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
MARCH 1974
U.S. ENVIRONMENTAL PROTECTION AGENCY
* Washington, D.C. 20460
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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
Russell Train
Administrator
Roger Strelow
Acting Assistant Administrator for Air and Water Programs
Allen Cywin
Director, Effluent Guidelines Division
George s. Thompson, Jr.
Project Officer
March, 1974
Effluent Guidelines Division
Office of Air and Water Programs
U.S. Environmental Protection Agency
Washington, D.c. 20U60
For aale by the Superintendent of Document*, U.S. Government Printing Office, Washington, D.C.20402 - Prloe $1.46
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ABSTRACT
This document presents the findings of a study of the bauxite
refining industry by the Environmental Protection Agency for the
purpose of developing effluent limitation guidelines and
standards of performance for the industry, to implement Sections
304, 306, and 307 of the Federal Water Pollution Control Act as
amended.
Effluent limitations guidelines contained herein for the bauxite
refining industry set forth the degree of effluent reduction
attainable through the application of the best practicable
control technology currently available, and the application of
the best available technology economically achievable, which must
be achieved by existing point sources by July 1, 1977, and July
1, 1983, respectively. The standards of performance for new
sources contained herein set forth the degree of effluent
reduction attainable through the application of the best
available demonstrated control technology, processes, operating
methods, or other alternatives.
The major process waste from bauxite refining is the red mud
residue remaining after extraction of the alumina. Thousands of
tons per day are produced by the typical refinery. Total
impoundment of process wastes was determined to represent the
best practicable control technology currently available for
existing point sources. No discharge of process waste water
pollutants to navigable waters is the effluent limitation to be
achieved by existing point sources by July 1, 1977, and as the
standard of performance for new sources.
Supportive data and rationale for development of the effluent
limitations guidelines and standards of performance are contained
in this report.
111
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XI NEW SOURCE PERFORMANCE STANDARDS
XII ACKNOWLEDGMENTS
XIII REFERENCES
XIV GLOSSARY
87
89
91
93
VI
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FIGURES
Number
1 Location of Alumina Refining Plants in the U.S.
2 Generalized Diagram of the Bayer Process
3 Generalized Diagram of the Combination Process
4 Generalized Diagram of Water Circuit for Bayer
Plant Employing Total Impoundment
5 Flowsheet of Digestion and Heat-Recovery System
6 Mean Annual Lake Evaporation in the United States
7 Mud Lake Dike Construction
8 Generalized Diagram of Basic Water Balance
for a 3000 ton/day Bauxite Refinery Processing
Jamaican Bauxite
10
16
17
19
26
29
56
71
Vll
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TABLES
6
7
8
9
10
11
12
13
1U
15
16
17
ESS®
Operating companies, Locations, capacities
and Date of Operation of U.S. Bauxite Refining Plants 8
Production of Primary Aluminum in the United
States 11
Maximum Rainfalls 24
Rainfall and Evaporation Data 28
Range of Composition of Bauxites for Alumina
Production 31
Characteristic Analyses for Various Bauxites 33
Red Mud Insoluble Solids 38
Red Mud Slurry Soluble Solids 39
Screen Analysis of Red Mud 39
Range of Chemical Analyses of Red Muds 41
Characterization of Principal Waste streams
from U.S. Bauxite Refineries 44
Summary of Effluent Reductions Achieved for
Bauxite Refinery Process Wastes Using Best
Practicable Control Technology Currently Available 61
Water Pollution Abatement Status and Planned
Changes (Process and Non-Process Waste Streams) 62
Unit Mud Production Rates for Various Bauxites 75
Summary of Waste Disposal Cost Data 76
Summary of Estimates of Future Waste Disposal
Cost Data 78
English/Metric Unit Conversion Table 99
viii
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SECTION I
CONCLUSIONS
For the purpose of establishing effluent limitations guidelines
and standards of performance, the aluminum segment of the
nonferrous metals manufacturing point source category was divided
into three subcategories. This report deals with the bauxite
refining subcategory. Consideration of the factors of age and
size of plant, processes employed, geographical location, wastes
generated, and waste water treatment and control techniques
employed support this conclusion. The similarities of the wastes
produced by bauxite refining operations and the control and
treatment techniques available to reduce the discharge of
pollutants further substantiate the treatment of bauxite refining
as a single subcategory.
It is concluded that the best practicable control technology
currently available consists of techniques including impoundment
(controlled disposal on land), the management of process waters
by methods dependent on the impoundment capability and the
evaporative capability inherent in the bauxite refining process
as currently practiced, and various measures applied to
individual waste streams including neutralization and impoundment
to eliminate . the discharge of process waste water pollutants to
navigable waters. Recycle of water contained in the impoundment
area should be practiced to the maximum extent possible.
It is further concluded that the current technology of
impoundment to control the major process waste (red mud) allows
the control of other wastes by use of the same impoundment
facilities with or without prior treatment such as
neutralization.
It is also concluded that the best available technology
economically achievable applicable to existing sources and the
best available demonstrated control technology, processes,
operating methods or other alternatives applicable to new sources
aad equivalent to the best practicable control technology
currently available.
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SECTION II
RggOMMEKDATIQNS
The effluent limitations and standards of performance for the
bauxite refining subcategory are no discharge of process waste
water pollutants into navigable waters.
The effluent limitations are considered achievable by all
existing sources by July 1, 1977, inasmuch as two plants
currently achieve the effluent limitations. The limitations are
based on the application of control and treatment technology
meeting the criteria for best practicable control technology
currently available, best available technology economically
achievable, and the best available demonstrated control
technology, processes, operating methods, or other alternatives.
The technologies on which such effluent limitations and standards
are based consist of impoundment, in the form of a red mud lake,
of the major solid waste from the bauxite refining processes, and
the management of process streams and waste waters using the red
mud lake, other impoundment lakes, and/or the evaporative
capability present in the bauxite refining operation. Thus, a
closed cycle system with reuse of water within the system is
achieved. The technologies identified also include the treatment
of smaller associated waste water streams by such means as
neutralization, with subsequent disposal of neutralization
sludges to the solid waste impoundment facility and the control
of remaining waste waters by impoundment, evaporation, or recycle
within the plant facility. Treatment may involve, for example,
neutralization before impoundment, as for spent cleaning acid; or
the treatment may involve evaporative cooling, as for barometric
condenser effluents. In such cases, the treated effluents are
contained within the cycle.
These identified waste water control technologies are directly
related to the characteristics of the bauxite refining process,
which, as currently practiced, inherently involves control of the
amount of water in relatively large volumes of process streams
and always contains evaporative capacity for control of the
composition of process streams and product drying.
Under certain conditions, the discharge of excessive
accumulations of rainfall may be allowed from point sources as an
exception to the above limitations and practices. This exception
is based on the recognition that most bauxite refining plants
occupy large areas, and are located in climatic regions where
short-term (i.e., hours or days) high rainfalls occur. Further,
annual variations in rainfall may exceed the capacity of even
reasonably designed impoundment facilities.
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SECTION III
INTRODUCTION
Purpose and Authority
Section 301 (b) of the Act requires the achievement by not later
than July 1, 1977, of effluent limitations for point sources,
other than publicly owned treatment works, which are based on the
application of the best practicable control technology currently
available as defined by the Administrator pursuant to Section
304(b) of the Act.
Section 301(b) also requires the acievement by not later than
July 1, 1983, of effluent limitations for point sources, other
than publicly owned treatment works. Which are based on the
application of the best available technology economically
achievable which will result in reasonable further progres s
toward the goal of eliminating the discharge of all pollutants,
as determined in accordance with regulations issued by the
Administrator pursuant to Section 304(b) to the Act.
Section 306 of the Act requires the achievement by new sources of
a Federal standard of performance providing for the control of
the discharge of pollutants which reflects the greatest degree of
effluent reduction which the Administrator determines to be
achievable through the application of the best available
demonstrated control technology, processes, operating methods, or
other alternatives, including, where practicable, a standard
permitting no discharge of pollutants.
Section 304(b) of the Act requires the Administrator to publish
within one year of enactment of the Act, regulations providing
guidelines for effluent limitations setting forth the degree of
effluent reduction attainable through the application of the best
practicable control technology currently available and the degree
of effluent reduction attainable through the application of the
best control measures and practices achievable, including
treatment techniques, process and procedure innovations,
operation methods and other alternatives. The regulations
contained herein set forth effluent limitations guidelines
pursuant to Section 304(b) of the Act for the bauxite refining
subcategory of the nonferrous metals category.
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Summary of Methods Used for Development of the
Effluent Limitations Guidelines and Standards of Performance
The effluent limitations guidelines and standards of performance
contained herein were developed in the following manner. General
information was obtained on all domestic bauxite plants in the
continental U.S. by means of a questionnaire.
Data for the development of effluent limitations guidelines were
based largely on site visits and interviews at the eight
continental U.S. plants, supplemented by published technical and
trade literature, telephone interviews, EPA technical reports,
and meetings with EPA personnel.
The industry was first examined for purposes of determining
whether separate limitations and standards are appropriate for
different subsegments within a point source category. Possible
further subcategori zation was considered, based upon raw
materials used, processes employed, product produced, geographic
location, size, and age of plants, wastes generated, and other
factors, as discussed in Section IV.
From the on-site inspections and the questionnaire responses,
flow diagrams, and information on water management practices,
control and treatment methods, equipment and costs were acquired.
From these data, the differences
were identified. This included:
in raw waste characteristics
1) Analysis of the source and volume of water used in the
process, the sources of waste and waste water in the plant,
and type and quantity of constituents in the waste waters, as
discussed in Section V.
2) Identification of those constituents, discussed in
Section VI, which are characteristic of the industry and are
present in significant quantities. These pollutants are
subject to effluent limitations guidelines and standards of
performance.
The information, as outlined above, was then evaluated in order
to determine what levels of technology constituted the best
practicable control technology currently available, best
available technology economically achievable, and the best
available demonstrated control technology processes, operating
methods and other alternatives. In identifying such
technologies, various factors were considered. These included
the total cost of application of technology in relation to the
effluent reduction benefits to be achieved from such application,
the facilities involved, the process employed, the engineering
aspects of the application of various types of control
techniques, process changes, nonwater quality environmental
impact (including energy requirements) and other factors, as
discussed in Sections IX, X, and XI.
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In view of the small number of plants and the geographical
concentration of the industry, it was possible to visit and
acquire detailed data from all 8 of the bauxite refineries in the
continental United states. Only the refinery in the Virgin
Islands was not included in the industry sample, so that 90
percent of the plants, and a larger percentage of production, was
included in the survey sample.
General Description of.the Industry
This document applies to the bauxite refining industry, standard
Industrial Classification (SIC) 2819 (alumina only).
Although the manufacture of aluminum metal dates back to the
simultaneous discovery by Hall and Heroult of the electrolytic
reduction process, the rapid growth of the industy began only
during World War II. Almost overnight, the demands for this
light metal for aircraft created the large industry of today.
Because of this growth pattern, aluminum is one of the youngest
metal industries, and very few plants, either primary aluminum or
bauxite refining, are more than 30 years old.
Bauxite is the principal ore of aluminum and the only one used
commercially in the United States. Aluminum is a unique metal in
that all of its purification is accomplished in the bauxite
refining step; none occurs in the subsequent reduction to metal.
Thus, the purification requirements in producing refined alumina
(A1203) from the raw ore are strict. Bauxite consists of
aluminum oxide, more or less hydrated and containing various
impurities, such as iron oxide, aluminum silicate, titanium
dioxide, quartz, and compounds of phosphorus and vanadium.
Bauxite ores vary in characteristics from stony materials to soft
clays. In general the term bauxite applies to weathered deposits
from which substances other than alumina have been leached to
leave a sufficient alumina content to make the deposit profitably
workable. The process chemistry of alumina refining is basically
quite simple, and the classic Bayer process is universally used
in the United States. In this process the impure alumina in the
bauxite is dissolved in a hot, strong alkali solution, generally
NaOH, to form sodium aluminate. Upon dilution and cooling the
sodium aluminate hydrolyzes, forming a precipitate of aluminum
hydroxide which is filtered and calcined to alumina. The
operations employed are those typical of very large scale
hydrometallurgical operations, conducted in essentially a closed
circuit, and economically possible only with maximum recovery of
heat and a near quantitative recovery of reagents.
Bauxite refining is carried on in the United States only by
primary aluminum producers. The majority are integrated back to
the bauxite refinery or to the mine. Bauxite refining is
characteristically conducted in very large scale installations.
There are only nine U.S. bauxite refineries, owned by five
primary aluminum producers. Alumina capacities, shown in Table 1,
vary from 325,000 to 1,3000,000 metric tons (360,000 to 1,440,000
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TABLE 1. OPERATING COMPANIES, LOCATIONS, CAPACITIES, AND DATE
OF OPERATION OF U.S. BAUXITE REFINING PLANTS
CD
Company
Aluminum Company
of America
Raiser Aluminum and
Chemical Corp.
Reynolds Metals Co.
Onnet Corporation
Martin-Marietta
Aluminum Co.
Plant Location
Mobile, Alabama
Pt. Comfort, Texas
Bauxite , Arkansas
Baton Rouge, Louisiana
Gramercy, Louisiana
Corpus Chris ti, Texas
Hurricane Creek, Arkansas
Burns ide , Louis iana
St. Croix, Virgin Islands
Total U.S.
Date of
Commercial
Approximate Plant Capacity.
Operation Metric Tons/Day
1938
1959
1952
1942
1960
1953
1942
1958
1967
Capacity
2,270
3,200
900
2,800
2,400
3,600
2,100
1,550
900
19 , 720
Short Tons/Day
2,500
3,500
1,000
3,100
2,650
4,000
2,300
1,700
1,000
21,750
, tons alumina
Metric Tons/Year(a)
820,000
1,150,000
325,000
1,010,000
865,000
1,300,000
755,000
560,000
325,000
7,200,000
(a) Basis 360 day/year operation (98.6% of capacity).
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short tons) per year. The locations of the eight refineries in
the continental United States are shown in Figure 1.
Alumina production capacity is in reasonable balance with
consumption, and the period of explosive growth of the industry
appears to have subsided (see Table 2). Over the last several
years, the industry has operated substantially below capacity.
The next round of growth is judged to be some years away and
industry consensus appears to be that no large additions to
bauxite refining capacity in the form of new, grass-roots plants
are anticipated over the next several years. Future expansion is
more likely to be in the form of incremental expansions and
additions to existing plants.
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NEW ENGLANC
PACIFIC
WEST NORTH CENTRAL
WEST SOUTH-CENTRAL
Annual Capacity, metric tons
+ < 500,000
O 501,000 TO 1,000,000
D > 1,000,000
Figure 1. Location of alumina refining plants in the U.S.
ST. CR01X
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TABLE 2. PRODUCTION OF PRIMARY ALUMINUM IN THE UNITED STATES
Year
1950
1951
1952
1953
1954
1955
&•
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
Production,
short tons
718,600
836,900
937,300
1,252,000
1,460,600
1,565,700
1,679,000
1,647,700
1,565,600
1,954,100
2,014,500
1,903,700
2,117,900
2,312,500
2,552,700
2,754,500
2,968,400
3,269,200
3,255,000
3,793,000
3,976,100
3,905,000
4,120,000
Annual Increase
Short Tons
115,100
118,300
100,400
314,600
208,600
105,100
113,300
3 1,300 00
83,100(a)
388,500
60,400
110,800(a)
214,200
194,600
240,200
201,800
213,900
300,800
14,800
225,000
Percent
19.1
16.5
12.0
33.6
16.6
7.2
7.2
1.900
4.9(a)
24.8
3.1
5.500
11.3
9.1 '
10.4
7.9
7.7
10.3
0.4(a>
16.5
4.8
i.sOO
5.4
(a) Decrease.
Source: Metal
Statistics, 1972
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SECTION IV
INDUSTRY CATEGORIZATION
Introduction
In developing effluent limitations guidelines and new source
performance standards for a given industry, a judgment must be
made as to whether these regulations can be uniformly and
equitably applied to the entire industry, or whether sufficient
differences exist to warrant the establishment of additional
subcategories. The factors considered in determining whether
such subcategories are justified for bauxite refining were:
(1) Manufacturing process.
(2) Raw materials.
(3) Products produced.
(4) Wastes generated.
(5) Plant size and age.
(6) Plant location.
(7) Air pollution control equipment.
As a result of a study of the literature, plant .inspections, and
communications with the industry, it was concluded that the
bauxite refining industry should be considered as a single
subcategory.
Factors Considered
Manufacturing Process
Process Description. The refining of alumina from bauxite is
accomplished by either of two processes, the Bayer process or the
combination process. The combination process is a variation of
the Bayer process in that the solid residue is retreated. The
Bayer process has been in use since about 1895, and is now a
mature technology.
l£Y®£ Process. In the Bayer process, the hydrated alumina in the
bauxite is converted to a soluble salt, sodium aluminate, by
reaction with either sodium hydroxide or a combination of lime
and sodium carbonate to accomplish the following net reaction:
(monohydrate) A1203«H20 + 2NaOH --- v2NaA102 + 2H20
(trihydrate) A1203«3H20 •*• 2NaOH --- >2NaAl02 + UH20,
In practice this reaction is accomplished by mixing the ground
ore with caustic solution in large iron mixing tanks. The
mixture is fed into pressure vessels or autoclaves, and heat and
pressure are developed by either steam heating of jacketed
autoclaves or, more generally, by direct injection of live steam.
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Conditions must be varied to suit the
but may be indicated as follows:
bauxite ore composition.
monohydrate forms - a solution containing 200 to 300 g/1 of
Na20 and temperature of 200 to 250°C at
pressures as high as 35 atmospheres (500
trihydrate forms - a solution containing 100 to 150 g/1 of
Na20 and temperatures of 120 to 170°c at
3.40 to a. 75 atmospheres (50 to 70psi)
pressure.
Most bauxite ores contain different proportions of the
monohydrate and trihydrate forms/ and operating conditions are
adjusted to obtain optimum processing. The greater portion of
bauxites processed in the United states are predominantly of the
trihydrate form, which permits the use of the lower
concentrations, temperatures, and pressures. There are minor
differences in severity of processing conditions between
refiners, which are described later, but these differences do not
significantly influence aqueous process effluents.
The bauxite ore, if imported, is dried before shipment to
eliminate excess moisture; locally mined ore, as in Arkansas, is
used as received, although it is stored under cover in a blending
building before use. Prior to leaching, bauxite ore is ground.
An exception is Jamaican ore, which has a particle size so small
that grinding prior to leaching is unnecessary,
The product of the above digestion process is a slurry containing
NaAl02 in aqueous solution and undissolved solids. The insoluble
residue remaining after the attack is commonly known as red mud,
and contains the iron oxides from the bauxite, as well as some
sodium aluminosilicate, titanium dioxide (Ti02) , and various
other secondary impurities.
Red mud from various bauxites has different characteristics.
These characteristics produce varying disposal problems at
different refineries. For example, the yield of red mud residue
from Surinam bauxite is low (approximately 1/3 ton per ton of
alumina product) , and the mud is amenable to filtration and
effective washing on a filter. Thus, the final residue is
relatively easy to handle and disposal area requirements are
moderate. On the other hand, red mud from Jamaican bauxite is
produced in much greater yield, (approximately 1 ton per ton of
alumina) , due to its larger content of contaminants. Its
physical characteristics are such that filtration may be
uneconomic at this time, and the muds are separated and washed by
as many as seven stages of countercurrent decantation. The
caustic values recovered by the washing are concentrated by
evaporation and returned to the process.
The red mud may be moved as a waterborne slurry to a waste area,
known as the red mud lake, and not further processed. In the
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past, and still occurring at some domestic refineries, the red
mud has been discharged to a river. Under an existing Federal
consent decree, these discharges will soon stop. Jamaican red
mud also has poor settling properties, so that its disposal on
land could pose serious problems. As noted in a later
discussion, a solution to this problem has recently been
developed to the point of commercial application.
A generalized schematic flowsheet of the Bayer process is shown
in Figure 2. As described above, the separation and washing of
the red mud residue may be accomplished by filtration or
countercurrent decantation, depending on its handling
characteristics. Another feature of the process, which is a
relatively large energy consumer, is the maximization of heat
recovery; heat exchangers are a major feature of the process
flowsheet. All possible caustic values are recovered from the
red mud residues for return to the digestion step. This
introduces a problem common to many closed extractive circuits,
namely, buildup of soluble contaminants. Excessive
concentrations of contaminants in the sodium aluminate liquor can
interfere with alumina precipitation, and control measures may be
required. Some contaminants can be eliminated by contact of the
spent liquor with the red mud residues in a holding tank.
Another approach is to pass a portion of the mother liquor
through a salting-out evaporation step.
combination Process.
In
.the combination process, applied to
high-silica bauxites such as those from Arkansas, the red mud
residue is treated to extract additional amounts of the alumina
and to recover sodium values. This additional extraction step is
accomplished by mixing the red mud with limestone (effectively
CaC03) and .sodium carbonate, and then sintering this mixture at
1100 to 1200°C. The important reactions are the conversion of
silica to calcium silicate and residual alumina to sodium
aluminate. The sintered products are leached to produce
additional sodium aluminate solution, which is either filtered
and added to the main stream for precipitation or is precipated
separately. The residual solids (brown mud) are slurried to a
waste lake. A generalized flowsheet of the combination process
is shown in Figure 3. Although omitted for simplicity, the
analogous use of heat exchangers and condensates shown in Figure
2 is used.
One feature of the combination process is that lime and soda ash
may substitute totally for caustic soda as the starting reagent,
utilizing the familiar reaction:
Ca(OH)2 + N3.2CO3---*- 2NaOH + CaCO3.
From either of the alternative processes, purified sodium
aluminate solution is passed through heat exchangers and cooled
to 50 to 60°C prior to being discharged into large precipitation
vessels. By the addition of seed material and by careful control
of composition and controlled agitation, alumina trihydrate is
precipitated in a controlled form, amenable to easy separation
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Bauxite
Reconcentrated Caustic Liquor
f Washing precipitates
Condensate - To J Boiler feed water
Dilution Green Liquor
Steam
To
Mud Lake
Calcined Alumina
Product
Figure 2* Generalized diagram of the Bayer Process.
16
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Brown Mud
To Lake
Product Product
Figure 3. Generalized diagram of the Combination Process.
17
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and washing. Precipitation may take one to three days. The
precipitated trihydrate (aluminum hydroxide) is dewatered and fed
to calcination which transforms the alumina to the anhydrous
crystalline form, most suitable for later use in the electrolytic
reduction to aluminum metal. Much of the alumina produced by the
combination process from Arkansas bauxite is utilized for other
purposes than the production of aluminum metal. These include
refractories, electrical insulators, catalyst supports, ceramics,
abrasives and polishes, heat exchange media, activated alumina,
and chemical alums.
A large percentage of U.S. production of gallium, used in
transitors, results as a by-product of the refining of Arkansas
bauxite. The gallium occurs in the ore as a trace element and is
recovered from the process for its commercial value. This
recovery operation is associated only with one plant operating on
a specific ore,
Water Circuit. The general pattern of water usage includes the
use of water for leaching solutions, washing of precipitates,
considerable use for heat exchange purposes in connection with
the control of temperatures in the reaction (i.e., steam heating,
flash evaporation or multiple-effect evaporators, etc.), and
other steps of the chemical extraction process, From the
viewpoint of water recirculation or discharge, the major feature
of all water circuits is the red or brown mud lake operated at
nearly all alumina refineries. This lake is analagous to a
tailings pond in a flotation concentrator operation. The mud
lake serves as a receiver of solid residues, a receiver and
reservoir of process water, a point of loss by evaporation and
seepage, and a collector of rainfall. Since some minimum amount
of water is required by the mechanics of flushing the material to
the disposal site, water also serves as the transport medium of
the waste portion of the ore to the lake.
In general, the standard or combination Bayer process has no
large demand for water for air pollution control. The processes
used are essentially carried out in closed vessels. As with any
plant, a sanitary water circuit is part of the operation,
requiring a source of potable water. Disposal may be to a
municipal sewer system, a plant sewer system, or to the red mud
lake, with or without any form of treatment.
Although all plants use either the Bayer or the combination
process, no two plants are alike with respect to water treatment
and management schemes. This makes characterizing plant
effluents somewhat complicated. Location, climate, type of ore,
and waste management philosphy all contribute to different
approaches to waste water management. Seven of the nine U.S.
bauxite refineries already practice total impoundment of mud
wastes, A very generalized water flow diagram for a bauxite
refinery practicing total impoundment is shown in Figure U.
while the diagram shows intake water treatment, sanitary uses,
and boiler plant water streams, these streams are not considered
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Bauxite
Rain
Runoff
Liquor from
Evaporation
Stormwater
Lake
Process
Lake
Liquor
To Salts -
Mixer To Waste
C. W. - Cooling Water
Figure 4. Generalized diagram of water circuit for
Bayer.plant employing total impoundment.
19
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to be bauxite process streams, and are shown merely
the water circuit.
to complete
Since most of the industry uses total recycle of the main process
stream and normally concerns itself with only combined streams,
complete analyses for process waste streams are not readily
available. The principal waste stream is the red mud stream.
When this is routed to a red mud lake, as part of a closed water
circuit, the parameter of concern is the alkalinity of the
recycling lake water. This is kept low because the lake serves
as an additional washing stage. Other ions in this recycle
stream (e.g., sulfate) are monitored only to the extent that
their levels will not interfere with plant operation.
A refinery may have, in addition to the main red mud lake, a
process water lake and a storm water lake. In addition, the
minor remaining storage capacity in abandoned red mud lakes may
be utilized to dispose of small quantities of aqueous wastes
intolerable in the recycle circuit. An example of this is the
sulfate streams resulting from acid cleaning of equipment or from
salting-out evaporators. A process water lake can be thought of
as a recycle reservoir used for higher grade operations than the
red mud lake, which has a lower alkalinity and generally a higher
water quality. It may also be used as a source of makeup water
for the mud lake circuit.
A storm water lake may be used to collect storm water runoff from
the plant site. Since the surface areas encompassed by a bauxite
refinery complex will range from a minimum of several hundred
acres to a thousand acres or more, very large volumes of storm
water must be planned for. This problem is discussed in some
detail later. Normally, a bauxite refinery will maintain its
main process water stream 'in approximate balance. In most cases,
there will be a large circulating load, tens of thousands of
liters per minute, but makeup additions will be relatively minor.
The prinicipal water streams in a bauxite refinery are the
following:
Red mud stream
Spent liquor
condensates
Barometric condenser cooling water
Miscellaneous cooling water streams
Miscellaneous waste streams
Storm water runoff.
Red Mud stream. Red mud is the insoluble residue remaining after
extraction of the alumina from bauxite, in the case of the
combination process used for Arkansas ore the final residue is
brown mud, but the same considerations apply. After filtration
or thickening to separate the pregnant sodium aluminate liquor
from the red mud gangue, the mud is pumped to disposal. If not
already at a pumpable consistency, it is first diluted. Disposal
may be to a river (two plants) or to a red mud lake (seven
20
-------
plants). If disposed of to a river, the mud is further diluted
to 0.5-1.5 percent solids to insure that rapid settling does not
occur at the point of discharge. Depending upon the bauxite ore,
the residue may range between 0.33 ton/ton of A1203 produced
(Surinam bauxite) to 2 tons/ton (Arkansas bauxite). At 17-20
percent solids, the water going to the red mud lake will
approximate 1,900,000 to 18,000,000 liters/day (500,000 to
4,800,000 gal/day). Not all of this water returns to the plant
since the terminal density of the settled solids may range from
35 to 75 percent. A substantial amount of water is retained in
the mud. This is one manner in which water is rejected from the
process water circuit.
Spent Liquor. After separation from the mud residue, either by
filtration or by countercurrent decantation plus a polishing
filtration, the pregnant liquor is cooled, diluted and sent to
the precipitators. Here, fine seeds of hydrated alumina are
added and after a cooling period of 1-3 days, the solution
hydrolyzes and the alumina precipitates as alumina hydroxide.
After filtration of the product alumina trihydrate, the spent
liquor is heated and concentrated for return to the digester.
Thus, the spent liquor is not a waste stream, although some
wastes may be withdrawn from it. In order to control buildup of
contaminants which might either retard precipitation or
precipitate with the product in the process liquor, a portion of
the spent liquor may be passed through a salting-out evaporator,
where it is evaporated to low volume in order to eliminate
contaminants, particularly sulfates. To prevent redissolution of
sulfates and their return to the process, the sulfate slurry is
normally disposed of to an abandoned mud lake or to a land fill.
The discharge of such wastes to surface waters was not observed
in any plant.
In another scavenging scheme, soluble contaminants tending to
build up in the spent liquor are allowed to adsorb and/or
precipitate on the bauxite slurry from the digesters. This is
accomplished by mixing spent liquor with the bauxite slurry,
cooling and diluting it before filtration, and allowing
sufficient contact time for the scavenging to occur. After this,
the red mud is filtered off and rejected. This scheme performs
satisfactorily for one producer, and eliminates a need for a
salting-out evaporator.
Condensates. Numerous large scale evaporation operations are
carried out in bauxite refineries. The high temperature, high
pressure slurry from the digesters is flashed down to atmospheric
pressure for filtration or thickening. The still-hot clarified
pregnant liquor may be vacuum-flashed to cool it for
precipitation. The spent liquor after precipitation is
evaporated to concentrate it. All of these operations produce
steam which is generally condensed in a heat exchanger to heat a
process stream. These steam condensates are high quality waters,
and are normally utilized for the most demanding plant uses
(i.e., boiler-feed water, product washing, and final washing of
21
-------
red muds). However, in some plants where the water balance is in
excess, some condensates may be rejected as a waste discharge.
Barometric Condenser Cooling Water. As noted in the preceding
section, cooling and concentration in evaporators is a common
feature of most bauxite refineries. However, one refinery,
processing high-grade Surinam bauxite by careful management of
the process water circuit, is able to avoid the use of
evaporators and barometric condensers. In most cases, in the
last stage, the multi-effect evaporators are under a relatively
high vacuum. Surface condensers are much more expensive than
barometric condensers and use more water. They are not used as
evaporators unless the vapor to be condensed must be recovered
separately from the cooling water. Thus, barometric condensers
are invariably used in the bauxite refining industry. Barometric
condensers are large consumers of water, and the water management
scheme adopted will depend upon water availability, water balance
considerations, and effluent discharge requirements.
Where a negative system water balance exists and water
conservation measures are practiced, the barometric condenser
water loop will be closed, using the red mud lake or other
process water. Where the process water system tends toward a
positive balance, or where ample supplies of water of
satisfactory quality are available, a once- through scheme may be
adopted, with the effluent rejected to a nearby surface water.
Water quantities required by barometric condensers used in this
service are large, characteristically several thousand
liters/minute for each condenser, water used may be as much as
20,000-40,000 liters/ton (5,000-10,000 gallons/ton) of product.
Theoretically, the overhead vapors to be condensed should
approach distilled water in composition. When entrainment
occurs, alkali and aluminum values will be carried over and will
appear in the effluent from the barometric condenser hot-well.
If this is discharged to a receiving water containing dissolved
magnesium or calcium compounds, these will be precipitated as
visible white hydroxides. Normally, entrainment will be minimal
from a well designed and operated evaporator and will reach
unsatisfactory levels only during periods of upset.
Incorporation of suitable demisters in the evaporator vapor space
will further minimize entrainment.
Miscellaneous Cooling Water Streams. Normally, the various
cooling streams in a bauxite refinery come from air compressor
aftercoolers and various cooling duties associated with the
rotary calcining kilns. These are characteristically non-contact
services.
storm Water Runoff. storm water runoff from bauxite refinery
sites may comprise a significant volume. This results from the
large ground areas occupied and general location in regions with
high and occasionally torrential rainfalls. There are no known
data on the changes in alkalinity of runoff water as a function
of amount of rainfall for a single storm, but it would be
22
-------
anticipated that the first portion of a rain would remove any
superficial alkaline dust, and that alkalinity of the runoff
would decrease thereafter.
If the plant areas were smaller or refineries were located in
more arid areas, storm water runoff would be of little
consequence. However, all bauxite refineries in the continental
United States have histories showing storm-type rainfalls.
Illustrative of the maximum rates of rainfalls which can be
experienced in these regions are some historical data from U.S.
Weather Bureau Records (Table 3). For example, during this study
about 60 cm (24 in) of rainfall were accumulated over a three-day
period in one area of the Texas Gulf Coast (3).
Current technology for control of storm water runoff appears to
be the selection of a maximum rainfall rate which can be
collected, and to divert storm water runoff, accumulating at
greater rates than this, by overflow weirs or similar
arrangements. One plant, for example, can collect and store
rainfall up to a rate of 7.6 cm (3 inch) per hour; rainfall at
rates greater than this is diverted to a nearby waterway. Storm
water runoff from rains exceeding this rate are considered by the
plant to be either essentially uncontaminated by process
pollutants, or so extremely dilute that any contaminants are
below significant levels.
Mass Water Balance in a Bauxite Refinery. A better understanding
of the state-of-the-art of treatment technology and the factors
affecting the feasibility of total impoundment is gained when the
possible water gains and losses in a bauxite refinery are
considered. Although these will vary, the following summarizes
the main sources of gain and loss:
Water Gains. In most cases, refineries processing imported ores
will not gain water from them, since these ores are dried before
shipment and normally stored under cover before use. if outdoor
storage piles are used, some moisture will enter with the ore.
Domestic ore (Arkansas) is not dried before processing, and there
is a definite water gain from this source. Almost all plants
have a fresh water intake, although this quantity is highly
variable. Water intake may be needed for potable purposes,
boiler feed water, barometric condensers, washing precipitated
aluminum hydroxide, or makeup for water losses from the circuit.
The other large and uncontrollable cause of water gain is
rainfall. Since bauxite refineries occupy large areas, runoff
quantities can significantly affect the water balance. There is
some possibility of diverting rainfall on plant grounds so that
it does not enter the water circuit. However, rain which falls
on mud lakes enters the water circuit directly, and can represent
a sizable water gain. For example, 31 cm (1 ft) of rain on a
40.5 ha (100 ac) mud lake is equal to a little over 125,000,000
liters (33,000,000 gal), and can accumulate in as little as 24
hours (Table 3).
23
-------
TSELE 3. MAXIMUM RAINFALLS
(a)
Cumulative Rainfall, cm (in.)
Location
1-hr
2-hr
3-hr
6-hr
12-hr
24-hr
Little Rock, Arkansas 7.62 (3.00) 11.68 (4.60) 17.32 (6.82) 19.50 (7.68) 20.80 ( 8.19) 24.33 ( 9.58)
Year -< 1955 >- 1913 1913
Mobile, Alabama
Year
8.91 (3.51) 11.35 (4.47) 12.70 (5.00) 20.88 (8.22) 32.97 (12.98) 33.93 (13.36)
1947 1922 1900 1911 1900 1955
to
Baton Rouge, Louisiana 6.12 (2.41) 9.27 (3.65) 11.56 (4.55) 12.34 (4.86) 12.60 ( 4.96) 21.34 ( 8.40)
Year 1959 •< 1954 »- 1947
New Orleans, Louisiana 11.97 (4.71) 14.91 (5,87) 16.61 (6.54) 21.89 (8.62) 32.41 (12.76) 35.58 (14.01)
Year -« 1953 *- 1927 1929 -« 1927 *-
Corpus Christi, Texas 9.22 (3.63) 11.81 (4.65) 13.59 (5.35) 15.95 (6.28) 17.78 ( 7.00) 20.98 ( 8.26)
Year 1928 1960 1956 1931 >- 1924
Victoria, Texas
Year
7.87 (3.10) 11.81 (4.65) 15.62 (6.15) 18.67 (7.35) 20.19 ( 7,95) 22.02 ( 8.67)
-* I960 »-
(a) Data through 1961.
Reference: The Water Encyclopedia.
-------
Water Losses.
the~following:
Water losses in a bauxite refinery may arise from
Drying and calcining of product.
Red mud.
Evaporative cooling of green liquor,
Concentration of spent liquor.
Evaporation from lakes,
Seepage*
Red mud calcination (combination process),
Drying and calcining of product: The precipitated aluminum
hydroxide, Al(OH)3, is filtered from the spent liquor, washed to
displace the entrapped caustic solution, dried, and calcined.
Assuming a 50 percent solids cake from the filter, a ton of water
is evaporated for each ton of alumina product (i.e., 520 to 3600
kkg (575 to 4000 ton) water).
Red mud: The red or brown mud carries water, which is not
reclaimed. Even when fully consolidated, the mud in a lake may
contain more than 50 percent moisture. This is approximately one
ton of water loss for each ton of mud. This loss will vary on an
alumina basis due to the range for various bauxite ores of from
0,33 to 2.0 tons mud per ton A1203 produced.
«.
Evaporative cooling of green liquor: Evaporation is a ubiquitous
operation in a bauxite refinery. It occurs first ,in cooling the
bauxite slurry issuing from the digesters. Typically, the green
liquor slurry from the digesters will be blown down (flashed) to
atmospheric pressure in several stages. The vapors released will
be condensed and reused as boiler feed water, cake washing, or
dilution of the filtered pregnant liquor before precipitation.
It is not normally discarded. The general system was described
by Hudson, (5) and is illustrated by the flowsheet in Figure 5.
Although the slurry must be cooled before going to the
precipitators, recovery of heat is an equally important
objective. The steam from the flash tanks is used in the shell
side of tubular heat exchangers to heat the process liquor
recycling to the digesters. As indicated by Figure 5, a portion
of the liquor is diverted through the mixer where the liquor and
bauxite are combined.
The final stage of cooling the green liquor before filtration or
countercurrent decantation of the mud may be performed by an
evaporator operating under vacuum. The vapors released are
condensed in a barometric condenser. There are several
possibilities for disposal of the mixture of cooling water and
process condensate from the barometric condenser. It may be
contained in a totally closed circuit, with the effluent going to
the lake or cooling tower from which the condenser cooling water
is drawn. The barometric condenser may use once-through cooling
water, in which case the mixed effluent is discharged from the
plant to a waterway and represents a water loss.
25
-------
Bauxite
Digester
0
Tubular
Heat
Exchangers
Steam
Condensate
Mixer
r Tl
+* i—A_,
Reconcentrated
Spent
Liquor
Slurry from Digester
Flash
Tanks
Digested Slurry
- to Clarification
Figure 5. Flowsheet of digestion and heat recovery system.
26
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The pregnant liquor filtrate from the red mud separation step
also needs further cooling before going to the precipitators.
This cooling may be done through evaporation or in heat
exchangers against the cold spent liquor enroute to the
evaporators. The effluent from the barometric condenser
generally will go to a reservoir for recycle to the process.
Concentration of spent liquor: A large heat duty is associated
with the concentration for reuse of the spent liquor filtrates
from separation of the aluminum hydroxide product from the mother
liquor. Typically, the multistage evaporators used will
concentrate the liquor from about 150 g/1 to about 170 g/1 Na203
(113 g/1 to 128 g/1 NaOH) . Again, the vapor from the first
stages will generally be condensed against some cold process
stream, but the last stage will be under high vacuum and will
utilize a barometric condenser. Depending on the balance in the
water circuit and the availability of the large quantities of
water needed for a barometric condenser, the effluent will be
discharged to a waterway or recycled to an impoundment lake in
the plant water circuit. If efficiently operated, there will not
be any appreciable carryover of caustic from an evaporator to a
barometric condenser.
Evaporation from lakes: The area of a bauxite refinery's red mud
lake may vary from, 40 to 800 ha (100 to 20CO ac). In addition, a
plant may have a series of lakes (process lakes, clear water
lakes, storm water lakes, etc.) used for other purposes.
Depending on the geographical location of a refinery, these lakes
may serve as net evaporators or net collectors. In more arid
locations along the Texas Gulf Coast, these lakes may be a source
of water loss; further east, in southern Louisiana or Alabama,
the reverse may be true. Table 4 depicts this situation, showing
average rainfall and mean annual lake evaporation, the latter
data taken from Figure 6.
Seepage: seepage from lakes is a possible minor source of water
loss. However, in constructing a lake, . attempts are made to
insure that the bottom provides an impervious layer. A ditch
surrounds the red mud lake dikes, in which any minor seepage will
be collected and pumped back to the lake. General practice is to
monitor this ditch by survey wells located around the lake.
Ground water does not exit the property through a recognizable or
identifiable outfall. Based on information supplied by plant
operators, there is no evidence to suggest that this is a
pollution problem to either surface or ground waters.
Red mud calcination: One special case of water loss is in the
red mud calcination peculiar to combination process bauxite
refineries. The red mud from the first stage is retreatd by
mixing with soda ash and lime and than calcined. The red mud
.underflow from the countercurrent decantation unit, at 25
percent solids, generally will undergo pressure filtration,
possibly to 40-50 percent solids, to reduce the water content and
the evaporative load. This will represent a loss from the system
of about a ton of water per ton of red mud processed.
27
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TABLE 4. RAINFALL AND EVAPORATION DATA
to
00
Mean Annual
Lake
Rainfall Data'3^
Location
Little Rock, Ark. /Robinson AAF
Little Rock, Ark. /Adams Field
Mobile, Ala. /Bates Field
Mobile, Ala./Brookley AFB
Baton Rouge, La. /Downtown
New Orleans, La./Moissant Field
Corpus Christ! , Tex./Cuddihy Field
Matagorda Island, Tex.
cm
128
126
158
154
133
146
72
94
(in.)
(50.3)
(49.5)
(62.2)
(60.7)
(52.3)
(57.4)
(28.3)
(37.1)
Years
9
23
90
12
16
84
19
12
Evaporation^)
cm
109
119
124
124
140
140
(in.)
(-43)
(-47)
(-49)
(-49)
(-55)
(-55)
Average Net
Accumulation
cm
18
37
9
22
68
46
(in.)
<~7,
(-14)
( ~3)
( ~9)
(-27)
(-18)
(a) U.S. Naval Weather Service World-Wide Airfield Summaries.'^'
(b) The Water Encyclopedia(^) (see Figure 6).
-------
Figure 6. Mean annual evaporation in the United States.
(Source: U.S. Weather Bureau)
[Values in inches for period 1946-55-1
VO
-------
Summary . As described in the foregoing paragraphs, there is
fundamentally only one process for refining bauxite, the Bayer
process. The combination process, a variation of the .Bayer
process, retreats the red mud waste from the Bayer process to
recover additional aluminum and alkali values. Upon review of
both methods, it is concluded that the differences in
manufacturing processes do not warrant further subcategorization.
Various means of condensation create varying quantities of waste
water. When barometric condensers are utilized, large quantities
of cooling water are required which may create an imbalance in
the water circuit. While these differences may justify adoption
of a different configuration or management of some water
circuits, there is no justification for establishment of a
subcategory to provide for them.
Raw Materials
The raw material for all U.S. alumina refineries is bauxite, an
ore of aluminum which consists of hydrated alumina (A1203/ 3H20) ,
known as gibbsite or hydrargillite. *~
This classification is of great practical importance in
processing, as the methods used to treat bauxites in order to
extract pure alumina are based on attacking the bauxites with
caustic soda. The trihydrate is much more soluble in alkali than
are the monohydrates , and processing conditions are appreciably
milder. Most of the bauxite processed in the United States is
predominantly of the trihydrate variety.
The suitablity of a bauxite as a raw material for aluminum
extraction depends on its alumina content and on its content of
combined silica in the form of kaolinite, A1203/ 2Si02- 2H20 . Not
only does such a silicate, if present, tie up~"a certain amount of
alumina that cannot be extracted, but, in the course of treatment
entails a heavy and expensive loss of caustic soda in the form of
insoluble sodium aluminum silicate compounds (such as sodalite,
3^20.^1203/68102/2^01, and cancrinite, (Na,K) (Al,Si) 204.) .
Each kilogram of "SiO^ in the bauxite involves the loss ~"of
approximately 1 kilogram of A120_3 and 0.6 to 0.7 kilogram of
The composition of the bauxite used in alumina production varies
a great deal. The variations generally fall within the following
limits shown in Table 5,
30
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TABLK 5. RANGE OF COMPOSITION OF BAUXITES
FOR ALUMINA PRODUCTION
Composition
Weight Percent
f total
Si02_, free and combined
Fei03
Ti02
p2.°5.' V2,05' etc-
H20, combined
40 to 60
1 to 20
7 to 30
3 to . 4
0.05 to 0.20
12 to 30
Reference: Kirk-Othmer (7)
31
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There are other ores of aluminum, such as nepheline, a double
silicate of alumina and an alkali metal, and alunite, a hydrous
potassium aluminum sulfate, K(A10) 3_(S04:)2^3H2p. The treatment of
these ores is complicated and expensive, and"no other ores except
bauxite are commercially processed in the United States.
Most of the bauxite used in the United States is imported.
Jamaica and Surinam (formerly Dutch Guiana) are the principal
suppliers. Some comes from Australia, Guinea (formerly French
Guiana), Haiti, and South America. The only commercial deposits
in the United States are in Arkansas, and are used by two bauxite
refineries located nearby. The differences in ore composition
mentioned previously are illustrated by typical analyses supplied
by the producers for these ores (as shown in Table 6).
The silica content in imported ores is not high enough to warrant
other than the basic Bayer process. It is less expensive to
accept the losses of alumina and caustic discussed above than to
attempt to recover them. However, the average silica content of
Arkansas ores is now in the 13 to 20 percent range. Ores as low
as 6 percent Si02 occurred in the past in the area, but these
were "high-graded" (Turing World War II. There is considerable
variation over this mineralized area, and selective mining is
practiced to produce a uniform feed material.
In order to avoid the high losses of alumina and alkali, which
would occur as a result of the high silica content, the
"combination" process is employed for Arkansas ores. In this
process the red mud residue from the Bayer process, containing
alumina and soda values insolubilized as sodium aluminum
silicate, is sintered with lime soda ash. The lime ties up the
silica as calcium silicate, and the soda ash promotes the
formation of sodium aluminate, which is then leached out and
precipitated in the usual fashion. The resultant solid residue
from the second leaching is known as "brown mud". Its calcium
silicate content confers some of the properties of a hydraulic
cement upon it, and brown mud can be safely accumulated in mud
lakes to'considerable heights.
In summary, the bauxite ores processed in the United States are
essentially all trihydrate-type ores, more amenable to control
and treatment than the monohydrate ores common to European
deposits. Even in the ores least amenable to treatment, 80
percent of the alumina is of the trihydrate form. The best ores
contain 95 percent of the alumina in trihydrate form. In any
case, the chief effect of the higher monohydrate content is to
require a higher temperature and pressure in the digesters. The
quantity and quality of wastes generated is not significantly
affected. Accordingly, a subcategory based upon raw material
differences is not warranted.
If imported bauxite ceases to become freely available at a
competitive price, other domestic ores such as nepheline or
anorthosite, CaO -Al^OS^SiO^, may be used. No domestic plants
32
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TABLE 6. CHARACTERISTIC ANALYSES FOR VARIOUS BAUXITES
Weight Percent
A1203, total
SiOa
Fe203
Ti°2
F
F205
V205
H20, combined
A 12^3) trihydrate
A ^03, monohydrate
Jamaican
49.0
0.8
18.4
2.4
--
0.7
- _»
27.5
40-47
2-9
Surinam
59.8
3.8
2.7
2.4
-_
0.06
0.04
31.2
59.6
0.2
Arkansas
48.7
15.3
6,5
2.1
0.2
._
--
25.8
34.1
14.6
Guiana
58.6
4.9
4.1
2.5
0.02
--
_.
29.6
52.7
5.9
33
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currently are using or plan to use such raw materials, but one
producer has begun exploratory investigations.
Products Produced
The only product from U.S. bauxite refineries is purified
alumina. Normally, this is calcined for use in the production of
aluminum metal. There are no significant differences in product
between the various producers. Minor quantities of other
aluminum compounds are produced, but the tonnages are
insignificant. There is no justification for further
subcategorization based on products.
Wastes Generated
The major process waste associated with the refining of bauxite
is the mud residue. There are differences between the residues
from the Bayer process (red mud) and the residues left after this
mud is retreated by means of the combination process (brown mud).
These differences do not appreciably alter the problem of
disposal. There are also differences in the amount of mud
generated per ton of alumina produced depending upon the source
of the bauxite. Only 1/3 ton/ton of alumina results from
processing Surinam bauxite; about 1 ton/ton from Jamaican
bauxite; and 2 to 2-1/2 tons/ton for Arkansas bauxite. However,
these differences change the size, not the nature of the problem
of disposal.
The bauxite refining industry has reduced itself to one category
for mud wastes. Seven of the existing nine U.S. refineries
practice total impoundment of the mud slurry waste stream. Two
refineries currently are discharging the mud residues into the
Mississippi River. Under a consent degree, these plants must
convert to the equivalent of impoundment by 1975. Thus, by 1975
total impoundment of mud wastes will be universal for the
industry.
As indicated by the process description in the preceding section,
the red mud wastes are accompanied by alkaline process water
containing some unrecovered aluminum. Because of the similarity
of process technology, the differences from plant to plant in
composition of the aqueous phase are minor. With respect to
treatability of red (brown) mud wastes, the differences are
insufficient to warrant establishment of subcategories based on
types of mud. Substantiation for this judgment is provided by
the current, or soon to be successful, total impoundment of each
of the various types of mud.
All bauxite refineries use sulfuric acid for removing scale from
heat exchangers, as well as filtration and other types of
equipment. The resultant spent acid is generally neutralized
with the alkaline mud waste in an active or abandoned mud lake.
Other wastes which may be generated by bauxite refineries include
the following:
34
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Boiler blowdown.
Cooling tower blowdown.
Water softener sludges.
Sanitary waste effluents.
None of these effluents is unique to bauxite refining. Since
none of .these are process streams, they are not , the subject of
effluent limitations.
Plant Size and Age
The aluminum industry and the bauxite refining industry are new,
relative to the other primary metals industries. The oldest
bauxite refinery dates back only to 1938 and two were constructed
during World War II by the Defense Plant Corporation. Four more
refineries were constructed in the 1950's. Since then, only one
has been constructed and it began operation in 1967. The only
old bauxite refinery was shut down in 1957 and dismantled.
Because all refineries use bauxite ore and employ either the
Bayer or combination process, there is a great deal of similarity
between plants. One primary aluminum producer designed and built
its own three plants and the two erected during World War II.
Many components are of identical design.
The smallest bauxite refinery has a production capacity of 900
kkg (1000 tons)/day of A1203. The largest has a capacity of 3265
kkg (3600 tons)/day. A Fourfold difference in plant size does
not significantly affect the quality or quantity of waste water
produced or its amenability to treatment. Thus, further
subcategorization on the basis of the age or size of refineries
is not justified.
Plant Location
As illustrated by Figure 1, two bauxite refineries are located
near the domestic bauxite deposits in Arkansas. The rest of
those in the continental United States use imported bauxite and
are located in the South. These locations are accessible to deep
water shipping, either 'directly on the coast, or along the
Mississippi River.
The relationship between annual rainfall and annual evaporation
may be significant for some plants. In some locations, such as
western Texas, annual rainfall averages about 72 cm (30
inches)/year, while the annual evaporation rate is about 140 cm
(60 inches)/year, a net deficit of 68 cm (30 inches)/year. Thus,
management of red mud lakes and water balances in the water
circuit is simplified. In southern Louisiana and Alabama,
average annual rainfall is approximately 130-160 cm (51-62
inches)/year, while evaporation averages only about 120-140 cm
(47-55 in)/yr, a net gain of 10-20 cm (4-8 in)/yr of rainfall.
This excess water complicates the management of the red mud lakes
and may pose a disposal problem.
35
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Rainfall is important because of the large land areas
characteristic of a bauxite refinery complex. Apart from the
rainfall collected directly in the red mud lake, which
unavoidably enters the water circuit, runoff from the plant site
must also be managed. Since the plant area may comprise several
thousand acres, the quantities of water collected can be large.
However, the differences between rainfall and evaporation for
various locations are susceptible to control by design and
process management. Runoff from plant sites can be discharged to
its normal water course, if the plant is designed to segregate
process waste waters and runoff. By allowing the discharge of
net rainfall for each monthly period from the overflow of the
impoundment areas, a subcategorization based upon plant location
is not necessary.
Air Pollution Control Equipment
The principal air pollution problem in a bauxite refinery is the
dust from the calcination of the alumina product. Electrostatic
precipitators have been used in the past, but have not always
provided adequate control. New designs for precipitators are
being developed. Baghouses are also used for final cleanup after
electrostatic precipitators. No plants use or plan to use wet
scrubbers on this operation. Where wet scrubbers are used on
other dust producing operations (e.g., lime kilns or conveyor
transfer points), the waste effluent normally is recycled to the
process or is included with the main red mud flow. Compared to
the very large volumes of red mud, these streams are
insignificant. Air pollution control equipment in bauxite
refineries appears unlikely to have any significant effect upon
aqueous effluents, and no further subcategorization is warranted.
36
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SECTION V
WASTE CHARACTERIZATION
Introduction
The dominant waste from a bauxite refinery is the gangue material
from the ore, known as red or brown mud, which is produced on a
very large scale (500 to nearly 4,000 kkgs per day). The most
common solution to this red mud waste problem is total
impoundment, but the tonnages to be disposed of can make the
problem difficult. Compared to the other wastes characteristic
of bauxite refining, the red mud waste stream poses only minor
problems.
Characteristics _of Types of Wastes
Red Mud wastes
Depending upon the type of bauxite used, from 1/3 ton to
approximately one ton of red mud will be produced per ton of
alumina. In the case of brown mud from Arkansas bauxite, this
increases to 2 to 2 1/2 ton/ton. The red mud is the major waste
stream from a bauxite refinery. It will generally issue from the
washing thickeners at approximately 17 to 20 percent solids, and
be pumped to a disposal lake. Iron impurities impart the red
color to the mud. If derived from Jamaican or Arkansas bauxite,
the red mud may contain as much as 50 percent iron.
Table 7 shows a typical chemical analysis of the insoluble solids
in Jamaican red mud. 98.5 percent of the material consists of
the oxides of only eight elements plus water and carbon dioxide.
The remaining 1.5 percent consists of the oxides of metallic
elements, such as MgO,K20,Cr203,ZnO,Zr02,NiOj2,V2C5,SrO, and
others.
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TABLE 7. RED MUD INSOLUBLE SOLIDS (a)
Loason Ingition (LOI)
Si02
A1203
Fe203
P205
CaO
Na20
Ti02
Mn02
Miscellaneous
Percent
11.0
5.5
12.0
49.5
2.0
3.5
5.0
1.0
1.5
8.0
(a) Specific gravity = 3.6
Reference: Rushing (8)
"Poor crystallization and agglomeration have made mineral
identification of red mud very difficult. By using X-ray
diffraction, petrographic microscopy and differential thermal
analysis, some of the mineral compounds have been identified.
Predominant compounds are iron oxides, hematite, Fe203, and
hydrated iron oxides such as goethite, FeO(OH), and limonite,
FeO (OH)»nH20 + Fe.203«nH2C. Other iron compounds such as
jacobsite, MnO«Fe2037 magnetite, -Fe304, hercynit, FeO»Al203, and
ilmenite, FeO», Ti02 have been tentatively identified. Aluminum
is present with silica in tentatively identified compounds such
as pyrophyllite, Al2O3*USiO2»H2O, sarcolite,
-------
TABLE 8. RED MUD SLURRY SOLUBLE SOLIDS
A12°3
NaOH
NaCl
Na2C204
Specific gravity
PH
BOD
COD
2.5 g/kg liq,
3.7 g/kg
1.6 g/kg
0.4 g/kg
0.7 g/kg
0.1 g/kg
1.008
12.5
6 ppm
148 ppm
Reference: Rushing
(8)
TABLE 9. SCREEN ANALYSIS OF RED MUD
Screen
Mesh
-10
-20
-50
-100
-200
-325
+10
+20
+50
+100
+200
+325
Percent
Dry Solids
0.0
0.2
0.8
0.8
0.8
1.9
95.5
Reference: Rushing
(8)
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"The small particle size of the red mud is similar to a
material of about 3 percent fine sand, 62% silt, and 35%
clay, but since few true clay minerals are present, the red
mud will present physical properties of salty fines. Red mud
slurry is moderately thixotropic in that the apparent
viscosity decreases or the fluidity increases as the
cumulative shear rate increases and acts as a Bingham plastic
in that a yield stress must be exceeded before flow
commences.
"Jamaican red mud will reach a maximum compaction of about
35% solids if allowed to settle and compact below a layer of
water. If the mud slurry is allowed to dry in air, surface
cracking will start at about 28% solids. Desiccation
fissuring will continue on air drying with a volume
shrinkage. The volume of one ton of red mud solids at 80%
solids will be 1/4 the volume required for one ton of mud at
35% solids. The air-dried mud will reslurry at solids
contents less than 60%; however, if the drying is continued
to solids contents greater than 60%, the dessicated mud
agglomerates will not reslurry although there may be some
parting of the lumps at fissure or crack planes." (8)
Red mud wastes contain significant amounts of suspended solids
and alkalinity. Depending upon the number of mud washing stages,
the water associated with the mud may contain 3-10 g/1 alkalinity
(expressed as Na^CO^), and 1-3 g/1 of sodium aluminate.
(Convention in the U.S. alumina industry is to express total
alkalinity, including both NaOH and Na£C03 as
The ideal solution to the red mud problem would be to develop a
use for it. An obvious possible application utilizes its high
iron content (Table 10). Fursman, et al (10) describe a process
based on sintering the red mud with carbon and limestone and
melting the sinter in an electric furnace to produce a low purity
iron which could be further processed into steel. Although the
basic process has been further developed (11) it has not yet
found commercial application. It may have some economic value in
countries which have bauxite refineries, but produce little or no
steel.
Other investigators have examined its applicability to the
manufacture of portland cement, bricks, and road construction,
(10) (12), But no domestic markets have yet been developed which
will economically justify processing the waste red mud. Total
impoundment however, affords the opportunity for reclamation of
the red mud when an economic recovery process and adequate
markets are developed.
gleaning Acid Wastes
The thermal efficiency of a bauxite refinery, an important
economic item, depends significantly upon the efficiency of the
many heat exchangers used to transfer heat from hot to cold
process streams. Many of the streams contain substantial
40
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TABLE 10, RANGE OF CHEMICAL ANALYSES OF RED MUDS
Wetszht Percent
Component
Fe2°3
A1203
Si02
Ti02
CaO
N820
Loss on
Ignition
Alcoa
Mobile, Ala.
(Surinam)
30-40
16-20
11-14
10-11
5-6
6-8
10,7-11.4
Reynolds
Bauxite, Ark.
(Arkansas)
55-60
12-15
4-5
4-5
5-10
2
5-10
Reynolds
Corpus Christ!, Texas
(Jamaica)
50-54
11-13
2.5-6
trace
6.5-8.5
1.5-5.0
10-13
Reference: IITRI Project No. G6015
(9)
41
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quantities of dissolved solids, and scaling of exchanger surfaces
is a recurring problem. Acid cleaning is universally employed,
generally with sulfuric acid. Small quantities of inhibited
hydrochloric acid or acetic acid are sometimes used. Scaling is
also a problem with filtration equipment and filter cloths, and
similar cleaning procedures are used. Normally, the resulting
spent acid is primarily a solution high in sulfates, but with
only low to moderate free acid concentrations. These sulfate
solutions are disposed of by most plants to active or,
preferably, to abandoned mud lakes where the neutralization is
completed. In a few instances they are neutralized and
discharged to waterways but this procedure is being replaced by
impoundment. The quantities of sulfuric acid used are not large,
averaging about 0,453 to 0.907 kkg (0.5 to 1.0 tons) of acid per
day.
Barometric condenser Effluents
Possible pollutants from the barometric condensers operation are
heat and alkalinity. As described earlier, sizable barometric
condensers are found at nearly all bauxite refineries, where they
are used on the evaporative coolers and the spent liquor
evaporators. Illustrative of the heat duty are the data from one
plant with five spent liquor evaporators. Here the barometric
condensers averaged 126 I/sec {2000 gal/min) and the temperature
rise was approximately 1U°C (25°FJ, for a total heat duty of
about 31 million kg-cal/hr (125 million BTU/hr). Entrainment of
significant amounts of alkali to the barometric condenser
effluent should be negligible except during periods of upset or
abnormal operation. However, barometric condenser effluents will
tend to have a pH over 7.
Thermal Effluents
Air compressor aftercoolers may also contribute heat to process
streams, compressed air is generally used in sizable amounts for
agitation in the numerous precipitators in a bauxite refinery.
Air from compressors is frequently passed through water-cooled
aftercoolers to remove the heat of compression and cool the air.
This service is a non-contact cooling application and the only
pollutant the cooling water can acquire is heat.
similarly, there may be other non-contact cooling water
applications, from which thermal discharges may result, such as
seal rings on rotary calcining kilns. Heat discharges from these
ancillary services are nominal,
Miscellaneous _Wastgs
Several bauxite refineries operate rotary lime kilns to produce
the lime needed to compensate for the carbonate accumulated in
the process liquor, or for use in the combination process, some
plants use wet scrubbers on these lime kilns, from which a
potential waste stream results, but the resultant hydrated lime
42
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slurry is invariably fed back to the process in order to
the contained lime, and is never discharged.
utilize
One miscellaneous waste stream from a bauxite refinery difficult
to characterize is the "housekeeping" or "hose-down" stream.
This results from minor spills, leaks, and wastes resulting from
clean-ups. In most plants the inplant drains are connected to
the storm sewer, which may be discharged to the storm water lake
or to the red mud lake.
In most plants, all process areas, where aqueous spills are
possible, are floored with concrete; curb about 6 inches high
surrounds the entire area. Any spill is thus contained for
recovery and controlled disposal. Several other waste streams
may also be associated with the operation of a bauxite refinery.
Examples of these are:
Sludge from treatment and softening of the raw intake water.
Spent regenerant from ion exchange treatment of intake water.
Boiler blowdown.
Cooling tower blowdown.
Treated sanitary waste effluent.
None of these streams is unique to bauxite refining. However, it
should be noted that all of them fit very well into the total
impoundment philosophy of disposal of process wastes from a
bauxite refinery and would represent one increment percent to the
normal red mud load. Effluent limitations for these streams have
not been established inasmuch as they are not considered process
waste streams.
The characterization of process waste streams from
of bauxite is summarized in Table 11.
the refining
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TAEEE 11. CHARACTERIZATION OF PRINCIPAL WASTE STREAMS FROM U.S. BAUXITE REFINERIES
Waste
Quantity
Red arud
Spent Cleaning Acid
Salts from salting -
out evaporator
Barometric condenser, C.W.*
Boiler and cooling tower
"slowdown
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
intermittently 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
Characterization
15-20 % solids
5-12 g/1 soda
2-5 g/1 aluminum
pH - 12.5
Na2SO,, plus some free H«SO^
HC1 or HAc" may also be used
pH - 0
Na2S04 - alkaline
pH - 12.5
Temp, rise of up to 15QC(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 Ib)/day/capita
*C.W.= Cooling Water
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SECTION VI
SELECTION OF POLLUTANT PARAMETERS
Introduction
The waste water parameters of pollutional significance for the
bauxite refining industry include:
Alkalinity
PH
Total dissolved solids
Total suspended solids
Sulfate
Since the waste streams are essentially inorganic,. biochemical
oxygen demand (BOD5) and chemical oxygen demand (COD) are
generally insignificant. On the basis of the evidence reviewed
there are hazardous or potentially toxic substances in the wastes
discharged from bauxite refineries. The use of waste water
recycle systems, along with complete waste retention, permits the
elimination of the discharge of all process waste water
pollutants to receiving waters.
Rationale_For_Selection of gQllutant_Paramgters
pH, Acidity, and Alkalinity
Acidity and alkalinity are reciprocal terms. Acidity is produced
by substances that yield hydrogen ions upon hydrolysis and
alkalinity is produced by substances that yield hydroxyl ions.
The terms "total acidity" and "total alkalinity" are often used
to express the buffering capacity of a solution. Acidity in
natural waters is caused by carbon dioxide, mineral acids, weakly
dissociated acids, and the salts of strong acids and weak bases.
Alkalinity is caused by strong bases and the salts of strong
alkalies and weak acids.
The term pH is a logarithmic expression of the concentration of
hydrogen ions. At a pH of 7, the hydrogen and hydroxyl ion
concentrations are essentially equal and the water is neutral.
Lower pH values indicate acidity while higher values indicate
alkalinity. The relationship between pH and acidity < or
alkalinity is not necessarily linear or direct. •
Waters with a pH below 6.0 are corrosive to water works
structures, distribution lines/ and household plumbing fixtures
and can thus add such constituents to drinking water as iron,
copper, zinc, cadmium and lead. The hydrogen ion concentration
can affect the "taste" of the water. At a low pH water tastes
"sour". The bactericidal effect of chlorine is weakened as the
45
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pH increases, and it is advantageous to keep the pH close to 7.
This is very significant for providing safe drinking water.
Extremes of pH or rapid pH changes can exert stress conditions or
kill aquatic life outright. Dead fish, associated algal blooms,
and foul stenches are aesthetic liabilities of any waterway.
Even moderate changes from "acceptable" criteria limits of pH are
deleterious to some species. .The relative toxicity to aquatic
life of many materials is increased by changes in the water pH.
Metalocyanide complexes can increase a thousand-fold in toxicity
with a drop of 1.5 pH units. The availability of many nutrient
substances varies with the alkalinity and acidity. Ammonia is
more lethal with a higher pH,
The lacrimal fluid of the human eye has a pH of approximately 7.0
and a deviation of 0.1 pH unit from the norm may result in eye
irritation for the swimmer. Appreciable irritation will cause
severe pain.
Since the Bayer refining process uses a strong caustic solution,
the process waste from a bauxite refinery will be alkaline. As
indicated above, the principal effluents are alkaline, with a pH
over 10.
Dissolved Solids
In natural waters the dissolved solids consist mainly of
carbonates, chlorides, sulfates, phosphates, and possibly
nitrates of calcium, magnesium, sodium, and potassium, with
traces of iron, manganese and other substances.
Many communities in the United States and in other countries use
Water supplies containing 2000 to 4000 mg/1 of dissolved salts,
when no better water is available. Such waters are not
palatable, may not quench thirst, and may have a laxative action
on new users. Waters containing more than 4000 mg/1 of total
salts are generally considered unfit for human use, although in
hot climates such higher salt concentrations can be tolerated
whereas they could not be in temperate climates. Waters
containing 5000 mg/1 or more are reported to be bitter and act as
bladder and intestinal irritants. It is generally agreed that
the salt concentration of good, palatable water should not exceed
500 mg/1.
Limiting concentrations of dissolved solids for fresh-water fish
may range from 5,000 to 10,000 mg/1, according to species and
prior acclimatization. Some fish are adapted to living in more
saline waters, and a few species of fresh-water forms have been
found in natural waters with a salt concentration of 15,000 to
20,000 mg/1. Fish can slowly become acclimatized to higher
salinities, but fish in waters of low salinity cannot survive
sudden exposure to high salinities, such as those resulting from
discharges of oil-well brines. Dissolved solids may influence
the toxicity of heavy metals and organic compounds to fish and
46
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other aquatic life, primarily because of the antagonistic
of hardness on metals.
effect
Waters with total dissolved solids over 500 mg/1 have decreasing
utility as irrigation water. At 5,000 mg/1 water has little or
no value for irrigation.
Dissolved solids in industrial waters can cause foaming in
boilers and cause interference with cleanliness, color, or taste
of many finished products. High contents of dissolved solids
also tend to accelerate corrosion.
Specific conductance is a measure of the capacity of water to
convey an electric current. This property is related to the
total concentration of ionized substances in water and water
temperature. This property is frequently used as a substitute
method of quickly estimating the dissolved solids concentration.
Dissolved solids will be high in effluents from a bauxite
refining process and will include the alkalies sodium hydroxide
and sodium carbonate, plus sodium sulfate, sodium aluminate and
other lesser constituents such as sodium chloride and sodium
oxalate. The total dissolved solids content is an aggregation of
the components listed above and serves as an overall monitor of
the effluent quality.
Total Suspended Solids
Suspended solids include both organic and inorganic materials.
The inorganic components include sand, silt, and clay. The
organic fraction includes such materials as grease, oil, tar,
animal and vegetable fats, various fibers, sawdust, hair, an4
various materials from sewers. These solids may settle out
rapidly and bottom deposits are often a mixture of both organic
and inorganic solids. They adversely affect fisheries by
covering the bottom of the stream or lake with a blanket of
material that destroys the fish-food bottom fauna or the spawning
ground of fish. Deposits containing organic materials may
deplete bottom oxygen supplies and produce hydrogen sulfide,
carbon dioxide, methane, and other noxious gases.
j
In raw water sources for domestic use, state and regional
agencies generally specify that suspended solids in streams shall
not be present in sufficient concentration to be objectionable or
to interfere with normal treatment processes. Suspended solids
in water may interfere with many industrial processes, and cause
foaming in boilers, or encrustations on equipment exposed, to
water, especially as the temperature rises. Suspended solids are
undesirable in water for textile industries; paper and pulp;
beverages; dairy products; laundries; dyeing; photography;
cooling systems, and power plants. Suspended particles also
serve as a transport mechanism for pesticides and other
substances which are readily sorbed into or onto clay particles.
47
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Solids may be suspended in water for a time, and then settle to
the bed of the stream or lake. These settleable solids
discharged with man's wastes may be inert, slowly biodegradable
materials, or rapidly decomposable substances. While in
suspension, they increase the turbidity of the water, reduce
light penetration and impair the photosynthetic activity of
aquatic plants.
Solids in suspension are aesthetically displeasing. When they
settle to form sludge deposits on the stream or lake bed, they
-are often much more damaging to the life in water, and they
retain the capacity to displease the senses. Solids, when
transformed to sludge deposits, may do a variety of damaging
things, including blanketing the stream or lake bed and thereby
destroying the living spaces for those benthic organisms that
would otherwise occupy the habitat. When of an organic and
therefore decomposable nature, solids use a portion or all of the
dissolved oxygen available in the area. Organic materials also
serve as a seemingly inexhaustible food source for sludgeworms
and associated organisms.
Turbidity is principally a measure of the light absorbing
properties of suspended solids. It is frequently used as a
substitute method of quickly estimating the total suspended
solids when the concentration is relatively low.
With a closed cycle and total impoundment of wastes, total
suspended solids should be low in any effluents discharged. High
suspended solids content would indicate a process upset or a
containment failure and is included as a significant parameter to
monitor such occurrences.
Sulfate
Sulfate concentrations in discharge streams and pH measurements,
would be indicative of the release of spent acid cleaning
solutions. Sulfate is an undesirable addition to navigable
waters.
Rationale for Rejection of Other Waste Water
Constituents as Pollutant Parameters
As suggested by the earlier process description and by the
preceding list of pollutant parameters, the process of refining
bauxite involves earthy inorganic minerals. Because of this,
several commonly encountered waste water constituents are
relatively unimportant as pollutants. These are noted below.
48
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Biochemical Oxygen Demand (BOD)
Biochemical oxygen demand (BOD) is a measure of the oxygen
consuming capabilities of organic matter. The BOD does not in
itself cause direct harm to a water system, but it does exert an
indirect effect by depressing the oxygen content of the water.
Sewage and other organic effluents during their processes of
decomposition exert a BOD, which can have a catastrophic effect
on the ecosystem by depleting the oxygen supply. Conditions are
reached frequently where all of the oxygen is used and the
continuing decay process causes the production of noxious gases
such as hydrogen sulfide and methane. Water with a high BOD
indicates the presence of decomposing organic matter and
subsequent high bacterial counts that degrade its quality and
potential uses.
Dissolved oxygen (DO) is a water quality constituent that, in
appropriate concentrations, is essential not only to keep
organisms living but also to sustain species reproduction, vigor,
and the development of populations. Organisms undergo stress at
reduced DO concentrations that make them less competitive and
able to sustain their species within the aquatic environment.
For example, reduced DO concentrations have been shown to
interfere with fish population through delayed hatching of eggs,
reduced size and vigor of embryos, production of deformities in
young, interference with food digestion, acceleration of blood
clotting, decreased tolerance to certain toxicants, reduced food
efficiency and growth rate, and reduced maximum sustained
swimming speed. Fish food organisms are likewise affected
adversely in conditions with suppressed DO. Since all aerobic
aquatic organisms need a certain amount of oxygen, the
consequences of total lack of dissolved oxygen due to a high BOD
can kill all inhabitants of the affected area.
If a high BOD is present, the quality of the water is usually
visually degraded by the presence of decomposing materials and
algae blooms due to the uptake of degraded materials that form
the foodstuffs of the algal populations.
Since the process waste streams are essentially inorganic rather
than organic, there is no significant BOD5_.
Chemical Oxygen Demand (COD)
The chemical oxygen demand in the process waste streams from a
bauxite refining process will be insignificant because of the
inorganic nature of the waste.
Oil and Grease
Oil and grease exhibit an oxygen demand. Oil emulsions may
adhere to the gills of fish or coat and destroy algae or other
plankton. Deposition of oil in the bottom sediments can serve to
exhibit normal benthic growths, thus interrupting the aquatic
food chain. Soluble and emulsified material ingested by fish may
taint the flavor of the fish flesh. Water soluble components may
exert toxic action on fish* Floating oil may reduce the re-
49
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aeration of the water surface and in conjunction with emulsified
oil may interfere with photosynthesis. Water insoluble
components damage the plumage and coats of water animals and
fowls. Oil and grease in a water can result in the formation of
Objectionable surface slicks preventing the full aesthetic
enjoyment of the water.
Oil spills can damage the surface of boats and can destroy the
aesthetic characteristics of beaches and shorelines.
Oil and grease are not normally found in the process waste
streams. The only source of oil or grease' would be from
lubrication of process machinery. The contribution from this
source is insignificant.
Temperature
Temperature is one of the most important and influential water
quality characteristics. Temperature determines those species
that may be present; it activates the hatching of young,
regulates their activity, and stimulates or suppresses their
growth and development; it attracts, and may kill when the water
becomes too hot or becomes chilled too suddenly. Colder water
generally suppresses development. Warmer water generally
accelerates activity and may be a primary cause of aquatic plant
nuisances when other environmental factors are suitable.
Temperature is a prime regulator of natural processes within the
water environment. It governs physiological functions in
organisms and, acting directly or indirectly in combination with
other water quality constituents, it affects aquatic life with
each change. These effects include chemical reaction rates,
enzymatic functions, molecular movements, and molecular exchanges
between membranes within and between the physiological systems
and the organs of an animal.
Chemical reaction rates vary with temperature and generally
increase as the temperature is increased. The solubility of
gases in water varies with temperature. Dissolved oxygen is
decreased by the decay or decomposition of dissolved organic
substances and the decay rate increases as the temperature of the
water increases reaching a maximum at about 30^C (86%F). The
temperature of stream water, even during summer, is below the
optimum for pollution-associated bacteria. Increasing the water
temperature increases the bacterial multiplication rate when the
environment is favorable and the food supply is abundant.
Reproduction .cycles may be changed significantly by increased
temperature because this function takes 'place under restricted
temperature ranges. Spawning may not occur at all because
temperatures are too high. Thus, a fish population may exist in
a heated area only by continued immigration. Disregarding the
decreased reproductive potential, water t temperatures need not
reach lethal levels to decimate a species. Temperatures that
50
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favor competitors, predators, parasites, and disease can destroy
a species at levels far below those that are lethal.
Pish food organisms are altered severely when, temperatures
approach or exceed 9 0%jF. Predominant algal species change,
primary production is decreased, and bottom associated organisms
may be depleted or altered drastically - in numbers and
distribution. Increased water temperatures may cause aquatic
plant nuisances when other environmental factors are favorable.
Synergistic actions of pollutants are more severe at higher water
temperatures. Given amounts of domestic sewage, refinery wastes,
oils, tars, insecticides, detergents, and fertilizers more
rapidly deplete oxygen in water at higher temperatures, and the
respective toxicities are likewise increased.
When water temperatures increase, the predominant algal species
may change from diatoms to green algae, and finally at high
temperatures to blue-green algae, because of species temperature
preferential. Blue-green algae can cause serious odor problems.
The number and distribution of benthic organisms decreases as
water temperatures increase above 90^F, which is close to the
tolerance limit for the population. This could seriously affect
certain fish that depend on benthic organisms as a food source.
The cost of fish being attracted to heated water in winter months
may be considerable, due to fish mortalities that may result when
the fish return to the cooler water.
Rising temperatures stimulate the decomposition of sludge,
formation of sludge gas, multiplication of saprophytic bacteria
and fungi (particularly in the presence of organic wastes), and
the consumption of oxygen by putrefactive processes, thus
affecting the esthetic value of a water course.
In general, marine water temperatures do not change as rapidly or
range as widely as those of freshwaters. Marine and estuarine
fishes, therefore, are less tolerant of temperature variation.
Although this limited tolerance is greater in estuarine than in
open water marine species, temperature changes are more important
to those fishes in estuaries and bays than to those in open
marine areas, because of the nursery and replenishment functions
of the estuary that can be adversely affected by extreme
temperature changes.
Thermal economy is important to a bauxite refining process, so
that thermal pollution is normally not significant. When once-
through cooling is employed, temperature increases in receiving
waters in the vicinity of outfalls will be noted and may be
significant near barometric condenser discharges. There is no
treatment technology for heat, other than its dissipation into
some sink, either water, the ground, or the atmosphere. For the
purposes of this document, control consists of preventing its
dissipation into navigable waters.
51
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Color
Color in bauxite refining effluents will usually result from
suspended gangue material and will have the characteristic
reddish-brown color of red mud. The parameter selected, total
suspended solids, is considered a better measure of the presence
of pollutants than color.
Turbidity
Turbidity is indirectly measured and controlled by the limitation
on suspended solids.
Trace Metals
Assuming total impoundment of red mud, the hydroxides of the
trace metals associated with the aluminum in bauxite are quite
insoluble and should not leach from a properly designed and
operated impoundment area.
52
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SECTION VII
CONTROL AND TREATMENT TECHNOLOGY
Introduction
The control and treatment technologies for the waste streams of a
bauxite refinery must be viewed in light of the unique
circumstances applicable to this specific industry subcategory.
The key factor is that bauxite refineries are hydrometallurgical
plants producing enormous tonnages of an aqueous waste
suspension. As illustrated in Table 11, these range from U54 to
3,265 kkg (500 to 3,600 ton)/day on a dry basis. On a settled
mud basis these qualities approximately double. In terms of the
slurry issuing from the process at 15 to 20 percent solids, the
tonnages can exceed 18,140 kkg (20,000 ton)/day. There is no
practicable or currently available treatment or control
technology for such a waste except impoundment. Thus, as a basic
operating premise, a bauxite refinery must provide a large diked
area for impounding the red mud produced. This has been the case
for all but two plants.
Construction of this large diked area creates the most logical
and cost effective receptacle for impounding all other liquid
wastes, associated with the refining process. The red mud lake,
as a recipient of the red mud and all other liquid wastes, offers
a practicable and currently available technology to achieve the
goals of the Act.
The nature of the other pollutants from a bauxite refinery, as
described and discussed in Sections V and VI, are such that
treatment is not a particularly viable option. These process
wastes are characterized by the objectionable characteristics of
alkalinity, acidity, and dissolved solids.
The first two characteristics can be neutralized, which
transforms them into the third objectionable pollutant. Thus,
the available facts lead to the conclusion that the optimum
solution for treatment and control of all other pollutants from
bauxite refining is impoundment in the red mud lake system. The
technology is currently available and practicable.
It has generally been recognized by the bauxite refining industry
that impoundment of the gangue from bauxite ore is feasible, and
the refinery water circuit can operate either as a closed or
nearly closed circuit* Accordingly, most plants currently
impound at least the mud wastes, and, in many instances, other
significant process waste streams.
There may be additional nonprocess streams, such as sanitary
effluents and boiler and cooling tower blowdowns which must be
disposed of. These lesser streams may or may not be included in
53
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the total impoundment site. In more arid climates, the tendency
is to totally impound all streams; in high rainfall regions, the
tendency is to discharge.
The parameters in the water circuit that inhibit adoption of
total recycle of all streams (no discharge) are dissolved solids,
and in some instances, heat. The precipitation step is the key
to purity of alumina product and the efficiency of the operation.
The effects of buildup of contaminants in process water do not
appear to be completly defined or fully understood, and may well
be significantly influenced by other variables. In any event, it
appears that there is a tendency to bar contaminants whose
behaviors are not understood, so that they will be discharged in
preference to recycling to the process stream as a part of a
total impoundment scheme.
The other problem is heat. The cooler the water the less
treatment is needed and the easier it is to achieve a desired
vacuum on a barometric condenser. Heat rejection may not be
sufficient in a closed-loop lake system to provide for adequate
cooling of barometric condenser effluents for reuse. Hence, some
of these systems will use once-through cooling water when
available in a satisfactory quantity and quality. Alternatives
are cooling towers or much larger lakes.
The state of the art control technology can be best described in
terms of the individual types of waste streams. The red mud
stream must be impounded. Other alternatives are possible for
the other waste streams. Due to the nature of the pollutants,
primarily dissolved solids not readily precipitated, there are
essentially no end-o'f-the-pipe pollution abatement schemes for
these other bauxite process wastes. Some treatment technologies
are described in the following paragraphs.
The only practicable control technology for the enormous tonnages
of muds produced by bauxite refineries each day is impoundment.
Muds are impounded in large diked lakes, which may range in size
from 40 ha (100 ac) to as much as 800 ha (2000 ac) .
Two approaches are used for construction of mud lakes. The dikes
are erected to their full height initially. The complete lake is
available from the beginning, and additional dike construction is
not required during the life of the lake. The construction of
this kind of dike has been described by Rushing, (8) and is
summarized below.
54
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The installation described contained two mud lakes containing 4.8
and 3.3 square kilometers (1200 and 800 acres) and represents the
largest such lakes in the bauxite refining industry, while the
dike construction is generally typical, it was modified slightly
because of some local considerations. The top layer of soil,
about 25-30 cm (9-12 inches) was highly weathered, and was removed
before construction of the dikes. The 25-30 cm below this was
scarified and compacted to form the dike foundation. A trench
was excavated around the entire perimeter of the lakes 3-4.5
meters (10-15 feet) deep and 2.5-3 meters (7.5-9 feet) wide. The
trench was backfilled with clay and compacted in 15 cm (6 inch)
layers as the dike was built. This feature helps to key the dike
to minimize seepage of lake water. Details of the construction
are shown in Figure 7. Embankments were laid out for a maximum
height of 9 meters (30 feet) due to the somewhat poor bearing
soils. Slopes of the dikes were lower (1:4 outside and 1:3
inside) than often used due apparently to local conditions. One
other construction feature peculiar to the location was the
facing of the dike nearest the bay with riprap to protect from
hurricane tide and wave action. Pipe was laid on the top of the
dikes with mechanical sections to allow for expansion movement
and ease in breaking the sections apart to modify the pipe line.
Several pipes also were routed to the center of the storage areas
so that the mud could be distributed more evenly. The initial
capital investment is higher for this method of dike
construction, but maintenance and operating costs will be lower.
In the other, "low capital investment-high maintenance cost"
approach, a low dike is initially built, which is continually
raised as the lake fills. The construction of this type of dike
is outlined schematically in Figure 7. Initially a low
combination roadway-dike is constructed to a height of 1.2-1.8
meters (4-6 feet) and with a width of 4.5-5.3 meters (15-18 feet)
from some stable sand-clay mixture. Along the inside perimeter,
steel standards are erected, from which the mud pipe zs
suspended. The pipe has a tapered bottom shape, in which th^e
coarser sands settle out. At intervals the tapered bottoms are
valved; attached hoses are used to convey the sand to form sand
dunes, with a gently sloping beach towards the inside of the
lake. To avoid erosion of the beach, the main flow of mud is
diverted well out into the lake. As the height of the dike
approaches the original pipe line, a new set of standards is
erected inside and the pipe lines relocated.
The success of this type of dike construction depends upon the
existence of a coarse sand fraction in the red mud. Thus, this
is practicable for Surinam bauxite, but less so for Jamaican
bauxite. The net disposal costs appear to be comparable for the
two approaches.
It is possible to raise the dike around a mud lake in stages by a
variation of the above technique. With the usage of a drag line,
previously settled and well-consolidated red mud can be dredged
from the lake and cast on the bank to raise it in 2.5 meter (8-
foot) increments. Slopes must be low and there is a significant
55
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Inside slope
Dike Key
3-4,5 m deep
2.5m min.width
a. Initial Full Dike Construction
Phase TL relocation
of mud line
Phasen dike
Mud line-Phase I
Phase X dike
Roadway
4,5-6m wide
high
b. Buildup Construction of Mud Lake Dike
Figure 7. Mjd lake dike construction.
56
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diversion of lake capacity to dikes. This technique can be
applied even to Jamaican red mud, in spite of its nonsandy
character.
Disposal of Jamaican red mud can pose special problems, resulting
from its very small particle size and somewhat thixotropic
character. Its settling properties are poor. For example, a
maximum compaction of about 35 percent solids is possible if
settling and compaction occur below a layer of water (8). If
Jamaican mud can be spread in layers only inches deep rather than
feet, and exposed to net evaporation conditions, it will dry
satisfactorily. Once past a critical moisture content (i.e., the
60 percent solids range), the mud does not resuspend when wetted
(8). However, adoption of this approach to the disposal of mud,
like Jamaican red mud, depends upon the existence of a relatively
arid climate, and the availability of large tracts of land for
the disposal area. Where land is unavailable and rainfalls are
high, this approach may not be practicable.
dewatering of Jamaican red
that the solids content
Approximately 40 percent of
clear effluent containing
for recycle to the plant.
Another approach may be required in nonarid regions. One
alternative, investigated at the U.S. Bureau of Mines by Good and
Fursman (13), utilized centrifugal
mud. Results of this study indicated
could be increased to 40 percent.
the slurry liquid was recovered as a
dissolved alumina and soda values
Economic analysis indicated that centrifugation and evaporation
of the filtrate for recovery of the alumina and soda values was
approximately a "break-even" operation. With this arrangement, a
satisfactory consolidation and dewatering of Jamaican red mud is
achieved, even in a region where the annual evaporation is less
than the annual rainfall. The net positive water balance makes
the management of the water circuit more difficult and may
require increased evaporator capacity, but the circuit is
controllable.
In all mud lake construction, care must be taken to insure that
the bottom is as impervious as possible. Soil tests may be made
to evaluate the bottom, and clay may be brought in for the bottom
if an undesirable porosity is indicated. Depending on the
structural characteristics of the underlying soil, the dike may
also be keyed-in by excavating a trench along its center line
before construction. Dikes were frequently built with a 1:1
slope; after some trouble with dike slippages and failures, a
slope of 1:2 or less is now more common.
Dike heights will depend upon soil and mud characteristics.
Heights of 6-9 meters (20-30 feet) are usual with good underlying
soil conditions and a mud which sets up. Arkansas dikes can be
as high as 18 meters (60 ft). Typically, a refinery initially
constructs a mud lake of 20-40 ha (50-100 ac), surrounded by a
dike on four sides. After this lake is filled, a new one is
constructed adjacent to it. By using one side as a common dike,
only three new sides need to be constructed, thus, reducing the
capital investment.
57
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Mud lakes are not single-purpose operations, nor is their cost
entirely assignable to pollution control. They are, of course,
primarily employed as receptacles for the waste mud residues.
Secondary uses include cooling ponds and water reservoirs, as
well as receptacles for other minor waste streams from the plant,
such as boiler and cooling tower blowdowns and treated sanitary
waste effluents. If soda concentrations are not excessively
high, they can also serve to some extent as an additional mud
washing stage. Thus, for the purpose of this report, the red mud
lake may be considered as the major feature of the bauxite
refinery. The intrinsic requirement for the disposal of the red
mud residue from alumina plants has inherent effects on plant
space requirements , plant site arrangement, and the initial
design of the plant water system.
Spent cleaning .Acid, spent cleaning acid from cleaning heat
exchange surfaces, filter cloths, etc., consists of solutions
containing high dissolved solids concentrations. One producer
neutralizes the spent acid with mud before discharging to the
river. Another producer is using an improved method, which
involves the reaction of the spent cleaning acid with lime and
forming insoluble calcium sulfate, which is then disposed of in
the red mud lake. Several other producers achieve neutralization
by conveying the spent acid to a red mud lake where it is
neutralized by alkaline mud slurry. Some use an abandoned mud
lake to eliminate any possibility of sulfate buildup in the red
mud lake circuit; others use an active lake and find that enough
sulfate is trapped by the settling mud to prevent sulfate
buildup in the water circuit.
Using readily available technology, the spent cleaning acid could
be neutralized to form an insoluble salt, evaporated to dryness,
and disposed of to a landfill. If it were not for the existence
of the alternative red mud lake "sink", this would no doubt
constitute the recommended treatment technology.
al£s_ _ from Salting-Out __ Eyapo?:atgr-
Where dissolved impurities
must be removed from the caustic liquor circuit of a bauxite
refinery to prevent accumulation to levels causing interference
with satisfactory operations, a salting-out evaporator is used on
spent liquor returning to the digesters from the precipitators.
By greatly concentrating the liquor, the solubilities of the
contaminants are exceeded and they crystallize out. Principal
components are sulfates, and sodium oxalate resulting from the
traces of humic acid in the bauxite feed material.
V
One control technology is to dispose of the solid product to a
landfill, with the waste being covered with soil to prevent
leaching. Another technology, mentioned in an earlier section,
avoids the problem by promoting the adsorption of contaminants
upon the red. mud prior to its separation from the pregnant
bauxite slurry. However, this technology may be applicable only
to Surinam bauxite.
-------
Perhaps the simplest control technology, adopted by several
producers, is the obvious one of disposal by impoundment in an
abandoned red mud lake.
Barometric Condenser Cooling Water. This water comes under the
heading of process water, because it comes into direct contact
with process reactants. As noted earlier, very large quantities
of water are used to provide the reduced pressure in the last
stages of flash evaporators or multiple-effect evaporators.
Because this condenser water is used in such high volume and the
carry-over of alkali to it is small, it is sometimes discharged
to surface waters without treatment. Two plants, (G and H),
employ this procedure for discharge of all barometric condenser
effluents. Another plant, (B), recycles the barometric condenser
effluents from the green liquor flash evaporators to the process
lake, but discharges the effluents from the barometric
condensers, operating on the spent liquor multi-effect
evaporators, to an adjacent bay. In all three cases, the
receiving body of water is very large, with a large thermal
capacity.
It must be recognized that waste heat, if not rejected to the
water phase of the environment, must be rejected either to the
earth or to atmosphere, and the latter is the more favored sink.
The best technology available to dissipate heat to the atmosphere
is evaporative cooling, and this technology is applied in several
forms such as cooling ponds and cooling towers. In both cases,
the water circuit is closed (except for blowdown) and the water
is recycled for reuse. The simplest application is the use of a
cooling pond or lake sufficiently large for the heat to dissipate
to the atmosphere by evaporative cooling.
Cooling towers, both mechanical draft and natural convection, are
also widely used, and would be considered as best practicable
control technology currently available. Such technology does not
require the large land area necessary for surface cooling
systems, normally an advantage, but not necessarily one for a
bauxite refinery, which requires a large pond area for other
reasons. Thus, while cooling towers are normally economically
competitive with evaporative cooling in ponds, towers may not be
an individual option in selecting a cooling method.
When the barometric condensers are operated in closed circuit, as
described above, the problem of potential alkaline Carryover is
taken care of, since any carryover is retained in the circuit.
Cooling Tower and Boiler Blowdown. Blowdown from a cooling tower
associated with process barometric condensers constitutes a
process waste. Since the contained pollutants are soluble salts,
no simple and practicable precipitation technique is applicable.
The blowdown could be evaporated to a solid state, suitable for
landfill disposal. Reverse osmosis could be applied as a
pretreatment to recover a pure water stream. Although the result
would be discharge of pollutants, reverse osmosis would be
significantly more expensive than direct disposal to a red mud
59
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lake. However, the best practicable control technology currently
available consists of impoundment of this waste stream in an
available red mud or process lake, which also achieves no
discharge,of pollutants to surface waters.
Blowdown from boilers and from associated cooling towers does not
constitute a process waste stream. Effluent limitations
guidelines and standards of performance for such streams will be
developed in the near future.
Clean-Up Waste Streams. Hose-down and other clean-up waste
streams are ubiquitous at a bauxite refinery. They contain
suspended bauxite solids and pollutants found in bauxite liquor.
These waste streams are low in alkalinity, but dilute. The best
practicable control technology currently available is to recycle
such wastes to the process, with the optimum point of recycle
being the red mud lake. In a plant not operating on a water
deficiency basis, economical usage of hose- down water will
minimize the water management problems associated with excessive
accumulation of water in the process water circuit.
Sanitary._Wa_ste s. Sanitary wastes are not
wastes from bauxite refineries.
considered as process
The application of the best practicable control technology
currently available to process waste streams of the bauxite
refining process is summarized in Table 12.
S t at us_aiid_Pians .
The bauxite refining industry has begun to reduce the discharge
of pollutants, and further reductions are planned. The present
industry status and reported plans are summarized in Table 13.
Exemplary plants, with no discharge of pollutants to surface
waters, are plants C and E.
Total Impoundment Management .
The mud lake is the central item in any total impoundment
management scheme. It is used for the alkaline mud stream and
possibly for one or more of the other waste streams previously
discussed. There is variability in the manner of handling the
ancillary waste streams. They may also be disposed of in the mud
lake or in other similar clear water or storm water reservoirs.
The requirements for the recycling of the other streams are
flexible, so that optional solutions are possible. This also
includes the recycling of barometric condenser cooling water.
An important item in a total impoundment scheme is management of
general aqueous wastes from the refinery. A well designed system
will include concrete curbs around all process areas where spills
or leaks of process solutions could occur, with the drains
connected to a collection system. Ultimate disposal will be to
the red mud lake or one of the other lakes in the total recycle
circuit. Some trouble has been encountered in the past from
60
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TABLE 12., SUMMARY OF EFFLUENT REDUCTIONS ACHIEVED FOR BAUXITE REFINERY
PROCESS WASTES USING BEST PRACTICABLE TECHNOLOGY CURRENTLY
AVAILABLE
Waste Stream
Parameters
Best Practicable(Level I)
Technology Currently Available
Effluent
Reduction Achieved
Red Mud
Spent Cleaning Acid
Barometric condenser
cooling water
Barometric condenser
C.T. blowdown
*lHose-downtf and clean-up
streams
TSS, TDS, Alkalinity
TDS, Sulfates, pH
TDS, sulfates, alka-
linity
Tlfe, Heat, alka-
linity
TSSj TDS, alka-
linity
Impound and recycles aqueous
phase; concentrate if nec-
essary (A,B,C,D,E,F,I)
Impound in red mud lake
(B,C,D,E,Ff)
Impound in red mudJlake
or landfill (C,E)
Cool and recycle
(1/2B,C,D,E,1/2F)
Impound in red mud lake
(B,C,D,E)
Recycle to process
(Insufficient data)
No discharge
No discharge
No discharge
No discharge
No discharge
No discharge
-------
TABLE 13 HATER POLLUTION ABATEMENT STATUS AND PLANNED CHANGES
(PROCESS AND NON-PROCESS WASTE STREAMS)
Plant
Disposition
Waste Stream
Parameter
Present Status
Planned Changes
A Red mud
Spent cleaning acid
Salts from evaporator
Barometric condenser
C.W.
Boiler and C,T. blow-
' down
10
Hose-down
TSS, TDS, alkalinity
TDS, sulfates, pH
TDS, sulfates, alkalinity,
oxalate
TSD, beat
TDS
Compressor-after cooler Heat
TDS, TSS, alkalinity
Water softener sludge TSS, alkalinity
Sanitary waste
BOD
No change planned
Neutralize with lime and
to abandoned red mud lake
To red mid lake
Discharged to river
No salting-out evapora-
tor
No barometric condenser
used
Boiler blowdown to river; No change planned
no cooling tower
Once-through non-contact Install cooling tower and
discharged to river close cycle
No data (return to cir- No data (recycle?)
cult?)
No softener; potable
water obtained from
city
Untreated; discharged to To be connected to city
river sewerage system
-------
TftBIE 13. (continued)t
Plant
Disposition
Waste -Stream
Parameter
Present Status
Planned Changes
B Red mud
*
Spent cleaning acid
Salts from evaporator
Barometric condenser
C.W. "
Boiler and C.T. blow-
down
w
TSS, TDS, alkalinity
TDS, sulfate, pH
IDS, sulfates, alkalinity,
oxalate
T0S; heat
Compressor after-
cooler
Hose»down
Sanitary wastes
IDS
Heat
TSS, TDS, alkalinity
BOD
To red mud lake
To abandoned red mud lake
No salting-out evaporator
Flash evaporator condensers
C,W. to process lake;
spent liquor evaporator
condenser C.U. discharged
to bay
Boiler blowdown to storm
water lake; no cooling
towers
To lake system; return to
circuit
Mo data
Secondary treated effluent
to lake system
No change planned
No change planned
No change planned
No change planned
No change planned
To lake system (?)
No change planned
C Red mud
Spent cleaning acid
Salts from evaporator
Barometric condenser
C.W.
TSS, TDS, alkalinity
TDS, sulfates, pH
TDS, sulfates,. alkalinity,
oxalate
TDS, heat
To brown mud lake
Neutralized and to brown
mud lake
Evaporator to dryness and
to covered landfill
To clear lake; recycled
to process
No change planned
No change planned
No change planned
No change planned
-------
TAE3JE 13. (continued)
Disposition
Plant
Waste Stream
Parameter
Present Status
Planned Changes
C (coat Mt)
Boiler and C.T. blowdown TDS
Heat
Compressor
after-cooler
Hose-down
Sanitary waste
TDS, TSS, alkalinity
BOP
To lake system; recycled
To lake system; recycled
No change planned
No change planned
No date (to lake system??) To lake system (?)
To lake system No change planned
Red mud
Spent cleaning acid
Salts from evaporator
Barometric condenser
C.tf.
Boiler and C.T. blow*
down
Hose-down
Sanitary wastes
TSS, TDS, alkalinity
TDS, sulfates, pH
To brown mud lake
To brown mud lake
TDS, sulfates, alkalinity, No data (not separated ?)
oxalate
TDS, heat
TDS
Compressor after-cooler Heat
TDS, alkalinity
BOD
Flash evaporator C.W. to
mud lake; spent liquor
evaporator C.W, to C.T.
in closed circuit
Boiler blowdown to lake; no
C.T. blowdown-intermittent
cleanout
Once-through non-contact,
discharged to river
No data
To mud lake
No change planned
No change planned
No data
No change planned
No change planned
No change planned
No data
No change planned
-------
TABt£ 13. (continued)
Plant
Disposition
Waste Stream
Parameter
Present Status
Planned Changes
in
Red mud
*
Spent cleaning acid
Salts from evaporator
Barometric condenser
C.W.
Boiler and C.T. blow-
down
Compressor after-cooler
Hose-down
Sanitary wastes
TSS, TDS, alkalinity
TDS, sulfates, pH
To red mud lake
To red mud lake
TDS, sulfates, alkalinity, Calcined with soda ash
oxalate and bauxite and leached
TDS, heat
TDS
Heat
TDS, alkalinity
BOD
To C.T. in closed circuit;
recycled
No change planned
No change planned
No change planned
No change planned
To process water reservoir No change planned
To C.T. in closed circuit
No data
Secondary treated effluent
to process reservoir
No change planned
No data
No change planned
Red mud
Spent cleaning acid
Salts from evaporator
Barometric condenser
C.W.
Boiler and C.T. blow-
down
TSS, TDS, alkalinity
TDS, sulfates, pH
TDS, sulfates, alkalinity
TDS, heat
TDS
To red mud lake
To red mud lake
No salting-out evaporator
To red mud lake; recycled
Summertime-use once-thru;
to river
Discharged to river
No change, planned
No change planned
No change planned
No change planned
No change planned
-------
T3VBLE 13. (continued)
Disposition
Plant
Waste Stream
Parameter
Present Status
Planned Changes
F Compressor after-cooler
(cont'd)
Hose-down
Water softener sludge
Sanitary wastes
Heat
TDS, alkalinity
TSS, alkalinity
BOD
Once-through; non-contact,
discharged to river
No data
Discharged to river
Secondary treated effluent
discharged to^riyer
No change planned
No data
No change planned
No change-'planned
ot
Red mud
Spent cleaning acid
Salts from evaporator
Barometric condenser
C.W.
TSS, TDS, alkalinity
XDS, sulfates, pH
TDS, sulfates, alkalinity,
oxalate
TDS, Heat
Compressor after-cooler Heat
Hose-down
Sanitary wastes
TDS, TSS, alkalinity,
BOD
Discharged untreated to
river
No data (discharged to
river ?)
No salting-out evaporator
Once-through river water;
discharged to river
Once-through,non-contact,
discharged to river
No data
Secondary treated effluent
discharged to river
Solids to red mud lake;
portion of supernate
nautralized and dis-
charged to river.
No data
No change planned
Neutralize before
discharged to river
No change planned
Recycled to process
No change
-------
TRBEE 13, Continued)
Disposition
Plant
Waste Stream
Parameter
Present Status
Planned Changes
H Red mud
Spent cleaning acid
Salts from evaporator
Barometric condense'"
C.W.
Boiler and C.T. blow-
down
Hose-down
'Water softener sludge
Sanitary wastes
TSS, TDS, alkalinity
TDS, sulfates, pH
TDS, sulfates, alka-
linity, oxolate
TDS, heat
TDS
Compressor after-cooler Heat
TDS, TriS, alkalinity
TSS,. alkalinity
BOD
Discharged untreated to
river
No data
No salting-out evaporator
Once-through river water;
discharged to river
Discharged to river
Once-through, non-contact,
discharged to river
No data
Discharge to river
Secondary treated effluent
discharged to river
Solids to red mud lake;
portion of supernafe
neutralized and die-
charged to river
No data
No change planned
Neutralize before d!0<
charged to river
No change
No change
Recycled to process
No change
Improve plant
-------
1BBIE 13. (continued)
Plant
Waste Stream
Disposition
Parameter
Present Status
Planned Changes
a\
CO
Red mud
Water softener sludge
Spent cleaning acid
Salts from evaporator
Barometric condenser, C.W,
Boiler and C.T. blowdown
Compressor after-cooler
Hose-down
Sanitary wastes
TSS, TDS, alkalinity
TDS, TSS
To red mud lake
Ocean water desalinated;
reject stream returned
to ocean «\
No data
No data
No data
-------
failure to install curbs, or from cracks and crevices in the
concrete floor slab which permitted escape of alkaline process
solutions. Most refineries have campaigns currently under way to
eliminate these sources of effluents, and are expected to have
them eliminated before July 1, 1977.
Another factor in a total impoundment scheme is whether the plant
is located in an area of net rainfall or evaporation. As
described in section IV (Table 4) , two refineries are located in
areas where average annual evaporation substantially exceeds
average annual rainfall. The other six refineries, located in
the continental U. S. , are in areas of net excess water
accumulation, with annual averages ranging from about 10 to 40 cm
(4-16 in) . This complicates the water management scheme. It
does not necessarily follow that a refinery, so located, must
expend energy evaporating rainfall. The bauxite refining process
intrinsically has a substantial negative water balance, which has
to be supplied by either fresh water intake (purchased or
otherwise, acquired) in rainfall- deficient areas, or is supplied
by the rainfall (in rainfall excess areas) .
The negative refinery water balance arises from the fact that
dried bauxite ore, is converted to anhydrous alumina product,
with the water of hydratipn being eliminated in the alumina
calcining kilns. The gangue material (red mud) is removed from
the process as a wet mud containing at least 50 % moisture. Much
water is recovered as high-purity condensate from the flash tanks
and added to the net positive rainfall accumulation, assuming a
minimum red mud lake collection area. The generalized example
described below is based on the following basic assumptions;
Plant capacity is 3,000 ton/day calcined alumina product,
Jamaican bauxite, dried = negligible free water;
49% A1202*3H20, 100% extraction efficiency (losses of Al to
mud neglected)";
1 ton (dry) mud/ton A1203 product;
CCD thickener and washer underflow = 2036 solids;
10 Ibs H20/lb, dry mud for washing; recycled water from mud
lake, supplemented by makeup water;
Mud lake water: 5 g/1 soda; 2.5 g/1 aluminum;
1 Ib H20/lb A1203 final wash of product, using condensate or
makeup water; eliminated in spent liquor evaporator;
Mud lake = 162 ha (400 ac) ;
Plant location gulf south, with net excess of rainfall over
evaporation = 9 in/yr (e.g.. New Orleans locations (Table
69
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With the 3000 tons of recoverable alumina in the bauxite feed,
there are, 1590 ton/day of combined water of hydration. This is
one of the key masses of water removed from the process; it
passes up the stack to the atmosphere when the product is
calcined.
As described in earlier sections, there are tremendous flows of
water in internal circuits within the plant. Very large
quantities of steam are used for heating, but nearly all of the
contained heat is recovered and the condensate reused throughout
the plant, similarly, there are tremendous flows through the
barometric condenser circuit. There are additions to and
blowdowns from these circuits/ but for this generalizied example,
it can be assumed that they are in nominal balance.
The other significant water withdrawal mechanism is the red mud.
The underflow from the last washing thickener will approximate
15,000 ton/day, at 20X solids. Of the 12,000 tons of water going
with 3,000 ton/day of mud to the red mud lake, only 7500 ton/day
return to the process; the remaining 4,500 tons is tied up with
the mud at the bottom of the lake. In total, these two
mechanisms represent a removal of water from the hypothetical
circuit of 6090 ton/day.
Rainfall is the only uncontrolled water input to the circuit. At
the location of the example plant, the net average annual
rainfall gain is 9-in/yr (Table 4). For the asaumed 400-acre red
mud lake, this represents 407,720 ton/yr, an average of
approximately 1120 ton/day. Overall system deficiency is then
4970 ton/day, as illustrated by the schematic diagram in Figure
8.
This estimate should be regarded as an approximation, so that not
all of the deficiency represents discretionary applications for
the introduction of makeup water into the system. However, one
comparable plant, operating with a closed circuit which is
located in a more arid area of the Gulf Coast, has an actual
water makeup requirement of this magnitude.
In spite of the approximate nature of the calculations of this
generalized example, it is apparent that even in an area of net
excess rainfall, it should not be necessary to distill rain in
order to close the water circuit of a bauxite refinery. There is
a sufficiently large difference between water inputs and outputs
to the cycle, that with careful water circuit management, there
should exist a net deficiency, which can be satisfied on a
discretionary basis.
Closing the water circuit will tend to increase the buildup of
soluble contaminants, making the incorporation of a salting-out
evaporator into the spent liquor circuit necessary. However,
there are also some monetary advantages which offset closing the
circuit, such as elimination of losses of the soluble soda and
aluminum associated with the red mud slurry. For the subject
example, the 12,000 ton/day of red mud liquor leaving the plant
70
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.
Combined HgO From Calciner
1590 T/D
Makeup Water
Bauxite
4590 T/D
A12O3 • SHgO
( - 3000 T/D AlgOg)
Condensate
t 1
Steam 1
f Bauxite J
v Refinery °j
i
Bar Cond
T c. w.
WATER BALANCE
IN
Rainfall, ave. 1120 T/D
TOTAL IN 1120
Deficiency = 4970
Supernate
8620 T/D
Red Mud Slurry
( 3000 T/D Mud ^
( 12000 T/D HO
ti
Net Rainfall
Accumulation
1120 T/D (Ave. )
400 Acre
Lake
/ S/ / SS///SS/' '// /
//{ 3000 T/D Mud 40°/o ///
// \ 4500 T/D HgO Solids XX/
' / / ////S/S///SS ///
OUT
Combined HO 1590 T/D
ii
Settled Red Mud 4500
Total OUT 6090 T/D
Figure 8. Generalized diagram of basic water balance for a
3000 T/D bauxite refinery processing Jamaican bauxite,
-------
carries approximately 60 ton/day of soda and 56 ton/day of
alumina. Closing the circuit returns 7500 ton/day of supernatant
to the plant, and recovers about 37.5 ton/day of soda and 35
ton/day of alumina.
In summary, 9current state of the art technology is to totally
recycle all process waters and to impound all solid process
wastes. Two plants are routinely doing this. Five others are
totally impounding the red mud, as well as part or all of various
other smaller streams.
Storm Water Management.
of
no
Most bauxite refineries have successfully solved the problem
providing for total impoundment of process wastes (i.e.,
discharge of process waste water pollutants). The problem is
defined and understood, and the technology is available to
implement the effluent limitations.
Storm water management is not so clearly defined. The position
generally held in the industry is that some quantities of storm
water runoff from plant sites can be subjected to management
controls, but that an upper limit needs to be established, above
which, management (and collection) of storm water need not be
attempted. Present technology (and that in planned
installations) is based on designing a collection and storage
system which will handle an average (not torrential) rainfall,
but limitations on maximum flows are achieved by sizing pumps and
piping in storm water systems or designing weirs at collection
points which will divert flows above a predetermined maximum.
As evidenced by some of the rainfalls which can occur in the
areas in which bauxite refineries are located (see Table 4), the
total collection and retention of all rainfall may not be
technically or economically practicable. The promulgated
regulations provide provisions for the discharge of such
rainfall.
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SECTION VIII
COST, ENERGY* AND NQNHATER QUALITY ASPECTS
Introduction
In this section, costs associated with the degree of effluent
reduction that can be achieved by exemplary treatment methods are
summarized. The nonwater quality aspects of solid waste disposal
and the energy impact of the in - process control and waste
treatment technologies are also discussed.
As noted in Section V, the pollutants found in waste water
effluents from bauxite refining are characteristically either
highly soluble, nonprecipitable, dissolved salts, or suspended
solids (i.e., not amenable to end-of-pipe treatment technology).
Thus, the only practicable treatment method for bauxite refining
wastes is total impoundment, and the degree of effluent reduction
achieved by impoundment is the total elimination of the discharge
of process waste water pollutants to navigable waters.
Treatment and Control Costs
Although certain process credits undoubtedly derive from the
quasi-washing stage, the costs of impoundment in the red mud lake
and total recycle are considered wholly as pollutant control
costs. Also, in the absence of a closed water cycle, additional
sources of water intake would be required at some cost. However,
the credits from the additional washing are difficult to
estimate, and the water cost savings are highly location-
dependent.
The capital cost of an impoundment and recycle system contains,
in its simplest form the following major cost elements:
(a) Cost of land.
(b) Cost of construction of reservoir(s).
(c) Cost of equipment and facilities.
Such a system may serve as a depository for red mud tailings, a
source of process water for the plant, and a cooling pond. In
some instances the system installed may be large enough to
satisfy the first two uses only. In this configuration, a
cooling tower is an alternative for the cooling water supply.
The cost of land is a major consideration in any impoundment
scheme. Estimated current land costs range from $20 0/ha
($500/ac) to $1200/ha ($3000/ac). However, most bauxite
refineries have acquired the needed land years ago at
substantially lower unit cost.
73
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The cost of constructing the earthen dikes of a totally new mud
lake reservoir are separable and identifiable, and are so
reported. Even here, costs may not be entirely comparable, if
one or more dikes of an existing lake is available.
The cost of equipment and facilities is difficult to reduce to a
unit cost basis, since the major portion of these costs are
associated with the construction of the first mud lake.
Relatively minor costs may be incurred in relocating some of the
equipment and facilities.
Thus, although the share elements, listed above, comprise the
cost for total impoundment, available cost data are not so
categorized. Not one producer supplied cost data by waste stream
in a usable form; only the aggregate figure was supplied. Thus,
only total capital costs are generally available, and the
accuracy of these are suspect to some extent, where a timespan of
10-30 years may be involved. Nevertheless, within these
limitations, capital costs reported are regarded as good order of
magnitude values for past construction.
An additional factor requiring consideration in comparing
reported costs is the type of bauxite to which the data apply.
As indicated by Table 14, there can be a sixfold difference
between mud production rates. However, total costs of disposal
do not appear to be directly proportional to ton of mud/day, or
size of plant. Reported costs for plants processing all three
basic categories of bauxite ore are presented in Table 15. The
dollar capital and annual operating costs are as reported. The
unit capital costs are based on the (estimated) total alumina
production represented by the capacity of the impoundment lakes.
Unit operating costs were determined by apportioning reported
operating cost expenditures over the annual alumina capacity of
the plant.
Based on these data, impoundment of the processing wastes from
Surinam bauxite requires a capital investment of $0.25 to
$0.50/ton mud impounded and an operating cost of about $0.90-
$1.30/ton of mud ($0.30 -$0.43/ton of alumina). For Jamaican
ore, with its higher mud yield, capital costs are about $0.20/ton
of mud and operating costs about $0.50/ton of alumina. Lowest
costs, on a mud basis, are associated with mud-prolific Arkansas
bauxite, of the order of $0.10 to 0.20/ton of mud capital costs
and about $0.10 to 0.25/ton of mud operating costs. In spite of
the approximate nature of the data, there is a surprisingly
narrow range in waste disposal costs.
Estimated costs have also been supplied by the producer for
Plants G and H. Neither of these plants currently has facilities
for impounding red mud, although both are committed to doing so
by order of a Federal consent decree (Plant G by July 1, 1975,
and Plant H by July 1, 1974). In both cases, the impoundment
will constitute a grass-roots installation, complicated by the
fact that the whole configuration of the water circuits will have
74
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TABLE 14. UNIT MUD PRODUCTION RATES FOR VARIOUS
BAUXITES(a>
Tons mud/ton Al-203 produced
Tons mud/ 1000 T/D A1203
Volume of mud, cu m/d^"3)
Volume of mud, cu m/yr
Volume of mud, acre feet/yr
Type
Surinam
0.33
330
410
147,600
120
of Bauxite
Jamaica
1.0
1,000
1,248
449,280
364
Ore
Arkans as
2.0
2,000
2,496
994,560
728
(a) Per 1000 metric tons of alumina production/day.
(b) Density of settled mud taken at 1600 kg/m3 (100 lb/ft3) and
solids at 50%.
-------
TABLE 15. SUMMARY OF WASTE DISPOSAL COST DATA
Lake Capacity,
metric tons dry nrud
Capital Cost, $
Unit Capital Cost,
$/metric ton mud
Annual Cost, $/yr
Mud, metric tons/yr
Unit Annual Costs,
$/metric ton mud
$/metric ton alumina
A
C
D
Old Pond^b^ New Pond
820,000
Surinam
0.33
4.2xl06
$1.13 x 10
0.26
$264,000
205,000
$1.29
0.43
325,000
Arkansas
2.0
ll.lxlO6
6 0.9xl06
0.08
75,600
660,000
0.11
0.22
755,000
Arkansas
2.0
7.5x106
0.69x106
0.09
373,000
1,520,000
0.24
0.48
755,000
Arkansas
2.0
11.7xl06
2.06xl06
0.18
—
—
—
Notes: (a) Mud basis, in 1971 dollars.
(b) Construction costs of old pond were expensed as incurred;
(c) Exemplary plant, zero discharge of pollutants.
(d) Annual costs represent average costs for two old ponds.
(e) Lbs mud/lb .of alumina produced.
(f) Very large lake; estimated capacity includes 20-year life
E
F
B
(b) Old Pond
9.52xl06
0.18
571,000
1,160,000
0.49
0.49
560,000 560,000
Surinam Surinam
0.33 0.33
3.0xl06 1.7xl06
1.26xl06 0.82x10$
0.52 0.48
166,000
187,000 -- -
0.89
0.30
1,150,000
Jamaican
1.0
—
0.30
,
—
0.35
new pond on capitalized basis.
still remaining.
-------
to be reoriented toward impounding rather than toward direct
discharge. Significant piping changes can be anticipated. The
problem at Plant G is further complicated by the fact that land
for impounding is not available adjacent to the plant, which is
in a metropolitan area, and the red mud lake will be located 10
miles from the plant.
The estimated costs, as supplied by the producer, are summarized
in Table 16. Estimated capital costs were not detailed so that
it cannot be stated how costs are apportioned. Plant H is part
of a large chemical complex and definitive data on division of
effluent treatment costs between the bauxite refinery and the
rest of the complex are not available. It is apparent, however,
that these estimated costs differ from those reported by the rest
of the industry by an order of magnitude.
It should be noted that the impoundment of red mud solids
achieved by the proposed installation by plants G and H is not
total. According to a letter to the U.S. Environmental
Protection Agency by the producer (14) t there will be
approximately 72 million ton/day of suspended solids discharged.
Nonwater Quality Aspects
Energy Requirements
Pumping Costs. The energy consumed in pumping red mud and other
effluents to an impoundment reservoir is comparable to that
required to pump them to a discharge outfall in a navigable
waterway, so the incremental energy usage is nominal. By the
same reasoning, energy consumed in returning the supernatant from
the lake to the plant is comparable to that required to pump
fresh water to the process.
Evaporation Costs. Depending upon the location and overall
design and management of the water circuit of a plant, the
evaporation of excess water may be necessary to avoid discharge
of effluents from the circuit. Thus, the expenditure of fossil
fuel, in variable quantities, may be necessary; this presumes
that the water to be evaporated will always be less than the
quantity routinely evaporated to satisfy process requirements.
In support of the latter conclusion, the producer has estimated
that 200 gal/min of rain water (1200 ton/day) might have to be
evaporated if Plants G and H went to a-closed circuit, with total
recycle of process waters. However, it is estimated that water
evaporated from the calcining kilns at these two plants is about
8680 ton/day, and the steam rate is about UOO ton/hr (9600
ton/day) for a total evaporative load of over 18,000 ton/day. If
evaporation of rain water became necessary the evaporative load
would be increased by only about 6 percent. (The water balance
calculations presented in Section VII suggest that this should
not occur). Also, discharge of excess rainwater has been
addressed in the promulgated regulations.
77
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16. SUMMARY OF ESTIMATES OF FUTURE WASTE DISPOSAL COST DATA
(a)
-J
00
Plant Capacity, metric tons/yr
fianxite Type
Mud Ratio
Lake Capacity, metric tons
dry mud^°}
Capital Cost, $^e)
Unit Capital Cost,
$/metric ton dry mud
Annual Cost/ $/y>r^e^
Mud, metric tons/yr
Unit Annual Costs, $/metric ton mud
$ /me trie ton A ^63
Plant G(b)
1,100,000
Jamaican
1.0
8.25 - 11 x 106
21,700,000
1.97 - 2.63
5,487,000
1,100,000
4.99
4.99
.mant H^
; '865,000
;^aican
1.0
^.5 - 8.7 x 10*
14,850,000
1.70 - 2. 28
4,391,000
865,000
5.07
5.07
(a) In 1973-1974 dollars
(b) .Plant does not now have a red mud laks
(c) Lbs mud/lb of alumina produced (approximate)
(d) Some uncertainty on life of pond, depending on efficiency of
proposed dewatering system; estimated by producer at from 705-10 years
(e) Estimate supplied by producer
-------
Solids Disposal
The volume of solid wastes (i.e., red mud) generated annually by
the bauxite refining industry has been calculated to be 7,500,000
kkgs, equivalent to approximately 9.3 million cubic meters (12
million cubic yards) per year. This represents about 7600 ac ft,
which, taken at an assumed mud lake-filled depth of 25 feet,
means the diversion from other uses of an average of 300 ac of
land per year.
79
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SECTION IX
BEST PRACTICABLE CONTROL TECHNOLOGY CURRENTLY
AVAILABLE —EFFLUENT LIMITATIONS GUIDELINES
Introduction
The effluent limitations which must be achieved by July 1, 1977,
are to specify the degree of effluent reduction attainable
through the application of the best practicable control
technology currently available. This technology is based upon
the average of the best existing performance by plants of various
sizes, ages, and unit processes within the industrial category
and/or subcategory. This average is not based upon a broad range
of plants within the bauxite refining industry, but is based upon
performance levels achieved by exemplary plants. Consideration
must also be given to:
(a) The total cost of application of technology in relation
to the effluent reduction benefits to be achieved from
such application.
(b) The size and age of equipment and facilities involved.
(c) The processes employed.
(d) The engineering aspects of the application of various
types of control techniques.
(e) Process changes.
(f) Nonwater quality environmental impact (including energy
requirements).
Best practicable control technology currently available not only
emphasizes treatment facilities at the end of a manufacturing
process, but includes the control technology within the process
itself, when the latter is considered to be normal practice
within an industry.
A further consideration is the degree of economic and engineering
reliability which must be established for the technology to be
currently available. As a result of demonstration projects,
pilot plants and general use, there must exist a high degree of
confidence in the engineering and economic practicability of the
technology at the time of commencement of construction or
installation of the control facilities.
Effluent Reduction Attainable Through The
"Application of Best Practicable Control"
Technology Currently Available
Based upon the information contained in Sections III through VIII
of this report, a determination has been made that the degree of
effluent reduction attainable through the application of the best
81
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practicable control technology currently available is no
discharge of process waste water pollutants to navigable waters.
j
Identification of Best Practicable Control
'" Technolog"currently_AyaiIable
Best practicable control technology currently available for the
bauxite refining industry is recycle and reuse of process waters
within the operation. To implement this requires:
(1) Acquisition of land, and construction, operation, and
maintenance of dikes to provide one or more permanent
lakes for ore tailings as well as reservoirs for the
plant water circuit.
^(2) Provision for means of cooling the effluent from
, barometric condensers for reuse in the plant, by the use
of cooling towers or by use of the plant lake system.
(3) Retention of all general wastes (e.g., solution spills,
floor and equipment washes, spent heat exchanger
cleaning acid, acid filter, cloth washes, and other
( miscellaneous waste waters within the processing plant)
by subsequent treatment and reuse or disposal on land.
'. Maintenance of the integrity of floor slabs and curbs
around plant areas will be a feature of such control
measures.
There will be, in addition, some nonprocess waste streams (e.g.,
w/ater softener backwash and boiler blowdown) for which control is
more applicable than treatment* These wastes, relatively small
^.n comparison with the main stream, can be readily incorporated
•into and included as part of the total impoundment system.
'The technologies and levels of effluent reduction stated above
have been demonstrated to the following degree by the existing
plants in the industy:
(a) Two plants are known to be currently operating with no
discharge of water.
(b) Four other plants have prepared or are implementing
plans to achieve no discharge of process waste waters
before the effective date of the effluent limitations.
(c) Two plants are currently discharging all wastes, but are
implementing plans to impound red mud.
Rationale for the gelection of the_Best Practicable
Control Technology Currently AvallaEle"
Acre and Size of Equipment and Facilities
As set forth in previous sections of this report, the bauxite
refining industry is characterized by:
82
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(a) very large plants, the smallest producing 900 kkgs(lQOO
tons) /day of alumina, and the largest producing 3600
kkg(4000 tons) /day.
(b) A plant age differential of 30 years.
(c) A commonality of process and equipment design arising
from the universal use of the Bayer or combination
process and that five of the nine existing plants were
designed and built by one company.
These similarities, coupled with the similarities of waste water
characteristics substantiate the best practicable control
technology currently available to be total recycle.
Total Cost of Application. in Relation_to .Effluent
Reduction~Benefits ~
Based upon the information contained in Section VIII, the
industry as a whole would have to invest an estimated maximum of
$42,000,000 to achieve the promulgated regulations* This amounts
to approximately a 0.5 percent increase in projected capital
investment for seven of the nine domestic refineries and 12.0
percent for the two remaining ones (Plants G and H) .
operating costs for the production of alumina from bauxite are
estimated to be on the order of $55/kkg <$50/ton) of alumina,
Increases in operating costs to achieve the limitations are
estimated at $1,200,000 for seven of the nine U.S. refineries and
$9,500,000 for the other two.
It is concluded that the benefits derived from the total
elimination of process waste water pollutants to navigable waters
outweigh the costs. Twenty-two percent of the plants are already
achieving no discharge of process waste water pollutants. Fifty--
five percent are achieving no discharge of red mud and are
discharging only minor quantities of other process waters to
surface waters; no discharge of pollutants from these plants can
be readily achieved at moderate cost. Only two plants (22
percent) still discharge major process waters to surface waters.
Process .Employed
There is only one product from U.S. bauxite refineries, purified
alumina. The process chemistry is basically quite simple. The
Bayer process or the combination process modification is
universally used in the United States. Accordingly, the process
flowsheets are essentially the same and the discharges are very
similar. There is no evidence that operation of any current
process or subprocess will substantially affect capabilities to
implement the best practicable control technology currently
available.
Engineering Aspects__of ^
This level of technology is practicable because twenty-two
percent of the plants in the industry are now achieving the
83
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effluent reductions set forth herein, and another fifty-five
percent can achieve them with only minor process changes. The
concepts are proven, available for implementation, and may be
readily adopted through adaptation or modification of existing
production facilities.
Process changes
This technology is an integral part of the waste management
program now being implemented within the industry. While it does
require process changes at some plants, these changes are
successfully practiced by other plants in the industry.
}
Nonwater Quality Environmental, pnpact
Total impoundment has a potential effect upon soil systems due to
strong reliance upon the land for ultimate disposition of final
effluents. Total annual land requirement for waste disposal is
of the order of 120 ha (300 ac) per year. Impoundment areas must
be impermeable to prevent the wastes from contaminating surface
or subsurface waters. Air pollution could be a problem in arid
locations from fugitive dust blowing from abandoned mud lakes.
This has been controlled by keeping the surface of the ponds
wetted.
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SECTION X
BIST_AyAILABLE_TECHNOLOGY_
ECONOMICALLY ACHIEVABLE —_EFFLUENT
LIMITATIONS GUIDELINES
The best available technology economically achievable is
identical to the best practicable control technology currently
available. The corresponding effluent limitations are no
discharge of process waste water pollutants to navigable waters.
85
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SECTION XI
NEW SOURCE PERFQRMANCE_STANDARDS
The best available demonstrated control technology, processes,
operating methods, or other alternatives is identical to the best
practicable control technology currently available. The
corresponding standard of performance is no discharge of process
waste water pollutants to navigable waters.
87
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SECTION XII
ACKNOWLEDGMENTS
The Environmental Protection Agency would like to thank the staff
of the Battelle Memorial Institute (Columbus) under the direction
of Mr. John B. Hallowell for their aid in the preparation of this
document. Assistance from representatives of General
Technologies Corporation is also appreciated.
The Project officer, George S. Thompson, Jr., would like to thank
his associates in the Effluent Guidelines Division, namely Mr.
Allen Cywin, Mr. Ernst P. Hall, and Mr. Walter J. Hunt for their
valuable suggestions and assistance.
Mr. Harry Thron, Effluent Guidelines Division, was responsible
for the proposed regulation and development document (October
1973) for this industry.
The members of the working group/steering
coordinated the internal EPA review are:
committee who
Mr. Walter J, Hunt, Chairman, Effluent Guidelines Division
Mr. Marshall Dick, office of Research and Development
Mr. John Ciancia, National Environmental Research
Center, Edison
Mr. Lew Felleisen, Region III
Mr. Swep Davis, Office of Planning and Evaluation
Mr. Taylor Miller, Office of General Counsel
Appreciation is also extended to the follwing trade associations
and corporations for assistance and cooperation provided in this
program:
Aluminum Company of America
Kaiser Aluminum and Chemical Corporation
Martin - Marietta
Ormet corporation
Reynolds Aluminum
Finally, many thanks are given to the hard working secretarial
staff of the Effluent Guidelines Division. In particular,
recognition is given to Ms. Linda Rose, Ms. Kay Starr, and Ms,
Nancy Zrubek*
89
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SECTION XIII
REFERENCES
(1) Metal Statistics, 1972, American Metal Marker, Fairchild
Publications, Inc., N.Y., N. Y.
(2) Hayward, C.R., "An Outline of Metallurgical Practice",
3rd Ed., D. Van Nostrand, N, Y., 728 pp (1952).
—»
(3) Garden, Clair, Texas Water Quality Board, Personal
Communication (June, 1973).
(4) Todd, D.K., "The water Encyclopedia", Water Information
Center, Water Research Building, Port Washington, N. Y.
(1970).
(5) Hudson, L.K., "Recent Changes in the Bayer Process",
from "Extractive Metallurgy of Alumina", Vol. I,
Alumina, Gerard, G., and Stroup, P. T., editors,
Interscience Publishers, N.Y., 355 pp (1963).
(6) U.S. Naval Service World wide Summaries, Vol. VIII,
Part 5, U.S.A., Mississippi Valley Area. Environmental
Technical Applications Center (U.S. Air Force),
Washington, D.C. (1961) AD699 917.
(7) Kirk-Othmer, "Encyclopedia of Chemical Technology",
2nd Ed., Vol. I (1963).
(8) Rushing, J.C., "Alumina Plant Tailings Storage", Paper
No. A73-58, Metallurgical Society of AIME, Chicago, 111.,
Feb. 25-28, 1973.
(9) "Utilization of Red Mud Wastes for Lightweight
Structural Building Products". IITRI Project No.
G-6015, prepared for U.S. Bureau of Mines.
(10)Fursman, O.C., Mauser, J.E., Butler, N. o,, and Stickney,
W. A., "Utilization of Red Mud Residues from Alumina
Production", U.S. Dept. of the Interior, Bureau of Mines,
Report of Investigations No. 7454 (1970).
(11)Guccione, E., "'Red Mud1, a Solid Waste Can Now be
converted to a High-Quality Steel", Eng. S Mining J.,
V72, 9, 136-7 (1971).
(12)Solyman, K., and Bujdoso, E., "Properties of Red Mud in
the Bayer Process and Its Utilization", Paper NO.
A73-56, Metallurgical Society of AIME, Feb, 28-Mar. 1, 1973,
Chicago, Illinois.
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(13)Good, P.C., and Fursman, O,C., "Centrifugal Dewatering
of Jamaican Red Mud", U.S. Dept. of the Interior, Bureau
of Mines, Report of investigation No. 7140 (June, 1968).
(14)Day, J.V. Letter to R,B. Elliott, Permits Branch,
U.S. Environmental Protection Agency, Region VI, Dallas
February 27, 1973.
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SECTION XIV
GLOSSARY
Acidity
The concentration of acid ions expressed as pH for a solution.
Act
The Federal Water Pollution Control Act Amendments of 1972.
Alkalinity
The alkali concentration or alkaline quality of an alkali-
containing substance.
Alumina
Any of several forms of aluminum oxide, Al^OS, occuring naturally
as corundum, in a hydrated form in bauxite, and with various
impurities as ruby, sapphire, and emery.
Autoclave
A strong, pressurized, steam heated vessel, used to establish
special conditions for chemical reaction, for sterilization, and
for cooking.
Baghouse
Large chamber for holding bags used in the filtration of gases
from a furnace, for the recovery of metal oxides and similar
solids, suspended in the gases.
Barometric Condenser
An apparatus used to condense vapor, in which the vapors are
condensed by direct contact with water in a vessel set
sufficiently high so that the water drains from it in a
barometric hot-leg into a sealed tank or hot-well.
Bayer Process
Process in which impure alumina in bauxite is dissolved in a hot,
strong alkali solution, normally NaOH, to form sodium aluminate,
which upon diluting and cooling the solution, hydrolyzes, forming
a precipitate of pure aluminum hydroxide.
Bauxite
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An impure mixture of earthy hydrous aluminum oxides and
hydroxides that commonly contain similar compounds of iron, the
principal ore of aluminum.
Best_Available Technoj.pgy Economically Achievable
Level of technology applicable to effluent limitations to be
achieved by July 1, 1983, for industrial discharges to surface
waters as defined by Section 301 (b)(1)(A) of the Act.
Igs^ggacticable^ ContrQ^T
Level of technology applicable to effluent limitations to be
achieved by July 1, 1977, for industrial discharges to surface
waters as defined by Section 301 (b) (1) (A) of the Act.
Bioghemica^ Oxygen Demand (BOD}
A measure of the oxygen demand in sewage and industrial wastes or
in the stream, determined by chemical techniques. One technique
(BOD5) determines the 5-day oxygen demand.
Slowdown
A discharge from a system, designed to prevent a buildup of some
material, as in a boiler to control dissolved solids.
Thefinal solid waste remaining after the alumina is leached from
the calcined red mud in the combination process.
The diked reservoir (tailings pond) used to impound brown mud,
The roasting or burning of any substance to bring about physical
or chemical changes; e.g. , the conversion of lime rock to
quicklime,
Financial charges which are computed as the cost of capital times
the capital expenditures for pollution control. The cost of
capital is based upon a weighted average of the separate costs of
debt and equity,
Category and Subcategpry
Divisions of a particular industry which possess different traits
which effect waste treatability and would require different
effluent limitations.
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Caustic Soda
Sodium hydroxide (NaOH)
Demand (COD)
A measure Of the oxygen demand equivalent of that portion of
matter in a sample which is susceptible to oxidation by a strong
chemical oxidant. •
Clear Water Lake
Nominally the lake relatively free of alkalinity and other
dissolved solids used as a fresh water reservoir for a bauxite
refinery.
Combination Process
Variation of Bayer process used for high-silica ores, in which
the red mud from the first stage Bayer process is calcined with
soda ash and lime and leached to recover additional alumina.
Conductivity
A measure of the ability of water in conducting an electrical
current. In practical terms, it is used for approximating the
salinity or total dissolved solids content of water.
Continuous Countercurrent Decantation (CCD)_
A continuous system of washing finely divided solids, such as red
muds, to free them from liquids containing dissolved substances.
In practice, the fresh wash water and the strong solids start at
opposite ends and move countercurrently toward each other, so
that the freshest water contacts the most thoroughly washed
solids.
Accounting charges reflecting the deterioration of a capital
asset over its useful life.
Pressure vessel or autoclave; vessels in which the alumina is
dissolved from the bauxite.
Effluent
The waste water discharged from a point source to navigable
waters.
Effluent Limitation
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A maximum amount per unit of production of each specific
constituent of the effluent that is subject to limitation in the
discharge from a point source.
Electrostatic Precjpitator
A gas cleaning device using the principle of placing an
electrical charge on a solid particle which is then attracted to
an oppositely-charged collector plate. The collector plates are
intermittently rapped to discharge the collected dust into a
hopper below.
Ganaue
The worthless rock or other material in which valuable metals
minerals occur.
or
The aluminum- bearing
further processing.
Industrial
solution from the bauxite digesters before
All wastes streams within a plant. Included are contact and
noncontact waters. Not included are wastes typically considered
to be sanitary wastes.
qpsts
The capital expenditures required to bring the treatment or
control technology into operation. These include the traditonal
expenditures such as design, purchase of land and materials, site
preparation, construction and installation, plus any additional
expenses required to bring the technology into operation
including expenditures to establish related necessary solid waste
disposal.
Milligrams per liter. Nearly equivalent to parts per million
concentration.
Any building, structure, facility, or installation from which
there is or may be a discharge of pollutants and whose
construction is commenced after the publication of the proposed
regulations.
Performance standards for the industry and applicable new sources
as defined by Section 306 of the Act.
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Operations and Maintenance
Costs required to operate and maintain pollution abatement
equipment, such as labor, material, insurance, taxes, solid waste
disposal, etc.
£H
A measure of the alkalinity or acidity of a solution, numerically
equal to 7 for neutral solutions, increasing with increasing
alkalinity and decreasing with increasing acidity. A one unit
change in pH indicates a tenfold change in acidity or alkalinity.
Plant Effluent_or_Dj.scharqe After Treatment
The volumes of waste water discharged from the industrial plant.
In this definition, any waste treatment device (pond, trickling
filter, etc.) is considered part of the industrial plant.
Pregnant Liquor
Solution containing the metal values prior to their removal and
recovery.
Point Source
A single source of water discharge such as an individual plant.
Process Effluent or Discharge
The volume of water emerging from a particular process use in the
plant.
Process Lake
Reservoir used for process water; often in closed circuit with
part of process; not used for mud disposal,
Red Mud Lake
The diked reservoir used to impound red mud.
Secondary Treatment
Biological treatment provided beyond primary clarification.
Silicates
A chemical compound containing silicon, oxygen, and one or more
metals.
Standard of Performance
A maximum weight discharged per unit of production for each
constituent that is subject to limitation and applicable to new
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sources, as opposed to existing sources which are subject to
effluent limitations,
storm Water Lake
Reservoir for storage of storm water runoff collected from plant
site; also/ auxilary source of process water.
Navigable waters. The waters of the United States including the
territorial seas.
Thixotropic
Having the property exhibited by certain gels of liquefying when
stirred or shaken and returning to the hardened state upon
standing.
Total Suspended Solids_ (TSS)
Solids found in waste water or in the stream, which in most cases
can be removed by filtration. The origin of suspended matter may
be man-made or of natural sources, such as silt from erosion.
Unit Operation
A single, discrete process as part of an overall sequence, e.g.,
precipitation, settling, filtration.
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CONVERSION TABLE
MULTIPLY (ENGLISH UNITS)
ENGLISH UNIT ABBREVIATION
acre ac
acre - feet ac ft
British Thermal
Unit BTU
British Thermal
Unit/pound BTU/lb
cubic feet/minute cfm
cubic feet/second cfs
cubic feet cu ft
cubic feet cu ft
cubic Inches cu in
degree Fahrenheit F°
feet ft
gallon gal
galIon/minute gpm
horsepower hp
inches in
inches of mercury in Hg
pounds Ib
million gallons/day mgd
mile mi
pound/square
inch (gauge) peig
square feet s
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