-------
Various means of condensation create different 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, they do not justify
establishment of a sutcategory 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 (A1203ป3H20), 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 that 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, A1203ป2Si02ป2H20. 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 it entails a heavy and expensive loss of
caustic soda in the form of insoluble sodium aluminum silicate compounds
such as sodalite, 3Na20ซ3A1203ซ6Si02ซ2NaCl(r and cancrinite,
(Na,K) (Al,Si)20Jl. Each kilogram of Si02 in the bauxite involves the
loss of approximately 1 kilogram of A1203 and 0,6 - 0.7 kilogram of
Na20.
The composition of the bauxites used in alumina production varies a
great deal. The variations generally fall within the following limits:
TABLE 6. RANGE OF COMPOSITION OF BAUXITES
FOR ALUMINA PRODUCTION
Composition Weight Percent
A1203, total HO to 60
Si02, free and combined 1 to 20
Fe203 7 to 30
Ti02 3 to 4
P205, V205, etc. 0.05 to 0.20
H20, combined 12 to 30
Reference: Kirk-Othmer (7).
35
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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 (AlO)3(SOU)2ป3H20, but the treatment 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 drawn upon 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 7) .
The silica content in imported ores is not high enough to warrant other
than the basic Bayer process since it is cheaper to accept the losses of
alumina and caustic discussed above than to attempt to recover them.
On the other hand, the average silica content of Arkansas ores is now in
the 13-20 percent range. Ores as low as 6 percent Si02 occurred in the
past in the area, but these were "high^graded" during World War II.
There is considerable variation over the 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
36
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TABLE 7. CHARACTERISTIC ANALYSES FOR VARIOUS BAUXITES
Weight Percent
A1203, total
Si02
Fe203
Ti02
F
F205
V205
HoO, combined
A1203, trihydrate
^2^3 > 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
37
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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,
CaOซAl203-2Si02, may be used. No domestic plants 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 subcategorizaticn based on products.
Wastes Generated^
The major process waste associated with the refining is the solid mud
residue. There are differences between the residues from the Bayer
process (red mud) and the residues left after this mud is retreated via
the combination process (brown mud). These differences do not
appreciably alter the problem of their disposal. There are also
differences in the amount of muds 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 successful total impoundment of each of the various types of mud.
38
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All bauxite refineries use sulfuric acid for removing scale from heat
exchangers, filtration equipment, etc.; The spent acid resulting
therefrom 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:
Boiler blowdown
Cooling tower blowdown
Water softener sludges
Sanitary waste effluents.
None of these effluents is unique to bauxite refining. Since they are
not process streams, they are not the subject of effluent limitations;
however, their control and treatment may become necessary for some
plants.
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 (DPC). 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 refiners 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 pwn three plants
and the two erected for the DPC during World War II. Many components
are of identical design.
The smallest bauxite refinery has a production capacity of 900 kkgs/day
of Al.20.3. The largest has a capacity of 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 plants is
not justified.
Plant Location
As illustrated by Figure 2, 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 Missippi 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
39
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evaporation rate is about 1<40 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. On the other hand, 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
to dispose of. This excess water complicates the management of the red
mud lakes and may pose a disposal problem.
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 unavoidabley immediately 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 allowed to discharge to its normal water
courses if the plant is designed to segregate process wastes so that
they are not included in this runoff. By elimination or minimization of
process operations or configurations which are large contributors to the
water circuit, i.e., by the use of a tightly designed water balance, the
water balance can be managed. Accordingly, a subcategorization based
upon plant location is not justified.
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 teen used in the past, but have not always provided
adequate control. New designs for precipitators are being developed.
Baghouses are alsc 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 on 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 not significant. Air pollution control equipment in bauxite
refineries appears unlikely to have any significant effect upon aqueous
effluents, and no further subcategorization is warranted.
-------
SECTION V
WASTE_CHARACTERIZATION
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 17-20
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 8 shows a typical chemical analysis of the insoluble solids in
Jamaican red mud. Although some 23 elements have been indicated as
analyzed, 98.5 percent of the material consists of the oxides of only
eight elements plus water and carbon dioxide as indicated by ignition
losses. The remaining 1.5 percent consists of the oxides of metallic
elements, such as MgO,K20,Cr203,ZnO,Zr02,Ni02rV205u,SrO, and others.
-------
TABLE 8. RED MUD INSOLUBLE SOLIDS (a)
Percent
LOI 11.0
Si02 5.5
A1203 12.0
Fe203 49.5
P205 2.0
CaO 8.0
Na20 3.5
Ti02 5.0
Mn02 1. 0
Miscellaneous 1.5
(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)ซnH20 + Fe203ซnH20. Other iron compounds such as
jacobsite, MnOซFe203, magnetite, Fe30jป, hercynit, FeOซA1203, and
ilmenite, FeOป, Ti02 have been tentatively identified. Aluminum is
present with silica in tentatively identified compounds such as
pyrophyllite, Al2O3ซ4SiO2ซH2O, sarcolite, (Ca,Na2) 3A12 (SiOjjt) 3, or
zunyite, [Al(OH, F, Cl) 2 ]6ซAl2Si30J2, and in manganspinel, MnOซAl203,
gahnite,ZnOปA!203, and beohmite, A1203ปH20, Other minerals identified
were alpha quartz, Si02., calcite, CaC03, and rutile, Ti02. (8) Thus,
red mud has a complex chemical makeup, dependent upon its parent bauxite
ore, aluminum extraction techniques, and impurity control.
The principal soluble constituents found in a typical Jamaican red mud
liquor at 17 percent solids are shown in Table 9. The concentrations of
metallic elements, including those listed in Table 8, are small. The
hydroxides of these non-amphoteric elements are quite insoluble. Also,
the alkaline leaching process is almost totally specific for aluminum
and results in a highly pure alumina product.
One of the characteristics of Jamaican red mud is its fine size. It has
been reported (8) that wet screening showed a particle size distribution
as shown in Table 10.
42
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TABLE 9. RED-MUD SLURRY SOLUBLE SOLIDS
A1203 2.5 g/kg liq.
NaOH 3.7 g/kg
Na2C03 1.6 g/kg
Na2S04 0.4 g/kg
NaCl 0.7 g/kg
Na2C204 0.1 g/kg
Specific gravity 1.008
pH 12.5
BOD 6 ppm
COD 148 ppm
( Q\
Reference: Rushingv '
TABLE 10. SCREEN ANALYSIS OF RED MUD
Screen
Mesh
-10
-20
-50
-100
-200
-325
+10
+20
+50
+10Q
+200
+325
Percent
Dry Solids
0.0
0.2
0.8
0.8
0.8
1.9
95.5
Reference: Rushing'"'
43
-------
Of the 95 percent below 325 mesh (4<4 micron) about 60 percent was
between 5 and HH microns, and some 35 percent was less than 5 microns in
size.
"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
Na2CO3), and 1-3 g/1 of sodium aluminate. (Convention in the U.S.
alumina industry is to express total alkalinity, including both NaOH and
Na2C03 as Na2C03).
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 11). 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, 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.
Cleaning Acid Wastes
-------
TABLE 11. RANGE OF CHEMICAL ANALYSES OF RED MUDS
Weight Percent
Component
Fe2ฐ3
A1203
Si02
Ti02
CaO
Na20
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 Christi, 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)
45
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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 quantities of dissolved solids, and
scaling of exchanger surfaces is a recurring problem. Acid cleaning is
universally employed, generally with sulfuric acid, although small
quantities of inhibited hydrochloric acid or acetic acid are also
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 1000 to 2000 Ib of acid per day.
Barometric^Condenser Effluents
Possible pollutants from the operation of barometric condensers are heat
and alkali. 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 14ฐC (25ฐF), 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 water-cooling applications,
such as, seal rings en rotary calcining kilns, from which thermal
discharges may result. Heat discharges from these ancillary Cervices
are nominal.
Miscellaneous Wastes
46
-------
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 slurry is invariably fed back
to the process in order to utilize the contained lime, and is never
discharged.
One miscellaneous waste stream from a bauxite refinery difficult to
characterize is the "housekeeping" or "hose-down" stream. This results
from minor spills and leaks and wastes resulting from clean-ups. In
most plants the in-plant 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, and 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 frcm 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 a 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 the refining of
bauxite is summarized in Table 12.
47
-------
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48
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SECTION VI
SELECTIQN^OF,POLLUTANT,. PARAMETERS
.SBtroduction
The waste water parameters of pollutional significance for the bauxite
refining industry include:
Alkalinity
pH
Total dissolved solids
Total suspended solids
Temperature
Sulfate
Since the waste streams are essentially inorganic, biochemical oxygen
demand (BOD5) or 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
pollutants to receiving waters.
Rationale^For_Selection of ..Pollutant Parameters
Alkalinity
Since the Bayer refining process uses a strong caustic solution, the
process waste from a bauxite refinery will be alkaline. Alkaline waters
are unpalatable and disruptive to aquatic biota and can be neutralized
with acid, at the expense of increasing the dissolved solids content.
Control, rather than treatment, is more applicable to such alkaline
wastes.
EH
As indicated above, the principal effluents are on balance, alkaline,
with a pH over 10. The pH is a convenient indicator for alkalinity. It
will also identify slug discharges of acid cleaning solutions.
-------
Total Dissolved Solids
Dissolved solids will be high in effluents from a bauxite refining
process and 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
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.
Temperature
Heat has been defined as a pollutant. 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.
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.
j
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.
Big-Chemical Oxygen Demand (BOD5}
Since the process waste streams are essentially inorganic rather than
organic there is no significant BOD5.
50
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Chemical Oxygen Demand
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 Greasg
Oil and grease are not normally found in the process waste streams. The
only sources of oil or grease would be from lubrication of process
machinery. The contribution from this source will be insignificant.
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
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.
51
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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 category. The key factor is that
bauxite refineries are hydrometallurgical plants daily producing
enormous tonnages of an aqueous waste suspension. As illustrated in
Table 12, these range from 500 to 3600 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 15-20 percent solids, the tonnages
can exceed 20r000 ton/day. There is no practicable or 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 a "sink" as the logical
and most cost-effective receptacle for also 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 available technology to achieve the goal of the Act, to
eliminate the discharge of pollutants into navigable waters by 1983.
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 following objectionable characteristics:
alkalinity
acidity
dissolved solids
52
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The first two categories can be neutralized, thus transformed into the
third, also objectionable pollutant. There is no particular advantage
in sodium sulfate or sodium chloride, as compared to their precursors.
Thus, the facts available lead to the conclusion that the optimum
solution for treatment and control of all other pollutants from bauxite
refining is also to consign them to 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 their mud wastes,
and in many instances, other significant process waste streams.
There may be, in addition, nonprocess streams such as sanitary effluents
and boiler and cooling tower blow-downs to be disposed. These lesser
streams may or may not be included in the total impoundment. In more
arid climates, the tendency will be to totally impound all streams; in
high-rainfall regions, the tendency will be more in the other direction.
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. Costly
alternatives are cooling towers or much larger lakes.
State-of-the-Art Control Technology
Waste Streams
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
53
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readily precipitated, there are essentially no end-of-the-pipe pollution
abatement schemes for these other bauxite process wastes. Some
treatment technologies are described in the following paragraphs.
RedTMud
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 UO ha (100
ac) to as much as 800 ha (2000 ac) .
There are two approaches to constructing 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.
The installation described contained two mud lakes containing U.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 higly 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 served two purposes;
first, it helped to key the dike to minimize seepage of lake water out
under the dike. Details of the construction are shown in Figure 8.
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 also 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 only is built initially, which is continually built up as the
lake fills. The construction of this type of dike is outlined
schematically in Figure 8. Initially a low combination roadway-dike is
constructed to a height of 1.2-1.8 meters (U-6 feet) and with a width of
U.5-5.3 meters (15-18 feet) from some stable sand-clay mixture. Along
the inside parameter steel standards are erected, from which the mud
54
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.Mud line
'Roadway 6m wide
Inside slope M3
PhaseII dike
Tamped earth77
and clay
Dike Key
3-4.5 m deep
2.5 m min.width
a. Initial Full Dike Construction
Phase IE relocation
of mud line
Mud line-Phase I
Phase I dike
Roadway
4.5-6m wide
.5-2m high
u u
b. Buildup Construction of Mud Lake Dike
FIGURE 8. MUD LAKE DIKE CONSTRUCTION
55
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pipe is suspended. The pipe has a tapered bottom shape, in industry
designation a "possum-belly", in which the coarser sands settle out. At
intervals the possum-belly is 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 will be
erected inside and the pipe lines reloacted, as indicated.
The success of this type of dike construction depends upon there being a
coarse sand fraction in the red mud. Thus, it is practicable for
Surinam bauxite but less so for Jamaican bauxite. Keep this term, 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 on the above technique. With the use of a drag line,
previously settled and well-consolidated red mud can be dredged from the
lake and cast on the tank to raise it in 2.5 meter (8-foot) increments.
Slopes must be low, so that there is a significant 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, it is reported to reach a
maximum compaction of about 35 percent solids if allowed to settle and
compact 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 out satisfactorily. Once past a critical
moisture content, somewhere in the 60 percent solids range, the mud does
not resuspend when rewetted (8). However, adoption of this approach to
the disposal of muds 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 practical.
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 dewatering of Jamaican red mud. Results of this
study indicated that the solids content could be increase to 40 percent.
Approximately 40 percent of the slurry liquid was recovered as a clear
effluent containing dissolved alumina and soda values for recycle to the
plant. Economic analysis indicated that centrifugation and evaporation
of the filtrate to recover 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.
56
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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 down 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 has constructed 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, reducing
the capital investment.
Mud lakes are not single-purpose operations, nor is their cost entirely
assignable to pollution control. They are, of course, first and
primarily receptacles for the waste mud residues. They can serve as
cooling ponds and water reservoirs. They can also be receptacles for
other minor waste streams from the plant, which may include 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 one more mud washing stage. Thus, for the purpose of this
report, red mud lake may be considered 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., consist of solutions containing high
dissolved solids concentrations, mostly sodium sulfate, plus remnants of
unreacted sulfuric acid. The simplest disposal method is direct
discharge to adjacent surface waters, but this technique is being
abandoned. Another producer neutralizes the spent acid with mud before
discharging to the river. One simple improved One producer is using a
simple improved method which involves the reaction of the spent cleaning
acid with lime, forming insoluble calcium sulfate, which is then
disposed of to 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.
57
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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.
Salts_ from_Salting-Out Evaporator. Where dissolved impurities must be
removed from the caustic liquor circuit of a bauxite refinery to prevent
their accumulation to levels causing interference with satisfactory
operations, a salting-out evaporator is used on spent liquor returning
to the digesters frcm 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.
One control technology is to dispose of the solid product to a landfill,
with the waste being covered with soil to prevent its 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, it appears that
this technology may be applicable only to Surinam bauxite.
Perhaps the simplest control technology, adopted by several producers,
is the obvious one of disposing of it by impoundment in an abandoned red
mud lake.
Barometric Condenser Cooling^Water. This water comes under the heading
of process water because Tt comes into direct contact with process
reactants. As noted earlier, very large quantities 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 (B) recycles the barometric condenser effluents from
the green liquor flash evaporators to the process lake, but discharges
the effluents from the barometric condensers 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 fpr reuse. The simplest
application is the use of a cooling pond or lake sufficiently large for
the heat to dissipate to the atmoshpere by evaporative . cooling,
sometimes also supplemented by sprays, and such ponds are widely used.
58
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Cooling towers, both mechanical draft and natural convection, are also
widely used, and would be considered the "best practicable control
technology currently available". It 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 reascns. Thus, while cooling towers are normally
competitive economically with evaporative cooling in ponds, they may not
be for 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 also
taken care, since any carryover is retained in the circuit.
Cooling Tower and Boiler Slowdown. Slowdown from a cooling tower
associated with process barometric condensers also 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 it would result in discharge of pollutants, reverse
osmosis would be significantly more expensive than direct disposal to a
red mud 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. However, since an
ideal receptacle is available in the red mud lake, logic dictates that
these blowdowns are treated and controlled in the same fashion.
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 undoubtedly to recycle such wastes to the
process, with the optimum point of introduction probably 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 manageme t
problems associated with excessive accumulation of water in the process
water circuit.
Sanitary Wastes. Sanitary wastes are not considered as process wastes
from bauxite refineries. However, the ideal receptacle for receiving
such wastes is the red mud lake. This may be the best generally
available technology for the treatment and control of sanitary wastes at
bauxite plants not served by municipal sewerage systems.
Water_Softener_Slud3e. Some plants using surface water for makeup
soften the water before use, which produces a sludge which must be
59
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disposed. The best available control and treatment technology for this
stream is land disposal of the sludge to a landfill or a red mud pond.
The application of the best practicable control technology currently
available to process waste streams of the bauxite refining process is
summarized in Table 13.
Industry Status and Plans.
The bauxite 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 14. Exemplary plants, with no
discharge of pollutants to surface waters are plants C and E.
To tal_I mgoundmen t_lMa nacje me nt_.
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 enumerated earlier. 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 enough so that optional solutions are
possible. This will also include the recycling of barometric condenser
cooling water. In others, the red mud lake or clear-water lake will be
used, mixing barometric condenser water with the process 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 are possible, 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 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 deficiency or excess. As described
in Section IV (Table 5), 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 (U-16 in). This complicates the water management
scheme, but 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 freshwater intake (purchased or otherwise acquired)
60
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68
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in rainfall- deficient areas, or is supplied by the rainfall (in rain-
fall 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 hydration 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;
A1203ซ3H20 100% extraction efficiency (losses of Al to mud
neglected)
1 ton (dry) mud/ton A1203 product.
i
CCD thickener and washer underflow = 20% solids.
10 Ibs H20/lbr 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 H2_0/lb A1203. final wash of product, using condensate or makeup
water; eliminated in spent liquor evaporator
Mud lake = 162 ha (UOO ac)
Plant location gulf south, with net excess of rainfall over
evaporation = 9 in/yr, e.g., New Orleans locations (Table 5).
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 goes up the stack when the
product is calcined. (Average recovery of alumina in the feed is
typically in the 85-90 percent range so that there is another
approximately 800 ton/day of unrecovered Alumina trihydrate in the
input, but since this is not dehydrated, it does not influence the water
balance calculations significantly) .
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
69
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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 20% 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 balance of 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 5) . For the assumed 400-acre red mud lake, this
represents 407,720 ton/yr, an average of approximately 1120 ton/day.
Overall system deficiency is then U970 ton/day as illustrated by the
schematic diagram in Figure 9.
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
mannitude.
In spite of the approximate nature of the calculations of this
generalized example 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 managment, 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 these
are thus monetary advantages which offset closing the circuit,
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" carries approximately 60 ton/day of soda
and 56 ton/day of alumina. Closing the circuit returns 7500 ton/day of
supernate to the plant, and recovers about 37.5 ton/day of soda and 35
ton/day of alumina.
In summary, it is quite possible for current "state-of-the- art
technology" to totally recycle all process waters and impound all solid
process wastes. Two plants are routinely doing this. Five others are
70
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71
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totally impounding the red mud and parts or all of various other smaller
streams.
Storm Water Management
Most bauxite refineries have successfully solved the problem of
providing for total impoundment of process wastes, i.e.t no 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 controlsT 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 seme of the rainfalls which can occur in the areas in
which bauxite refineries are located (see Table 5), the total collection
and retention of all rainfall may not be technically or economically
practicable.
72
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SECTION VIII
COSTt_ENERGYi_ANp_NONWATER_2UALITY_ASPECTS
Introduc tion
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, 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 character of 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 leave 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.
73
-------
The cost of land is a major consideration in any impoundment scheme.
Estimated current land costs range from $200/ha ($500/ac) to $1200/ha
($3000/ac). However, most bauxite refineries have acquired the needed
land years ago at substantially lower unit cost.
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
existing lakes walls.
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. No
producer supplied cost data by waste stream in a useable 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
15, there can be a sixfold difference between. 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 16. 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, it appears that 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 -$0.13/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 any facilities for impounding
74
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76
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red mud, although both are committed to doing so, Plant G by July 1,
1975r 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 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 into available
adjacent to the plant, which is in a metropolitan area, and the red mud
lake will be 10 miles from the plant.
The estimated costs, as supplied by the producer, are summarized in
Table 17. 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. Sufficiently detailed information is not available to fully
explain this difference.
It should be noted that the impoundment of red mud solids achieved by
the proposed installation by plants G 6 H is not total. According to a
letter to the U.S. Environmental Protection Agency by the producer (14) ,
there will be approximately 72 million ton/day of suspended solids
discharged.
Nonwater_QualitY_Aspects
Energy Requirements
Eljm2ing_Costs_. Tne 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.
Evaporat ion Costs. Depending upon the location and overall design and
management o? the water circuit of a plant and 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
77
-------
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78
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rate is about 400 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 VTI suggest that this should
not occur)
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, which, taken at an
assumed mud-lake-filled depth of 25 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*
The effluent limitations which must be achieved 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 achievec 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 emphasizes
treatment facilities at the end of a manufacturing process but includes
the control technology within the process itself when the latter are
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
80
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Application of Best Practicable^ggntrpl
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 practicable
control technology currently available is no discharge of process waste
water pollutants to navigable waters.
Identification of Best Practicable Control
Technology Currently Available
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 of 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, other nonprocess waste streams, e.g., water
softener backwash, boiler blowdown for which control is more applicable
than treatment. These wastes, relatively small in 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.
81
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(b) Four other plants have prepared or are implementing plans to
achieve no discharge of process waste waters before the
effective date of the recommended effluent limitations.
(c) Two plants are currently discharging all wastes, but are
implementing plans to impound red mud.
Rationale for the^Selection of the Best Practicable
Control Technology Currently Availablg
Age_and Size Of Equipment and Facilities
As set forth in previous sections of this report the bauxite refining
industry is characterized by:
(a) Very large plants, the smallest producing 900 kkgs/day of
alumina, and the largest producing 3600 kkg/day,
(b) A small spread in age, only 30 years from oldest (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 that the best practicable control
technology currently available is total recycle.
Total Cost of Application in Relation to Effluent Reduction_Benefits
Based upon the information contained in section Vi;il, the industry as a
whole would have to invest an estimated maximum of $62,000,000 to
achieve limitations prescribed herein. This amounts to approximately a
3 percent increase in projected capital investment.
Operating costs for the production of alumina from bauxite are estimated
to be on the order of of $55/kkg ($50/ton) of alumina. Increases in
operating costs to achieve the limitations are estimated to range from
zero to $0.22-0.28/kkg ($0.20-0.25/ton) for six of the eight U.S.
refineries. This is up to 0.5 percent of production costs. Producer-
estimated costs for the two plants now practicing essentially total
discharge to achieve near total impoundment of red mud are $4.U5-4.80
/kkg alumina ($t.91-5.29/short ton). Estimated annual operating costs
attributable to effluent reduction to finish closing the circuit are
estimated by the producer at from $1.95-2.9U/kkg ($2.15-3.2iป/short ton) ,
for a total of $6.40-7.74/kkg ($7.06-8.53/short ton). If the cost of
82
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producing alumina from bauxite is $55/metxic ton ($50/short ton), this
would represent an increase of 14-17 percent.
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
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^Control Technigue^Applications
This level of technology is practicable because twenty-two percent of
the plants in the industry are now achieving the 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.
Procgss 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, they are ones successfullly practiced by other
plants in the industry.
Ngnwater Quality Environmental Impact
Total impoundment has a potential effect upon soil systems due to strong
reliance upon the land for ultimate disposition of final effluents.
Total annual requirement for land for disposal for the industry is of
the order of 120 ha (300 ac) per year. Impoundment areas must be
impermeable to prevent the wastes therein 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.
83
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SECTION X
BEST AVAILABLE TECHNOLOGY
ECONOMICALLY ACHIEVABLE ^EFFLUENT
LIMITATIONS GUIDELINES
The best, available technology economically achievable is identical tx>
the best practicable control technology currently available. The
corresponding effluent limitations are no discharge of process waste
water pollutants to navigable waters.
SECTION XI
NEW SOURCE PERFORMANCE 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.
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SECTION XII
ACKNOWLEDGMENTS^
The following organizations provided information on bauxite refining and
waste treatment technology:
Aluminum Company of America, Pittsburgh, Pennsylvania
Kaiser Aluminum and Chemical Corporation, Oakland,
California
Martin-Marietta, Torrance, California
Ormet Corporation, Hannibal, Ohio
Reynolds Aluminum, Richmond, Virginia
Acknowledgment is made of the cooperation of personnel associated with
the companies above, most of which were visited, in providing process
technology and effluent quality information. Special acknowledgment is
made of those plant personnel and company officers that cooperated in
providing the detailed plant operating and cost data to support this
study.
The technical review committee members, Walter Hunt, Marshall Dick, John
Ciancia, Lew Felleisen, Swep Davis, and Taylor Miller are acknowledged
for their significant contributions to the guidelines development.
Ms. Chris Miller, Ms. Nancy Zrubek and Ms. Kit Krickenberger are largely
responsible for the timely preparation of this report.
85
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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).
(U) 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 5r 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. 745U (1970) .
(11) Guccione, E., "ซRed Mud1, a Solid Waste Can Now be
Converted to a High-Quality Steel", Eng. & Mining J.,
112' 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, Metallurfical Society of AIME, Feb, 28-Mar. 1, 1973,
Chicago, Illinois.
(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.
87
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SECTION XIV
GLOSSARY
Acidity
The concentration of acid ions expressed as pH for a solution. 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 03, 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.
Large chamber for holding bags used in the filtration of gases from a
furncae, 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
88
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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 Technology Economically Achievable
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.
Best^Practicable^Control TechnologY^Currently Available
Level of technology applicable to effluent limitations to be achieved by
July 1r 1977, for industrial discharges to surface waters as defined by
Section 301 (b) (1) (A) of the Act.
2iosiJฎmical_Oxy3en_jDemand __ (BOD)_
A measure of the oxygen demand in sewage and industrial wastes or in the
stream, determined by chemical techniques. One technique (BOD )
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.
Brown_Mud
The final solid waste remaining after the alumina is leached from the
calcined red mud in the combination process.
Brown Mud^ Lake
The diked reservoir (tailings pond) used to impound brown mud.
Calcination
The roasting or burning of any substance to bring about physical or
chemical changes; e.g., the conversion of lime rock to quicklime.
Capital Costs
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 weighed average of the separate costs of debt and equity.
Category and Subcateqory
89
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Divisions of a particular industry which possess different traits which
effect waste treatability and would require different effluent
limitations.
Caustic Soda
Sodium hydroxide (NaOH)
Centimgter (CM)
0.3937 inch
Demand_ JCOD)
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.
Q22!feiD<|tion_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 r it is used for approximating the salinity or total
dissolved solids content of water.
Continuous Countercur rent Decantation (CCD^
A continuous system of washing finely divided solids, such as red muds,
to free them from liquieds containing dissolved substances. In
practice, the fresh wash water and the strong solids start at opposite
ends and move counter currently to each other, so that the freshest water
contacts the most thoroughly washed solids.
Depreciation
Accounting charges reflecting the deterioration of a capital asset over
its useful life.
Digester
90
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Pressure vessel or autoc: ave; vessels in which the alumina is dissolved
from the bauxite.
Effluent
The waste water dischargt d from a point source to navigable waters.
Ef f 1 uen t_Li mit a t i on
A maximum amount per unit of production of each specific constituent of
the effluent that is sub -'sect to limitation in the discharge from a point
source.
Electrostatic Precipitator
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 plat. The device used a d-c potential approaching
40,000 volts to ioniz< and collect the particualte matter. The
collector plates are int< rmittently rapped to discharge the collected
dust into a hopper belov;.
Gallons per minute.
The worthless rock or other material in which valuable metals or
minerals occur.
Green Liguor
The aluminum-bearing solution from the bauxite digesters before further
processing.
Industrial Waste
All wastes streams within a plant. Included are contact and noncontact
waters. Not included are wastes typically considered to be sanitary
wastes.
Investment Costs
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; etc; plus any additional expenses
required to bring the technology into operation including expenditures
to establish related necessary solid waste disposal.
91
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Liter
1000 cubic centimeters.
M_
Thousand (e.g. , thousand kkgs) .
Micron
0.0001 cm (10-6 meter).
Milligrams per liter. Nearly equivalent to parts per million
concentration.
MM_
Million (e.g., million pounds).
New Source
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.
New Source Performance Standards
Performance standards for the industry and applicable new sources as
defined by Section 306 of the Act.
No Discharge of Pollutants^
No net increase of any parameter designated as a pollutant to the
accuracy that can be determined from the designated analytical methods.
Operations and Maintenance
Costs required to operate and maintain pollution abatement equipment.
They include labor, material, insurance, taxes, solid waste disposal,
etc.
22
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 inpH indicates a
tenfold change in acidity or alkalinity.
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Plant_Effluent or Discharge 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^Ligupr
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.
Biological treatment provided beyond primary clarification.
Silicates
ซ.
A chemical compound containing silicon, oxygen, and one or more metals.
Standard^gf^Performance
A maximum weight discharged per unit of production for each constituent
that is subject to limitation and applicable to new sources as opposed
to existing sources which are subject to effluent limitations.
Storm^Watgr^Lake
Reservoir for storage of storm-water runoff collected from plant site;
also, auxilary source of process water.
Surface Waters
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Navigable waters. The waters of the United States including the
territorial seas.
Th ix otr opi c
Having the property exhibited by certain gels of liquefying when stirred
or shaken and returning to the hardended state upon standing.
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 natural sources such as silt from erosion.
Unit_Op_eration_
A single, discrete process as part of an overall sequence, e.g. ,
precipitation, settling, filtration.
94
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TABLE 18
CONVERSION TABLE
MULTIPLY (ENGLISH UNITS) by TO OBTAIN (METRIC UNITS)
ENGLISH UNIT ABBREVIATION CONVERSION ABBREVIATION METRIC UNIT
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 Fฐ
feet ft
gallon gal
gallon/minute gpm
horsepower hp
inches in
inches of mercury in Hg
pounds lb
million gallons/day mgd
mile mi
pound/square
inch (gauge) psig
square feet sq ft
square inches sq in
tons (short) t on
yard y d
0.405
1233.5
0.252
ha
cu m
kg cal
0.555
0.028
1.7
0.028
28.32
16.39
0.555(ฐF-32)1
0.3048
3.785
0.0631
0.7457
2.54
0.03342
0.454
3,785
1.609
kg cal/kg
cu m/min
cu m/min
cu m
1
cu cm
ฐC
m
1
I/sec
kw
cm
atm
kg
cu m/day
km
(0.06805 psig +1)1 atm
0.0929 sq m
6.452 sq cm
0.907 kkg
0.9144 m
hectares
cubic meters
kilogram - calories
kilogram calories/kilogram
cubic meters/minute
cubic meters/minute
'cubic meters
liters
cubic centimeters
degree Centigrade
meters
liters
liters/second
killowatts
centimeters
atmospheres
kilograms
cubic meters/day
kilometer
atmospheres (absolute)
square meters
square centimeters
metric tons (1000 kilograms]
meter's
1 Actual conversion, not a multiplier
95
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