Note: Descriptions are shown in the official language in which they were submitted.
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5Concentration of Solids in the Bayer Process
Field of the Invention
The present invention is directed to a process of alumina manufacture via the Bayer
10 process. More particularly, it is concerned with improvements in the Bayer alumina process
by the removal of suspended solids by contacting process streams with a polymer which
contains hyd~oka",ic acid groups or salts thereof. flocclll~ting said suspended solids, and
subjecting the resultant flocculated solids to centrifugation.
15 Background of the Invention
The almost universally used process for the manufacture of alumina is the Bayer
process. In a typical commercial Bayer process, raw bauxite ore is pulverized to a finely
divided state. The pulverized ore is then fed to a slurry mixer where a slurry is prepared
20 using water, spent liquor and added caustic. This bauxite slurry is then diluted and sent
through a series of digesters where, at about 300 - 800 F. and 100-2000 p.s.i., most of
the total available alumina is extracted from ore which may contain both trihydrate and
monohydrate forms of alumina. The effluent from the digesters passes through a series of
flash tanks wherein heat and condensate are recovered as the digested slurry is cooled to
25 about 230' F and brought to atmospheric pressure. The aluminate liquor leaving the
flashing operation (blow-off .i;;,charge) contains about 1-20% solids, which consist of the
insoluble residues that remain after reaction between the bauxite ore and basic material
used to digest the ore and the insoluble products which precipitate during digestion. Herein,
all percentages are by weight, based on total weight, unless otherwise stated. The coarser
30 solid particles are generally removed with a "sand trap" cyclone. To separate the finer
insoluble solid particles from the liquor, the slurry is normally fed to the center well of a
primary mud settler where it is treated with a flocculant such as a polyacrylamide polymer,
polyacrylate polymer, hydroxamated polymer, flour and/or starch. As the mud settles,
clarified sodium aluminate solution, referred to as "green" or "pregnant" liquor, overflows a
35 weir at the top of the mud settling tank and is passed to the subsequent process steps.
The settled solids ("red mud") are w;lhdlaw~l as underflow from the bottom of the primary
mud settler and passed through a countercurrent washing circuit, generally con,~.ri~ed of
a series of washers, for recovery of sodium aluminate and soda. Aluminate liquorove:,~lo~i.,g the primary settler still contains typically 50 to 200 milligrams of suspended
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solids per liter. This liquor is then generally further clarified by filtration to give a filtrate with
less than about 10 milligrams suspended solids per liter of liquor. A-fter passage through
the lill,alion step, the level of suspended solids should be sufficiently low to provide an
alumina product from the precipitation step which meets all of the industry standards.
Alumina, in relatively pure form, is then precipitated from the filtrate as alumina
trihydrate crystals. The re",ail,i"g liquid phase or spent liquor is returned to the initial
digestion step and employed as a digestant of additional ore after being recor,s~iluted with
additional caustic.
The efficient removal of suspended solids from Bayer process streams has been a
major problem for many years. The aforementioned insoluble components should be
separated at a relatively fast rate to make the overall Bayer process efficient. Ideally, a
highly efficient Bayer process would separate the insoluble materials from the aluminate
liquor cleanly and completely, to give high solids red mud containing little or no caustic or
aluminate liquor, and so!ub 'i7ed alumina liquor with little or no insoluble dispersed residue.
Among the methods of overcoming the above problems and materially speeding up
separation of suspended solids from process streams as well as effecting a cleaner
separation of the constituents are those disclosed in U.S. Pat. No. 3,390,959 which employs
polyacrylates as anionic flocculants and U.S. Pat. No. 3,681,012, which uses combinations
of polyacrylates and starch in Bayer alumina recovery circuits. Also of interest in this
connection are U.S. Pat. No. 3,975,496 which uses a copolymer of acrylic acid and
methylolated acrylamide for the same purpose, and U.K. Patent Speciricdtion Nos. 2080272
and 2112366, which use, sequentially, combinations of polyacrylic acid and acrylate-
acrylamide copolymers. Other approaches have been proposed: in Japanese Patent
Pl~t lic-tion No. 56092116 (7125/81) is disclosed starch cationized with a quaternary
ammonium salt for use as a coagulant; U.S. Pat. No. 4,083,925 promotes separation from
alkali metal aluminate liquor by contacting it with anionic polyacrylamide under special
conditions within the mud settler; East German (I~E) Pat. No. 2552804 (8/11/77) subjects
starch to treatment with sodium let-t-bor~te and a magnesium salt to provide improved
floccul~ting properties with lower levels of starch; Russian Pat. No. 507526 (4/06/76) reports
that cationic flocculants of the formula (R--AR--CH 2--N--Ph)~ Cl~ are better for solids
flocculation than other known flocculants; Japanese Pat. No. J74018558 (10/05/74)
discloses using an inorganic calcium compound and sodium polyacrylate for sedimentation
and filtration. The use of hydroxamated polymers as flocculants for cassiterite is disclosed
in Jour. So. African Inst. of Mining and Metallurgy; Vol. 76; pgs. 117-119 (1975) by Appleton
et al. Polymers containing hydroxamic acid groups for reduction of suspended solids in
_
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Bayer process streams are described in U.S. Patent No. 4,767,540, which is hereby
incorporated herein by reference. Separation processes such as settling in the pr~sence
of a synthetic flocculant, filtering, or centrifugation, wherein the separation must be carried
out at a pressure above atmospheric pressure, are described in U.S. 4,994,244.
Because of the rheological characteristics of the solids in most Bayer process
streams, including flocc~ t~d solids, centrifugation is not typically used to separate solids
from the process stream. Instead, separation of the solids is generally acco~ hed by the
use of settlers, decanters, thickeners, classifiers. and filters. With the exceplion of filters.
these devices rely on the gravitational settling of the solids to achieve separation.
Flocculation of the solids aids in the settling process by tending to agglomerate smaller
particles into larger ones, which tend to settle faster. Floccu'~tion also aids in the filtering
process because larger agglo~lelahs are easier to filter than smaller ones, and less likely
to plug the filtering means.
NRed mud" is generally obtained as the underflow from a settler. It consists mainly
of extremely fine, difficult-to-filter, insoluble residue that remains after the caustic-soluble
components have been extracted. Typically, the red mud underflow from a primary semer
passes through a countercurrent washing circuit, generally comprised of a series of
washers, for recovery of sodium aluminate and soda. Current practice is to dispose of the
last washer underflow stream and other red mud streams by pumping them as a relatively
dilute slurry to holding ponds and lakes constructed for that purpose. The practical limit of
such a slurry is 25 to 40 percent solids; 40 percent solids content is usual. Those skilled
in the art agree that red mud impoundment is not an ideal solution to the disposal pn;L'e l,.
The dikes of mud lakes must be maintained, and there is always the risk of a break and
spill of the mud into a nearby stream or waterway. In addition, the large amounts of water
going to the impoundment along with the suspended mud may contain caustic and
soM~ d alumina, which are lost from the process and present a large economic penalty.
Experts have studied the problem of red mud utilization, e.g. "An Assessment of
Technology for Possible Utilization of Bayer Process Muds" by B. K. Parekh and W.M.
Goldberger, U.S. Environmental Prott:clion Agency, Off. Res. Dev., EPA-600/2-76-301
(1976), which is hereby incorporated herein by reference. Virtually all potential corll~ ,;al
uses of the muds require that the muds be dewatered to the extent that the solids can be
transported and/or stored in a consolidated dry form without tendency to leach or pulp.
Low-cost dewatering of the muds is therefore considered the key to their possible future
~tiii7~tion. It wQ ,!ld be very advantageous to increase the solids content of red mud. High-
solids mud could bë~ ~ econorn~i'cal~y transported to other locations and utilized as an
OCT-02-1997 12:13 CYTEC P~CA 022349l7 l998-o4-ls 223 321 2971
2~ ~21 291i
ingredient in e~g. ceramics, cement, construction materials, etc~ Such uses might also
mitigate the impoundment problem. Centrifugation is a well-known process for achieving soli~-
liquid separations, but has not been typically used to dewat~r red mud. It is known to those
skilled in the art that centrifu~ation of red mud is only mar~inally effective for increasing the
5 solids. Centrifugation in conjunction wlth the use of a surfactant was reported to be useful for
reducing the moisture content of red rnud, see Eisetsu Oi and Hiroshi Kame~aya, Kogai
Shigen Kenk~rusho Iho, 6(3)15-21 ~1976).
Surprisingly, it has now been discovered that greatly improved dewatering of Bayer
process streams, particularly settler underflow and digester blow-off, is obtained by a
10 combination of centrif~ation and the use of, as aftocculant, a polymer which contains
hydroxamic acid groups. The efficiency of solids/liQuids separation in the Bayer process is
thus improYed by increasing the solids content of the separated solids stream.
The processes of the present invention are desi~ned to increase red mud solids and
to recover the dlssolved components, such as aluminate and soda, contained therein. The
15 improvement forming the ~asis of the present invention lies in the centrifugation of suspended
sollds-containin~ streams. particularly those containing red mud solids, that have been
flocculated using polyrners that contain hydroxarnic acid ~roups. Centrifugation of solids that
were not flocc~ ta~ with polyrners, or that were floccl ~l~ted with polymers that did not contain
hydroxamic acid groups, has been found to be less effective than current commercial
20 procedures.
n~t~ Description of the Pr~f~r~d EmL,o~ ents
AccOrc~il,g to the present in~/ention, there is provided a process for improving the
25 dewatenn~ of suspended solids, par~cularly red rnud, of ttle Bayer process where~y a poiymer
containing hyd~o~ llic acid groups or salts thereof is added to the Bayer process stream in
order to effectiYely remove suspended solids therefrom, and the resulting floccul~t~d solids
aredewatered bycentrifugation.
The polyrner to be employed in the present invention can vary rather broadly in type.
30 It should be sufficiently stable to be effective under the process conditions used, e.g., high
temperatures and strong caustic ccnditions, typically, 185~ - 225' F., and 80 400 grams per
liter total alkali content (expressed as sodium carbonate equivalent).
Thus, for exarnple, any water-soluble hy~ ",~ acld or salt group-containing polymer
may b~ used in the process of the present invention. The use~ul polyrners can best be
35 exemplified by those containin~ pendant ~roups of the Formula (1):
AMENDI~D SHEET
- IP~A,'EP -
iii 7 nl!t lR 11~ Afdrllk ti jd 2. okt 18:09
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--C r~l l OR
wherein R is hydrogen or a cation. These polymers are well known in the art and can be
derived from polymers containing pendant ester, amide, anhydride, nitriie, etc., groups by
the reaction thereof with hydroxylamine or its salt, or by polymerization of a monomer which
contains a hydroxamic acid or salt group. Hydroxamated polymers derived from polymers
containing amide groups e.g. polyacrylamide are preferred.
Exemplary of the polymers which may be hydroxamated for use in the process of
the present invention are acrylic, methacrylic, crotonic etc., acid ester polymers such as
polymers produced from the polymerization of methyl acrylate, ethyl acrylate, t-butyl
acrylate, methyl methacrylate, ethyl methacrylate, cyclohexyl methacrylate, dimethyl
aminoethyl methacrylate, dimethyl aminoethyl acrylate, methyl crotonate, etc., polymers of
maleic anhydride and esters thereof, and the like; nitrile polymers such as those produced
from acrylonitrile etc; amide polymers such as those producea from acrylamide,
methacrylamide and the like.
Hydroxamated polymers are well known to those skilled in the art and are
specifically disclosed, as are methods for their production, in U.K. Patent App'l--tion
2171127 and U.S. Pat. Nos. 3,345,344; 4,480,067, 4,532,046; 4,536,296; 4,587,306;
4,767,540; 4,902,751; and 5,128,420; all of which are hereby incorporated herein by
reference. Generally, these hydroxamated polymers may be produced by reacting the
polymer containing a pendant reactive group, in solution, with a hydroxylamine or its salt
at a temperature ranging from about 10' C to 100' C, preferably below 50 C, for several
hours, and more preferably, at a pH over about 10. From about 1-90% of the available
pendant reactive groups of the polymer may be replaced by hydroxamic groups in
accordance with said procedures.
In addition to reaction of a hydroxylamine or its salt with a polymer solution, it is
known that a polymer latex or emulsion may be reacted directly with a hydroxylamine or its
salt. The latex may be, e.g., a copolymer of acrylamide and methyl acrylate or a copolymer
of acrylic acid and methyl acrylate. In these cases, the hydroxylamine or its salt reacts
primarily with the ester groups to form hydroxamic acid groups.
Also, it i5 known that aqueous solutions of polymers derived from inverse emulsions
and inverse microemulsions (herein referred to also as emulsions and microemulsions)
function erricienlly in the process of the present invention. These emulsions and
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microemulsions are made of, for example, aqueous polyacrylamide, or acrylamide/acry~ic
acid copolymers dispersed in oil and reacted directly with a hydroxylamine or its salt to give
very high molecular weight polymers containing hydroxamic acid groups. Dilute aqueous
solutions of these polymers, useful in the instant invention, are derived from emulsions and
microemulsions by ''breakingU; e.g. adding the emulsions and microemulsions to water,
optionally adding surfactant, and agitating to dissolve the polymer.
The degree of hydroxamation, i.e., the concentration of Formula I units in the
polymers useful herein, may range from about 1 to about 90 mole percent, preferably from
about 5 to about 75 mole percent and, most preferably, from about 10 to about 50 mole
percent. The degree of hydroxamation may be determined by nuclear magnetic resonance
spectroscopy techniques well known to those skilled in the art.
Suitable hydroxylamine salts include the sulfates. sulfites, phosphates, perchlorates,
hydrochlorides, acetates propionates and the like. The pH of the solution is adiusted to be
in the range of about 3 to about 14, preferably over about 7, more preferably over about 10,
by means of acid or base addltiGn to the solution.
Any water-soluble polymer may be used in the present process which, after
hydroxamation, performs to settle suspended solids. Thus, homopolymers, copolymers,
terpolymers, etc. of the above exemplified monomers may be used. Suitable comonomers
which, by copolymerization, may form, for example, up to about 95 mole percent of the
polymers useful herein can include acrylic acid, sodium acrylate, methacrylic acid, maleic
anhydride, vinyl acetate, vinyl pyrrolidone, butadiene, styrene as well as others of the above
enumerated esters, amides and/or nitriles and the like as is known in the art and is set forth
in the above-incorporated patents as long as such copolymers, terpolymers etc., are water-
soluble after hydroxamation. The weight average molecular weight of the polymers useful
in the process of the present invention range from about 1 X 104 to about 1 X 1 Oa,
preferably from about 3 X 105 to about 5 X 107. Weight average molecular weight may be
determined by light scattering techniques well known to those skilled in the art.
The polymers used in the present invention are employed by adding them, usually
in the form of a dilute aqueous solution, to any digested bauxite ore process stream
containing solubilized alumina and suspended solids dispersed throughout, in an amount
at least sufficient to settle said suspended solids. Preferably, the polymers are added to
settler underflow streams, washer train underflow streams, and/or digester blow-off streams.
The process stream may undergo other chemical treatment e.g. acidification before, during
or after the time that the polymer is added. Generally, for best results, at least about 0.1
milligrams (mg) of the hydroxamated polymer is added per liter of process stream.
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Mixtures of hydroxamated polymers with other water-soluble polymers e.g
polyacrylates, acrylate/amide copolymers. starch, dextran, etc. are effective and may be
preferred. For instance, a 1% solution of a polymer containing pendant hyd~uxa~ ~ acid
or salt groups could be blended with a 1% solution of polyacrylic acid or its salt and the
resultant mixture used to floccl~t~ red mud, or the polymers could be blended while still
J in the emulsion form. Mixtures of hydroxamated polymers with other chemical agents useful
in the Bayer process e.g surfactants may also be effective.
It is understood, that higher amounts than those just stated may be employed
without departing from the scope of the invention, although generally a point is reached in
which additional amounts of hydroxamated polymer do not improve the separation rate over
already achieved maximum rates. Thus, it is uneconomical to use excessive amounts when
this point is reached.
The technology of centrifugation is well known to those skilled in the art and adetailed description may be found in e.g Ullman's Encyclopedia of Industrial Chemistry,
Volume B2, pp. 11-1 to 11-27, which is hereby incorporated herein by reference. Any
centrifuge, including filter centrifuges, screen centrifuges, sedimentation centrifuges,
decanting centrifuges, etc. may be used in the present invention. Sedimentalion and
decanting centrifuges are preferred, and classifying decanter centrifuges are most preferred.
The optimization of centrifuge performance is well known in the art e.g. D.E. Sullivan
and P.A. Vesiland, ~Centrifuge Trade-Offsn, Operations Forum, pp. 24-27 (1986), which is
hereby incorporated herein by reference. Feed volume depends on the size of the
centrifuge and type of centrifuge. For a hori~onl~l classifying decanter centrifuge with a
bowl diameter of about 20 inches and a length of about 80 inches, a feed volume of about
4 to about 250 gallons per minute may be used, preferably about 20 to about 100 gallons
per minute, most preferably about 30 to about 90 gallons per minute. Feed solids may
range from about 0.01% to about 45%, preferably from about 15% to about 30%. The G-
force is generally in the range of about 500 to about 3000 X G, preferably in the range of
about 1000 to about 1500 X G. The differential between the scroll and the bowl is generally
less than 150 revolutions per minute (rpm), preferably from about 1 to about 100 rpm, more
preferably from about 10 to about 50 rpm, most preferably from about 30 to about 40 rpm.
Water-soluble polymers containing pendant hydroxamic acid or salt groups may be
mixed with the Bayer process stream, preferably the settler underflow or digester blow-off,
in a holding tank prior to being introduced to the centrifuge, or pumped into the process
- stream feed line, or added via a feed tube directly inside the centrifuge. Preferably, the
polymer is added in the form of a dilute solution. e.g. from about 0.01% to about 3%,
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directly inside the centrifuge. Those skilled in the art recognize that the optimum polymer
concentration in the dilute solution depends on the solids level in theBayer prucess stream,
and can be ascertained by routine ex,veri-"e--lation.
When hydroxamated polymers are used, preferably within the ranges specified
above, to flocculate suspended Bayer process solids, preferably settler underflow, settler
overflow, washer train underflow, washer train overflow, or digester blow-off streams, the
floccu~ted solids are centrifuged to produce centrifuged solids (cake) and aqueous liquid
(centrate). Preferably, the operation of the centrifuge is optimized accG,~ ~9 to principles
well known in the art. The settler underflow streams are preferably primary settler
underflow streams. The washer train underflow streams may be streams from any washer
in the washer train, preferably the last washer underflow stream. The cake solids (the
weight percent water-insoluble material) of the cake, or centrifuged solids, is higher than the
feed solids, preferably greater than about 40%, more pr~ferably greater than about 50%,
most preferably greater than about 60%. Although is it generally preferred for the cake
solids to be as high as possible, plugging of the centrifuge may occur at very high solids
levels e.g. 90%. For obvious reasons plugging of the centrifuge is to be avoided. In
practice, the desired solids level is generally dependent on whatever handling
characteristics are desired in the centrifuged solids. The processes of the instant invention
are particularly useful for concentrating, or dewatering, red mud, typically from settler
underflow streams, and/or blow-off d; jcharge.
It is generally desirable for the centrate, which is co-l-,uri~ed of the aqueous liquid,
or aluminate liquor, to be as clear as po-c ~ !~; i.e., to have as low a concentration of
suspended solids as possible to avoid contamination of the final product. The solids level
(the weight percent water-insoluble material) in the aqueous liquid is less than the feed
solids, preferably 1% or less, more prefelably 0.5% or less, even more preferably 0.2% or
less, and most preferably 0.1% or less. The solids level in the centrate is frequently
expressed as the centrate clarity, as specified in the examples.
In practical terms, the centrifugation of flocculated solids to achieve both highly
dewatered red mud and clear aqueous liquor is most often optimized in the context of other
plant operations. For instance, the degree of red mud dewatering and the clarity of the
aqueous liquor may be adjusted up or down to achieve other desirable outcomes such as
lower power consumption, reduced waste disposal costs, increased rates of production,
increased product purity, reduced consumption of raw materials, etc. Floccul~tion and
centrifugation may be used in place of, or in addition to, or in combination with, the usual
means of solids/liquids separation employed in the Bayer process e.g settlers, decanters,
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thickeners, classifiers, and filters. For instance, the use of settlers may be reduced or
avoided by floccul~fing and centrifuging blow-off discharge directly-. A consecutive or
i"le""iLlent series of centrifuges may also be employed, with the output of one as the input
for another.
The f~ w;. -g examples are set forth for illustration purposes only and are not to be
J construed as limits on the present invention.
In the following Examples, the solids content (cake solids) of centrifuged solids is
deten--i,-ed by weighing a sample of centrifuged solids, washing the solids with deioni~ed
water, and drying the sample to constant weight in a forced air oven maintained at about
105' C. The cake solids are expressed in wt. % as (dried weight / initial weight) X 100.
Centrate (aqueous liquor) clarity, or wt % water-insoluble material in the aqueous liquid, is
determined by wei~l . ~9 a centrate sample, filtering the centrate through a previously
weighed 45 micron polypropylene or glass filter, washing the solids with water, and drying
the filter to constant weight in a forced air oven maintained at about 105- C. Values for
centrate clarity are expressed in wt. % as [(dried filter weight- initial filter weight) / (centrate
weight)] X 100.
Polymer D is obtained commercially; it contains about 90 mole % ammonium
acrylate and about 10 mole % acrylamide and has a molecular weight of about 15,000,000.
EXAMPLE A
Polymer A is prepared as follows: 100 Parts of 18 % aqueous solution of polyacrylamide
(molecular weight of about 500,000) is combined with 3 parts of sodium thiosulfate
stabilizer, 54 parts of 30 % aqueous hydroxylamine sulfate, and 35 parts 50 % aqueous
25 sodium hydroxide in a suitable vessel. The mixture is stirred at a temperature of about 30-
40 C for two hours, then allowed to cool to ambient temperature. After two days, the
degree of hyd,uxa".ation of the polymer in the resulting 12.5% solution is found to be about
60 mole %.
EXAMPLE B
Polymer B is prepared as follows: 65 Parts of 30 % aqueous hydroxylamine sulfate, 25
parts of sodium thiosulfate stabilizer, 142 parts water and 160 parts 50 % aqueous sodium
hydroxide are mixed in a suitable vessel to give a solution. This solution is added to a
mixture of 141 parts aliphatic oil, 1 part of an ethoxylated amine surfactant, and 438 parts
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of a polyacrylamide microdispersion having a molecular weight of about 15,000,000 and
containing 25 % polymer solids, with the temperature being maintained below about 35'C
for about 24 hours or more. The resulting hydroxamated polymer microdispersion contains
about 11% polymer solids and the degree of hydroxamation is about 14 mole %.
EXAMPLE C
Polymer C is prepared as follows: 70 parts of a 1% solution of a polymer prepared as in
Example B is blended with 30 parts of a 1% polymer solution of a commercially available
sodium polyacrylate having a molecular weight of about 10,000,000.
EXAMPLES 1-12
The Bayer process stream used in these examples is underflow from a red mud settler.
15 The underflow slurry is fed with a variable speed pump to a horizontal classifying decanter
centrifuge having a bowl diameter of about 20 inches and a length of about 80 inches. The
G force is between about 1000 X G and about 1600 X G. The differential speed is about
15 to about 35 revolutions per minute (rpm). The polymer, as a ~0.5% solution, is fed
directly into the feed chamber of the centrifuge via a feed tube. The dosage of the polymer,
20 in units of grams of real polymer per dry ton (g/DT) of centrifuged solids, is shown in Table
1. Centrifugation of red mud without the use of polymer gives an unacceptably cloudy
filtrate. Table 1 also shows the identity of the polymers used, prepared as in Examples A,
B and C, the wt. % solids of the red mud slurry, the feed rate of the red mud slurry (in units
of gallons per minute, gprn~, the cake solids (wt. % solids in the centrifuged red mud solids)
25 and the centrate clarity (wt. % filterable solids in the aqueous liquor). The results
demonstrate that the hydroxamated polymers provide high centrifuge cake solids and clear
centrate.
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Table 1
Red Mud
Slurry Red Mud PoiymerCake Centrate
Example Solids,Slurry PolymerDosage, solids, Clarity,
5 No. Wt % Feed Flocculant g/DT Wt % Wt %
Rate, gpm
20.1 50 Polymer B 243 71.4 0.4
-
Z 21.3 55 Polymer B249 66.1 0.055
3C 21.3 55 Polymer D741 Very Very
Poor Poor
4 16.3 84 Polymer B663 60.3 0.09
21.4 55 Polymer B275 63.7 0.09
6 15.5 55 Polymer C412 63.7 0.16
7 18.9 55 Polymer C260 63.6 o.1
8 18.9 55 Polymer A1156 65.2 nd
9 18.9 55 Polymer C301 63.2 0.07
15 10 20.3 55 Polymer B218 63 0.1
11 20.3 55 Polymer B172 64.2 nd
12 20.3 55 Polymer B224 63.4 nd
C = Comparative
20 nd = not determined
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EXAMPLES 13-15
The Bayer process stream used in these Examples is primary settler overflow having a feed
solids of about 0.015%. The conditions used are the same as in Examples 1-12, Wit.? r
appropriate adjustment for the lower solids content of the slurry. Using polymers prepared
as in Examples A, B, and C, values of cake solids are obtained that are substantially
equivalent to those in Table 1; values of centrate clarity less than 0.015% are obtained.
EXAMPLES 16-18
The Bayer process stream used in these Examples is last washer underflow having a feed
solids of about 30%. The conditions used are the same as in Examples 1-12, with
appropriate adjustment for the higher solids content of the slurry. Using polymers prepared
as in Examples A, B, and C, values of cake solids and centrate clarity are obtained that are
substantially equivalent to those in Table 1.
EXAMPLES 19-25
The red mud slurry used in these Exar"~lcs is blow-off discharge. The feed solids of the
slurry is about 2% and the feed rate of the slurry is shown in Table 2 The slurry is fed with
a variable speed pump to a horizontal classifying decanter centrifuge having a bowl
diameter of about 20 inches and a length of about 80 inches. The G force is about 1200
X G. The differential speed is about 10 rpm. Polymers A and B are obtained as above,
diluted to 1% solution, and fed directly into the feed chamber of the centrifuge via a feed
tube. The dosage of the polymer is as shown in Table 2. The centrate clarity both with and
without polymer is shown in Table 2.
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Table 2
Slurry
Feed PolymerCentrate
Example rate, Dose,Clarity, wt
No. gpmPolymer Flocculant g/DT %
1 9 50 Polymer A 1 50 0.37%
Polymer A 300 0.31%
21 50 Polymer A 375 0.31%
22 50 Polymer B 131 0.23%
23C 50 None N/A 0.42%
24 42 Polymer B 150 0.05%
25C 42 None N/A 0.38%
C = Comparative
N/A = Not ~pp~-cz~hlE
