600/2-77-023y
Environmental Protection Technology Series
INDUSTRIAL PROCESS PROFILES FOR
ENVIRONMENTAL USE: Chapter 25.
Primary Aluminum Industry
Industrial Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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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 five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to develop and
demonstrate instrumentation, equipment, and methodology to repair or prevent
environmental degradation from point and non-point sources of pollution. This
work provides the new or improved technology required for the control and
treatment of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-77-023y
February 1977
INDUSTRIAL PROCESS PROFILES
FOR ENVIRONMENTAL USE
CHAPTER 25
PRIMARY ALUMINUM INDUSTRY
by
Terry Parsons
Radian Corporation
Austin, Texas 78766
Contract No. 68-02-1319
Project Officer
Alfred B. Craig
Metals and Inorganic Chemicals Branch
Industrial Environmental Research Laboratory
Cincinnati, Ohio 45268
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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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 commercial products constitute endorsement
or recommendation for use.
n
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TABLE OF CONTENTS
CHAPTER 25
Page
INDUSTRY DESCRIPTION 1
Raw Ha ten' al s 3
Products 4
Compani es 4
Envi ronmental Impact 4
Bibliography 9
INDUSTRY ANALYSIS 10
Bauxite Processing 11
Process No. 1. Mining 13
Process No. 2. Grinding, Digestion, and Thickening 14
Process No. 3. Precipitation, Filtration, and Calcining 16
Process No. 4. Red Mud Filtration and Washing 17
Process No. 5. Red Mud Digestion and Sintering 18
El ectrode Preparati on 19
Process No. 6. Crushing, Screening, and Mixing 21
Process No. 7. Molding and Baking 22
Al umi num Producti on 24
Process No. 8. Electrolytic Reduction 26
Process No. 9. Refining and Casting 28
APPENDIX A - Aluminum Company Product Listing 29
APPENDIX B - Chemical Composition of Bauxites 33
APPENDIX C - Size of Particulates from Reduction Cell Vent System... 35
m
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LIST OF FIGURES
CHAPTER 25
Figure Page
1 Bauxite Processing to Alumina 12
2 Electrode Preparation 20
3 Electrolytic Reduction of Alumina to Aluminum 25
C-l Particle Size Weight Distribution in Alumina Reduction
Cell Potline Primary Effluent 36
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LIST OF TABLES
CHAPTER 25
Table Page
1 Raw Materials Required to Produce Aluminum 3
Primary Aluminum Plant Locations and Capacity.
Alumina Plants
Characterization of Principal Waste Streams From
U. S. Bauxite Refineries
5 Chemical Analyses of Red Muds 15
6 Input Materials for Electrode Preparation 21
7 Atmospheric Emissions from Anode Baking 22
8 Atmospheric Emissions from Electrolytic Reduction
of Alumina 27
A-l Aluminum Company Product Listing 30
B-l Chemical Composition of Domestic Bauxites (Weight
Percent) 34
B-2 Chemical Composition of Imported Bauxites (Weight
Percent) 34
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ACKNOWLEDGEMENTS
This catalog entry was prepared for EPA by PEDCo-Environmental Specialists*
Inc., under Contract No. 68-02-1321, Task 26. Richard Gerstle was the
author of this report.
Helpful review comments from Doug Harrison and J. 0. McLean were reviewed
and incorporated in this chapter.
VI
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PRIMARY ALUMINUM INDUSTRY
INDUSTRY DESCRIPTION
The primary aluminum industry as defined for this study consists of
processing bauxite ore to produce alumina and occasionally aluminum
hydroxide and processing alumina to produce aluminum. The manufacture
of other aluminum chemical compounds is not considered a part of this
industry, since only two companies that produce primary aluminum also
produce a few aluminum based chemicals. (See Company-Product listing
in Appendix A).
The two main industry segments consist of bauxite processing
to alumina and alumina processing to aluminum. They are not usually
performed at the same site, since they are distinct and separate processes,
A third industry segment, electrode preparation, is accomplished at the
aluminum production site. Production of aluminum from recycled scrap
aluminum and the production of many other aluminum based chemicals are
not considered parts of this industry. These industries utilize different
raw materials and include mainly companies and/or divisions which do not
produce aluminum from alumina.
This study describes the processes which form each of three
segments. Flow sheets are provided for each segment which show the proc-
esses and the materials entering and leaving each process and the emission
points.
Approximately 7.6 billion kg (8.4 million tons) of alumina were
produced in this country in 1972, including 0.27 billion kg (0.3 million
tons) in the Virgin Islands, from processing about 15.4 billion kg (17
million tons) of bauxite. Approximately 11 percent of this bauxite was
mined in this country, and the balance was imported mainly from Jamaica
and Surinam. The primary aluminum industry utilized about 94 percent of
this alumina to make aluminum. Bauxite is processed to alumina by five
companies at nine sites (one in the Virgin Islands). Plants range in
capacity from 0.32 to 1.22 billion kg (0.350 to 1.380 million tons) per
P
year. Limited growth of bauxite processing plants in this country is
expected.
-------
Production of alumina compounds such as aluminum hydroxide and sodium
aluminate amounts to approximately 0.36 billion kg (0.4 million tons) per
year.
Aluminum is produced by 13 companies at 32 locations, but three
companies produce most (87 percent) of the alumina and 65 percent of the
A M
aluminum in the U.S. ' The basic process used for producing raw aluminum
metal in all plants in the U.S. consists of the electrolytic dissociation
of alumina (AKO-) dissolved in a molten bath of cryolite (NaJ\lFg). Oxygen
released in this process reacts with the carbon anode to form carbon dioxide
and some carbon monoxide. The molten aluminum settles to the bottom of the
cell, directly above the cathode. The three types of cells or pots used
to accomplish this reaction are the prebake cell and the vertical and
horizontal Stud Soderberg designs. These cells all operate under the same
principle, but they differ in anode configuration. The prebake design is
3
used in about 70 percent of total production.
Individual aluminum plants range in size from 31.7 to 254 million kg
(35,000 to 280,000 tons) per year capacity. Total capacity is about
4.445 billion kg (4.9 million tons) per year. The industry operates at
about 85 percent of capacity and employs approximately 146,600 people under
Standard Industrial Classification Code 3334. Aluminum currently sells
for approximately $0.39 per pound, yielding a total value of approximately
$3.8 billion based on 1973 production rates.
Aluminum plants are generally not located near large population centers
and are always located near sources of relatively low-cost electrical power.
Approximately 70 percent of the aluminum manufacturing capacity is located
3 7
in areas with a population density of less then 80 people per square mile. '
The environmental effects from aluminum production on livestock and vegeta-
tion are very significant due to the potentially high fluoride emissions.
Alumina plants are located near mining areas in Arkansas and in port cities
along the Gulf of Mexico and tend to be in more populated areas.
Aluminum production is projected to grow at a rate of about 5.2 percent
3 7
per year until 1980, based on a demand growth of 7.5 percent. ' The excess
in demand over growth will be made up by an increased operating ratio, by
the gradual disposal of the GSA stockpile, and by construction of new plants.
-------
The promulgation of emission standards by EPA is not expected to limit
industry growth significantly. Increased electrical power costs will,
however, cause secondary (recycled) aluminum to compete more economically
with primary aluminum for some markets.
A number of aluminum reduction plants produce their own electricity
by fuel combustion and/or hydroelectrically.
Raw Materials
Bauxite, of which approximately 87 percent is imported, is the raw
material for alumina production. This material is composed mainly of
metallic oxides with aluminum oxide comprising from 20 to 60 percent of
o
the ore as mined. Domestic ores tend to be leaner in alumina content
as shown by data in Appendix B. Heavy metals are not usually found in
this ore. The major environmental problems associated with bauxite
mining and shipping are caused by fugitive dust and water runoff.
Alumina and carbon (petroleum coke) are the major constituents used
for making aluminum as shown in Table 1. Calcined petroleum coke, pitch,
Table 1. RAW MATERIALS REQUIRED TO PRODUCE ALUMINUM
8
Material
Amount,
% by weight
of aluminum products
Sulfur
Alumina (A1203)
Cryolite (Na3AlF6)
Aluminum fluoride (A1F-)
Fluorspar (CaF2)
Anode
Petroleum Coke
Pitch Binder
Cathode (carbon)
1-5
190
3-5
3-5
0.3
49 (Prebake) 45 (Soderberg)
12.7 (Prebake) 16.7 (Soderberg)
2
and some anthracite are used to make anodes and cathodes for the aluminum
reduction process.
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Products
Alumina and aluminum metal are the primary products of the industry.
Much smaller amounts of aluminum hydroxide, sodium aluminate, and aluminum
fluoride are also made by a few plants. The alumina is used largely in the
aluminum smelting industry, and the aluminum is used for manufactured products.
Companies
The primary product of most aluminum companies is aluminum metal cast
in a variety of rough shapes such as sheets, billets, and wire.
Table 2 lists the aluminum plants in this country, their approximate
capacities, and the type of cell used. Table 3 lists the alumina plants,
their locations, and their capacity in 1971.
Environmental Impact
Waste sludge (red mud) is the primary pollution problem associated
with bauxite processing. For each kilogram of alumina product, two kilo-
grams of bauxite must be processed. Atmospheric emissions of particulate
are caused by raw material and product handling, by calcining the hydrated
alumina in a rotary furnace, and by sintering of the mud when required. Table
4 quantifies and characterizes liquid waste streams from U.S. bauxite refineries,
Atmospheric emissions of coke dust from crushing and screening operations
occur in the electrode manufacturing process. Volatile hydrocarbons from the
paste and binder mixing operations also occur. When prebaked electrodes are
manufactured, atmospheric emissions of fluoride, hydrocarbons, and sulfur
oxides also occur. The fluoride compounds come from the recycled anode scrap
material from the aluminum smelting operation. Emissions of SO and total
A
fluorides amount to between 0.35 to 1.0 and 0.15 to 0.75 percent of aluminum
o
produced, respectively.
Primary aluminum reduction mainly causes atmospheric emissions of
particulate and gaseous fluorides. Emissions vary with the type of reduction
cell and with the type of hooding and control device utilized. Approximately
20 to 30 grams of fluoride are evolved per kilogram of aluminum (40 to 60
pounds/ton), with the gaseous fluorides accounting for up to about 60 percent
3 7
of the total emissions. ' On the average about 25 to 30 percent of this
emission escapes to the atmosphere from the cell . Total particulate (in-
cluding solid fluoride) emissions from the cell have not been well quantified,
but amount to approximately 45 grams/kg of product (90 pounds per ton).
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Table 2. PRIMARY ALUMINUM PLANT LOCATIONS AND CAPACITY
3,4
Aluminum Company of America
Alcoa, Tennessee
Badin, North Carolina
Massena, New York
Point Comfort, Texas
Rockdale, Texas
Vancouver, Washington
Warrick, Indiana
Wenatchee, Washington
Anaconda Aluminum Company
Columbia Falls, Montana
Sebree, Kentucky
Consolidated Aluminum Corp.
New Johnsonville, Tennessee
Lake Charles, Louisiana
Eastalco Aluminum Company
Frederick, Maryland
Martin-Marietta Aluminum Inc.
The Dalles, Oregon
Goldendale, Washington
Intalco Aluminum Co.
Ferndale, Washington
Kaiser Aluminum and Chem. Corp.
Chalmette, Louisiana
Mead, Washington
Ravenswood, West Virginia
Tacoma, Washington
National-Southwire Aluminum Co.
Hawesville, Kentucky
North West Aluminum Co.
Astoria, Oregon
Noranda Aluminum, Inc.
New Madrid, Missouri
Ormet Corporation
Hannibal, Ohio
Revere Copper and Brass, Inc.
Scottsboro, Alabama
Reynolds Metals Co.
Arkadelphia, Arkansas
Jones Mills, Arkansas
Listerhill, Alabama
Longview, Washington
Massena, New York
Corpus Christi, Texas
Troutdale, Oregon
Total - 32 plants
Capacity3
265
115
130
184
280
100
225
175
180
120
140
35
87
91
110
265
260
206
163
81
180
68
70
250
112
63
122
221
190
128
111
140
4868
Anode type
Soderberg
Vertical
X
X
X
X
X
Horiz.
X
X
X
X
X
X
X
Pre-
baked
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
a Capacity is a variable value. Stated values are estimates expressed
in 1000 short tons.
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Table 3. ALUMINA PLANTS'
Company and location
Aluminum Company of America
Bauxite, Arkansas
Mobile, Alabama
Point Comfort, Texas
Martin-Marietta Aluminum Inc.
St. Croix, Virgin Islands
Kaiser Aluminum and Chemical Corp.
Baton Rouge, Louisiana
Gramercy, Louisiana
Ormet Corp.
Burnside, Louisiana
Reynolds Metals Co.
Hurricane Creek, Arkansas
Corpus Christi, Texas
Total
Capacity3
375
1,025
1,350
350
1,025
800
580
840
1,380
7,725
1000 short tons per year. Capacity varies with bauxite feed.
0.906 metric tons = 1 short ton
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Table 4. CHARACTERIZATION OF PRINCIPAL WASTE STREAMS FROM U.S. BAUXITE REFINERIES
10
Waste
Quantity
Characterization
Red Mud
Spent Cleaning Acid
Salts from salting -
out evaporator
Barometric condenser,
cooling water
Boiler and cooling
tower blowdown
Water softener sludge
Sanitary waste
500-3600 T/D (dry basis)
1,000-7,200 T/D (wet, settled)
3,000-20,000 T/D (slurry at
18% solids)
Variable, 5-10 T/week inter-
mittently discharged
Variable-estimated up to
several thousand kg/day
Millions of liters/hr
Variable-thousands of liters/
day
One to few T/D
375 liters/D/capita
15-20% solids
5-12 g/1 soda
2-5 g/1 aluminum
pH - 12.5
NapSO,, plus some free H?SO-
RC1 or HAc may also be us§d
pH - 0
Na2SO» - alkaline
pH - 12.5
Temp, rise of up to 15°C
(25°F) may contain traces
entrained alkali
Dilute alkaline solutions
pH - 12.5
Lime and suspended solids
from intake water
B.O.D. 70 g(0.15 lb)/day/
capita
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An overall control efficiency of 70 to 80 percent for fluoride
emissions is achieved by most plants. A primary control system vents
the cell, and the pollutants captured in this system are reduced by
about 95+ percent with wet scrubbers, electrostatic precipitators, or
alumina coated fabric filters. The emissions that escape from the cell
are vented through the cell building roof. A number of plants are now
venting the entire cell room gases through low pressure drop baffled
spray systems to reduce emissions.
Recovery of fluoride compounds from dry sorption systems employing
fabric filters or from the scrubber sludges is practiced at some plants.
Sources of waste water from primary aluminum reduction include wet
scrubbing, boiler blowdown, and cooling water. The reported volume of solid
wastes resulting from water treatment in a number of plants was 15 to 30 kg
Q
per metric ton of aluminum produced. These solid wastes are composed of
cryolite, carbon, and calcium fluoride sludge. Spent carbon cathode pot
linings are another source of solid waste. The estimated annual volume of
such wastes produced is 1200 cubic meters (about one acre foot). The Office
of Solid Waste Management Programs is currently sponsoring an investigation
of the wastes and disposal technologies for the primary metals industry
which includes aluminum production. These results will be available in the
near future.
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Bibliography
(1) Saxton, 0. C. and M. Kramer, EPA Findings on Solid Wastes from
Industrial Chemicals, Chem. Eng., April 28, 1975, p. 107-111.
(2) Stamper, J. W., Aluminum, In: Minerals Yearbook, Vol. 1, U.S.
Bureau of Mines, 1972.
(3) Crane, G. and B. A. Varner, Guidelines for State Emission Standards
for Primary Aluminum Plant Fluorides - Draft, U.S. EPA, Office of
Air Quality and Planning and Standards. Research Triangle Park,
North Carolina.
(4) Chem. Sources - U.S.A., Directories Publishing Co. Inc., New Jersey,
1975.
(5) Characteristics of Population, Bureau of Census, 1970.
(6) Wall Street Journal, June 5, 1975.
(7) Air Pollution Control in the Primary Aluminum Industry, Singmaster
and Breyer Co., EPA Publication 450/3-73-004A, pg. 4-11.
(8) Trace Pollutant Emissions from the Processing of Metallic Ores, EPA
Publication 650/2-74-115, October 1974.
(9) Development Document for Effluent Limitations Guidelines and New Source
Performance Standards for the Primary Aluminum Smelting Subcategory of
the Aluminum Segment of the Nonferrous Metals Manufacturing Point Source
Category, EPA Publication 440/1-74-019-3, 1974.
(10) Development Document for Effluent Limitations Guidelines and New Source
Performance Standards for the Bauxite Refining Subcategory of the
Aluminum Segment of the Nonferrous Metals Manufacturing Point Source
Category, EPA Publication 440/1-74-019-C, 1974.
(11) Pierce, Alan, Office of Solid Waste Management Programs, EPA, Cincinnati,
Ohio, personal communication, September, 1975.
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INDUSTRY ANALYSIS
The environmental impact of the primary aluminum industry has received
wide attention because of the atmospheric emissions of fluorides. Emission
and processing data for the electrolytic reduction and electrode production
segments of this industry have been fairly well defined in the recent EPA
studies cited in references 3, 7, and 8 of the bibliography. Emission data
on bauxite processing are, however, very sparse.
Information for this study was obtained from the literature and in-house
experience in this industry. Descriptions of three industry segments are
provided; namely bauxite processing to yield alumina, electrode production,
and alumina reduction to aluminum. Separate process flow sheets are provided
for each segment.
10
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Bauxite Processing
This segment of the primary aluminum manufacturing industry includes
those processes required to reduce bauxite ore to alumina. About 10 percent
of the bauxite processed in this country is mined here; the balance is
imported. About 90 to 95 percent of the bauxite is processed to alumina.
Five process steps have been identified for this segment. As shown in
Figure 1, three of these steps are involved in the direct production of
alumina, and two alternate steps are involved in the processing of the
waste sludge or red mud.
The major environmental problems associated with this industry segment
are disposal of sludge and emission of particulates from the material handling
and calcining operations. Bauxite processing is mainly performed near mining
areas or ore receiving terminals.
11
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FLOCCULENT
MINING
FILTRATION
AND WASHING
Ce
TEAN
'l 1
GRINDING,
TION, A
THICKENI
1
NaOH
?
DIGES-
fjn -m
NG 2
HEAT
\ ?
2
f ALUMINATE ]
I LIQUOR i
PRECIPITATION,
FILTRATION,
CALCINING 3
ALTERNATE
HEAT
DIGESTION
SINTERING
AND WASHING 5
A
x>
GASEOUS EMISSION
LIQUID WASTE
X> SOLID WASTE
CaO/CaCOa
NaOH
Figure 1. BAUXITE PROCESSING TO ALUMINA
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BAUXITE PROCESSING PROCESS NO. 1
Mining
1. .Function - Mining is primarily accomplished by quarrying the ore
in open pits. The ore is blasted loose and then shoveled via draglines,
conveyors, and other heavy earth-moving equipment to transfer areas for
shipping via rail and/or ship. Some bauxite contains up to 30 percent
moisture and may be dried at 110°C before shipping.
2. Input Materials - Ore deposits, dynamite.
3. Operating Parameters - Open-pit mine.
4. Utilities - Fuel and water for drilling.
5. Waste Streams - Overburden, fugitive dust, and water runoff from
mined areas.
6. EPA Source Classification Code - None exists.
7. References -
(1) Air Pollution Control in the Primary Aluminum Industry,
Singmaster and Breyer Co., EPA Publication 450/3-73-004A.
(2) Crane, G. and B. A. Varner, Guidelines for State Emission
Standards for Primary Aluminum Plant Fluorides - Draft, U.S.
EPA, Office of Air Quality and Planning and Standards,
Research Triangle Park, North Carolina.
13
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BAUXITE PROCESSING PROCESS NO. 2
Grinding, Digestion, and Thickening
1. Function - The raw ore is beneficiated by grinding to about 100
mesh, digested in caustic at elevated temperatures and pressures (Bayer
digestor), and then filtered or thickened in the presence of floccu-
lants. Lime may also be added to the digestor, depending on the ore's
composition. These steps yield a sodium aluminate liquor and a waste
stream of "red mud" which contains the impurities in the bauxite ore.
2. Input Materials - Bauxite Ore - The quantity of ore required varies
from 1.3 to 3 times the amount of alumina obtained depending on the
original alumina content. Typical ore analyses are provided in Appen-
dix B. Caustic Solution - 2 moles of sodium hydroxide are required to
stoichiometrically react with 1 mole of alumina. At a 30 percent
excess, 1.5 kg of NaOH are required per kg of alumina. However most of
this caustic is recycled and only a much smaller portion is required for
make-up. Lime - Quantity varies with ore.
3. Operating Parameters - Grinding and mixing take place at ambient
conditions. Digestion takes place at approximately 145°C and 4.2 kg/cm2
(290°F and 60 psig).
4. Utilities - Water: Approximately 3.5 kg per kg of alumina. Steam is
required to heat the digestor and electricity is required to drive pumps
and fans.
5. Waste Streams - Red mud, a waste slurry, is the main waste stream
from this process. Typical compositions of this stream are shown in
Table 5. Depending on the type of bauxite processed, from 1/3 to 2 kg
of red mud is produced for each kg of alumina product. Uncontrolled
atmospheric particulate emissions amount to approximately 0.003 kg per
kg of bauxite processed (6 Ib/ton). Atmospheric emissions are usually
well controlled.
14
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Table 5. CHEMICAL ANALYSES OF RED MUDS3
Component
Fe2°3
Al,0,
£ O
Si02
Ti02
CaO
Na20
Loss on ignition
Weight percent
Surinam
30-40
16-20
11-14
10-11
5-6
6-8
10.7-11.4
Arkansas
55-60
12-15
4-5
4-5
5-10
2
5-10
Jamaica
50-54
11-13
2.5-6
trace
6.5-8.5
1.5-5.0
10-13
6. EPA Source Classification Code - 3-03-000-01.
7. References -
(1) Air Pollution Control in the Primary Aluminum Industry,
Singmaster and Breyer Co., EPA Publication 450/3-73-004A.
(2) Crane, G. and B. A. Varner, Guidelines for State Emission
Standards for Primary Aluminum Plant Fluorides - Draft,
U. S. EPA, Office of Air Quality and Planning and Standards,
Research Triangle Park, North Carolina.
(3) Trace Pollutant Emission from the Processing of Metallic
Ores, EPA Publication 650/2-74-115, October 1974.
(4) Vandergrift, A. E. et al., Particulate Pollutant Systems
Study, Vol. 1, Mass Emissions, Midwest Research Institute,
APTD 0743, May 1, 1971.
(5) Development Document for Effluent Limitations Guidelines
and New Source Performance Standards for the Bauxite
Refining Subcategory of the Aluminum Segment of the
Nonferrous Metals Manufacturing Point Source Category,
EPA Publication 440/1-74-019-C, 1974.
15
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BAUXITE PROCESSING PROCESS NO. 3
Precipitation, Filtration, and Calcining
1. Function - The rich sodium aluminate (AICO solution is
hydrolyzed to aluminum hydroxide which is precipitated by cooling the
solution. The precipitate is filtered and washed, and the wash solution
and filtrate are concentrated and recycled. The aluminum hydroxide
precipitate is calcined to alumina product in a rotary kiln or furnace.
2. Input Materials - The aluminate liquor from Process No. 2
is the only input material.
3. Operating Parameters - Precipitation is accomplished at approxi-
mately ambient conditions. Calcining occurs at about 1000°C (1800°F)
in the presence of excess air.
4. Utilities - Oil or gas fuel for calcining; approximately 516 gm-
cal/kg (3.7 x 106 BTU/ton of product).3
5. Waste Streams - Atmospheric emissions of particulate amounting to
approximately 10 percent of the alumina product are evolved (0.1 kg per
kg of alumina or 200 Ib/ton). Particulate control devices are utilized
to reduce emissions. Water vapor is also emitted along with smaller
amounts of combustion products.
6. EPA Source Classification Code - 3-03-000-01.
7. References -
(1) Air Pollution Control in the Primary Aluminum Industry,
Singmaster and Breyer Co., EPA Publication 450/3-73-004A.
(2) Crane, G. and B. A. Varner, Guidelines for State Emission
Standards for Primary Aluminum Plant Fluorides - Draft,
U. S. EPA, Office of Air Quality and Planning and Standards,
Research Triangle Park, North Carolina.
(3) Shreve, R. N., Chemical Process Industries, 3rd. Edition,
McGraw-Hill Book Co., New York, 1967, pg. 353-354.
(4) Vandergrift, A. E. et al., Particulate Pollutant Systems
Study, Vol. 1, Mass Emissions, Midwest Research Institute,
APTD 0743, May 1, 1971.
a Estimate based on cement manufacture.
16
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BAUXITE PROCESSING PROCESS NO. 4
Red Mud Filtration and Washing
1. Function - The primary purpose of this step is to recover caustic
and additional alumina compounds which can be recycled to the digester
in Process No. 2. This is accomplished by filtration and/or washing of
the sludge. The filtrate (or wash liquor) 1s then concentrated and re-
cycled.
2. Input Material - Red mud slurry from the thickener in Process No. 2.
3. Operating Parameters - Ambient conditions.
4. Utilities - Water and electricity for pumping.
5. Waste Streams - Approximately 1 kg of filter cake or washed sludge
is dumped into tailings ponds per kg of alumina product.
6. EPA Source Classification Code - None
7. References -
(1) Air Pollution Control in the Primary Aluminum Industry,
Singmaster and Breyer Co., EPA Publication 450/3-73-004A.
(2) Crane, G. and B. A. Varner, Guidelines for State Emission
Standards for Primary Aluminum Plant Fluorides - Draft,
U. S. EPA, Office of Air Quality and Planning and Standards,
Research Triangle Park, North Carolina.
17
-------
BAUXITE PROCESSING PROCESS NO. 5
Red Mud Digestion and Sintering
1. Function - Additional processing of red mud from high silica (8% or
more) bauxite is performed at some plants to recover alumina. The red
mud is digested with caustic and lime or limestone and sintered to
convert silica to calcium silicate (brown mud). The sintered material
is reacted with water and filtered. The soluble sodium aluminate is
recycled.
2. Input Materials - Red mud, caustic solution and lime or limestone
are utilized.
3. Operating Parameters - The digestion is accomplished at approxi-
mately 145°C and 4.2 kg/cm (290°F and 60 psig), similar to that in
Process No. 2. Sintering is accomplished at 1100 to 1200°C.
4. Utilities - Gas and/or oil for the sintering step is required.
5. Waste Streams - Brown mud (calcium silicate) and other impurties in
the bauxite occur as waste. On the order of 1 kg of mud is formed per
kg of alumina. Brown mud has limited uses in cement manufacture.
6. EPA Source Classification Code - None
7. References -
(1) Air Pollution Control in the Primary Aluminum Industry,
Singmaster and Breyer Co., EPA Publication 450/3-73-004A.
(2) Crane, G. and B. A. Varner, Guidelines for State Emission
Standards for Primary Aluminum Plant Fluorides - Draft,
U.S. EPA, Office of Air Quality and Planning and Standards,
Research Triangle Park, North Carolina.
18
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Electrode Preparation
The electrode preparation segment of the primary aluminum industry
involves two processes to produce the anode and cathode electrodes used
in the electrolytic reduction of alumina. Electrode preparation is
usually performed near the alumina reduction process.
Figure 2 is a flow sheet of this segment of the industry. Particulate
and fluoride emissions to the atmosphere are the primary environmental
problems associated with this segment.
19
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PETROLEUM
COKE AND
RECYCLED
ANODES
HEAT
1 1
CRUSHING,
SCREENING
AND MIXING 6
j>
HEAT
1
MOLDING AND
BAKING
C
7
•)
PREBAKED
ELECTRODES
GASEOUS EMISSION
FIGURE 2. ELECTRODE PREPARATION
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ELECTRODE PREPARATION PROCESS NO. 6
Crushing, Screening, and Mixing
1. Function - This process sizes and mixes the carbon in the form of
petroleum coke, recycled scrap anode material, and asphaltic binder into
a homogenous paste.
2. Input Materials - Raw material requirements are described in Table 6.
Table 6. INPUT MATERIALS FOR ELECTRODE PREPARATION (kg/kg ALUMINUM)
Anode Type
Prebake anode
Paste (Soderberg)
Petroleum Coke
0.49
0.45
Asphalt Pitch Binder
0.12
0.17
Total
0.61
0.62
3. Operating Parameters - Mixing of the ingredients takes place in jacketed
heaters at 95°C (200°F) at atmospheric pressure.
4. Utilities - Electricity is required to power the ball and hammer mill
grinders. Steam is used to heat the mixing chamber and asphalt binder.
5. Waste Streams - Particulate emissions occur from conveying, grinding
and mixing transfer points. These sources are usually controlled to some
extent. Volatile hydrocarbons from the binder are also vented. Quantitative
emission data are not available.
6. EPA Source Classification Code - 3-03-001-04.
7. References -
(1) Air Pollution Control in the Primary Aluminum Industry, Singmaster
and Breyer Co., EPA Publication 450/3-73-004A.
(2) Crane, G. and B. A. Varner, Guidelines for State Emission Standards
for Primary Aluminum Plant Fluorides - Draft, U. S. EPA, Office of
Air Quality and Planning and Standards, Research Triangle Park,
North Carolina.
21
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ELECTRODE PREPARATION PROCESS NO. 7
Molding and Baking
1- Function - This process is performed only when the prebaked anode
cell system is used. The green paste is molded into the anode shape and
then baked at elevated temperatures for about 40 hours to form a solid
carbon electrode. In the Soderberg cell system the green paste is
transferred directly to the electrolytic reduction cell and the molding
and baking process is not required.
2. Input Materials - Green paste from Process No. 6.
3. Operating Parameters - Molding is accomplished by large presses.
Baking is performed in sunken pits surrounded by interconnecting flues.
The anode is slowly raised to its baking temperature of approximately
1200°C and held at that temperature for about 40 hours. The anode is
then slowly cooled. The entire heating, baking, and cooling cycle
requires about 28 days.
4, Utilities - Oil and/or gas.
5. Waste Streams - Broken and rejected anodes are recycled to Process
No. 6. Atmospheric emissions occur as shown in Table 7.
Table 7. ATMOSPHERIC EMISSIONS FROM ANODE BAKING
Pollutant
Particulate
Hydrocarbons
Total fluorides
Sulfur
Emissions. % of aluminum product
1,3
0.15 (0.1 to 0.5)
0.025 to 0.075
0.047 (0.015 to 0.075)
0.035 to 0.1
The fluorides occur almost entirely in the gaseous form.
6. EPA Source Classification Code - 3-03-001-05.
7. References-
(1) Air Pollution Control in the Primary Aluminum INdustry,
Singmaster and Breyer Co., EPA Publication 450/3-73-004A.
(2) Crane, G. and B. A. Varner, Guidelines for State Emission
Standards for Primary Aluminum Plant Fluorides - Draft,
U. S. EPA, Office of Air Quality and Planning and Standards,
Research Triangle Park, North Carolina.
22
-------
(3) Compilation of Air Pollutant Emission Factors EPA Publication
AP-40, 2nd edition, April 1973, pg. 7.1-5 and 7.1-6.
23
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Aluminum Production
This industry segment includes the electrolytic reduction of alumina to
aluminum (the Hall-Heroult process) and the casting and refining of the alu-
minum before it is shipped to other companies for rolling and casting. Figure
3 is a process flow sheet for this industry segment. It includes two processes;
namely, the electrolytic reduction step, and the refining and casting steps.
Because of the extremely large electrical requirements, electrolytic
reduction is always performed near sources of relatively inexpensive elec-
tricity. Atmospheric emissions of fluorides and the emissions resulting from
fuel combustion required to generate the large electrical demand are the major
environmental problems associated with this industry segment. Emission data
are fairly well documented.
24
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ro
tn
ELECTRODES\ ^
OR } *
^PASTE/ J(
ELECTROLYTIC
REDUCTION _
o
\
ELECTRICITY
N> /
MOLTEN \
ALUMINUM ) ^
/ S
REFINING AND
CASTING
'CRYOLITE'
FLUORSPAR
LALUMINATRI
.FLUORIDE,
ITROGE
CHLORINE
AND
CHLORIDE
SALTS
GASEOUS EMISSION
SOLID WASTE
FIGURE 3. ELECTROLYTIC REDUCTION OF ALUMINA TO ALUMINUM
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ALUMINUM PRODUCTION PROCESS NO. 8
Electrolytic Reduction
1. Function - Alumina is reduced to aluminum electrically according to
the following reaction A1203 + 1 1/2C •* 2A1 + 1 1/2 C02- This reduction
is carried out in long rows of cells or pots made of carbon lined steel
with carbon anodes suspended above the cell. The carbon lining serves
as the cathode and the suspended carbon, the anode. Synthetic cryolite
(Na3AlFg) serves as an electrolyte and solvent for the alumina. During
the reduction process, the carbon anode is consumed and combines with
oxygen to form CO and CO^. The reduced heavier aluminum sinks to the
bottom of the cell and is periodically tapped. Fresh alumina and
cryolite are added periodically to the top of the melt.
2. Input Materials - The following raw materials are required per kg
of aluminum product:
Alumina 1.9 kg
Carbon (electrodes) 0.62 kg
Cryolite 0.04 kg
3. Operating Parameters - The individual cells operate between 950 and
1000°C. This heat is generated by the flow of electricity between the
two electrodes. A current of about 100,000 amps at 4.5 volts is typical.
The cells are maintained at a slight negative pressure to reduce emis-
sions into the cell room.
4. Utilties - 13.2 to 19.8 kWh/kg of aluminum (6 to 9 kWh per pound).
5. Waste Streams - Atmospheric emissions from the cell are described
in Table 8. in addition, polynuclear hydrocarbons are generated from
organic compounds in the electrodes. The S02 emissions originate from
sulfur in the electrode materials.
26
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Table 8. ATMOSPHERIC EMISSIONS FROM ELECTROLYTIC
REDUCTION OF ALUMINA
Component
so2
Gaseous fluorides
Solid fluorides
Total parti cul ate
Average emission rate,3
expressed as % of
aluminum product
3
1.2 (0.7 - 1.7)
1.0 (0.5 - 1.8)
4.6 (0.6 - 8.8)
aBased on Reference 3 and industry questionnaire data in Reference 1.
A wide variety of control devices are in use to reduce both
particulate and gaseous emissions.
Particle size data from samples collected in the primary cell vent
system are shown in Appendix C. These data show that 50 percent of the
particles by weight are smaller than about 1 to 3 microns.
Solid waste in the form of prebaked anode butts is recycled to the
electrode preparation plant.
6. EPA Source Classification Code -
Prebake type cell: 3-03-001-01
Horizontal stud Soderberg cell: 3-03-001-02
Vertical stud Soderberg cell: 3-03-001-03
7. References -
(1) Air Pollution Control in the Primary Aluminum Industry,
Singmaster and Breyer Co., EPA Publication 450/3-73-004A.
(2) Crane, G. and B. A. Varner, Guidelines for State Emission
Standards for Primary Aluminum Plant Fluorides - Draft,
U. S. EPA, Office of Air Quality and Planning and Standards,
Research Triangle Park, North Carolina.
(3) Compilation of Air Pollutant Emission Factors EPA Publication
AP-40, 2nd edition, April 1973, pg. 7.1-5 and 7.1-6.
27
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ALUMINUM PRODUCTION PROCESS NO. 9
Refining and Casting
1. Function - Molten aluminum is tapped (siphoned) from the reduction
cells into crucibles and transferred to gas-fired holding furnaces or cast
in large sows for later remelt. Refining is accomplished by fluxing with
gas or various salts to remove oxides and gas inclusions.
2. Input Materials - Raw molten aluminum; flux gases such as mixtures
of chlorine, and nitrogen or flux salts as hexachloroethane, aluminum
chloride, or magnesium chloride are used.
3. Operating Parameters - Refining and casting occur at approximately 700°C
and atmospheric pressure in gas-fired, hooded furnaces.
4. Utilities - Natural gas and/or electricity are required to maintain
the aluminum in a molten state.
5. Waste Streams - Dross is skimmed from the bath and treated to recover
any aluminum. Residual slag containing chloride flux salts is a solid waste
which is usually sent to landfill. Emissions of aluminum chloride are evolved
when gaseous chlorine is used for fluxing. Traces of gaseous fluorides may
also be emitted.
6. EPA Source Classification Code - 3-03-001-99.
7. References -
(1) Air Pollution Control in the Primary Aluminum Industry, Singmaster
and Breyer Co., EPA Publication 450/3-73-004A.
(2) Crane, G. and B. A. Varner, Guidelines for State Emission Standards
for Primary Aluminum Plant Fluorides - Draft, U. S. EPA, Office of
Air Quality and Planning and Standards, Research Triangle Park,
North Carolina.
28
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APPENDIX A
ALUMINUM COMPANY PRODUCT LISTING
29
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Table A-l. ALUMINUM COMPANY PRODUCT LISTING3
Aluminum Co. of America
Aluminum
Alumina
Alumina gel
Aluminum fluoride and sodium aluminum fluoride
Aluminum hydroxide
Calcium cement
Chlorine
Gallium metal and salts
Hydrofluoric acid
Sodium hydroxide
Anaconda Aluminum Company,
Division of the Anaconda Company
Aluminum
Consolidated Aluminum Corporation
Aluminum
Eastalco Aluminum Company
(Subsidiary of Howmet Corporation)
Aluminum
Gulf Coast Aluminum Corporation
(Division of Consolidated Aluminum Corp.)
Aluminum
Intalco Aluminum Company
Aluminum
Kaiser Aluminum & Chemical Corporation
Kaiser Aluminum Division
Aluminum (Chemicals Div. makes alumina)
Calcined coke
Martin Marietta Aluminum Inc.
(Formerly Harvey Aluminum Inc.)
Aluminum
Alumina (In Virgin Islands)
30
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Table A-l (Continued). ALUMINUM COMPANY PRODUCT LISTING0
National-Southwire Aluminum Company
Aluminum
Noranda
Aluminum
Northwest Aluminum Company
Aluminum
Ormet
Aluminum
Alumina
Revere Copper & Brass, Inc.
Aluminum
Reynolds Metals Company
Aluminum
Alumina
Aluminum hydroxide
Calcium fluoride
Pet. coke compounds
PVC
Sodium aluminate, sodium aluminum fluoride
a Chemical Sources
1974 Directory of Chemical Producers SRI
31
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APPENDIX B
CHEMICAL COMPOSITION OF BAUXITES
33
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Table B-l. CHEMICAL COMPOSITION OF DOMESTIC BAUXITES (WEIGHT PERCENT)
A1203
Si02
Fe203
Ti02
Loss on ignition
Arkansas
40-60
1-20
3-6
1-3
15.35
Oregon
35.0
6.7
31.5
6.5
20.2
Washington
38.8
6.6
28.7
4.2
21.7
Hawaii
25.9
4.7
39.4
6.7
20-23
Table B-2. CHEMICAL COMPOSITION OF IMPORTED BAUXITES (WEIGHT PERCENT)
A1000, total
2 3
Si02
Fe00-
2 3
Ti02
F
PoOc
2 5
VoOr
2 5
H20, combined
A1203> tri hydrate
A1203> monohydrate
Jamaica
49.0
0.8
18.4
2.4
-
0.7
—
27.5
50-47
2-9
Surinam
59.8
3.8
2.7
2.4
-
0.06
0.04
31.2
59.6
0.2
Guinea
58.6
4.9
4.1
2.5
0.02
M
29.6
52.7
5.9
34
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APPENDIX C
SIZE OF PARTICIPATES FROM REDUCTION
CELL VENT SYSTEM
35
-------
wo
»0
*l
»3
WIIOHT PIRCINT LARGER PARTICLES
»• •• 70 M M 40 M It
10
0.2 —
0.1
0.1
— 0.1
10 10 40 M M 70 10 »0 »i
WEIGHT PERCENT SMALLER PARTICLES
FIGURE C-l. PARTICLE SIZE WEIGHT DISTRIBUTION IN ALUMINA REDUCTION
CELL POTLINE PRIMARY EFFLUENT3
Cell Design
PB - Prebake
HSS - Horizontal Stud Soderberg
Source: Air Pollution Control in the Primary Aluminum Industry.
Singmaster and Breyer Co., EPA Publication 450/3-73-OQ4A?
0 I
36
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TECHNICAL REPORT DATA
(Please read Instructions on ilic reverse before completing)
1. F1EPORT NO.
EPA-600/2-77-023y
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Industrial Process Profiles for Environmental Use:
Chapter 25. Primary Aluminum Industry
5. REPORT DATE
February 1977
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO
Terry Parsons, Editor
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Radian Corporation
8500 Shoal Creek Boulevard
P.O. Box 99^8
Austin, Texas 78766
10. PROGRAM ELEMENT NO.
1AB015: ROAP 21AFH-025
11. CONTRACT/GRANT NO.
68-02-1319, Task
12. SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Laboratory
Office of Research and Development
U.S. ENVIRONMENTAL PROTECTION AGENCY
Cincinnati, Ohio ^5268
13. TYPE OF REPORT AND PERIOD COVERED
Initial: 8/75-11/76
14. SPONSORING AGENCY CODE
EPA/600/12
15. SUPPLEMENTARY NOTES
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 aluminum industry as defined for this study consists of processing
bauxite ore to produce alumina and occasionally aluminum hydroxide and processing
alumina to produce aluminum. The two main industry segments are bauxite processing
to alumina and alumina processing to aluminum. These distinct and separate pro-
cesses are not usually performed at the same site. A third industry segment
electrode preparation is accomplished at the aluminum production site. Three
industrial process flow sheets and nine process descriptions have been prepared to
characterize the industry. Within each process description available data have been
presented on input materials, operating parameters, utility requirements and waste
streams. Data related to the subject matter including feedstock characteristics,
and company/product listings are included as appendices.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
C. COSATI l-'icUl/Grotip
Pollution
Aluminum
Bauxite Ore
Alumi na
Aluminum Hydroxide
Reduction Electrodes
Process Description
Air Pollution Control
Water Pollution Control
Solid Waste Control
Stationary Sources
Monferrous Metal Industry
Aluminum Industry
07B
13B
11F
8. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
42
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
37
*USGPO: 1979 — 659-510/37
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