
introduced into a sulfur recovery process. Electrostatic precipitators and
wet scrubbers are in use with the operating fluidization roasters. Since the
dusts and condensed fumes contain valuable materials, they are normally
returned to the pyrometallurgical processing units, usually to the smelting
furnace, but some may be discarded.
7. EPA Source Classification Code - 3-03-005-02
8. References -
1. Development Document for Interim Final Effluent Limitations Guide-
lines and Proposed New Source Performance Standards for the Primary
Copper Smelting Subcategory and the Primary Copper Refining Sub-
category of the Copper Segment of the Nonferrous Metals Manufac-
turing Point Source Category. EPA 440/1-75/032-b. U.S. Environ-
mental Protection Agency, Washington, D.C. February 1975.
39
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2. Jones, H.R. Pollution Control in the Nonferrous Metals Industry.
Noyes Data Corporation, Park Ridge, New Jersey. 1972.
3. McAskill, D. Fluid Bed Roasting: A Possible Cure for Copper
Smelter Emissions. Engineering and Mining Journal, pp. 82-86.
July 1973.
4. Compilation and Analysis of Design and Operation Parameters for
Emission Control Studies. Pacific Environmental Services, Inc.
(Individual draft reports).
5. Background Information for New Source Performance Standards:
Primary Copper, Zinc, and Lead Smelters. Volume I, Proposed
Standards. EPA-450/2-74-002a. Environmental Protection Agency,
Research Triangle Park, North Carolina. October 1974.
40
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PRIMARY COPPER PRODUCTION PROCESS NO. 5
Drying
1. Function - Copper concentrates that are not to be processed by roasting
must pass through a dryer, whose only function is to decrease the moisture
content. Drying may be practiced to simplify handling of the concentrate.
In recent years it has been practiced to make the concentrate suitable for
direct feed to the reverberatory furnace; this is described in the industry
as "green feed." Excessive moisture in the concentrate may cause minor
eruptions or explosions that may damage the furnace (1).
Some smelters continue to use existing multiple-hearth roasters, oper-
ated at much lower temperatures, to accomplish this drying operation.
Special dryers, such as rotary kilns, are also being used. The dryer may be
more conveniently located at the concentrator rather than at the smelter (see
Process No. 2).
2- Input Materials - The concentrate containing 5 to 25 percent moisture is
the only input. Analysis is given in Table 10.
3. Operating Conditions - Except at flame fronts, temperatures in the
drying operation do not exceed 150°C. Pressures are atmospheric.
4. Utilities - Fuel gas is most frequently used for concentrate drying, al-
though facilities for substitution of oil are usually provided. One report
culates that for a plant yielding 91,000 metric tons of refined copper per
year, the drying heat from fossil fuels would be equivalent to 17,200 kilo-
calories per hour of dryer operation (2).
Electricity is used for conveyors and mechanical operation of a dryer.
The report cited above estimates 2700 kilowatt-hours for the same size
plant (2).
5. Waste Streams - Dust generated by a drying operation would be of the
same composition as the input concentrate. A foreign plant using a multiple-
hearth roaster for drying reports particulate emissions of 0.05 percent of
the weight of the feed. No data for domestic plants have been reported.
Small quantities of organic materials in the concentrate could be
decomposed or volatilized in the drying operation, but no data have been
reported. Emissions of metallic fumes or oxides of sulfur are unlikely.
6. Control Technology - Dust from a drying operation frequently consists of
the fine particles present in the ore, and their collection is complicated by
the ready condensation of moisture in the warm effluent. If a dryer is
installed at a concentrator plant, the best control is to remove the dust by
wet scrubbing and return it to the final stages of the flotation process. If
a multiple-hearth roaster is used for drying, balloon flues or other particu-
late removal equipment may be modified to handle this wet dust. Bag filters
generally produce a caked product that must be redried; they are effective,
although troublesome, collectors (3,4).
41
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Quantities of the organic materials in the concentrate are believed to
be small enough that these materials require no separate treatment.
7. EPA Source Classification Code - 3-03-005-06
8. References -
1. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc., New York. 1967.
2. Background Information for New Source Performance Standards:
Primary Copper, Zinc, and Lead Smelters. Volume I, Proposed
Standards. EPA-450/2-74-002a. U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina. October 1974.
3. Jones, H.R. Pollution Control in the Nonferrous Metals Industry.
Noyes Data Corporation. Park Ridge, New Jersey. 1972.
4. Systems Study for Control of Emissions Primary Nonferrous Smelting
Industry. Arthur G. McKee & Co. for U.S. DHEW. June 1969.
42
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PRIMARY COPPER PRODUCTION PROCESS NO. 6
Reverberatory Smelting
1. Function - Copper smelting is the process of removing from a roasted or
dried ore concentrate much of its iron and some undesirable impurities,
leaving a molten mixture that can be processed efficiently by a copper con-
verter. This is most often accomplished with a reverberatory furnace. It
may, however, be accomplished by other methods (see Process No's. 7, 8, and
11).
Reverberatory smelting, the oldest of the copper smelting processes now
in use, is little different now than when it was first practiced in 1879. It
is in use at 11 of the 16 smelters in this country, in one or two modifica-
tions, described as either "deep bath" or "dry hearth." Some reverberatory
furnaces are very large, capable of accepting as much as 1800 metric tons of
material per charge (1).
The reverberatory furnace is a large, arch-roofed, horizontal chamber
into which ore concentrate and flux are charged. The term "reverberatory"
refers to the configuration of the flame which enters the chamber from one
end, reverberates off the roof and strikes the charge from above. As the
temperature of the charge increases, a complex series of reactions takes
place and the charge separates into fractions. One fraction is a gas, con-
sisting of S02 and volatiles, which mix into the combustion off-gases. Two
other fractions are molten liquids, the copper matte and slag, which are not
soluble in each other and therefore separate into layers.
The matte layer consists primarily of copper and iron sulfides and small
quantities of molten copper metal, which are mutually soluble. Since copper
has a weak chemical affinity for oxygen, very little copper oxide is formed
and almost all of the copper in the charge accumulates in the matte layer.
Iron, on the other hand, combines readily with oxygen to form iron oxides,
which in turn react with silica flux to form iron silicates. These compounds,
plus the calcium, magnesium, and aluminum minerals that were present in the
concentrate, form a lighter-density slag that floats on top of the matte.
Any sulfur in the charge that is left over from the slag- and matte-forming
reactions reacts with additional oxygen to form S02 gas.
The charge to the reverberatory furnace is proportioned so that the
resulting matte typically contains 40 to 45 percent copper and 25 to 30
percent each of iron and sulfur (2). The matte contains most of the heavy
elements present in the charge, practically all the gold and silver, and part
of the arsenic and antimony. Some of the arsenic, selenium, and other trace
elements form volatile compounds and are carried away in the gas stream.
Slag is drained periodically from a skimming bay at one end of the
reverberatory furnace. Matte is also withdrawn periodically through tap
holes in the lower furnace wall. Off-gas from the furnace is usually sent
through waste heat boilers to recover a portion of the excess energy.
43
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2. Input Materials - The primary input material is the roasted or dried
concentrate, not much different from the concentrate received from the mill.
Slags from the converter and anode furnace are added for reprocessing, as are
flue dusts from dust collection equipment throughout the smelter. Precipi-
tates from hydrometallurgical operations or materials from refinery process-
ing may be added at this step. At some smelters, impure scrap copper is re-
processed as part of the change.
Flux normally consists of sand high in silica content, and usually
limestone to make the slag more fluid. Sometimes "direct smelting ore" is
used, which adds both fluxing material and additional copper.
Composition of one charge to a reverberatory furnace in Arizona is re-
ported as follows in Table 16.
TABLE 16. COMPOSITION OF CHARGE TO A
REVERBERATORY FURNACE (1)
Ore concentrate
Converter slag
Hydrometallurgical precipitate
Flue dusts
Silica flux
Limestone flux
65%
25%
2%
1%
1%
6%
This charge produced molten materials of which 47 percent was matte and
53 percent was slag.
3. Operating Conditions - When possible, the concentrate is charged into
the furnace while still hot from the roaster (400°C or more). Converter slag
is charged as a liquid (1100°C approximately). Other materials are usually
charged at ambient temperatures. The reverberatory furnace usually heats the
mixed charge to at least 1000°C before the matte forms and separates; tem-
peratures up to 1300°C have been reported (3). All operations are at or near
atmospheric pressure.
4. Utilities - It is estimated that 90 percent of the energy requirements
for a smelting operation is consumed in the reverberatory furnace (4). It is
reported that 18 billion kilowatt-hours of energy was used in domestic copper
smelters in 1973 (4). Consumption of energy by this process is very high;
it is usually supplied in the form of natural gas, but pulverized coal or fue"
oil can be used. It is estimated that 500,000 kilocalories of heat is re-
quired to smelt 1 metric ton of concentrate if the charge is preheated by a
roasting operation. If the charge is not preheated, an additional 390,000
kilocalories is required (5). These values give credit for steam generated
by waste heat boilers, which are almost always installed with a reverbera-
tory furnace. The reverberatory furnace is in itself thermally inefficient,
using more than 4 times the heat theoretically required (6).
Noncontact cooling water is used by copper smelters primarily for the
protection of equipment auxiliary to the roaster, converter, and reverbera-
tory furnace. Data that allocate this cooling load specifically to each
process are not available. Reported data indicate that the total cooling
44
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water consumption for smelting operations can vary from 4000 to 61,000 liters
per metric ton of copper product.
Contact cooling water is used at four smelters to granulate the slag
from the reverberatory furnace. One smelter uses 1.7 million liters of
water per day for this purpose (2).
5. Haste Streams - It is reported that 20 to 45 percent of the sulfur that
enters with the ore concentrate is emitted by the reverberatory furnace as
S02 (3,7,8). Although most smelter operators have attempted to make opera-
tional changes to reduce this quantity, no recent data are available. The
gas is released as a dilute stream of variable composition, reported as being
from 0.5 to 2.5 weight percent S02 (3,8,9,10,11,12). Other constituents in
the exit gas are shown in Table 18, for unroasted and roasted concentrate
feeds. The volume of this gas is very large since it consists primarily of
the combustion gases from the heating fuels. Temperature of the exit gases
may reach 1150° to 1200°C (10).
Between 14 and 40 kilograms of particulate matter is emitted in this
gas stream per metric ton of copper matte produced (8,11,13,14). One analysis
of the particulates showed 24 percent copper and concentrations of other
elements as shown in Table 17.
TABLE 17. ANALYSIS OF PARTICULATES EMITTED FROM
A REVERBERATORY FURNACE (15)
Zinc
Cadmium
Manganese
Chromium
Nickel
Mercury
mg/1
44,000
310
100
45
35
2.5
Other investigations indicate that most of the volatilized arsenic,
selenium, lead, antimony, cadmium, chromium, and zinc emissions will be
generated in the reverberatory furnace (10,11,14,16,17,18).
Fugitive dust is generated in this process as materials are loaded into
the furnace, but no quantities have been reported.
The only liquid waste from this process is the run-off from slag granu-
lation. Three complete analyses are shown in Table 19. Liquid waste is
most often generated as the overflow from a pond into which the molten slag
is dumped. Since the pond is an open body of usually hot water, subject to
rainfall and evaporation, quantity and composition of the overflow may be
highly variable.
One copper smelter is situated close to a market for the furnace slag it
produces; for all the others, slag constitutes a large quantity of solid
45
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TABLE 18. COMPOSITION OF REVERBERATORY FURNACE
EXHAUST GASES (12)
Component
Carbon dioxide
Nitrogen
Oxygen
Water
Sulfur dioxide
Green feed,
% weight
8.4
69.3
0.25 - 1.0
18.8
1.5 - 2.5
Calcined feed,
% weight
10.2
71.0
0.25 - 1.0
17.7
0.6
46
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TABLE 19. EFFLUENTS FROM SLAG GRANULATION (16)
(mg/1)
Parameter
pH
TDS
TSS
so4=
CN-
As
Cd
Cu
Fe
Pb
Hg
Ni
Se
Te
Zn
Oil and grease
Plant 103
7.7
140.
6.8
62.
0.005
3.7
0.001
0.12
0.04
0.04
0.0001
0.001
0.001
0.001
0.44
Plant 110
8.1
3800.
151.
310.
0.050
0.048
0.001
0.05
0.03
0.070
0.0001
0.06
0.54
0.023
0.0
Plant 102
6.4-7.6
0.030
5.70
0.042
0.604
340.
7.4
0.0001
0.16
0.040
0.100
36.
0.02
47
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waste, as much as 3000 kilograms per metric ton of copper produced (15).
Table 20 gives an analysis of trace elements found in a reverberatory furnace
slag. The bulk of the slag is a mixture of iron silicates, as shown also in
Table 20.
6. Control Technology - Gases from the reverberatory furnace pass through a
waste heat boiler and then through an electrostatic precipitator for particu-
late removal. The gases may pass through spray collectors or balloon flues
before entering the ESP units. The degree of particulate removal ranges from
50 to 99.9 percent. Particulates collected are recycled into the metallur-
gical process, normally as part of the reverberatory furnace charge, but
accumulation of trace elements causes some flue dusts to be discharged or
processed separately. Quantities and their disposition are not reported.
At present, there is virtually no demonstrated economic method for con-
trol of the S02 emissions from reverberatory shelters. One smelter con-
structed a plant to absorb the S02 from this stream in dimethylaniline and
regenerate it as a concentrated stream for further processing, but it is not
now operating. One Canadian smelter uses an ammonia absorption process on
some smelter streams, but this system is not in use domestically. Other
scrubbing solutions, containing compounds of zinc and aluminum, are used on
smelter gases in Japan. Scrubbers using lime or limestone, with and without
magnesium addition, are being used on sulfur-containing flue gases from coal-
fired boilers in the United States, and might be adopted for use in U.S.
smelters, as has been done in Japan. Another absorption process based on
sodium sulfite-bisulfite is being tested.
An alternate method of controlling S02 emissions is to increase the con-
centration of the off-gas to a level sufficient for sulfuric acid production.
Such a strategy has been successfully implemented in a number of Japanese
furnaces of conventional design and operation. Methods include fuel-rich or
oxygen-enriched combustion, use of preheated secondary air in order to achieve
rapid smelting and sulfur release, use of high grade concentrates, instrument
controlled combustion and feeding for steady level of operation, or simply
tighter construction and leak control. One Japanese smelter achieves high S02
concentrations by blending the reverberatory off-gas with the exhaust from a
continuous furnace that combines the functions of roasting, smelting, and
converting. At another Japanese smelter, the reverberatory exhaust is blended
with the converter off-gas and scrubbed with a magnesium hydroxide slurry,
forming magnesium sulfite, which can be decomposed by calcination to MgO and
concentrated S02 (19).
Of the four smelters that practice slag granulation, one reports no
wastewater from this source since the rate of evaporation at this location
necessitates a continuous water make-up to the quenching pond. The other
three smelters mix the water from slag granulation with other wastes (2,20).
48
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TABLE 20. GENERAL RANGE OF REVERBERATORY FURNACE
SLAG COMPOSITION
Compound
or element
FeO
Si02
CaO
MgO
A1203
Copper
Sulfur
Composition,
percent weight
34 to 40
35 to 40
3 to 7
0.5 to 3
4.5 to 10
0.4 to 0.7
1.0 to 1.5
Trace elements
Zinc
Magnanese
Antimony
Lead
Chromium
Selenium
Nickel
Cadmium
Mercury
Arsenic
Tellurium
Cobalt
—A
Parts per million
Approximately 7800
Approximately 450
Approximately 400
Approximately 100
Approximately 100
Approximately 20
Approximately 25
Approximately 10
Less than 1.0
Trace
Trace
Trace
49
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Granulated slag is usually a coarse-grained material of low to medium
density, usually discarded near the smelter. A small amount may find a
market for use as road fill or concrete aggregate. Crushed slag that has not
been granulated also finds a small market for these same purposes. Most slag
is not granulated, but is simply poured out and allowed to solidify. There
is no easy way to reclaim the slag dumping areas, and there are no published
reports on how this could be done. It is generally assumed that the poten-
tial of secondary water pollution from slag dumps is less than that from mine
spoil or tailings beds.
7. EPA Source Classification Code - 3-03-005-03
8. References -
1. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc., New York. 1967.
2. Hallowell, J.B., et al. Water Pollution Control in the Primary
Nonferrous Metals Industry - Volume I. Copper, Zinc, and Lead
Industries. EPA-R2-73-274a. U.S. Environmental Protection Agency,
Washington, D.C. September 1973.
3. Background Information for New Source Performance Standards: Pri-
mary Copper, Zinc, and Lead Smelters. Volume I, Proposed Standards.
EPA-450/2-74-002a. U.S. Environmental Protection Agency, Research
Triangle Park, North Carolina. October 1974.
4. Rejer, M.E., and D.H. Larson. Study of Industrial Uses of Energy
Relative to Environmental Effects. U.S. Environmental Protection
Agency. Research Triangle Park, North Carolina. July 1974.
5. Metallurgy Processing in 1974, Mining Congress Journal. February
1975.
6. Treilhard, D.6. Copper-State of the Art, Chemical Engineering
Journal. April 1975. *
7. Halley, J.H., and B.E. McNay. Current Smelting Systems and Their
Relation to Air Pollution. Arther G. McKee and Company, San
Francisco, California 35224. September 1970.
8. Jones, H.R. Pollution Control in the Nonferrous Metals Industry.
Noyes Data Corporation. Park Ridge, New Jersey. 1972.
9. Compilation and Analysis of Design and Operation Parameters for
Emission Control Studies. Pacific Environmental Services, Inc.
(Individual draft reports).
10. Measurement of Sulfur Dioxide, Particulate, and Trace Elements in
Copper Smelter Converter and Roaster/Reverberatory Gas Streams.
EPA 650/2-74-111. U.S. Environmental Protection Agency, Washington,
D.C. October 1974.
50
-------
11. Statnick, R.M. Measurement of Sulfur Dioxide, Particulate, and
Trace Elements in Copper Smelter, Converter and Roaster/Reverbera-
tory Gas Streams. PB-238 095. U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina. October 1974.
12. Systems Study for Control of Emissions Primary Nonferrous Smelting
Industry. Arthur G. McKee & Co. for U.S. DHEW. June 1969.
13. Vandegrift, A.E., L.J. Shannon, P.G., Gorman, E.W. Lawless, E.E.
Sallee, and M. Reichel. Particulate Pollutant System Study - Mass
Emissions, Volumes 1, 2, and 3. PB-203 128, PB-203 522, and PB-203
521. U.S. Environmental Protection Agency, Durham, North
Carolina. May 1971.
14. Trace Pollutant Emissions from the Processing of Metallic Ores.
PEDCo Environmental Specialists, Inc. August 1974.
15. Assessment of Industrial Waste Practices in the Metal Smelting and
Refining Industry - Volume II Primary and Secondary Nonferrous
Smelting and Refining (Draft). Calspan Corporation, Buffalo, New
York. April 1975.
16. Development Document for Interim Final Effluent Limitations Guide-
lines and Proposed New Source Performance Standards for the Primary
Copper Smelting Subcategory and the Primary Copper Refining Sub-
category of the Copper Segment of the Nonferrous Metals Manufac-
turing Point Source Category. EPA 440/1-75/032-b. U.S. Environ-
mental Protection Agency, Washington, D.C. February 1975.
17. Davis, W.E. National Inventory of Sources and Emissions: Copper,
Selenium, and Zinc. PB-210 679, PB-210 678, and PB-210 677. U.S.
Environmental Protection Agency, Research Triangle Park, North
Carolina. May 1972.
18. Phillips, A.J. The World's Most Complex Metallurgy (Copper, Lead,
and Zinc). Transactions of the Metallurgical Society of AIME.
Volume 224: pp. 657-668. August 1962.
19. S02 Control for the Primary Copper Smelter Reverberatory Furnace,
Pacific Environmental Services, Inc. EPA Draft Report. April
1977.
20. Assessment of the Adequacy of Pollution Control Technology for
Energy Conserving Manufacturing Process Options. Industry Assess-
ment Report on the Primary Copper Industry. Arthur D. Little, Inc.
Draft. October 1974.
51
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PRIMARY COPPER PRODUCTION PROCESS NO. 7
Electric Smelting
1. Function - Copper smelting is the process of removing from an ore
concentrate a portion of its iron and sulfur content in order to produce a
molten mixture that can be treated efficiently in subsequent processing.
Smelting requires only the application of heat to produce matte and slag from
a charge of minerals. Three other smelting methods are used (Process No's.
6, 8, and 11). In electric furnace smelting, heat is supplied by electricity.
Electric furnaces for copper smelting are similar to those used in other
metallurgical industries. Three electric furnace installations in the United
States are used for copper smelting. Capacities are up to 1350 metric tons
of total charge per day.
2. Input Materials - The principal input is copper ore concentrates pro-
cessed or blended to a suitable composition. Various fluxing materials are
also required. The charge materials are similar to those outlined for a
reverberatory furnace (Process No. 6).
Electric smelting requires the use of carbon electrodes to conduct
electric current into the layer of slag. Various types of carbon electrodes
can be used. These electrodes are consumed during operation. In one U.S.
smelter, a proprietary paste carbon mixture is consumed at a rate of 2.5
kilograms per metric ton of charge (1).
3. Operating Conditions - The charge is usually heated to temperatures
between 1000° and 1300°C, and the electric furnace is operated at a small
negative pressure (2). Electric furnaces are normally enclosed in a large
building.
4. Utilities - When hot concentrate is fed from a roasting process, elec-
tric energy is consumed at a rate of 605 kilowatt-hours per metric ton of
total feed (1). Use of cold feed requires 990 kilowattrhours per metric
ton of concentrate (3). No direct combustion of fuel takes place in electric
smelting.
The furnace must be cooled to protect some of the components from high
temperatures. Cooling is done partially by infiltration of air into the
furnace, but some external cooling is also required. Either water or air can
be used, the quantity depending on furnace design. Infiltration of air is
also required to ensure complete oxidation of liberated sulfur. Operators of
one electric smelter report that T10 cubic meters per minute of air is cir-
culated each second to cool a furnace of 51,000 KVA transformer capacity (4).
5- Waste Streams - SOg in the gas emitted from an electric furnace is more
highly concentrated and temperatures are lower than in emissions from a
reverberatory furnace. SOz concentration can range from 3 to 8 percent (3).
Within limits this can be adjusted to make the gas suitable for sulfuric acid
production. The electric furnace may produce small amounts of hydrogen gas
and carbon monoxide, but sufficient air infiltrates to oxidize these combus-
52
-------
tible materials. Very small amounts of hydrocarbons released from the
electrode compounds will also burn.
Because of the lower gas volumes and more uniform gas flow, emissions of
particulate matter would be expected to be lower than with a reverberatory
furnace; no published estimates are available. Particulate composition would
be about the same as from a reverberatory furnace (Process No. 6).
Slags and wastewaters from slag granulation would be similar to those of
the reverberatory furnace, although more complete removal of copper and
sulfur compounds from electric furnace slags is likely.
6. Control Technology - The three operating electric smelters in this country
use the gases from the furnaces for sulfuric acid manufacture. In each case
the gas stream is first combined with that from another furnace, such as a
fluidized roaster or converter. Acid manufacture is the best available
technology for S02 removal from electric furnaces, since the sulfur content
is high enough for that application.
Control of the slag as a solid waste, or lack of controls, is described
in reference to the reverberatory furnace (Process No. 6).
The small waste water stream from slag granulation is invariably mixed
with other streams for treatment.
7. EPA Source Classification Code - 3-03-005-03
8. References -
1. Hallowell, J.B. et al. Water Pollution Control in the Primary
Nonferrous Metals Industry - Volume I. Copper, Zinc, and Lead
Industries. EPA-R2-73-274a. U.S. Environmental Protection Agency,
Washington, D.C. September 1973.
2. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc., New York. 1967.
3. Background Information for New Source Performance Standards:
Primary Copper, Zinc, and Lead Smelters. Volume I, Proposed
Standards. EPA-450/2-74-002a. U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina. October 1974.
4. Cole, R.C. Inspiration's Copper Smelter Facilities. Mining
Congress Journal. October 1973. p. 22-32.
53
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PRIMARY COPPER PRODUCTION PROCESS NO. 8
Flash Smelting
1. Function - Copper smelting is the process of removing from an ore
concentrate a portion of its iron and sulfur content in order to produce a
molten mixture that can be treated efficiently by a copper converter. Until
about 25 years ago, only two batch-type smelting processes were available,
both inefficient in energy consumption (see Process No's. 6 and 7). Since
that time, a continuous flash smelting process has been developed. This
process performs the smelting function at a much higher thermal efficiency
while producing a continuous, more easily controlled stream of flue gas, with
a high SOz content (1).
In flash smelting, ore concentrates are injected along with flux and
preheated air into a combustion chamber. Part of the sulfur of the concen-
trate burns in fa "flash" combustion while the particles are falling through
the chamber. The heat from this combustion maintains smelting temperature.
Matte and slag form in the chamber and separate into layers as in a rever-
beratory furnace. The matte is sent to a conventional converter for further
processing, and the slag, which contains too much copper to discard, is also
further processed (see Process No. 12).
One smelter in the United States is operating an Outokumpu flash smelt-
ing unit that was developed in Finland. This version is in extensive use in
several other countries. Another flash smelter design (INCO), using pure
oxygen, is operating in Canada.
2. Input Materials - Copper concentrates especially tailored for flash
smelting are the primary input. Not all concentrates are suitable for this
process. The concentrates must be finely pulverized (50 percent minus 200
mesh) (2), and must contain very low concentrations of lead, zinc, and other
volatile metals. They must have a fairly high sulfur-to-copper ratio, and
thus are not high-grade concentrates. The concentrates are not preroasted,
unless they contain considerable arsenic, but must be dried. Precipitates
from hydrometallurgical operations cannot normally be handled by a flash
smelter.
Flux in the form of silica sand or crushed rock must be prepared in a
separate milling process to 80 percent through 14 mesh (2) and must also be
dried. High grade "direct smelting" concentrates can be substituted if
available.
3. Operating Conditions - Temperature in the flash chamber is maintained at
approximately 1100°C (1). Pressure is approximately atmospheric.
4. Utilities - Fuel consumption in the Outokumpu flash smelter is only
about two-thirds of that required by a reverberatory furnace in equivalent
production (2,3). Except for startup or abnormal operations, fuel is re-
quired only to preheat the combustion air. This is reported as 7,560,000
kilocalories per hour for copper production of 100,000 metric tons per year
(2). Any fossil fuel can be used.
54
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Natural gas or oil is used to heat the furnace to startup temperature.
Oil can also be used, if required, to maintain smelting temperatures with
some concentrates.
Electrical power is used to operate feed and air injection equipment as
well as the complex instrumentation this process requires. An estimate of
600 kilowatt-hours for a 91,000 metric ton per year copper plant has been
reported (4).
5. Waste Streams - Flash smelting removes a large percentage of the sulfur
from the concentrate. From 50 to 80 percent is converted to S02, which
leaves as a stream of 10 to 20 percent concentration. In Finland the con-
centrates are blended to produce a 14 percent S02 concentration, which is
ideal for a suitably-designed sulfuric acid plant (5).
Particulates in the gas stream are expected to equal about 6 to 7
percent of the feed, which is about the same as in the reverberatory furnace.
Composition should be about the same as that of effluent from a reverberatory
furnace, except that content of volatile metals should be lower since they
are lower in the feedstock. Care is taken to keep zinc and lead to a minimum
in the concentrates, since they tend to plate out within the flash chamber.
There are no solid or liquid wastes from flash smelting. The slag is
discharged to waste from the electric furnace slag treatment process (Process
No. 12).
6- Control Technology - An important objective in development of the flash
smelting process was sale of the sulfur. There was a good market for sul-
furic acid near the Finnish smelter (5); continuous and stable production of
S02 made acid production most efficient. Flash smelting therefore was not
developed with production of copper as the sole consideration.
It is possible, for reasons of energy economy, that flash smelters will
be built in this country where there is no local market for sulfur compounds.
The best currently available technology for control of S02 emissions would
still be sulfuric acid production, even if the acid were then neutralized and
discarded. Wet scrubbing would be an expensive, although satisfactory,
alternative. The flash smelter in this country uses the gas for acid manu-
facture.
Complete removal of particulates is required for sulfuric acid manufac-
ture, and recovered dusts would be blended back into the flash smelter feed.
Cyclones, balloon flues, electrostatic precipitators, and wet scrubbers
afford satisfactory methods for removal.
7. EPA Source Classification Code - 3-03-005-03
55
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8. References -
1. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc., New York. 1967.
2. Background Information for New Source Performance Standards:
Primary Copper, Zinc, and Lead Smelters. Volume I, Proposed
Standards. EPA-450/2-74-002a. U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina. October 1974.
3. Metallurgy Processing in 1974. Mining Congress Journal, February
1975.
4. Personnal Communication with Mr. Paterson. El ken - Spigerverket
a/s, New York, New York.
5. Treilhard, D.G. Copper-State of the Art. Engineering/Mining
Journal. April 1973.
56
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PRIMARY COPPER PRODUCTION PROCESS NO. 9
Peirce-Smith Converting
1. Function - A copper converter produces crude blister copper metal from
the matte that is formed in the smelting process. The Peirce-Smith converter
is the type most often used by copper producers in this country. See also
Process No. 10 for an alternate converting method.
Matte is a molten mixture containing copper, iron, and sulfur. In the
converter, a flux is added to the matte and compressed air is blown into the
mixture through a series of openings called tuyeres. The remaining sulfur is
oxidized to S02 and leaves with the flue gases. The iron forms into a slag
that is returned to the smelting process. The blister copper is removed for
further processing.
2. Input Materials - Matte from the smelting process is the principal in-
put. Scrap copper being recycled is also introduced at this step, as is
scrap produced within the smelter from spills or ladle "skulls," and mate-
rials from other processes with high concentrations of metallic copper. Flux
used in the converter is sand or crushed rock with a high silica content.
Sulfur is added if necessary to maintain the proper ratio of copper to sulfur.
Table 21 shows an average charge and product distribution from one
copper converter.
3. Operating Conditions - To ensure that a slag of proper composition is
formed and separated from the molten copper, converter temperatures are
carefully controlled at 1175° to 1200°C (1,2). The converter operates at
atmospheric pressure.
4. Utilities - The converting process itself consumes no fuel, since oxidation
of the remaining sulfur furnishes enough heat to keep the mixture at the
proper temperature. Any excess heat is removed by addition of cold copper
scrap. The proper quantity of sulfur is obtained by carefully controlling the
previous smelting operation. However, considerable quantities of fuel are
required to reheat a cold converter, especially if it has been retired from
the campaign for repairs.
Electricity is used to rotate the converter to discharge the slag and
product.
Compressed air is required for oxidation of sulfur and iron. No data are
reported on the required quantities.
A small amount of cooling water is used for noncontact cooling of some of
the converter sections and auxiliaries.
5. Waste Streams - The converter emits about 120 kilograms of particulate
matte per metric ton of copper produced (3,4,5,6). Tables 22 and 23 provide
data on converter dust from some Arizona smelters, and Table 24 gives an
analysis of particulates from a smelter in Nevada.
57
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TABLE 2V. MATERIAL BALANCE ON CONVERTERS -
SMELTER IN ARIZONA (1)
percent, weight
Material
Input
Output
Reverberatory matte
Silica
Scrap and brass, etc.
Reverts
Sulfur
Blister copper
Slag
Sulfur Dioxide
Flue dust
78
13
4
4
0.5
28
67
2
3
58
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TABLE 22. COMPOSITION OF CONVERTER DUST (7)
Component
Cu
Fe
Pb
Bi
F
Sb
As
Se
Si
Mg
Mo
Al
°2
Cl
Te
S
Ca
Percent, weight
10 - 19.0
10 - 20.0
0.83 - 2.5
0.61
nil
nil
0.04 - 0.6
0.03 - 0.5
5.0 - 15.0
0.57
0.08
0.4 - 3.60
21.0
nil
0.005 - 0.01
12.0
1.0
59
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TABLE 23. PARTICLE SIZE DISTRIBUTION IN CONVERTER DUST (7)
Mesh
-48 to + 65
-65 to + 100
-100 to + 150
-150 to + 200
-200 to + 270
-270 to + 325
-325 to + 32 microns
-32 microns to + 25 microns
-25 microns
Percentj
weight
0.5
1.5
2.5
3.5
5.0
5.0
16.6
55.6
9.8
TABLE 24. PARTICULATE EMISSIONS ANALYSIS AT STACK OUTLET FOR
REVERBERATORY FURNACE AND CONVERTER9
Metal
Arsenic
Cadmium
Copper
Selenium
Zinc
Chromium
Manganese
Nickel
Vanadium
Boron
Barium
Mercury
Lead
Total
Percent,
weiqht
0.038
0.008
5.6
0.014
1.1
0.006
0.023
0.0045
0.0023
0.12
0.03
0.0007
0.065
7.0115
Stack test data (5/13/71).
60
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Peirce-Smith converters are designed to be partially covered by a hood
that catches the S02 and participate emissions from the converter, but also
draws in a considerable amount of uncontaminated air. By stoichiometric
calculations, the S02 content in converter gases varies from 15 to 20 percent
at various stages in the processing of a charge, but when diluted by the
excess air the resulting mixture contains from 4 to 10 percent S02
(2,4,5,7,8,9). Some converters may produce gas with S02 content as low as 2
percent (5,7). Because the mouth of the Peirce-Smith converter is rotated
from under the hood when flux is added and when slag and copper are poured
out, local losses of S02, particulate, and fume occur during those periods.
Table 25 gives the composition of converter off-gas from an Arizona
smelter.
Fugitive dust and fumes are generated in considerable quantities in a
converting operation. Measurement of the quantities has not been possible to
date.
There are no solid or liquid wastes from the converter process.
6. Control Technology - Gases from a Peirce-Smith converter are sometimes
combined with the gas stream from a smelting or roasting process for particle
removal and further treatment. The converter S02 stream is usually controlled
through sulfuric acid plants.
Technology for control of a mixed gas stream including converter off-gas
is discussed with the various smelting and roasting processes (Process No's.
3, 4, 6, 7, and 8).
7. EPA Source Classification Code - 3-03-005-04
8. References -
1. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc., New York. 1967.
2. Background Information for New Source Performance Standards:
Primary Copper, Zinc, and Lead Smelters. Volume I, Proposed
Standards. EPA-450/2-74-002a. U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina. October 1974.
3. Vandegrift, A.E., L.J. Shannon, P.6. Gorman, E.W. Lawless, E.E.
Sallee, and M. Reichel. Particulate Pollutant System Study - Mass
Emissions, Volumes 1, 2 and 3. PB-203 128, PB-203 522, and
PB-203 521. U.S. Environmental Protection Agency, Durham, North
Carolina. May 1971.
4. High, M.D. and M.E. Lukey. Exhaust Gases from Combustion and
Industrial Processes. PB-204 861. U.S. Environmental Protection
Agency, Durham, North Carolina. October 1971.
61
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TABLE 25. CONVERTER OFF-GAS COMPOSITION (7,11)
Component
Percent by volume
°2
so2
so3
Dust
80
11
6.9 - 9.8
0.05 - 0.07
0.0053 g/lit max.
62
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5. Jones, H.R. Pollution Control in the Nonferrous Metals Industry.
Noyes Data Corporation, Park Ridge, New Jersey. 1972.
6. Statnick, R.M. Measurement of Sulfur Dioxide, Particulate and
Trace Elements in Copper Smelter, Converter and Roaster/Rever-
beratory Gas Streams. PB-238 095. U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina. October 1974.
7. Compilation and Analysis of Design and Operation Parameters for
Emission Control Studies. Pacific Environmental Services, Inc.
(Individual draft reports). November 1975.
8. Control of Sulfur Oxide Emissions in Copper, Lead, and Zinc Smelt-
ing. Bureau of Mines Information Circular 8527, 1971.
9. Halley, J.H. and B.E. McNay. Current Smelting Systems and Their
Relation to Air Pollution. Arthur G. McKee and Company, San
Francisco, California 35224. September 1970.
10. Systems Study for Control of Emissions Primary Nonferrous Smelting
Industry. Arthur G. McKee & Co. for U.S. Department of HE&W. June
1969.
63
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PRIMARY COPPER PRODUCTION
Hoboken Converting
PROCESS NO. 10
1. Function - The Hoboken converter is one type of furnace used to produce
crude blister copper from the matte formed in the smelting process. Its func-
tion is identical to that of the Peirce-Smith converter (Process No. 9). The
principal difference is that the flue that removes the gas from the converter
is an integral part of the converter construction instead of being a hood
mounted above it. This design minimizes infiltration of uncontaminated air,
should minimize local losses of S02 from the converter mouth, and allows pro-
duction of a gas with a higher and more uniform S02 content.
One smelter in this country uses Hoboken converters; however, optimal
operation has not been achieved. They are used at several smelters in Europe
and South America. The potential operating advantages of this design have
not been clearly documented, and there have been no test programs to character-
ize the level of fugitive emissions.
2. Input Materials - These are the same as for Peirce-Smith converters, con-
sisting largely of matte from the smelters, plus silica flux and cold copper
scrap.
3. Operating Conditions - These are also the same as for a Peirce-Smith
yp_
it, 1
unit, 1200°C at atmospheric pressure.
4. Utilities - These are also the same as for Peirce-Smith. No supplemental
fuel is required for the converting process.
5. Waste Streams - Since particulate matter is generated by the air being
blown through the converter charge, particulate emissions should be com-
parable to those of the Peirce-Smith.
The S02 content of the gas stream from this converter could be at least
8 percent if three or more converters are operating, and may reach as high
as 13 percent. It is calculated that with oxygen enrichment, the S02 con-
centration could be increased to 10 to 14 percent (1,2).
There are no solid or liquid wastes.
6. Control Technology - Production of S02 by the Hoboken converter is inter-
mittent, but a battery of several of the converters will produce a stream
sufficiently constant in rate to allow the gas to be used for sulfuric acid
manufacture. This has been demonstrated by a smelter in Poland in which this
is the normal operating procedure. The one domestic smelter using Hoboken
equipment mixes the gas stream with the emissions from an electric smelter,
and after particulate removal, uses the combined stream for sulfuric acid
manufacture. At the Polish smelter separate fans remove the gases from each
converter, and fugitive emissions are minimized by increasing the draft to
each converter and creating negative pressure during such operations as
charging and pouring. At the U.S. smelter with Hobokens, the converter ex-
hausts are connected in parallel and such individual control is not possible.
64
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7. EPA Source Classification Code - 3-03-005-04
8. References -
1. Cole, R.C. Inspiration's Copper Smelter Facilities. Mining
Congress Journal. October 1974. pp. 22-32.
2. Background Information for New Source Performance Standards:
Primary Copper, Zinc, and Lead Smelters. Volume I, Proposed
Standards. EPA-450/2-74-002a. U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina. October 1974.
65
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PRIMARY COPPER PRODUCTION PROCESS NO. 11
Noranda
1. Function - Noranda is one design of a continuous smelter, which in a
single furnace combines most of the functions of roasting, smelting, and
converting. This process approaches a one-step method of producing copper
metal from ore concentrates. A Noranda installation is operating in Utah.
One other unit is operated by the developer in Canada.
The Noranda furnace is a horizontal cylinder about 21 meters long, into
which a mixture of concentrate and flux is continuously fed, along with fuel
and oxygen. The furnace is fired from both end walls. The mixture reacts to
form copper, matte, and slag, which separate into layers as in the batch smelting
processes. Additional oxygen-enriched air is blown through 63 side-mounted
tuyeres into the matte layer, forming blister copper, which collects in a third
liquid layer below the matte. Slag and copper matte are intermittently tapped
from the furnace. Noranda slag contains 3 to 8 percent copper, and is pro-
cessed to recover the copper content (see Process No. 13).
Noranda does not completely eliminate the use of the copper converter.
Blister copper from Noranda contains from 1.5 to 2.0 percent sulfur, and is
usually batch treated in a standard converter to remove additional sulfur
prior to fire refining. If the concentrate contains considerable impurity
elements, the developer-recommends that Noranda be used as a smelter only,
to produce a high-grade matte for separate conversion to blister copper
(1,2,3). This is the mode of operation at the one U.S. facility (4).
2. Input Materials - As operated at the U.S. installation, the charge
consists of smelter reverts, and a pelletized mix of copper concentrate,
reactor slag concentrate, copper precipitators, and flux.
3. Operating Conditions - This process operates at approximately atmospheric
pressure. Temperatures in the U.S. installation are higher than 1200°C,
which is the slag temperature (4).
4. Utilities - A principal advantage of Noranda is its efficient utiliza-
tion of fuel. Heat losses during transfer of concentrate from the roaster to
the reverberatory furnace are suppressed, as well as heat losses during the
transfer of the matte from the reverberatory furnace to the converter. In
addition, the net heat of oxidation is used for smelting. Fuel is only re-
quired to augment the fuel value of the sulfur and iron in the concentrate.
With oxygen enrichment, about 440,000 kilocalories of heat is required to
produce a metric ton of copper, which is about 22 percent of that required
by a reverberatory furnace. The domestic Noranda reactor uses a gas-oil
burner at one end and an oxygen-fuel burner at the other (1,2,3,4).
The fuel consumption reported above was based upon enrichment of combus-
tion air to 50 percent oxygen, and of tuyere air to 35 percent. Although
oxygen enrichment is not necessary with the Noranda process, best economy
requires its use.
66
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Small amounts of electricity are used for feed injection and auxiliary
services (1,2).
5. Haste Streams - With oxygen enrichment, gas from the furnaces contains
16 to 20 percent S02 at the offtakes. These units, together with the con-
verters, supply an 8 percent S02 stream to the acid plants (4).
Particulate emission rates have not been reported, but are probably
dependent on the size distribution in the feed. Since feed is continuously
injected at high velocity into a moving gas stream, particulate loadings
could be substantial.
There are not solid or liquid wastes from this process. Slag is trans-
ferred to Process No. 13 for further treatment (1,2,4).
6. Control Technology - At the operating U.S. smelter, the particulates are
collected in a waste heat boiler connected to the furnace hood, and in hot
cyclones and finally an ESP unit. The dust is either pelletized or directly
recycled. The gas is further cleaned and used for sulfuric acid production.
7. EPA Source Classification Code - None
8. References -
1. Environmental Considerations of Selected Energy Conserving Manufac-
turing Process Options, Volume XIV, EPA 600/7-76-034n. U.S.
Environmental Protection Agency, Cincinnati, Ohio. December 1976.
2. Advertising literature and letter, Noranda Mines Limited, Toranto.
3. Mills, L.S., G.D. Hallett, and C.J. Hewman. Design and Operation
of the Noranda Process Continuous Smelter. Extractive Metallurgy
to Copper. AIME. 1976.
4. Dayton, Stan. Utah Copper and the $280 Million Investment in Clean
Air. Engineering and Mining Journal. April 1979.
67
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PRIMARY COPPER PRODUCTION PROCESS NO. 12
Electric Furnace Slag Treatment
1. Function - Slag from a flash or continuous smelter contains too much
copper to discard economically. Also, in flash or continuous smelting there
is no way to recycle the slag formed in the converters and the anode furnaces.
Among the various ways to reclaim the copper content of these slags is the
use of an electric furnace. This is the procedure being used with the flash
smelter now operating in the United States. Slag can also be treated by
flotation, as described in Process No. 13.
In electric furnace slag treatment, coke is used to reduce sulfates and
metallic copper and to reconstitute the copper as a sulfide. A molten matte
is formed that can be recycled to a converter for production of copper metal;
the process leaves a slag low in copper content that can be discarded.
2. Input Materials - The slags are similar to those from the reverberatory
furnace (Process No. 6), the copper converters (Process No's. 9 and 10), and
the fire refining furnaces (Process No. 18), except with higher copper con-
tent. Flash smelting slags contain 1 to 2 percent copper, and slags from
Noranda, 10 to 12 percent copper.
Carbon electrodes, as described for electric smelting (Process No. 7)
are consumed. Reported usage is 1.5 kilograms per metric ton of slag pro-
cessed (1). Iron pyrites are usually added to the furnace charge to adjust
sulfur content. The coke is similar to that used in electric furnace opera-
tions in other industries. High grade coal can be substituted. No data on
quantities consumed are available.
3. Operating Conditions - Temperatures are maintained somewhere in the
range of 1200° to 1300°C (2). Pressures are approximately atmospheric.
4. Utilities - Electric consumption is reported as 221 kilowatt-hours per
metric ton of slag treated (1). There is no reported use of cooling water or
air in the slag treatment furnace.
5. Waste Streams - Since this is a reducing furnace, it is expected that
S02 in the exit gases is negligible. Carbon monoxide and particulates are
present, however, including metallic fumes of zinc and other elements, and
there will be some hydrogen if moisture is introduced into the furnace along
with the coke. There are no reported analyses of these gases. Gas volumes
are relatively small.
No liquids are discharged from this process.
Slag discharged from this treatment is primarily iron silicate, similar
to the slag from the reverberatory furnace (Process No. 6). No analyses are
available.
68
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6. Control Technology - In other industries, gases from reducing electric
furnaces are passed through a wet scrubber for cooling and particulate removal,
and are then either burned for fuel, incinerated with no recovery of the
heat, or discharged through a stack. Venturi scrubbers are normally used to
cool the gas quickly and minimize the possibility of explosions. This is a
preferred design. Combustion of hot gases prior to particulate removal is
sometimes practiced; the gases are then cooled with water sprays and passed
through an ESP for particulate removal.
Particulates will probably be sluiced into a tailings pond and discarded,
since they should be low in volume. They may contain quantities of trace
elements, however, and their proper disposal warrants further study.
Slags from the slag treatment furnace are discarded, with or without
granulation, as outlined for the reverberatory furnace (Process No. 6).
7. EPA Source Classification Code - None
8. References -
1. Personal Communication with Mr. Paterson Elken - Spigerverket a/s.
New York, New York.
2. Background Information for New Source Performance Standards:
Primary Copper, Zinc, and Lead Smelters. Volume I, Proposed
Standards. EPA-450/2-74-002a. U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina. October 1974.
69
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PRIMARY COPPER PRODUCTION PROCESS NO. 13
Flotation Slag Treatment
1. Function - Slags from a flash or continuous smelter contain a signifi-
cant amount of copper, which can be reclaimed either by electric furnace
treatment, as described in Process No. 12, or by slow cooling, crushing, and
flotation. The flotation method will be used to treat slags from the Noranda
installation now beginning operation in this country (1).
As a molten slag cools, each constituent in the slag will solidify
sequentially in an order determined by the freezing temperatures of the
individual minerals. If the slag is cooled very slowly, crystals of rela-
tively pure materials will form that are large enough to be separated by
conventional concentrating procedures. Copper in the slag will form either
as small particles of metallic copper or as crystals of copper-iron sulfide,
both held in a matrix primarily of iron silicate.
Details of the existing U.S. process have not been released. It is
believed, however, that molten slag from the Noranda furnace is to be trans-
ported while still molten to a series of deep covered pits, where over a
period of days, or perhaps weeks, the slag will cool by natural conduction
through the surrounding earth. When fully cooled, the slag will be reclaimed
by conventional mining techniques, crushed, and concentrated. The resulting
concentrate will be processed in smelting furnaces in the same manner as an
ore concentrate (2).
2. Input Materials - Slag from the Noranda furnace, containing 10 to 12
percent copper, is the only known input.
To reclaim the cooled slag, explosives and concentrating reagents will
be used, as described in Process No's. 1 and 2.
3. Operating Conditions - Slag is withdrawn from the smelting furnace at
approximately 1200°C. The slag will cool to approximately ambient tempera-
ture after an extended period of time.
4. Utilities - It is believed that the molten slag will be transported to
the slag cooling area in specially-designed vehicles, requiring diesel fuel.
Whether or not slag must be heated before being added to the cooling pits has
not been announced.
Reclamation of the slag will require the same utilities used for mining
and concentrating, consisting of electrical energy for crushing and large
quantities of water for concentrating.
5. Waste Streams - A large proportion of the slag will eventually become a
waste in the form of tailings whose chemical composition is similar to slag
from a reverberatory furnace (Process No. 6). Additional wastes will be
created such as airborne particulates from mining and crushing and waterborne
contaminants from concentrating, as described in Process No's. 1 and 2.
70
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6. Control Technology - The flotation treatment of high copper content
furnace slags does not appear to introduce additional requirements for
environmental control beyond those needed for control of mining and con-
centrating wastes. In the existing U.S. application of this process, it is
not known whether special facilities will be built to reclaim the cooled
slag, or whether existing mining and concentrating facilities will be adapted
to this purpose.
7. EPA Source Classification Code - None
8. References -
1. Process Announcement. Kennecott Copper Corporation.
2. Environmental Considerations of Selected Energy Conserving Manufac-
turing Process Options: Vol. XIV, Primary Copper Industry Report.
EPA-600/7-76-034n. U.S. Environmental Protection Agency, Cin-
cinnati, Ohio. December 1976.
71
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PRIMARY COPPER PRODUCTION PROCESS NO. 14
Contact Sulfuric Acid Plant
1. Function - An acid plant catalytically oxidizes S02 gas to sulfur
trioxide, and absorbs it in water to form sulfuric acid. S02 gas may also be
controlled by DMA absorption (Process No. 15) or elemental sulfur production
(Process No. 16).
Contact sulfuric acid plants are continuous steady-state processing
units that are operated in other industries using S02 made by burning ele-
mental sulfur. They may be used with waste S02 streams if the gas is suf-
ficiently concentrated, is supplied at a reasonably uniform rate, and is free
from impurities.
The heart of a sulfuric acid plant is a fixed bed of vanadium pentoxide
or other special catalyst which oxidizes the S02.. All other components of
the plant are auxiliary to this catalytic converter. The other components
clean and dry the stream of gas, mix the proper amount of oxygen with it
(unless sufficient oxygen is present), preheat the gas to reaction tempera-
ture, and remove the heat produced by the oxidation.
The plant incorporates one or two absorbers to contact the gas with
water to form the acid. If only one absorber is provided, this is described
as a single-contact sulfuric acid plant. If two are provided, the second is
placed between stages of the converter, and this is a double-contact plant.
The second absorber allows a larger proportion of the S02 to be converted
into acid, and thus removes more S02 from the gas stream if the initial
concentration is high.
Thirteen of the copper smelters in this country operate contact sulfuric
acid plants to treat all or part of the gases from the metallurgical opera-
tions.
2. Input Materials - Most contact sulfuric acid plants operate most effi-
ciently with a constant gas stream that contains 12 to 15 percent S02-
Performance almost as good can be achieved in plants that are designed for 7
to 10 percent S02 content. The ability of a plant to convert most of the S02
to sulfuric acid declines either as gas streams become weaker in S02 or as
the flow rate or concentration becomes less consistent. A concentration lower
than 4 percent S02 is extremely inefficient, since sufficient catalyst tem-
perature cannot be maintained (1). Certain modifications of the process,
which add heat by combustion of fuel, can provide better conversion at low
S02 concentrations.
The gas that enters the catalyst bed must be cleaned of all particulate
matter, be almost completely dried, and contain no gases or fumes that act as
poisons to the catalyst. The acid plant is always supplied with special
scrubbers to remove final traces of objectionable materials. Table 26
provides information on the acceptable limits of these impurities.
72
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TABLE 26. ESTIMATED MAXIMUM IMPURITY LIMITS FOR METALLURGICAL
OFF-GASES USED TO MANUFACTURE SULFURIC ACID (1)
Approximate limit, (mg/Nm3)a
Substance
Chlorides, as Cl
Fluorides, as F
Arsenic, as AS203
Lead, as Pb
Mercury, as Hg
Selenium, as Se
Total Solids
H2S04 Mist, as 100% acid
Water, as H20
Acid Plant Inlet
1.2
0.25
1.2C
1.2
0.25
50C
1.2
50
-
Gas Purification System Inletb
125d
25e
200
200
2.5f
100
10009
-
400 x 103
Notes:
(a) Basis: dry off-gas stream containing 7% sulfur dioxide.
(b) For a typical gas purification system with prior coarse dust removal.
(c) Can be objectionable in product acid.
(d) Must be reduced to 6 if stainless steel is used.
(e) Can be increased to 500 if silica products in scrubbing towers are
replaced by carbon; must be reduced if stainless steel'is used.
(f) Can be increased to 5-12 if lead ducts and precipitator bottoms
are not used.
(g) Can usually be increased to 5000-10,000 if weak acid settling tanks
are used.
73
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Clean water is required to react with the $03 to form sulfuric acid. It
may be necessary to deionize the water in a special ion exchange system in
order to avoid excessive corrosion or to meet acid quality specifications.
Steam condensate may also be used.
3. Operating Conditions - The catalyst bed operates properly only if
temperatures are maintained between 450° and 475°C. Pressures do not usually
exceed 2 kilograms per square centimeter. The plants are usually not enclosed
in a building.
4- Utilities - Noncontact cooling water is required. At one plant producing
1500 metric tons of acid per day, about 12 million liters of water is
required each day (2).
A small amount of electricity is required for pumps and blowers. This
may be generated on-site in some cases, where recovery of waste heat is
maximized.
In certain patented modifications, heat from combustion of natural gas
is used to provide better efficiency at low S02 concentrations. Natural gas
or oil is also required to heat any acid plant to operating temperature
following a shutdown.
5. Waste Streams - Single-contact sulfuric acid plants using weak gas
streams can at best absorb only 96 to 98 percent of the S02 fed to them. The
remaining quantity passes through to the atmosphere. Efficiencies as low as
60 percent have been reported (3). In addition, it is likely that some S02
may be vented without treatment in some smelters since an acid plant cannot
instantly change the flow to match the intermittent production typical in the
copper industry. Of gas that is treated, it is reported that most absorber
exit gases contain from 0.01 to 0.5 percent S02 (4). Total flow rates may
range from 34,000 to 68,000 normal cubic meters per hour (5).
Double-contact acid plants provide a higher percentage of S02 removal if
they are fed gas with a higher S02 content. Efficiencies higher than 99
percent have been reported. Exit gas S02 concentration is still usually
within the same range as shown above, although one recently developed process
claims stack emissions of less than 0.005 percent S02 (6).
At a Japanese smelter the exit gas from the acid plant is routed to a
gypsum plant and the S02 concentration is less than 0.002 percent at the
stack exit (7).
In sulfuric acid plants, it is difficult to prevent some loss of S03, in
the form of a fine mist of sulfuric acid, with the absorber exit gases. This
is usually 0.02 to 0.04 kilogram of 503 per metric ton of 100 percent acid
produced.
The scrubbing columns that clean the waste gas stream create off-grade
weak acid that cannot be sold. The amount is estimated as 4 to 8 liters for
each 10 cubic meters of gas treated (8). Table 27 provides typical analyses
for acid plant blowdown.
74
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TABLE 27. RAW WASTE CHARACTERIZATION: ACID PLANT SLOWDOWN (2)
en
Parameter
pH
IDS
TSS
S04=
Cn-
As
Cd
Cu
Fe
Pb
Hg
Ni
Se
Te
Zn
Oil and Grease
Flow, TO6
Production
Flow/ Prod
Units
PH
kg/metric ton
kg/metric ton
kg/metric ton
kg/metric ton
kg/metric ton
kg/metric ton
kg/metric ton
kg/metr-ic ton
kg/metric ton
kg/metric ton
kg/metric ton
kg/metric ton
kg/metric ton
kg/metric ton
kg/metric ton
I/day
metric ton/daj'
kg/metric ton
Plant 1
2.0-2.5
[0.99]a
0.0000
0.044
0.0002
0.0001
0.0014
0.0051
0.0000
0. 0000
0.0001
0.0000
0.0017
0.0000
0.147
311. (62)
2,400.
Plant 2
1.8
78.5
0.102
7.&
0.0000
0.129
0.0014
0.0018
0.0015
0.0142
0.0000
0.0000
0.0000
0.0000
0.215
—
4.16
528. (264)
15,800,
Plant 3
2.0
410.
3.74
64.0
0.0024
0.004
0.0276
[188.2]
0.1116
0.2501
0.0002
0.0030
0.0268
--
0.436
0.0
10.1
655. (393)
25,700.
Average
2.0
244.
1.92
36.0
0.0008
0.059
0.0097
0.0010
0.0382
0.0898
0.0001
0.0010
0.0090
0.0000
0.218
0.0
—
—
14,700.
Bracketed values not used in averaging computation.
-------
In this industry, most participate matter from gas cleaning equipment is
recycled in dry form or as a water slurry back to the metallurgical processes.
The small quantities of particulate removed by the acid scrubbing operations,
however, are mixed with a stream of weak sulfuric acid and cannot readily be
recycled. They are discharged with the acid plant blowdown.
In some sections of the country it is difficult to sell the product
acid, even for less than the cost of manufacture. Therefore, it may be less
expensive to neutralize and discard the acid than to absorb the costs of
shipment to a distant user. Thus, the product acid can itself become a waste
stream.
An acid plant does not produce solid wastes directly, but the gypsum
formed in neutralization of acid can constitute a significant solid waste.
6. Control Technology - In this country the S02 in the tail gas from the
sulfuric acid plant is not controlled. When S02 emissions are large, the
best control may be to increase operating efficiency by adding additional
catalyst stages or by adding heating equipment to maintain proper catalyst
temperature. Changes in the metallurgical operations to produce a stream of
higher S02 concentration at a more uniform rate are also good controls, if
this is possible. Scrubbing of the acid plant tail gas for final S02 absorp-
tion is practiced in Japan to achieve very low levels.
Mist eliminators in the form of packed columns or impingement metal
screens can minimize acid mist emissions. Manufacturers claim elimination of
all but 35 to 70 milligrams of mist per cubic meter of gas, and the units at
times perform better. To prevent formation of plumes of mist during periods
of abnormal operations, however, electrostatic precipitators are often used.
Better regulation of feed rate and quality also minimizes acid loss.
As frequently happens in this industry, acid plant blowdown is sometimes
mixed with other waters for treatment or recycle. Table 28 lists the
practices of existing smelter acid plants in 1970-71. The practices outlined
for Plants 1 and 3 appear to describe the best available control technology,
since by recycle to hot ESP units the heavy metals content of this waste
partially returns to the metallurgical processing.
If volumes of strong acid must be neutralized, treatment with limestone
followed by more precise pH adjustment with lime, and discharge to a pond for
in-perpetuity storage of the resulting gypsum is the only tested and econom-
ical method of disposal.
7. EPA Source Classification Code - None
8. References -
1. Jones, H.R. Pollution Control in the Nonferrous Metals Industry.
Noyes Data Corporation. Park Ridge, New Jersey. 1972.
76
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TABLE 28, ACID PLANT SLOWDOWN CONTROL AND TREATMENT PRACTICES (4)
Plant
Code
1
2
3
4
5
6
7
8
9
10
11
Discharge
0
0
Oa
0
0
0
0
0
oa
3.4 1 /sec
50-190 I/sec*
Control and/or treatment practice
Slowdown neutralized with ammonia and used
to precondition converter gases prior to
hot ESP. No discharge.
2/3 of blowdown to reverb brick flue spray
chamber for cooling reverb gases, other 1/3
used to precondition converter gases prior
to hot ESP. Any excess is solar evaporated
on slag dump. No discharge.
Blowdown from packed tower used in open
tower blowdown to clarifier. One-half
recycled to packed tower, other half to
two-stage ammonia neutralization facility.
Then 2.2 I/sec to converter hot ESP for gas
preconditioning and 0.6 T/sec to hot ESP
for gas preconditioning (joins 0.6 T/sec
DMA purge). No discharge.
Blowdown to tailings pond. Pond water
recirculated to mill concentrator. No
discharge.
Blowdown from new scrubbers and mist pre-
cipitators to recycle and tailings thickener
underflow. No discharge.
Blowdown used in mill concentrator circuit.
No discharge.
Blowdown to settling pond and either re-
cycled or wasted. No discharge.
Blowdown to acid ponds and reused in copper
precipitation leach facility. No discharge.
Blowdown currently used to blend fluid-bed
roaster feed. Anticipate closed circuit,
but will eventually send to proposed treat-
ment facility.
Blov/down to lime pond, then to tailings pond.
Eventual (8 km of ponds) discharge.
Blowdown to go to new treatment facility
with subsequent discharge.
Anticipated, practice under construction.
77
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2. Hallowell, J.B. et al. Water Pollution Control in the Primary
Nonferrous Metals Industry - Volume I. Copper, Zinc, and Lead
Industries. EPA-R2-73-274a. U.S. Environmental Protection Agency.
Washington, D.C. September 1973.
3. Confidential information from EPA.
4. Control of Sulfur Oxide Emissions in Copper, Lead, and Zinc Smelt-
ing. Bureau of Mines Information Circular 8527, 1971.
5. Systems Study for Control of Emissions Primary Nonferrous Smelting
Industry. Arthur G. McKee & Co. for U.S. DHEW, June 1969.
6. Browder, T.J. Advancements and Improvements in the Sulfuric Acid
Industry. Tim J. Browder Co. San Marino, California.
7. Evaluation of the Status of Pollution Control and Process Tech-
nology - Japanese Primary Nonferrous Metals Industry. EPA Contract
No. 68-02-1375, Task 36. PEDCo Environmental, Inc. Cincinnati,
Ohio. July 1977.
8. Vandegrift, A.E., L.J. Shannon, P.6. Gormena, E.W. Lawless, E.E.
Sallee, and M. Reichel. Particulate Pollutant System Study - Mass
Emissions, Volumes 1, 2, and 3. PB-203 128, PB-203 522, and
PB-203 521. U.S. Environmental Protection Agency. Durham, North
Carolina. May 1971.
78
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PRIMARY COPPER PRODUCTION PROCESS NO. 15
DMA SOp Absorption
!• Function - The DMA absorption process scrubs S02 from a stream of gas,
then releases the S02 as a concentrated stream. The principal applications
have been to concentrate streams too weak for efficient use in sulfuric acid
manufacture, to absorb surges in waste gas flow that could not otherwise be
handled by the acid plants, and to manufacture liquified S02 for sale.
Sulfuric acid (Process No. 14) or elemental sulfur production (Process No.
16) may also be used to control S02 emissions.
Waste gases, after first being cleaned of particulate matter and dried,
pass through a scrubber where most of the S02 is absorbed by dimethyl aniline
(DMA). The gases are then scrubbed with sodium carbonate to remove the
remaining S02, then with weak sulfuric acid to reclaim the DMA in the gas
stream. The gases are then released to a stack. In a series of chemical
operations, the DMA is recovered for recycling, and the S02 is recovered as
dry, 100 percent S02 which is compressed, cooled, and stored as a liquid.
The DMA system has the advantage of being relatively insensitive to
changes in S02 concentration of the gas stream, and to changes in gas flow
rate. If part of a waste gas stream is sent directly to an acid plant at a
constant rate, the DMA can handle the remaining gas, which may be of variable
composition with uneven flow. The concentrated S02 from the DMA plant can be
bled back into the acid plant stream as required to maintain a constant and
higher S02 concentration. Thus the acid plant operates more efficiently and
more of the S02 in the waste gas stream is recovered.
Three smelters in this country have constructed DMA absorption plants,
designed to handle waste streams that contain from 1.5 to 10 percent S02 (1).
Efficiencies of up to 99 percent removal from a 5 percent gas stream have been
reported (2). Plant capacities are as high as 180 metric tons of liquid S02
per day.
2. Input Materials - Waste gas containing S02 is the principal input.
Designers of the process do not recommend its use on streams weaker than 2 to
3 percent S0£. The gases must be cleaned and dried as described for the
contact sulfuric acid plant (Process No. 14).
A constant feed of soda ash (sodium carbonate) is required for this
process. One smelter reports use of 16 kilograms per metric ton of S02
produced.
Sulfuric acid, 98 percent concentration, is used for drying and scrub-
bing. The same smelter reports consumption of 18 kilograms per metric ton of
S02 produced, as well as a small loss of the expensive dimethyl am" line, 0.5
kilogram per ton of S02.
3. Operating Conditions - Feed gas must be cooled to ambient temperatures
prior to DMA absorption. Temperature in some of the regeneration steps may
reach 150°C. Pressures in the waste gas stream are near atmospheric, and may
79
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approach 3 kilograms per square centimeter in parts of the regeneration
system.
4. Utilities - Electricity is normally used to drive pumps and blowers.
The process is efficient in energy conversion; treatment of a 5 percent S02
gas stream requires about 160 kilowatt-hours per metric ton of SC>2 produced (2),
Steam is required at a rate of 1.0 to 1.5 tons per ton of S02 produced
(2). Noncontact cooling water is required in the amount of 1250 liters per
metric ton of S02 (3). A small amount of process water is needed to com-
pensate for purge and evaporation.
5. Waste Streams - Exit gas contains 0.05 to 0.3 percent S02 and no partic-
ulate matter. Temperatures are approximately ambient. The DMA process adds
only an insignificant quantity of carbon dioxide to the stream, and very
small amounts of DMA or its decomposition products may escape the third stage
of scrubbing.
The waste gas stream may carry with it an entrained mist of dilute
sulfuric acid from the third stage.
This process requires scrubbing of the gas stream in a weak sulfuric
acid column and thus may produce a liquid waste blowdown stream similar to
that from a sulfuric acid plant. Normally, however, the same scrubber is
used to treat gases that feed both the acid plant and DMA system.
A liquid waste, continuously purged from the DMA process, consists of
water, sodium sulfite or bisulfite, and sodium sulfate. The quantity is
about 18 kilograms per metric ton of S02 produced, when treating gas with 5
percent S02 content. The stream typically contains about 4.5 percent dis-
solved solids, 25 milligrams DMA per liter, and 18 milligrams suspended
solids per liter, with a pH around 5.8 (1).
The process produces no solid wastes.
6. Control Technology - Following DMA absorption, further treatment of the
waste gas stream for S02 removal is not normally required. An electrostatic
precipitator is usually installed to eliminate acid mist carryover.
If a separate dryer is used for DMA gas treatment, disposition of the
blowdown would be the same as that for the sulfuric acid plant blowdown.
Best available control technology is to neutralize this stream and recycle it
as coolant to a hot ESP unit, thus returning the metals content to metal-
lurgical processing.
The purge stream from the DMA process is the only waste of this character
generated by the primary copper industry. It is a clear stream with a BOD
and a COD and is quite concentrated with nonrecoverable minerals. Each of
the three operating DMA installations handles the purge stream differently.
One adds it to the concentrator circuits; one mixes it with the acid plant
blowdown, which is in turn sent to a hot ESP unit; the third uses activated
carbon to absorb the DMA content, then uses it as part of a fluid-bed wet
80
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feed blending, which returns it directly to the metallurgical processing.
This last alternative may be the best control technology, with or without
activated carbon absorption. The sodium may then combine into the slag where
it will not increase alkali content of the concentrator water, thus reducing
potential of recycle. An excess of sodium salts may plate out in a hot ESP
unit. Further study to establish the best disposition of this stream is
indicated.
7. EPA Source Classification Code - None
8. References -
1. Background Information for New Source Performance Standards:
Primary Copper, Zinc, and Lead Smelters. Volume I, Proposed
Standards. EPA-450/2-74-002a. U.S. Environmental Protection
Agency. Research Triangle Park, North Carolina. October 1974.
2. Fleming, Edward P. and Fitt, T. Cleon. Liquid Sulfur Dioxide from
Waste Smelter Gases. I&EC. Vol. 42, No. 11. pp. 2253-2258.
November 1950.
3. Halley, J.H. and McNay, B.E. Current Smelting Systems and Their
Relation to Air Pollution. Arthur G. McKee and Company. San
Francisco. September 1970.
81
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PRIMARY COPPER PRODUCTION PROCESS NO. 16
Elemental Sulfur Production
1. Function - Sulfur dioxide from a waste stream can be converted into
elemental sulfur by one of several methods. Other S02 removal methods are
sulfuric acid production (Process No. 14) and DMA absorption (Process No.
15). Sulfur is easier to store than sulfuric acid and is less expensive to
transport. Although the market is also better than for acid, the sulfur now
produced by this process is not economically competitive with mined sulfur
from the Texas coast.
All variations of the process use high temperatures to oxidize methane
to carbon dioxide and water, while simultaneously reducing the S02 to sulfur.
All use special catalysts and are sophisticated multi-step processes, effi-
cient in energy utilization. Like the ammonia plants or oil refinery units
they resemble, sulfur plants are most efficient as large-capacity installa-
tions.
None of the smelters in this country now include sulfur production
facilities, although one plant is being constructed.
2. Input Materials - Gas must enter the process at constant flow rate and
composition. The gases must contain 5 to 7 percent S02 (1) and must be free
from particulate matter and metal-containing fumes.
Methane in the form of natural gas is added in the stoichiometric ratio
of 1 kilogram to each 8 kilograms of S02- Additional natural gas is required
as fuel.
3. Operating Conditions - Although temperatures and pressures differ in
the various process modifications, most operate between 1000° and 1500°C at
pressures less than 25 kilograms per square centimeter. One variation
requires 1250°C for proper equilibrium (2). The equipment is not normally
enclosed in a building.
4. Utilities - Natural gas fuel is assumed for most designs, and electricity
is required for pumps, blowers, and compressors. One variation incorporates
electrostatic precipitators as integral components, which require electric
power. No quantitative utility estimates have been reported.
Cooling water is required for portions of the process.
5. Waste Streams - All these processes claim removal of more than 90
percent of the S02 from the gas stream, and one claims up to 95 percent. The
waste gas stream can therefore be expected to contain no more than 0.7 percent
S02. Slight emissions of H2S gas may occur in some of the process variations.
No liquid wastes are expected from this process. The water formed by
the reaction normally escapes by evaporation into the waste gas stream.
This process produces no solid wastes.
82
-------
6. Control Technology - The only further control of the waste gases from
this process is wet scrubbing, as described in connection with the rever-
beratory furnace (Process No. 6).
7. EPA Source Classification Code - None
8. References -
1. Jones, H.R. Pollution Control in the Nonferrous Metals Industry*
Noyes Data Corporation, Park Ridge, New Jersey. 1972.
2. Fleming, E.P. and T.C. Fitt. High Purity Sulfur from Smelter
Gases. Industrial and Engineering Chemistry. Volume 42, No. 11.
March 1950. pp. 2249-2253.
v
83
-------
PRIMARY COPPER PRODUCTION PROCESS NO. 17
Arsenic Recovery
1. Function - Much of the arsenic present in a copper ore concentrate will
be volatilized in the roasting and smelting processes, and will appear as ar-
senic trioxide in the dusts collected from the electrostatic precipitators and
other particulate removal equipment. One smelter treats those dusts to extract
arsenic for sale. Since demand for arsenic as a commercial item is very small,
this one smelter satisfies much of the U.S. demand for this material. The
balance is met by imports.
The recovery process consists of placing the collected dusts in a
Godfrey roaster, a small special heated enclosure, in which they are heated
until the arsenic trioxide vaporizes. The vapors are condensed in chambers, and
are then resublimed and condensed to yield an arsenic trioxide product more than
99 percent pure. Arsenic metal is also occasionally produced by reducing the
oxide with carbon in an atmosphere deficient in oxygen (1).
All these operations are batch-type and are done on a small scale.
2. Input Materials - Flue dusts from multiple-hearth roasters and rever-
beratory furnaces are the principal input. Dusts of high arsenic content
from other smelters were also used at one time, but are no longer accepted by
this smelter. Flue dusts are charged into the furnace along with a small
amount of pyrite to minimize conversion to arsenites (1).
Charcoal in small quantity may be used for arsenic metal production.
3. Operating Conditions - Arsenic trioxide is assumed to be completely
vaporized from the dusts when the temperature reaches 650° to 700°C. It
recondenses in the cooling chambers at around 200°C (1). Atmospheric pres-
sures are used.
\
4- Utilities - Gas-fired burners are used to heat the charge, and non-
contact cooling water to assist in condensing. No quantities have been
reported.
Water is used to wash down dust and spills within the plant.
5. Waste Streams - Because there is no mechanical movement of material
within the Godfrey roaster, few particulates are generated during the opera-
tion. Fugitive dusts are generated during the handling of the dry materials.
The gas stream from the roaster contains carbon dioxide and water
vapor, and may contain small amounts of S02 and arsenic fumes. No analysis
has been reported.
A water waste is generated by daily washdown of the plant to remove
settled dusts from materials handling. Table 29 gives the analysis of this
water.
84
-------
TABLE 29. ANALYSIS OF ARSENIC PLANT WASHDOWN WATER (2)
Parameter
As
Cu
Zn
Pb
Cd
Hg
Se
Te
Ni
Fe
so4=
Cn-
Oil and grease
pH
Concentration
mg/1
310.
88.4
37.0
7.7
1.05
0.0003
0.04
0.43
0.75
9.4
340.
0.01
0.04
3.8 to 4.4
85
-------
No solid wastes are generated by this process.
6. Control Technology - Fugitive dust emissions in and from the plant
building are controlled by the use of fabric filter baghouses on ventilating
air streams.
Effluent process gas streams are currently routed through an electro-
static precipitator before being vented to a tall stack. After treatment for
arsenic removal, the remaining dusts are returned to the smelting furnace. In
the near future, a fabric filter will be installed to remove particulate from
the waste gas.
The washdown from this plant mixes with another waste stream and dis-
charges to a pond. Table 29 indicates that up to a kilogram of arsenic may
enter the pond each day from this source. The degree to which it becomes
soluble has not been reported.
7. EPA Source Classification Code - None
8. References -
1. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc. New York. 1967.
2. Development Document for Proposed Effluent Limitations Guidelines
and New Source Performance Standards for the Primary Copper, Lead,
and Zinc Segment of the Nonferrous Metals Manufacturing Point Source
Category (Draft). Contract No. 68-01-1518. U.S. Environmental
Protection Agency. Washington, D.C. December 1973.
86
-------
PRIMARY COPPER PRODUCTION PROCESS NO. 18
Fire Refining and Anode Casting
1 • Function - Impure or "blister" copper from the converters must be
refined to remove impurities. This is partially accomplished by fire re-
fining, which is the last major process that occurs at a copper smelter.
Blister copper is placed in a fire refining furnace, a flux is usually
added, and air is blown through the molten mixture. This blow oxidizes most
of the remaining sulfur, vaporizes some impurities and converts others into a
slag. The mixture is then "poled" with wooden logs or otherwise treated to
reduce the excess oxygen in the mixture. The copper is then poured into
molds and cooled with water sprays or by immersion in a tank of water. The
resulting anodes are sent to an electrolytic refinery for further processing.
A small percentage of the copper may be subjected to more complete fire
refining to produce ingots or special castings for direct sale. This fire
refined copper is used for manufacture of alloys and other special purposes,
and contains no impurities other than oxygen in significant amounts. Anode
copper is less completely refined, but is more than 99 percent pure. The
general range of analysis is shown in Table 30.
2. Input Materials - Copper from the converting operation (Process No's. 9
and 10) is the principal input, usually charged into the fire refining fur-
nace while still molten.
Various slag-forming fluxes may be added. These include silica sand and
sodium carbonate.
Wooden poles are still occasionally used for the reducing step of the
process. The wood decomposes when thrust into the molten copper, producing a
variety of carbonaceous products that remove oxygen from the mixture. Instead
of wood, most smelters now use hydrogen, natural, gas, or ammonia for reduction,
The casting molds are sprayed with a mold dressing of silica flour or
potassium alum to keep the castings from sticking (1).
3. Operating Conditions - Temperature in the furnace is around 1100°C.
Pressure is atmospheric.
4- Utilities - If molten blister copper is charged to the furnace, addi-
tional fuel is required only in small amounts. Gas or oil is used for
heating, or to melt the charge if cold feed is used. In a plant producing
91,000 metric tons of copper per year, fuel consumption for this process has
been estimated at 8600 kilocalories per hour of operation (1).
Compressed air is used to oxidize the molten mixture in the furnace. No
quantities have been reported.
87
-------
TABLE 30. GENERAL RANGE ANALYSIS OF ANODE COPPER3 (1)
Constituent
Copper
Oxygen
Sulfur
Arsenic
Antimony
Bismuth
Lead
Nickel
Selenium
Tellurium
Gold
Silver
Platinum
Palladium
Content, % weight
99.0-99.6
0.1-0.3
0.003-0.01
0.003-0.2
0.001-0.1
0.001-0.01
0.01-0.2
0.01-0.2
0.01-0.06
0.001-0.02
3. 4-102. 6b
68-3080b
N.A.
N.A.
Extremes omitted
g/metric ton
N.A. - not available
-------
Water is used for direct cooling of the casting machine and the copper
anodes. This is usually a recirculated stream or is reclaimed water from
combined sources. Quantities are shown in Table 31 for five smelters.
5. Waste Streams - Gases from the fire refining furnace may contain fumes of
zinc and cadmium (2). Concentration of S02 has been estimated at 0.38
kilogram per metric ton of copper treated (3). There are no recorded data
giving the quantity of this waste gas, but particulate loading has been re-
ported as 5-20 kilograms per metric ton of copper produced (4). Gas tempera-
ture is about 1000°C (5).
The water used for anode cooling is reported to pick up additional
amounts of arsenic, copper, and zinc, and also to pick up aluminum and chlo-
rides, probably from mold dressing compounds. Table 32 lists the data re-
ported for one anode cooling operation. The "net change" represents the
difference between inlet and outlet concentrations.
There are no solid wastes from this process. All slags are returned to
the metallurgical processing.
6. Control Technology - No control of waste gas from the fire refining
process is being exercised by any of the operating copper smelters. Appar-
ently it is assumed that this is one of the cleaner gas streams from pyro-
metallurgical operations because of the relative purity of the input copper.
Table 33 lists the controls of contact cooling water being practiced by
the domestic smelters. This list includes water used for cooling of both
anodes and blister copper direct from the converter.
7. EPA Source Classification Code - 303-005-05
8. References -
1. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc. New York. 1967.
2. Background Information for New Source Performance Standards:
Primary Copper, Zinc, and Lead Smelters. Volume I, Proposed
Standards. EPA-450/2-74-002a. U.S. Environmental Protection
Agency. Research Triangle Park, North Carolina. October 1974.
3. Jones, H.R. Pollution Control in the Nonferrous Metals Industry.
Noyes Data Corporation. Park Ridge, New Jersey. 1972.
4. Compilation of Air Pollutant Emission Factors. AP-42. U.S.
Environmental Protection Agency. Research Triangle Park, North
Carolina. March 1975.
89
-------
5. Ha11 owe!1, J.B. et al. Water Pollution Control in the Primary
Nonferrous Metals Industry - Volume I. Copper, Zinc, and Lead
Industries. EPA-R2-73-274a. U.S. Environmental Protection Agency.
Washington, D.C. September 1973.
6. Development Document for Interim Final Effluent Limitations Guide-
lines and Proposed New Source Performance Standards for the Primary
Copper Smelting Subcategory and the Primary Copper Refining Sub-
category of the Copper Segment of the Nonferrous Metals Manufac-
turing Point Source Category. EPA-440/l-74/032-b. U.S. Environ-
mental Protection Agency. Washington, D.C. February 1975.
90
-------
TABLE 31. WATER REQUIREMENTS FOR COPPER REFINERIES (5)
V^V -,' ---!"-— ,
Plant
A
B
C
D
E
Water intake, liters
per metric ton
of metal produced
4,000
9,000
13,000
3,000
6,000
j — - , ,_. ~ ... .^ ar
Water consumed
(Intake minus discharge),
liters per metric
ton of metal produced
4,000
700
1,200
1,900
0
TABLE 32. WASTE EFFLUENTS FROM ANODE COOLING WATER (6)
Parameter
Chloride
Aluminum
Arsenic
Copper
Zinc
Flow, 106
I/day
Production,
metric ton/day
Net change,
mg/1
8.7
0.12
0.01
8.53
0.25
0.95
265
Net loading
kg/day
7.8
0.11
0.01
8.07
0.24
kg/metric ton
0.029
0.0004
<0.0001
0.030
0.0009
Source: RAPP.
91
-------
TABLE 33. CONTACT COOLING WATER CONTROL AND TREATMENT PRACTICES (6)
Plant
code
1
2
3
4
5
6
7
8
9
10
11
12
Discharge
0
0
0
0
Intermit-
tent
0
0
0
0
0
0
5670 m3/day
Control and/or treatment practice
Anode casting: water in closed circuit with
cooling tower, cooling tower blowdown joins
blowdown from wire-bar casting cooling tower
blowdown, entire blowdown to side-stream
filter, anticipate total water recycle.
Anode casting: water directly reused in mill
concentrator circuit. No discharge.
Anode casting: water collected in mill tail-
ings thickener, all flow recycled (with some
evaporation) to mill concentrator. No dis-
charge.
Blister cake cooling: air cooled with some
water spray; spray water totally recycled
from cooling pond. No discharge.
Fire-refined (cathode) - shape casting: water
mostly recycled, with small intermittent
discharge.
Fire-refined casting: water to thickener,
overflow recycled. No discharge.
Anode casting: water in closed circuit with
cooling tower, blowdown to evaporation pond.
No discharge.
Anode casting: water in closed circuit with
cooling tower, blowdown reused in mill con-
centrator. No discharge.
Anode casting: water to tailings thickener,
reused in mill concentrator. No discharge.
Anode casting: water all used in mill con-
centrator circuit. No discharge.
Anode casting: water in closed circuit with
100 percent circulation. No discharge.
Anode casting: water collected in slag
settling pond, part is recirculated for
slag granulation 53,000 m3/day. Remainder
5700 m^/day discharged to tailings ponds.
Eventual (8 km of ponds) discharge.
92
-------
TABLE 33. (continued).
Plant
code
13
14
15
Discharge
18 I/sec
(125 I/sec,
45 min/day)
0
Control and/or treatment practice
Anode casting: once-through water, part used
for shot copper cooling, remainder discharged.
Shot copper cooling: Intermittent flow, all
discharged. Plan to treat water in proposed
treatment facility with anticipated discharge.
Blister cake cooling: water consumed during
spraying and air cooling. No discharge.
93
-------
PRIMARY COPPER PRODUCTION PROCESS NO. 19
Electrolytic Refining
1. Function - Although copper produced at a smelter contains less than
1 percent impurities, this is too much to meet most of today's quality
specifications. The electrolytic refinery reduces the impurities to approxi-
mately 0.05 percent.
The refining is done by passing a direct current of electricity through
two copper electrodes that are immersed in a bath of acidic copper sulfate
solution. The anode is a casting of impure copper from the smelter, and the
cathode is a "starting sheet" stripped from a previously refined block of
electrolytic copper. The electric current causes the copper to dissolve from
the anode and deposit at the cathode. Impurities either will not dissolve in
the electrolyte, or will not plate out at the cathode, so they collect either
as slimes in the bottom of the cell or as soluble ions in the electrolyte.
Fourteen electrolytic refineries are operating in the United States. Five
are located near a copper smelter, and the others are distant from smelters.
2. Input Materials - The principal input is the anode castings from copper
refining. About 85 percent of the anodes in use at any one time are directly
from the smelter. The remainder are made at the refinery by melting and re-
casting partially electrolyzed anodes.
The electrolyte is sulfuric acid, which is either fresh acid or acid
reclaimed from the electrolyte purification process (Process No. 20).
Various additives are used to ensure a smooth deposit at the cathode.
Chlorides are added to cause silver to precipitate into the slimes.
3. Operating Conditions - Electrolytic cells are normally maintained at
60° to 65°C (1).Pressures are atmospheric.
4- Utilities - Electric power is the only source of energy. Approximately
175 to 220 kilowatt-hours are required to produce a metric ton of
cathode copper (2). The direct current required for the cells is produced
within the refinery by rectifiers or motor-generator sets. Additional elec-
tricity is required for the auxiliary materials handling equipment.
Water is used for washing the cathodes as they are removed from the
cells. In most refineries, this is specially treated water, usually steam
condensate, since untreated water contains minerals that affect the quality
of the product. This same water is used for make-up to the electrolyte
system to replace that lost in purge and evaporation.
5. Haste Streams - The only pollution of the air by an electrolytic refinery
is a fine mist of sulfuric acid reported to be created near the electrodes.
Data on this source of pollution are not available.
94
-------
Most refineries reclaim the copper from impure solutions (see Process
No. 20), but two do not, and therefore create a substantial liquid waste
directly from the electrolytic cells. Table 34 gives- the range of composi-
tion of the electrolyte solution, along with the composition of the refined
copper and the slime that is recovered from the bottom of the cells.
Slime is periodically cleaned from the cells and processed for recovery
of the gold, silver, and other valuable elements (see Process No's. 22 and
24). Because this slime represents a product of considerable value to the
copper industry, procedures at most smelters are designed to place as much of
these valuable elements as possible into the anode copper.
In any plant that handles highly corrosive liquids in large quantities,
there are leakages, spills, and occasionally major discharges, frequently not
expected and normally not included in waste tabulations.
No solid wastes are produced by an electrolytic refinery.
6. Control Technology - Of the two refineries that do not reclaim the
impure electrolyte solution, one treats this stream separately by placing it
in a lined pond and allowing it to evaporate to dryness. Climatic conditions
at this site make this procedure workable. The other refinery follows a
practice often used in the copper industry and mixes the solution with other
wastes into a tailings pond, where lime is added to neutralize the acid.
This refinery is also in an arid section of the country. Both refineries
report no discharge into public waters. Ultimate disposal of the solids from
these evaporations has not been reported.
Most refineries have demonstrated an economic benefit from the reclama-
tion and partial recycle of spent electrolyte; this represents the best
available control technology (see Process No. 20).
There are usually no controls specifically designed to handle spills,
leakages, and accidental discharges of electrolyte.
7. EPA Source Classification Code - 303-005-05
8. References -
1. Development Document for Interim Final Effluent Limitations Guide-
lines and Proposed New Source Performance Standards for the Primary
Copper Smelting Subcategory and the Primary Copper Refining Sub-
category of the Copper Segment of the Nonferrous Metals Manufac-
turing Point Source Category. EPA 440/1-75/032-b. U.S. Environ-
mental Protection Agency. Washington, D.C. February 1975.
95
-------
TABLE 34. GENERAL RANGE ANALYSIS OF ELECTROLYTE, REFINED
COPPER, AND ANODE SLIME3 (2,3)
Constituent
Sul f uric acid
Copper
Oxygen
Sulfur
Arsenic
Antimony
Bi smuth
Lead
Nickel
Selenium
Tellurium
Gold
Silver
Platinum
Palladium
Iron
Electrolyte,
9/1
170-230
45-50
0.5-12
0.2-0.7
0.1-0.5
2.0-20.0
Refined copper,
% weight
99.95
0.03-0.05
0.001-0.002
0.0001-0.001
0.0002-0.001
0.00001-0.00002
0.002-0.0010
0.0001-0.002
0.0003-0.001
0.0001-0.0009
0.68-0.242b
1. 71-17. lb
tr.
tr.
tr.
Raw slime,
% weight
(dry basis)
20-40
2-6
0.5-4.0
0.5-5.0
tr.
2.0-15.0
0.1-2.0
1.0-20.0
0.5-8.0
1714-10286
34285-274283
N.A.
N.A.
0.1-0.2
Extremes omitted.
g/metric ton.
tr. = trace.
N.A. = Not available.
96
-------
2. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc. New York. 1967.
3. Hallowell, J.B. et al. Water Pollution Control in the Primary
Nonferrous Metals Industry - Volume I. Copper, Zinc, and Lead
Industries. EPA-R2-73-274a. U.S. Environmental Protection Agency.
Washington, D.C. September 1973.
97
-------
PRIMARY COPPER PRODUCTION PROCESS NO. 20
Electrolyte Purification
1. Function - In operation of the electrolytic cells in a refinery, certain
impurities become dissolved in the electrolyte solution. If a portion of the
electrolyte is not removed from the circulating stream, concentrations of
these impurities will become so high that they begin to deposit at the cathode
with the refined copper. In most cases, the purge stream is processed to
recover some of its constituents.
All but two of the refineries in this country remove the copper from the
purge stream. This is done in special "liberator" electrolytic cells that
use insoluble lead anodes and sheets of copper as cathodes. The copper and
frequently some of the impurities deposit on the cathode. The plates of
copper are returned to the metallurgical processing either within the refinery
or in the smelter, depending on quality. Some of the remaining impurities
collect in the liberator cells as a sludge.
A few refineries recover a portion of the sulfuric acid from the purge
stream by use of dialysis equipment. The dialyzers provide a partial separa-
tion of the acid and produce a stream in which impurities are more concen-
trated. The acid is returned to the electrolyte circulation.
Effluent from the liberator cells or the dialysis equipment may be
concentrated further by removing water in vacuum evaporators. Concentration
of the acid produces a sludge, which has a high concentration of nickel
sulfate and usually contains iron and zinc. This sludge can be filtered out,
and then part of the acid can be returned to the electrolyte system, or it
may be discarded or sold.
Various refineries may practice all, part, or none of these treatments.
Three refineries recover nickel. One refinery consumes all spent electrolyte
in an associated chemical operation (1).
2. Input Materials - The input is the purge stream from the recirculating
electrolyte. The range of analysis is given in Table 34 (Process No. 19).
This shows it to be a stream of warm, concentrated acidic copper sulfate
solution, also containing nickel, arsenic, antimony, and bismuth. Smaller
quantities of iron, cobalt, zinc, lead, selenium, tellurium, and other
elements are a).so found in the stream.
3. Operating Conditions - Temperatures are less than 100°C and pressures
are atmospheric, except in some evaporation operations (2).
4. Utilities - Electricity is used to drive pumps and mechanical equipment,
and to operate the liberator cells. Since the average concentration of salts
in the liberator electrolyte is much less than in the main electrolytic
cells, the liberator requires 2 to 5 times as much current to remove the same
amount of copper. Usage is reported as 350 to 700 kilowatt-hours per metric
ton (1).
98
-------
Steam may be required for vacuum production, and fossil fuels may be
used for direct-fired evaporation.
5. Waste Streams - The principal characteristic of the waste streams from
electrolyte treatment is that, combined, they must contain almost all the
arsenic, antimony, and bismuth that comes in with the anode copper (3). Some
of these elements may be returned to the smelter with liberator cathodes,
even though there is no way to dispose of them there. Examination of Table
30 (Process Mo. 18) shows that a ton of arsenic enters the electrolytic
refinery with as little as 500 tons of anodes, and the best analysis shown in
this table would provide a ton of arsenic waste for each 40,000 tons of
copper.
Some of the arsenic is known to escape from the second stage of the
liberator cells as arsine (AsHs) (4). This very poisonous gas can accumulate
to dangerous levels if the liberator cells are not well ventilated. Arsine
will slowly oxidize in the atmosphere to arsenic trioxide and water. Quan-
tities apparently have not been measured. This is also the only reference to
arsenic in a waste stream from this process.
Unless all of these elements are returned to the smelter with the
liberator cathodes, the arsenic, antimony, and bismuth must exit with a purge
of electrolyte acid. It appears that accumulation of these elements must
result in either continuous or occasional disposal of a quantity of "black
acid", regardless of the extent of electrolyte treatment employed.
In some refineries evaporated water from the electrolyte constitutes
another waste stream, which usually is mixed with volumes of steam condensate
and direct cooling water in barometric leg discharge devices. Table 35
provides an analysis from such a source.
No solid wastes are discharged from this process.
6. Control Technology - Arsine formed in the liberator cells can be readily
oxidized or can be scrubbed to form a liquid waste. Best control technology
cannot be evaluated unless the order of magnitude of the quantity being
released is known. If the amount is fairly large, it should be possible to
design an oxidation process that could recover this as dry arsenic trioxide.
If it is possible to sell or give away the black acid to the fertilizer
industry, as has been reported, the impurity elements would be transferred
into the gypsum ponds from phosphate rock treatment. This would eliminate
disposition in local tailings ponds, which are already loaded with metal ions
from other sources. The neutral to acidic nature of phosphate ponds may
cause a greater degree of precipitation of arsenic and antimony than would
occur in the alkaline water designed to precipitate copper. On the other
hand, phosphate ponds may already have a heavy load of radium, and are usually
located in an area of greater precipitation than copper smelters.
99
-------
TABLE 35. WASTE EFFLUENTS FROM NiS04 BAROMETRIC CONDENSER (1)
Parameter
PH
Alkalinity
COD
Total Solids
Dissolved Solids
Suspended Solids
Sulfate (as S)
Arsenic
Cadmium
Copper
Iron
Lead
Nickel
Zinc
Flow, 106
I/day
Production,
metric ton/day
Intake,
mg/1
6.5
90
750
21.080
21 ,060
18
1,722
<0.010
<0.20
<0.20
<0.50
<0.50
<0.50
<0.20
Discharge,
mg/1
6.6
450
24,000
24,000
18
1,060
<0.010
<0.20
<0.20
1.30
<0.50
<0.50
0.48
11.4
415
Net change,
mg/1
neg
2,920
2,920
neg
<1.3
<0.48
Net loading
kg/day
<15
<5.4
100
-------
For the effluent from a vacuum evaporator condenser, the best control
technology is to avoid overloading the evaporator. Because of the low
volatility of sulfuric acid and other components of this stream, evaporation
of the water should be easy if the evaporator is properly designed, instru-
mented, and operated.
7. EPA Source Classification Code - None
8. References -
1. Development Document for Interim Final Effluent Limitations Guide-
lines and Proposed New Source Performance Standards for the Primary
Copper Smelting Subcategory and the Primary Copper Refining Sub-
category of the Copper Segment of the Nonferrous Metals Manufac-
turing Point Source Category. EPA 440/1-74/032-b. U.S. Environ-
mental Protection Agency. Washington, D.C. February 1975.
2. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc. New York. 1967.
3. Hallowell, J.B. et al. Water Pollution Control in the Primary
Nonferrous Metals Industry - Volume I. Copper, Zinc, and Lead
Industries. EPA-R2-73-274a. U.S. Environmental Protection Agency.
Washington, D.C. September 1973.
4. Trace Pollutant Emissions from the Processing of Metallic Ores.
PEDCo-Environmental Specialists, Inc. August 1974.
101
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PRIMARY COPPER PRODUCTION PROCESS NO. 21
Melting and Casting Cathode Copper
1. Function - Refined copper from the electrolytic cells is melted and
recast into the shapes required by fabrication industries. There is usually
also a final adjustment of the oxygen content of the finished product.
Special equipment used for these operations ranges from direct-fired
reverberatory furnaces to continuous casting machines. Electric arc and
induction furnaces may be used to melt or hold the molten copper. The trend
in this process is toward continuous or semicontinuous equipment to provide
closer control of product quality and to minimize energy requirements.
2. Input Materials - The principal input is cathodes from the electrolytic
cells. These are washed free of electrolyte and slime prior to delivery to
this process.
Mold dressings such as bone ash may be used in some operations. For
production of certain grades of copper, special oils, graphite, and phospho-
rous-copper alloys may be added at various stages in the process.
Use of reverberatory furnaces for this process requires addition of a
flux and possibly a "poling" operation (1). This modification is comparable
to fire refining and anode casting (Process No. 18).
3. Operating Conditions - Depending on the process details, temperatures
range from 1150° to 1215°C (2). Pressures are atmospheric. Special reducing
atmospheres may be used in some operations. Open molds are usually cooled
with water sprays to around 150°C.
4. Utilities - Electricity or fossil fuel may be used for melting. The
newest electrical furnaces are reported to operate at high thermal effi- .
ciencies; power consumption is rated at 250 to 300 kilowatts for maintaining
a molten charge of 55 to 90 metric tons of copper in an electric arc furnace
(3).
Electricity is used to power materials handling and casting equipment.
Both contact and noncontact cooling waters are used to cool the casting
equipment and the cast shapes. One refinery reports a water usage of 320,000
1iters per day (4).
5- Haste Streams - Reverberatory furnaces, still occasionally used for
refined copper melting, produce a gaseous discharge to the atmosphere; the
quality of this emission has not been reported.
Table 36 provides the analysis of water used for cooling the refined
copper shapes at two refineries. Another report showed an increase in
chlorides of 58.6 grams per liter (3), but the origin of this ion was not
defined.
102
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TABLE 36. ANALYSIS OF WATER USED TO COOL REFINERY SHAPES (4)
(Concentrations in mg/1)
Parameter
pH
TDS
TSS
so4
As
Cd
Cu
Fe
Pb
Hg
Se
Te
Zn
Oil and
grease
Plant X
Inlet
water
7.6
1430.
0.0
240.
0.001
0.001
0.30
0.02
0.007
0.00350
0.001
0.001
0.0
Wirebar
cooling
7-8
1250.
12.5
240.
0.001
0.001
0.69
0.13
0.007
0.00425
0.001
0.067
2.0
Semi contin-
uous cake
casting
8.
1400.
0.0
270.
0.001
0.001
0.18
0.04
0.003
0.0001
0.001
0.001
0.0
Plant Y
Inlet
water
7.1-7.6
0.2
0.5
0.001
0.0008
0.021
1.2
0.078
3.00004
0.040
0.35
0.14
Wirebar cooling
recycle
8.0-8.4
0.1
0.4
0.001
0.0021
3.5
1.7
0.068
0.00004
0.040
0.088
0.1
103
-------
There are no solid wastes from this process.
6. Contro1 Techno 1ogy - There is no control of air emissions from a melting
or casting operation, and specific control is probably not required.
Water from this process is often cooled prior to discharge, but is not
usually otherwise specially treated.
7. EPA Source Classification Code - 3-03-005-008
8. References -
1. Development Document for Interim Final Effluent Limitations Guide-
lines and Proposed New Source Performance Standards for the Primary
Copper Smelting Subcategory and the Primary Copper Refining Sub-
category of the Copper Segment of the Nonferrous Metals Manufac-
turing Point Source Category. EPA 440/1-75/032-b. U.S. Environ-
mental Protection Agency. Washington, D.C. February 1975.
2. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc. New York. 1967.
3. Trace Pollutant Emissions from the Processing of Metallic Ores.
PEDCo-Environmental Specialists, Inc. August 1974.
4. Hallowell, J.B. et al. Water Pollution Control in the Primary
Nonferrous Metals Industry - Volume I. Copper, Zinc, and Lead
Industries. EPA-R2-73-274a. U.S. Environmental Protection Agency.
Washington, D.C. September 1973.
104
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PRIMARY COPPER PRODUCTION PROCESS NO. 22
Slime Acid Leach
1. Function - The first step in treatment of slimes from the cells of an
electrolytic refinery is removal of the copper. This may be by direct
roasting (Process No. 24), or the slimes may be first leached with acid to
extract a portion of the copper prior to the roasting step. The acid leach
is accomplished in a pressure filter, through which sulfuric acid is cir-
culated. Copper dissolves in the acid as a solution of copper sulfate. This
solution is either mixed with the electrolyte in the refinery cells (1), or
with the electrolyte purge to the liberator cells, or may be used for copper
sulfate production (Process No. 23).
2. Input Materials - The primary input is the slime from the electrolytic
cells (Process No. 19), which may contain 20 to 40 percent copper (2). Small
particles of metallic copper will be present.
Sulfuric acid is the leach solvent. Concentration and quantity of the
acid vary with the slime composition.
3. Operating Conditions - There is normally no heating of the circulating
solution, but chemical action may cause a slight temperature rise above
ambient. Pressures are atmospheric to slightly higher, not exceeding ene
kilogram per square centimeter.
4. Utilities - A small quantity of electricity is used to power pumps for
acid circulation. Water or steam concentrate is used to wash the leached
slimes prior to transferring them to the roaster.
5. Waste Streams - A minor evolution of S02 in this process is due to the
reaction of copper metal with the acid (3).
Except for accidental spills or pump leakage, there are no liquid or
solid wastes. All materials are transferred to other processes.
6. Control Technology - If this were a larger-scale process, control of
S02 by blending with other streams (if available) or by scrubbing would be
the best control technology. Since quantities are small, none of the re-
fineries control this emission except by local ventilation.
7. EPA Source Classification Code - None
8. References -
1. Development Document for Interim Final Effluent Limitations Guide-
lines and Proposed New Source Performance Standards for the Primary
Copper Smelting Subcategory and the Primary Copper Refining Sub-
category of the Copper Segment of the Nonferrous Metals Manufac-
turing Point Source Category. EPA 440/1-74/032-b. U.S. Environ-
mental Protection Agency. Washington, D.C. February 1975.
T05
-------
2. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc. New York. 1967.
3. Leigh, A.M. Precious Metals Refining Practice International
Symposium on Hydrometallurgy. Chicago, Illinois. February 25 -
March 1, 1973. pp. 95-110.
106
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PRIMARY COPPER PRODUCTION PROCESS NO. 23
Precipitation
1. Function - The function of this process is to precipitate copper sulfate
in crystal form as a marketable by-product. The solution from water or acid
leach constitutes part or all of the source. Copper powder is first added
if there is excess acidity, and excess water is evaporated. When the mixture
cools, crystals of copper sulfate form. The concentrated liquor either re-
turns to the electrolytic cells or is transferred to chemical operations for
the manufacture of other products. The crystals may be heated to remove
water of hydration prior to sale.
2. Input Materials - The input is the leached solution from the Slime Acid
Leach (Process No. 22), containing copper sulfate and sulfuric acid, or from
the Slime Water Leach (Process No. 25), containing copper sulfate in water.
Copper powder may also be added.
3- Operating Conditions - Atmospheric evaporators are usually used, with
boiling temperatures less than 125°C. Crystallization occurs in atmospheric
vessels. The crystals may be heated as high as 600°C after separation from
the mother liquor if anhydrous copper sulfate is being produced (1).
4- Utilities - This is primarily a chemical type process, using either
direct gas-fired or steam-heated evaporation equipment, noncontact cooling
water for crystallization, and electricity for solution transfer and auxil-
iaries. Utility usage is not reported, but quantities are small.
5- Haste Streams - Use of copper powder for neutralizing excess acid will
cause a slight evolution of S02, which will be stripped into the atmosphere
during evaporation (2).
Water evaporated from the solution will condense as a wastewater, or
will be lost into the atmosphere if direct- fired evaporators are used. Some
carryover of entrained solution could occur. There are no reports of the
waste from this source.
The process produces no solid wastes.
6- Control Technology - No controls are currently associated with this
process. If quantities of S02 evolution were greater, scrubbing or mixing
with another stream for combined S02 treatment would provide adequate control.
There is no report on the disposition of water from this source.
7. EPA Source Classification Code - None
107
-------
References -
1. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc. New York. 1967.
2. Leigh, A.M. Precious Metals Refining Practice International
Symposium on Hydrometallurgy. Chicago, Illinois. February 25 -
March 1, 1973. pp. 95-110.
108
-------
PRIMARY COPPER PRODUCTION PROCESS NO. 24
Slimes Roasting
1. Function - Roasting of slimes from the cells of an electrolytic refinery
allows removal of the copper content. A portion may be removed by acid leach
of the slimes (Process No. 22). Heating the slimes in a strong acid environ-
ment converts the remaining copper to soluble copper sulfate, which can be
removed by a subsequent water leach process (Process No. 25) (1). Roasting
also converts some of the silver and tellurium to soluble salts and volatil-
izes some of the selenium.
2. Input Materials - The principal input is the slime materials, either
direct from the electrolytic cells or as residue from acid leach.
Fluxes in the form of sulfuric acid and sodium sulfate are used to
ensure complete reaction of almost all the copper present in the slime, which
may be as much as 40 percent by weight of the slimes (2). One report gives
the sulfuric acid consumption as 1.74 kilogram of acid per kilogram of slime
treated (2).
Muds from the scrubber (Process No. 27) are also recycled to this
roaster (3).
3. Operating Conditions - Temperatures in the roaster are maintained
between 540° and 650°C. Pressures are atmospheric (1).
4« Utilities - Gas or oil is used for heating, and electricity for driving
mechanical equipment. Quantities are not large, because of the small scale
of this equipment.
5- Waste Streams - The gas leaving the roaster contains highly mineralized
particulates and fumes. Roasting breaks down silver and copper selenides,
releasing Se02 (1). Arsenic, tellurium, and trace amounts of lead also are
present as fumes. The stream contains S02 and dusts, which consist of all
the elements present in the slime. This gas stream normally passes to the
scrubber (Process No. 27), but any loss can represent a hazardous waste. No
analyses of this stream have been reported.
No liquid wastes are generated.
Solids from the roaster contain the most valuable metals, and are
usually carefully transferred to the water leach equipment (Process No. 25).
There is no solid waste.
6. Control Technology - Proper transfer of the highly mineralized gases
from this process to the scrubber is the best control.
7. EPA Source Classification Code - None
109
-------
8. References -
1. Leigh, A.M. Precious Metal Recovery Practice International
Symposium on Hydrometallurgy. Chicago, Illinois. February 25 -
March 1, 1973. pp. 95-110.
2. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc. New York. 1967.
3. Development Document for Interim Final Effluent Limitations Guide-
lines and Proposed New Source Performance Standards for the Primary
Copper Smelting Subcategory and the Primary Copper Refining Sub-
category of the Copper Segment of the Nonferrous Metals Manufac-
turing Point Source Category. EPA 440/1-75/032. U.S. Environ-
mental Protection Agency. Washington, D.C. February 1975.
110
-------
PRIMARY COPPER PRODUCTION PROCESS NO. 25
Slime Water Leach
1. Function - The objective of this process is to reprecipitate all the
silver and tellurium that has been made water-soluble in the roasting pro-
cess, and to dissolve and separate all the soluble copper (1).
Powdered copper is added to roasted solids in calculated quantity (2).
The mixture is then slurried with water in a tank, and by a cementation
reaction, the silver and tellurium are precipitated. The mixture is allowed
to stand to cause these reactions to approach completion and to allow the
solids to settle. The liquid is then decanted off, and the slurry is fil-
tered. The liquid solution of copper sulfate returns to the electrolytic
cells or is used for copper sulfate production (Process No. 23). The filter
cake is transferred to the Dore1 Furnace (Process No. 26) (3).
2. Input Materials - Roasted slime from Process No. 24 is the principal
input. Powdered copper in slightly less than stoichiometric proportions is
added. Water is also added.
3. Operating Conditions - The temperature in the leach tank is less than
100°C, but is not carefully controlled (3). Pressures are atmospheric,
rising to less than 3 kilograms per square centimeter during filtering.
4. Utilities - No external heat is added to this process. The hot solids
from the roaster add incidental heat.
Either deionized water or steam condensate is used to prevent introduc-
tion of foreign elements into the electrolyte solution.
5. Waste Streams - Except for accidental spills, no wastes are generated by
this process.
6. Control Technology - None
7. EPA Source Classification Code - None
8. References -
1. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc. New York. 1967.
2. Development Document for Interim Final Effluent Limitations Guide-
lines and Proposed New Source Performance Standards for the Primary
Copper Smelting Subcategory and the Primary Copper Refining Sub-
category of the Copper Segment of the Nonferrous Metals Manufac-
turing Point Source Category. EPA 440/1-75/032-b. U.S. Environ-
mental Protection Agency. Washington, D.C. February 1975.
Ill
-------
3. Leigh, A.M. Precious Metals Refining Practice International
Symposium on Hydrometallurgy. Chicago, Illinois. Feburary 25
March 1, 1973. pp. 95-110.
112
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PRIMARY COPPER PRODUCTION PROCESS NO. 26
Dorg Furnace
1. Function - This process separates the trace elements contained in the
slimes into several distinct fractions, each of which is either sold or
further treated. The most valuable fraction is a Dore" metal, consisting
primarily of silver, gold, and the platinum group metals.
The equipment is a special small reverberatory furnace, which removes
groups of elements in separate slag-producing steps. The filter cake from
the water leach process is mixed with a silica flux, charged into the furnace,
and heated. A slag forms, containing primarily the lead, iron, arsenic, and
antimony (1). This "sharp slag" is withdrawn and can be sent for further
processing to a lead smelter. Sodium salts are then added to the furnace,
and a soda slag forms. This slag contains selenium and tellurium and any
residual arsenic and antimony (2) and is further treated (see Process No.
28). An oxidative slag is then formed by blowing air through the molten
metal (3), removing bismuth and any remaining copper. This slag is returned
to the copper smelter. At least one refinery performs a final cleanup using
Portland cement, which returns to the Dore" furnace at the start of the next
charge.
The Dore" metal that remains may be sold to a specialty processor, or
may be further refined (see Process No. 30). Table 37 gives the approxi-
mate range of analysis.
Table 37. DORE METAL ANALYSIS (2)
% Weight
Gold
Silver
Copper
Palladium
Platinum
Lead
Tellurium
Selenium
8 to 9%
90 to 92%
0.5 to 1.0%
0.16 to 0.18%
0.05 to 0.009%
0.02%
0.003%
0.00002%
2. Input Materials - Filter cake from the water leach process is the
primary input. The slimes at this stage are fairly low in copper content;
they contain about 18 percent water (2) and no sulfur.
Silica sand is the first flux, and a 2:1 mixture of sodium carbonate and
sodium nitrate is the second. Quantities depend on the analysis of the
filter cake (4). Portland cement is used in very small quantities (2).
3. Operating Conditions - Temperatures in the furnace rise as high as
1400°C. Pressures are atmospheric (1).
113
-------
4- Utilities - Gas or oil fuel a Dore" furnace (1,2). Compressed air is
used in the third stage slagging operation. Electricity is not required
except for auxiliary purposes.
5. Haste Streams - Flue gas temperatures may reach 1370°C (2). The stream
may be high in particulate matter and in fumes containing selenium, tellurium,
some arsenic, antimony, and lead. These are normally sent to a wet scrubber
(Process No. 27). The precious metals content of the particulate matter is
high enough that care is taken to collect them, but no analyses have been
reported.
There are no liquid wastes from the Dors' furnace.
This process produces no solid wastes if all the slags are processed or
recycled as outlined above. The soda slag would be especially troublesome if
it became a solid waste, since it is rich in soluble oxidized salts of
arsenic, antimony, tellurium, and selenium.
6. Control Technology - Wet scrubbing of the gases for removal of parti-
culates and fumes is the best control of this gas stream.
Care should be taken in the handling of slags from the Dore" furnace to
avoid secondary water pollution from this source.
7. EPA Source Classification Code - None
8. References -
1. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc. New York. 1967.
2. Leigh, A.H. Precious Metal Refining Practice International Sym-
posium on Hydrometallurgy. Chicago, Illinois. February 25 - March
1, 1973. pp. 95-110.
3. Development Document for Interim Final Effluent Limitations Guide-
lines and Proposed New Source Performance Standards for the Primary
Copper Smelting Subcategory and the Primary Copper Refining Sub-
category of the Copper Segment of the Nonferrous Metals Manufac-
turing Point Source Category. EPA 440/1-75/032-b. U.S. Environ-
mental Protection Agency. Washington, D.C. February 1975.
4. Hall owe!1, J.B. et al. Water Pollution Control in the Primary
Nonferrous Metals Industry - Volume I. Copper, Zinc, and Lead
Industries. EPA-R2-73-274a. U.S. Environmental Protection Agency,
Washington, D.C. September 1973.
114
-------
PRIMARY COPPER PRODUCTION PROCESS NO. 27
Scrubber
1. Function - Gases from the slimes roaster and the Dore" furnace contain
participates in quantities that justify their recovery for further processing.
The gases also contain fumes, especially of selenium, which hydrolyze in the
water scrubber, allowing their separation for sale.
The scrubbers are generally of the water spray type (1), with the water
continuously recirculating. As solid material accumulates, periodic blowdown
is performed. The amorphous selenium is often removed by flotation (2), or
occasionally the blowdown is combined with the soda slag leach liquor (Pro-
cess No. 28). Muds from the scrubber are recycled to the slimes roaster
(Process No. 24).
2. Input Material's - Flue gases from the Dore" furnace and the slimes
roaster are the principal inputs.
If flotation recovery of selenium from the blowdown is practiced,
methylamyl alcohol and liquid colloid glue are used as flotation reagents
(2).
3. Operating Conditions - The gases entering the scrubber are extremely
hot, about 1000° to 1300°C. The water sprays are at ambient temperatures
(3). Pressures are near atmospheric.
4. Utilities - Water is used as makeup to replace evaporation losses and
electricity is used to drive the exhaust blower. Quantities are not large.
5. Haste Streams - Gases leaving the scrubber may contain particulates and
fumes that were not removed. Selenium is expected to be a major constituent.
If all the scrubbing liquor and particulates are recycled to previous
operations, no liquid or solid wastes are produced.
6. Control Technology - Most refiners find it economical to install electro-
static precipitators on the scrubber effluent to remove the highly metal-
liferous dusts and fumes that escape collection. The use of a more efficient
venturi-type scrubber would also be an acceptable control.
7. EPA Source Classification Code - None
8. References -
1. Development Document for Interim Final Effluent Limitations Guide-
lines and Proposed New Source Performance Standards for the Primary
Copper Smelting Subcategory and the Primary Copper Refining Sub-
category of the Copper Segment of the Nonferrous Metals Manufac-
turing Point Source Category. EPA 440/1-75/032-b. U.S. Environ-
mental Protection Agency. Washington, D.C. February 1975.
115
-------
2. Leigh, A.H. Precious Metals Refining Practice International
Symposium on Hydrometallurgy. Chicago, Illinois. February 25 -
March 1, 1973. pp. 75-110.
3. Particulate and Sulfur Dioxide Emission Control Cost Study of the
Electric Utility Industry. 68-01-1900. U.S. Environmental Pro-
tection Agency. Washington, D.C.
116
-------
PRIMARY COPPER PRODUCTION PROCESS NO. 28
Soda Slag Leach
1. Function - The soda slag, the second slag removed from the Dore* furnace,
is rich in selenium and tellurium, both of which are marketable by-products
(1). The function of this leach process is to selectively dissolve these
elements from the slag (2).
The slag is leached in a tank of water, which becomes alkaline because
of the sodium oxide content of the slag. Selenium and tellurium dissolve as
sodium selenite and tellurite (3). The resulting solution is filtered from
the insoluble components of the slag, and the solids are returned to the
Dor6 furnace for reprocessing. The leached solution is further treated (see
Process No. 29).
2- Input Materials - The soda slag from the Dore* furnace is the only
input.
3- Operating Temperature - Residual heat in the slag and chemical action
between the slag and the water cause some temperature increase during leach-
ing, to less than 100°C (2,4). Pressures are atmospheric during the leach,
and less than 2 kilograms per square centimeter during filtration.
4- Utilities - Water is required as the leaching solvent.
The literature does not state whether supplemental heat is required
during this step.
Electricity in small quantity is used to pump the leached slurry through
the filter.
5. Waste Streams - There are no gas, liquid, or solids wastes from this
process. All materials at this stage are valuable and are carefully handled
6. Control Technology - None is required.
7. EPA Source Classification Code - None
8. References -
1. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc. New York. 1967.
2. Leigh, A.H. Precious Metal Recovery Practice International
Symposium on Hydrometallurgy. Chicago, Illinois. February 25 -
March 1, 1973. pp. 95-110.
117
-------
3. Development Document for Interim Final Effluent Limitations Guide-
lines and Proposed New Source Performance Standards for the Primary
Copper Smelting Subcategory and the Primary Copper Refining Sub-
category of the Copper Segment of the Nonferrous Metals Manufac-
turing Point Source Category. EPA 440/1-75/032-b. U.S. Environ-
mental Protection Agency. Washington, D.C. February 1975.
4. Hallowell, J.B. et al. Water Pollution Control in the Primary
Nonferrous Metals Industry - Volume I. Copper, Zinc, and Lead
Industries. EPA-R2-73-274a. U.S. Environmental Protection Agency.
Washington, D.C. September 1973.
118
-------
PRIMARY COPPER PRODUCTION PROCESS NO. 29
Selenium and Tellurium Recovery
1. Function - The processing solutions which have become rich in selenium
and tellurium are treated in laboratory-scale equipment to recover these
elements as by-products (1). Both are valuable for use in manufacture of
electrical and electronic products, and in xerographic copying machines.
The alkaline solutions are made acidic with sulfuric acid to a pH of
5.5 to 6.5 (2,3). Tellurous acid (H2Te03) precipitates, and is removed by
filtration. Then the solution is treated by bubbling SO? through it.
Selenium and any remaining tellurium precipitate in elemental form, and can
be selectively separated by several stages of precipitation and filtration.
Both are dried to become marketable products, or they may be further purified
prior to sale.
The crude tellurous acid is dissolved in caustic, treated with sodium
sulfide to precipitate impurities, and filtered. The clear solution is again
acidified, and the pure tellurous acid again precipitates. When filtered and
dried, it can be sold in this form or may be further processed to elemental
tellurium.
A number of purification and reduction processes are used to produce
pure materials. All are very small-scale operations.
Only a very small percentage of the tellurium in the original copper ore
is reclaimed. Ninety percent is lost during ore flotation, while in each
subsequent processing step, from 20 to 60 percent of the tellurium that
remains is lost (4). Selenium recovery is reported to be much higher -
recovery of 80 percent, with the remainder lost to slags, flue dusts, and
gases (4).
2. Input Materials - The principal input is the filtered solution from soda
slag leaching (Process No. 28), to which are added selenium and tellurium
extracted or floated from scrubber precipitates (Process No. 27).
Laboratory-grade reagents are normally used, such as sulfuric acid,
sodium hydroxide, compressed and liquified SO?, and others. Quantities are
very small.
3- Operating Conditions - Temperatures may reach 450°C during some purifica-
tion steps. Pressures are normally atmospheric.
4- Utilities - A variety of laboratory utilities may be employed. Consump-
tion of each is negligible.
5. Waste Streams - No gas or solid wastes are generated by this process in
anything other than trace amounts.
Liquids are low in volume and normally discharge through standard
laboratory waste systems.
119
-------
6. Control Technology - None applicable
7. EPA Source Classification Code - None
8. References -
1. Leigh, A.M. Precious Metal Recovery Practice International Sym-
posium on Hydrometallurgy. Chicago, Illinois. February 25 -
March 1, 1973. pp. 95-110.
2. Development Document for Interim Final Effluent Limitations Guide-
lines and Proposed New Source Performance Standards for the Primary
Copper Smelting Subcategory and the Primary Copper Refining Sub-
category of the Copper Segment of the Nonferrous Metals Manufac-
turing Point Source Category. EPA 440/1-75/032-b. U.S. Environ-
mental Protection Agency. Washington, D.C. February 1975.
3. Hallowell, J.B. et al. Water Pollution Control in the Primary
Nonferrous Metals Industry - Volume I. Copper, Zinc, and Lead
Industries. EPA-R2-73-274a. U.S. Environmental Protection Agency.
Washington, D.C. September 1973.
4. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc. New York. 1967.
120
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PRIMARY COPPER PRODUCTION PROCESS NO. 30
Pore" Metal Separation
1. Function - In a series of complex chemical and electrochemical labora-
tory operations, the Dore" metal, a mixture primarily of silver, gold, and the
platinum group metals, is separated into specification grades of each of
these metals (1).
A special small electrolytic cell, the Moebius cell, is used to separate
the silver, which is further processed to produce bullion bars, analyzed at
99.97 percent silver, of 1000 troy ounces each (2,3).
Mud from the Moebius cell is melted into anodes and processed in another
special electrolytic device, the Wohlwill cell, which produces gold of
marketable quality.
The remaining electrolyte is chemically processed to separate platinum,
palladium, and occasionally other metals. Iridium, rhodium, ruthenium, and
others may be present.
2. Input Materials - The principal input is Dore" metal (see Process No.
26).
Small quantities of many inorganic chemicals are used. The list includes
sulfuric, nitric, and hydrochloric acids, powdered iron and copper metals,
and sulfur dioxide.
3. Operating Conditions - Temperatures during the various steps of pro-
cessing range up to 1300°C in the casting of the metals, but most operations
are at less than 100°C. No unusual laboratory pressures are employed.
4- Utilities - Electricity is used for the electrochemical operations, and
either electricity or gas for operation of the casting furnace. Utility
consumption is negligible in comparison with other processes in this industry.
5. Waste Streams - No losses of unusual metallic elements occur in this
process. There are minor evolutions of nitrous oxides, sulfuric acid mists,
and other acid fumes, and occasional liquid discharges of electrolyte acids
in quantities of a few gallons at most. No solid wastes are produced, although
residues may occasionally be returned to the Dore" furnace.
6. Control Technology - Local ventilation is the only control exercised for
this process.
7. EPA Source Classification Code - None
121
-------
8. References -
1. Development Document for Interim Final Effluent Limitations Guide-
lines and Proposed New Source Performance Standards for the Primary
Copper Smelting Subcategory and the Primary Copper Refining Sub-
category of the Copper Segment of the Nonferrous Metals Manufac-
turing Point Source Category. EPA 440/1-75/032-b. U.S. Environ-
mental Protection Agency. Washington, D.C. February 1975.
2. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc. New York. 1967.
3. Leigh, A.M. Precious Metal Refining Practice the International
Symposium on Hydrometallurgy. Chicago, Illinois. February 25 -
March 1, 1973. pp. 95-110.
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PRIMARY COPPER PRODUCTION PROCESS NO. 31
Vat Leaching
1. Function - Vat leaching is a simple form of hydrometallurgy in which
copper is dissolved from oxide ores to form aqueous solutions. The leaching
takes place in an arrangement of tanks or vats.
Oxidized copper minerals, occurring as partially weathered deposits in
the mine, cannot easily be processed by conventional smelting processes.
These deposits are selectively mined and crushed to about 1 to 1.25 centi-
meters (1). The crushed ore is then placed in concrete vats of up to 18,000
metric tons capacity, and subjected to alternate flooding with sulfuric acid
and draining. After the copper oxides are converted to soluble copper sul-
fate, the remaining soluble copper is removed by a countercurrent wash of
fresh water. The vat floor is a filter which facilitates upflow and downflow
of wash and leach solutions. The resulting solutions are too dilute for
electrowinning; they are usually treated by cementation (Process No. 33) or
solvent extraction (Process No. 34) (1).
One proprietary process has been developed for vat leaching of a roasted
sulfide ore in which the sulfide ore is converted into sulfates prior to
hydrometallurgical processing (see Process No. 36).
Vat leaching is similar in principal to the leaching of sulfide ores
(Process No. 32), but the vat leaching operations are usually more carefully
controlled and result in lower potential for damage to the environment. Vat
leaching is the most efficient process yet developed for the recovery of
copper values from oxidized copper minerals.
2. Input Materials - The principal input is the oxide ore material, as
described above.
Sulfuric acid has been the only solvent used for simple leaching since
it is not only inexpensive and nonvolatile, but also has a slight selective
action for copper. Consumption will vary, but extraction of a metric ton of
copper from a 1 percent ore body containing oxidized minerals will require
about 4400 liters of 96 percent acidity (2).
3. Operating Conditions - The process operates at atmospheric pressure and
ambient temperatures.
4. Utilities - Diesel fuel and electricity are used in the materials
handling operations, and electricity in pumping the leach solution. Process
water must be added to most of these operations, since in this country they
are located in arid regions with high evaporation losses. In 1973 water
usage was 50 to 200 cubic meters per metric ton of copper precipitate (2).
5. Haste Streams - Vat leaching produces a large amount of tailings of
waste rock that is sluiced into a tailings pond. This material is comparable
with the waste from a concentrator plant (Process No. 2). Frequently the same
pond is used for both concentrator and vat-leaching tailings.
123
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The circulating stream of a leaching operation may become so rich in
impurities that it must be discarded. No analyses have been reported; the
volume is reported as varying from 350,000 to 1,000,000 liters of spent
liquor per metric ton of copper produced (3).
6. Control Technology - Most installations mix the discharge of this
process with mining or concentrating wastes. Control is described in con-
nection with Process No's. 1 and 2.
7. EPA Source Classification Code - None
8. References -
1. Williams, Roy E. Waste Production and Disposal in Mining, Milling
and Metallurgical Industries. Miller Freeman Publications, Inc.
San Francisco. 1975.
2. Roberts, R.W. San Xavier Vat Leach Plant Operation. Mining
Congress Journal. December 1974.
3. Davis, W.E. National Inventory of Sources and Emissions: Copper,
Selenium, and Zinc. PB 210-677, 678, and 679. U.S. Environmental
Protection Agency. Research Triangle Park, North Carolina. May
1972.
124
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PRIMARY COPPER PRODUCTION PROCESS NO. 32
Sulfide Ore Leaching
1. Function - Heap and dump leaching are simple forms of hydrometallurgy in
which copper is dissolved from sulfide ores to form aqueous solutions. In
heap leaching, the ore is placed in a pile on the ground. In dump leaching,
the overburden and low grade waste from the mine are leached in the dumps
formed during the mining operation. In situ and thin layer leaching may also
be utilized for sulfide ores.
This process is an accelerated form of natural weathering. It is
usually applied to low-grade ore that contains less than 0.4 percent copper
(1,2,3). Material is placed in an area provided with drainage ditches and
basins, and is alternately flooded with sulfuric acid solution and allowed to
drain. This procedure causes rapid oxidation of the copper minerals. Soluble
copper sulfate is formed, and washes from the heap with the acid solution.
From 70 to 82 percent of the copper in these low-grade ores can be recovered
(3,4). The liquor that seeps from the heap has a pH of 1.5 to 2.5 (5) and
may contain from 1.0 to 18 grams of copper per liter (4,5).
In the leaching of sulfide ores, barren solutions of sulfuric acid from
a copper cementation process are applied originally, after which only makeup
water is required periodically to sustain the leaching process. Water and
oxygen react with pyrite in the dump to generate sulfuric acid and ferric
sulfate; this solution effectively dissolves the copper present. If the ores
contain significant amounts of oxides or carbonates, sulfuric acid must be
added periodically. A dump leaching site is characterized by a grid of ponds
that collect the pregnant leach liquor (6).
In situ leaching involves breaking the ore in place and alternately
circulating air and leach solution through the fractured material. The
pregnant liquor is collected in a system of tunnels.
A recent modification of sulfide ore leaching is the "thin layer"
process, in which still further acceleration of the weathering reactions is
brought about by spreading the ore thinly over a large surface area. This
modification is in use in South America, but has not been reported to be in
use in this country.
These techniques of hydrometallurgy allow the extraction of copper from
low-grade ores without evolution of sulfur dioxide. These can be small
operations that require less capital expenditure than pyrometallurgical
processing. The overall cost to produce a ton of copper is greater, however,
and there is no way in simple leaching to recover the precious metals content
of the ores.
2- Input Materials - The principal input is the ore materials, as described
above. In most cases, these would otherwise be waste materials, unprofitable
to process by conventional techniques.
125
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Sulfuric acid is the leaching chemical. To some extent, leaching opera-
tions are practiced as a means for disposition of excess smelter acid.
Consumption will vary and will depend largely on the composition of the
gangue rock. If there is no limestone in the gangue, very little acid is
consumed.
3. Operating Conditions - Since the process occurs in an open, outdoor
area, it operates at atmospheric pressure and ambient temperatures.
4. Utilities - Diesel fuel and electricity are used in the materials
handling operations, and electricity in pumping the leach solution. Process
water must be added to most of these operations, since in this country they
are located in arid regions with high evaporation losses. In 1973, water
usage in heap leaching ranged from 920 to 4850 cubic meters per metric ton of
crude copper precipitate produced (4).
5. Haste Streams - Wastes from heap leaching include fugitive dusts from
materials handling, and quantities of highly mineralized solid wastes con-
taining residual sulfuric acid. It is usually difficult to separate these
wastes from those of the mining process, as discussed in more detail in
Process No. 1.
The circulating stream of a leaching operation may become so rich in
impurities that it must be discarded. No analyses have been reported; the
volume is reported as varying from 350,000 to 1,000,000 liters of spent
liquor per metric ton of copper produced (7).
6. Control Technology - Most installations mix the discharge of this
process with mining or concentrating wastes. Control is described in connec-
tion with Process No's. 1 and 2.
7. EPA Source Classification Code - None
8. References -
1. Background Information for New Source Performance Standards:
Primary Copper, Zinc, and Lead Smelters. Volume I, Proposed
Standards. EPA-450/2-74-002a. U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina. October 1974.
2. Copper Hydrometallurgy: The Third-Generation Plants. Engineering
and Mining Journal. June 1975.
3. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc. New York. 1967.
4. Roberts, R.W. San Xavier Vat Leach Plant Operation. Mining
Congress Journal. December 1974.
5. Gardner, S.A. and G.C.I. Warwick. Pollution-Free Metallurgy:
Copper via Solvent-Extraction. Engineering and Mining Journal.
April 1971.
126
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6. A Study of Waste Generation, Treatment and Disposal in the Metals
Mining Industry. PB-261 052. U.S. Environmental Protection
Agency, Washington, D.C. October 1976.
7. Davis, W.E. National Inventory of Sources and Emissions: Copper,
Selenium, and Zinc. PB-210 679, PB-210 678, and PB-210 677. U.S.
Environmental Protection Agency. Research Triangle Park, North
Carolina. May 1972.
127
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PRIMARY COPPER PRODUCTION ' PROCESS NO. 33
Cementation
1. Function - The cementation process converts soluble copper into a
metallic precipitate through chemical reaction with metallic iron. It is
used to recover copper from strong solutions created by other processes,
especially those from heap and vat leaching.
This process is dependent upon the relative activity of a metal to
become a soluble ion. Metals can be listed in a continuous electromotive
series; iron, having higher activity, will preferentially replace a copper
ion in solution and thus produce an insoluble precipitate, often called
"cement copper". In a typical application, liquor draining from a heap
leaching operation flows through a trough that is filled with scrap iron.
Part of the copper precipitates, and the liquor is recycled back to the heap.
It is reported that 94 percent of the copper can be recovered by this method
(1,2).
Periodically, the trough is cleaned and the cement copper is sent to a
smelter for processing. The cement copper is usually a mixture of copper
with iron compounds and other insoluble minerals. The copper content is
generally around 70 percent and is rarely more than 90 percent (1,3).
In many of its applications, cementation is being replaced by solvent
extraction and electrowinning techniques (see 'Process No's. 34 and 35).
The term cementation is also applied in this industry to other similar
chemical reactions. Zinc metal is used in cementation of gold and copper,
and copper powder is used in cementation of silver (4).
2. Input Materials - Aqueous liquors containing dissolved copper are the
principal input. The process is efficient only with fairly concentrated
solutions.
Scrap iron is most commonly used for cementation if it can be obtained.
Because it is becoming difficult to obtain sufficient scrap of good quality,
a process for manufacture of a sponge iron is in the final steps of develop-
ment (see Process No. 37).
3. Operating Conditions - Cementation processes normally operate at atmo-
spheric pressure and ambient temperatures.
4- Utilities - No utilities are consumed unless special pumps are required
to cause the liquor to flow through the cementation tanks.
5. Waste Streams - Atmospheric pollution from the cementation process, is
negligible. There may be tiny amounts of hydrogen gas created by a side
reaction of acid with the iron.
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No liquid wastes can be directly assigned to this process when used as
an auxiliary to a larger liquid handling operation. In the case of a sepa-
rate operation, analysis of a typical treated leach liquor is presented below
in Table 38.
TABLE 38. ANALYSIS OF TAILINGS EFFLUENT
FROM A PRECIPITATION PLANT (5)
Parameter
Sulfate
Copper
Iron
Lead
Mercury
Selenium
Zinc
Maximum, mg/1
53,000
76.3
3100
0.92
0.0006
0.95
146
Minimum, mg/1
33,000
27.7
2050
0.05
0.0001
0.01
129
Average, mg/1
38,882
52.2
2632
0.67
0.0003
0.12
136
Solid waste resulting from cementation includes scrap iron partially
used, discarded, or abandoned, causing some of these operations to resemble
a junk yard.
6- Control Technology - No controls are specific to this process.
7. EPA Source Classification Code - None
8. References -
1. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc. New York. 1967.
2. Roberts, R.W. San Xavier Vat Leach Plant Operation. Mining
Congress Journal. December 1974.
3. Background Information for New Source Performance Standards:
Primary Copper, Zinc, and Lead Smelters. Volume I, Proposed
Standards. EPA-450/2-74-002a. U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina. October 1974.
4. Development Document for Interim Final and Proposed Effluent
Limitations Guidelines and New Source Performance Standards for the
Ore Mining and Dressing Industry. Point Source Category, Volumes I
and II. EPA/1-75/032-6. U.S. Environmental Protection Agency.
Washington, D.C. February 1975.
5. Personal Communication with J.V. Rouse, U.S. Environmental Protec-
tion Agency. National Enforcement Investigations Center. Denver,
Colorado. 1976.
129
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PRIMARY COPPER PRODUCTION PROCESS NO. 34
Solvent Extraction
!• Function - As applied in the copper industry, solvent extraction is a
method to produce a concentrated copper solution, relatively free of other
metal ions, from a solution of copper that does contain other dissolved
metals. The process uses a special mixture of organic solvents in an agitated
vessel. When the solvents are mixed with the impure solution, the copper
combines with the solvents as a complex. Agitation of the vessel is then
stopped and the solvents, now containing the copper, form a separate layer.
The water layer is drained off. Sulfuric acid is then mixed with the sol-
vent. This breaks down the complex and regenerates the solvent for reuse.
The copper is withdrawn as a solution in the acid.
Solvent extraction has been applied to liquors from vat leaching, and
it is being incorporated into some of the developing hydrometallurgical
processes (1). The concentrated acid solution can be directly treated by
electrowinning (see Process No. 35). This process can also be made con-
tinuous, rather than batch, to adapt it to large-scale operations.
It is reported that about 95 percent of the copper in a solution can be
extracted by this technique (2).
2. Input Materials - Water solutions of copper are the primary input.
There is no published information on the composition ranges that can be
efficiently treated with this process.
The solvents mixture is kerosene containing about 12 percent of a
proprietary chemical made by General Mills called LIX (3,4). The total rate
of recycle is not known, but losses of 0.1 liter per 1000 liters of impure
solution have been reported (4). Two other chemicals, "Kelex" and "Shell
.529," are also being advertised for this application.
Concentrated sulfuric acid is required (normally recycled through
electrowinning cells), but quantities have not been reported.
3. Operating Conditions - No special temperature limits are reported; it is
assumed that ambient temperatures and atmospheric pressure are satisfactory.
4. Utilities - A small amount of electricity is required for agitation and
liquid pumping.
5. Waste Streams - There are no reports of atmospheric pollution from this
process. For operating safety, evaporation of the solvent is undoubtedly
minimized.
The manufacturer of the LIX solvent states that small amounts of iron,
arsenic, and zinc are extracted along with the copper (1). The procedure for
disposal of these materials has not been reported. It is likely that there
130
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will be a bleed of the concentrated acid to prevent accumulation of these
other elements.
The loss of solvent is reported as 1 liter per 10,000 liters of raf-
finate (2). It is likely that this is almost entirely kerosene, which has a
slight water solubility. The more expensive chelating compounds should stay
largely dissolved in the kerosene layer. No confirmation of this has been
published.
No solid wastes are generated by this process.
6. Control Technology - No special controls are indicated. The possible
acid blowdown should be of a quality that could be reused in other processes.
The organic loss would be biodegradable if this waste stream were combined
into other wastewaters.
7. EPA Classification Code - None
8. References -
1. In Clean-Air Copper Production, Arbiter is First off the Mark.
Engineering and Mining Journal. 1973.
2. Gardner, S.A. and Warwick, G.C.I. Pollution-Free Metallurgy:
Copper via Solvent-Extraction. Engineering and Mining Journal.
April 1971.
3. Background Information for New Source Performance Standards:
Primary Copper, Zinc, and Lead Smelters. Volume I, Proposed
Standards. EPA-450/2-74-002a. U.S. Environmental Protection
Agency. Research Triangle Park, North Carolina. October 1974.
4. Ion Exchange: The New Dimension in Copper Recovery Systems.
Engineering and Mining Journal. June 1975.
131
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PRIMARY COPPER PRODUCTION PROCESS NO. 35
Electrowinning
1. Function - Electrowinning is a process for the extraction of relatively
pure copper metal from a solution containing copper ions. This is an electro-
lytic process, similar to the cells of an electrolytic refinery (see Process
No. 19), except than an inert anode is used. Copper metal deposits at the
cathode, and the water in the solution is electrolytically decomposed,
liberating oxygen at the cathode, and regenerating the sulfate ion as sul-
furic acid.
If the copper solution is relatively pure, the copper produced by
electrowinning is comparable with the best electrolytic copper, assayed as
99.9 percent plus (1). If impure solutions direct from vat leaching are
used, the purity is equivalent to that of the anode copper from a conventional
smelter and the product thus requires electrolytic refining prior to sale.
2. Input Materials - Electrowinning is in use to recover copper directly
from vat leaching solutions (Process No. 31), and from purified solution from
solvent extractions (Process No. 34). It is also being tested as a part of
some of the more sophisticated hydrometallurgical processes that are being
developed, in which chlorides rather than sulfates will be the input mate-
rials (see Process No. 38) (2).
Additives to produce a uniform cathode deposit are necessary. They are
the same as for electrolytic refining. One report lists glue for electro-
winning being added at a rate of 0.02 to 0.06 kilogram per metric ton of
cathode copper (3).
3. Operating Conditions - Electrowinning cells are maintained at about 60°
to 65°C and at atmospheric pressure (2,3).
4- Utilities - Electrowinning requires 8 to 10 times as much electric
current as does an electrolytic refining cell to produce the same amount of
copper (3). In a loop with a solvent extraction process, 2.44 kilowatt-
hours are required to produce a kilogram of copper (4). In direct electro-
winning of a vat or heap leach solution 2.79 kilowatt-hours per kilogram of
copper are required (3). These high values reflect the energy required to
dissociate water into its elements and are the principal reason that the
simple hydrometallurgical processes have been more expensive than conventiona
smelting.
A small amount of water is used to clean the cathodes after removing
them from the cell.
5- Waste Streams - The oxygen produced at the anode of an electrowinning
cell can be considered either as an atmospheric emission or as a by-product.
If it is discarded to the atmosphere, there are no deleterious environmental
effects.
132
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A small amount of liquid waste may be discharged in connection with
cleaning of the completed cathodes. No reports of this source have been
published.
The possible larger purge of electrolyte, necessary to prevent accumula-
tion of other elements, was discussed in connection with Process No's. 31,
32, and 34.
There are no solid wastes from this process.
6- Control Technology - No special controls are applicable to the waste-
water that may develop from this process.
7. EPA Source Classification Code - 3-03-005-0
8. References -
1. Gardner, S.A. and Warwick, G.C.I. Pollution-Free Metallurgy:
Copper via Solvent-Extraction. Engineering and Mining Journal.
April 1971.
2. Atwood, G.E., and Curtis, C.H. Hydrometallurgical Process for the
Production of Copper. U.S. Patent No. 3,785,944. January 15,
i
3. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc. New York. 1967.
4. Ion Exchange: The New Dimension in Copper Recovery Systems.
Engineering and Mining Journal. June 1975.
133
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PRIMARY COPPER PRODUCTION PROCESS NO. 36
Sulfation Roasting
1. Function - One company has developed a hybrid process that will use a
fluidization roaster (Process No. 4) to prepare a calcine especially suited
to vat leaching (Process No. 31). This is the technique of sulfation roast-
ing. In this process, concentrate is roasted to oxidize the copper to copper
sulfate and the iron to iron oxide, and to remove the excess sulfur as sulfur
dioxide. Roasting is a batch rather than a continuous operation.
2. Input Materials - This plant will use an ore concentrate that is pre-
dominantly chalcopyrite (CuFe$2) (1). It is expected that any sulfide con-
centrate could be used. The concentrate is blended with Fe203, which moder-
ates the heat produced by the exothermic oxidation reaction and promotes
sulfation of the copper. A ratio of two parts concentrate to one of iron
oxide is believed to be about optimum (2).
3. Operating Conditions - Temperatures are kept much lower than in con-
ventional roasting. Instead of 760°C, the range is 400° to 600°C (2,3).
Pressures are approximately atmospheric.
4- Utilities - Gas or oil is used to preignite the charge and to maintain
temperature.
Noncontact cooling water is used to regulate temperatures of the roaster.
Air or oxygen is injected through the bottom of the charge for oxidation.
Twenty percent above theoretical amount of oxygen will be required for the
duration of each batch (2).
5. Haste Streams - It is believed that emission of metallic fumes will be
considerably less than in a conventionally operated roaster. Particulate
emissions following the roaster cyclones have not been estimated.
Organic flotation reagents are expected to be volatilized into the exit
gases and oxidized. The gas stream is expected to contain 8 percent S02 and
4 percent oxygen (4). Gas temperature should be less than 400°C.
There will be no solid or liquid wastes from this process.
6. Control Technology - A 225 metric ton per day single-contact sulfuric
acid plant will remove from 70 to 80 percent of the S02 from this process
(4,5). This operation will require complete particulate removal, but it is
not known what devices will be used.
7. EPA Source Classification Code - 3-03-005-02
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8. References -
1. Haver, P.P. and M.M. Wong. Lime Roast-Leach Method for Treating
Chalcopyrite Concentrate. U.S. Bureau of Mines, Washington, D.C,
8006. 1975.
2. Foley, R.M. Method of Treating Copper Ore Concentrates. U.S.
Patent No. 2,783,141. February 26, 1957.
3. Haskett, P.R., D.J. Bauer, and R.E. Lindstrorn. Copper Recovery
from Chalcopyrite by a Roast-Leach Procedure.
4. Background Information for New Source Performance Standards:
Primary Copper, Zinc, and Lead Smelters. Volume I, Proposed
Standards. EPA-450/2-74-002a. U.S. Environmental Protection
Agency. Research Triangle Park, North Carolina. October 1974.
5. Potter, J. Personnel Communication on Hydrometallurgical Pro-
cesses. Bureau of Mines. Salt Lake City, Utah. 1976.
135
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PRIMARY COPPER PRODUCTION PROCESS NO. 37
Sponge Iron Plant
1. Function - One company is building a sponge iron plant to accompany
its sulfation roasting installation (Process No. 36)(1). After leaching
the copper from the calcine produced by sulfation roasting, the leach residue
contains mostly iron oxide plus smaller amounts of copper and precious metals.
This process will partially reduce the iron, which will then be used for
cementation of liquor from the vat leaching of oxidized copper ores. The
precipitate from this process is expected to contain the precious metals from
the concentrate originally fed into the sulfation roaster (2), and will
therefore provide a means of recovery.
The sponge iron will be produced in a kiln by reduction with coal. The
iron is not to be high-purity grade, but will be adequate for cementation.
2. Input Materials - The principal input i,s the residue from vat leaching
of sulfation roasted concentrates.
Coal is to be used in the proportion of one ton of coal for each two
tons of sponge iron produced.
3. Operating Conditions - Kiln temperatures are expected to be approximately
1100°C (3j.Pressures are approximately atmospheric.
4. Utilities - Gas or oil is used to heat the charge until the coal is
ignited, and is then used only if required to maintain temperature.
Combustion air is allowed to enter the kiln in carefully regulated
amounts. Air quantity is calculated to be 1.5 tons of air per ton of iron
produced (3).
5. Waste Streams - No emission data are available, since this process is
not yet in operation. Particulates and fumes of volatile metals would be
expected in a gas containing appreciable carbon monoxide.
There should be no liquid waste.
The process will generate a solid waste in the form of a slag.
6. Control Technology - It is not yet known what atmospheric control
devices will be employed with this process.
The slag is expected to be discarded in a waste dump also used for
wastes from ore concentrating operations.
7. EPA Classification Code - None
136
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8. References -
1. Potter, J. Personal communication on Hydrometallurgical Pro-
cesses. Bureau of Mines. Salt Lake City, Utah, 1976.
2. Hydrometallurgy Makes Advances in Copper Processing. Engineering
and Mining Journal. 1973.
3. Encyclopedia of Chemical Technology. Interscience Publishers, a
division of John Wiley and Sons, Inc. New York. 1967.
137
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PRIMARY COPPER PRODUCTION PROCESS NO. 38
CLEAR Reduction
1. Function - An advanced hydrometallurgical process has been developed
with the trade name of CLEAR (Copper Leaching, Extraction, and Refining).
The descriptions for Process No's. 38 through 40 outline the three sections
of this method.
The first step of the CLEAR system, called a reduction, could also be
called a leaching operation. It uses as a solvent a water solution of
cupric, ferrous, and sodium chlorides (1). Primarily the cupric chloride is
active during this step, reacting with copper ore minerals to form cuprous
chloride, additional ferrous chloride, and elemental sulfur. The sulfur is a
solid material and remains with the leach residue. Since only about half the
copper in the concentrate is solubilized in this first leach, it is treated a
second time in the oxidation process (Process No. 40).
Although leaching of fresh concentrate does occur, the principal purpose
of this step is to prepare the liquor for electrowinning. It may be reduced
with other materials if necessary, then filtered and sent to electrowinning
cells (2). These cells are similar to those described in Process No. 35,
but are slightly modified for chloride service, operating at a slightly lower
temperature, around 55°C. After electrowinning removes part of the copper,
the liquor is sent to the Regeneration-Purge step (Process No. 39).
2. Input Materials - A typical Arizona ore concentrate is the primary
input. Chalcopyrite is the predominant ore mineral.
The leach liquor at this stage contains about 8 percent cupric chloride,
12 percent ferrous chloride, and 13 percent sodium chloride (1). It is
received directly from the oxidation leach of the previous batch (see Process
No. 40).
To complete the reduction of the liquor, scrap iron or copper, sodium
sulfite, or sulfur dioxide may be added (2).
3. Operating Conditions - The CLEAR process operates at higher temperatures
than some other hydrometallurgical processes; 107°C has been reported (1).
Pressures are atmospheric.
4. Utilities - Although there are no published reports, the source of heat
is probably steam. Electricity is also undoubtedly required for materials
handling and pumping.
5 Waste Streams - Some loss of hydrochloric acid vapor from a residual in
the leach liquor may occur, but the leaching step is enclosed to minimize
this emission. Dust may arise from materials handling.
The process generates no intentional waste streams; with the corrosive
solutions, however, accidental losses of liquids are likely.
138
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6- Control Technology - Any losses of hydrochloric acid vapors can be
controlled by scrubbing with an alkaline solution.
7. EPA Classification Code - None
8. References^ -
1. Atwood, G.E., and C.H. Curtis. Hydrometallurgical Process for the
Production of Copper. U.S. Patent No. 3,785,944. January 15,
2. Rosenzweig, M.D. Copper Makers Look to Sulfide Hydrometallurgy.
Chemical Engineering. Volume 83, No. 1: pp. 79-81. January 5,
139
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PRIMARY COPPER PRODUCTION PROCESS NO. 39
CLEAR Regeneration - Purge
1. Function - Exhausted and stripped solvent from the electrowinning cells
that follow the reduction process (Process No. 38) is oxidized with air to
remove excess iron and to prepare the solution for the pressurized leach
operation (Process No. 40). Air is blown through the solution, and ferrous
iron is oxidized to ferric chloride and ferric hydroxide. Copper in the
solution acts as a catalyst for this oxidation (1). Sulfates are also formed
and collect into an insoluble compound similar to the mineral jarosite (2).
The jarosite and ferric hydroxide are filtered out and discarded.
2. Input Materials - Liquor from the electrowinning cells is the only
input. At this stage, the solution contains about 6 percent cuprous chloride,
8 percent ferrous chloride, and 14 percent sodium chloride (3).
3. Operating Conditions - This is a pressurized process, operating at
107°C and 2.7 kilograms per square centimeter (3).
4. Utilities - Source of heat has not been reported. Either steam or
direct firing could be applicable.
Compressed air is required, and process water is added at this step to
compensate for evaporation and losses. Quantities are unknown.
5. waste Streams - Although no data have been reported, a gaseous stream
must be released from this step carrying hydrochloric acid vapor and steam.
Solids removed by filtration are discarded. Composition is reported to
be primarily an iron sulfate/hydroxide mixture (3). Other elements leached
from the concentrate will be present. The quantity of solids produced is
about 2 to 4 percent of the total weight of spent electrolyte (3). Liquids
will probably drain to waste from the solids.
6. Control Technology - The gas stream from this oxidation operation is
undoubtedly processed to recover the vaporized and entrained materials. This
is probably accomplished by external cooling, condensation, and water scrub-
bing. No details have been disclosed.
The solid wastes from this process are mixed with the wastes from the
oxidation step (Process No. 40) and sluiced into a settling pond. In loca-
tions other than the arid region where this plant is operating, secondary
water pollution could be substantial.
7. EPA Classification Code - None
140
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8. Reference^ -
1. Potter, J. Personnel Communication on Hydrometallurical Process.
Bureau of Mines. Salt Lake City, Utah, 1976.
2. Rosenzweig, M.D. Copper Makers Look to Sulfide Hydrometallurgy.
Chemical Engineering. Volume 83, No. 1: pp. 79-81. Januarys,
1976.
3. Atwood, G.E., and C.H. Curtis. Hydrometallurgical Process for the
Production of Copper. U.S. Patent No. 3,785,944. January 15,
1974.
141
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PRIMARY COPPER PRODUCTION PROCESS NO. 40
CLEAR Oxidation
1. Function - This is the principal leaching operation of the CLEAR system,
in which partially leached ore concentrate is contacted with freshly regen-
erated leach solution. Primarily the ferric chloride is active during_this
step, reacting with copper ore minerals to form ferrous chloride, cupric
chloride, and elemental sulfur.
The sulfur is a solid material that remains with the leach residue. It
is reported that 98 percent of the residual copper is extracted in this step
(1). The solids from this process are discarded, although cyanide treatment
for gold recovery may be performed if the gold analysis warrants it (see
Process No. 2).
The leachf solution is filtered and sent to the reduction step (Process
No. 38) (2).
2. Input Materials - Solid residue from Process No. 38 and liquor from
Process No. 39 are the only input materials. The ratios have not been dis-
closed. The liquor at this stage contains about 6 percent cupric chloride
and 15 percent each of ferric and sodium chlorides (1).
3. Operating Conditions - This is a high-temperature, pressurized leaching
operation. Temperatures of 140°C and pressures of 2.7 kilograms per square
centimeter are used (3).
4- Utilities - Source of heat has not been reported; either steam or
direct firing could be applicable. Electricity is undoubtedly required, but
again no information has been published.
5. Waste Streams - Details of the process have not been disclosed in
sufficient detail to establish whether emissions of gases to the atmosphere
occur. Hydrochloric acid vapors could be generated.
The major waste of the CLEAR system, consisting of the solid residue, is
discharged from this step. This residue may be a large fraction of the
original concentrate. It is expected to be 99 percent free of copper (1) and
much reduced in iron; it must contain considerable colloidal sulfur and
soluble chlorides. It may contain cyanides if gold extraction was performed.
No analyses have been published.
6 Control Technology - The process will likely incorporate an operating
control of hydrochloric acid emission, since even small concentrations of
this very corrosive gas can damage plant equipment. If needed, scrubbing
with an alkali can further reduce the concentration.
Solid wastes from this process are sluiced into a settling pond. The
location of this first application is such that natural evaporation should
dispose of the water content, and secondary water pollution should be minimal
142
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In other locations, however, this waste could cause severe secondary pollu-
tion in the form of an acidic seepage high in chlorides, sulfates, and heavy
metals. J
1• EPA Source Classification Code - None
8. References -
1. Atwood, 6.E., and C.H. Curtis. Hydrometallurgical Process for the
Production of Copper. U.S. Patent No. 3,785,944. January 15,
I -7 / i •
2. Potter, J. Personnel Communication on Hydrometallurgical Process
Bureau of Mines. Salt Lake City, Utah, 1976.
3. Rosenzweig, M.D. Copper Makers Look to Sulfide Hydrometallurgy
' Engineerin9- Volume 83, No. 1: pp. 79-81. Januarys,
143
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TECHNICAL REPORT DATA .
(Please read Instructions on the reverse before completing)
1. REPORT NO. 2.
EPA 600/2 80-170
4. TITLE AND SUBTITLE
r,-,/4iio<-vi ai p-rnrpqq Profiles for Environmental Use:
Chapter 29 Primary Copper Industry
7. AUTHOR(S)
Same as Below
9. PERFORMING ORGANIZATION NAME AND ADDRESS
PEDCo Environmental, Inc.
11499 Chester Road
Cincinnati, Ohio 45246
12. SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Laboratory
•Office of Research and Development
JU. S. Environmental Protection Agency
Cincinnati, Ohio 45268
3. RECIPIENT'S ACCESSION NO.
5. REPORT DATE
July 1980 issuing date
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
1AB604
11. CONTRACT/GRANT NO.
68-03-2577
13. TYPE OF REPORT AND PERIOD COVERED
One of Series
14. SPONSORING AGENCY CODE
EPA/600/12
15. SUPPLEMENTARY NOTES
Project Officer: John 0. Burckle
16. ABSTRACT .. ,
The catalog of Industrial Process Profiles for Environmental Use was developed as
an aid in defining the environmental impacts of industrial activity in the United
States. Entries for each industry are in consistent format and form separate chapters
of the study.
The primary copper industry as defined for this study consists of mining
beneficiation, smelting, and refining. A profile of the industry is given including
. ' 7 . , _,._...: ,,4-i „„ ^on-av/iinCT nTT>Hiirt i on and consumption
plant locations, capactes, an varous s
of copper, co-products, and by-products. The report summarizes the various commercial
routes practiced domestically for copper production in a series of process flow diagrams
and detailed process descriptions. Each process description includes available data
regarding input materials, operating conditions, energy and utility requxrements, waste
streams produced'(air, water, and solid waste), and control technology practices and
problems.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COS AT I Field/Group
Exhaust Emissions
Smelting
Trace Elements
Pollution
Copper Production
13B
18. DISTRIBUTION STATEMENT
Publi(
19. SECURITY CLASS (This Report)
Unclassified
152
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
144
If U.S.GOVERNMENT PRINTING OFFICE:1980--657-l65/0093
-------
-o. Environmental Protection Agency
Region V, Library
230 South Dearborn Street
Chicago, Illinois 60604
-------
Agency
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Environmental
Protection
Agency
EPA-335
Official Business
Penalty for Private Use,
$300
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Book
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detach or copy, and return to the address in the upper
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detach, or copy this cover, and return to the address in the
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