CROSS-LINKED ETHYLSULFONATED DIHYDROXYPROPYL
CELLULOSE
Background of the Invention
In the typical Bayer process for the production of alumina trihydrate,
bauxite ore is pulverized, slurried with caustic solution, and then digested at elevated
temperatures and pressures. The caustic solution dissolves oxides of aluminum,
forming an aqueous sodium aluminate solution. The caustic-insoluble constituents of
bauxite ore are then separated from the aqueous phase containing the dissolved
sodium aluminate. Solid alumina trihydrate product is precipitated out of the
solution and collected as product.
As described at least in part, among other places, in U.S. Pat. No.
6,814,873, the Bayer process is constantly evolving and the specific techniques
employed in industry for the various steps of the process not only vary from plant to
plant, but also are often held as trade secrets. As a more detailed, but not
comprehensive, example of a Bayer process, the pulverized bauxite ore may be fed
to a slurry mixer where an aqueous slurry is prepared. The slurry makeup solution is
typically spent liquor (described below) and added caustic solution. This bauxite ore
slurry is then passed through a digester or a series of digesters where the available
alumina is released from the ore as caustic-soluble sodium aluminate. The digested
slurry is then cooled, for instance to about 220 degrees F, employing a series of flash
tanks wherein heat and condensate are recovered. The aluminate liquor leaving the
flashing operation contains insoluble solids, which solids consist of the insoluble
residue that remains after, or are precipitated during, digestion. The coarser solid
particles may be removed from the aluminate liquor with a "sand trap", cyclone or
other means. The finer solid particles may be separated from the liquor first by
settling and then by filtration, if necessary.
The clarified sodium aluminate liquor is then further cooled and
seeded with alumina trihydrate crystals to induce precipitation of alumina in the
form of alumina trihydrate, Al(OH)3. The alumina trihydrate particles or crystals are
then classified into various size fractions and separated from the caustic liquor. The
remaining liquid phase, the spent liquor, is returned to the initial digestion step and
employed as a digestant after reconstitution with caustic.
Within the overall process one of the key steps is that of precipitation
of the alumina trihydrate from the clarified sodium aluminate liquor. After the
insoluble solids are removed to give the clarified sodium aluminate liquor, also
referred to as "green liquor", it is generally charged to a suitable precipitation tank,
or series of precipitation tanks, and seeded with recirculated fine alumina trihydrate
crystals. In the precipitation tank(s) it is cooled under agitation to induce the
precipitation of alumina from solution as alumina trihydrate. The fine particle
alumina trihydrate acts as seed crystals which provide nucleation sites and
agglomerate together and grow as part of this precipitation process.
Alumina trihydrate crystal formation (the nucleation, agglomeration
and growth of alumina trihydrate crystals), and the precipitation and collection
thereof, are critical steps in the economic recovery of aluminum values by the Bayer
process. Bayer process operators strive to optimize their crystal formation and
precipitation methods so as to produce the greatest possible product yield from the
Bayer process while producing crystals of a given particle size distribution. A
relatively large particle size is beneficial to subsequent processing steps required to
recover aluminum metal. Undersized alumina trihydrate crystals, or fines, generally
are not used in the production of aluminum metal, but instead are recycled for use as
fine particle alumina trihydrate crystal seed. As a consequence, the particle size of
the precipitated trihydrate crystals determines whether the material is to be
ultimately utilized as product (larger crystals) of as seed (smaller crystals). The
classification and capture of the different sized trihydrate particles is therefore an
important step in the Bayer process.
This separation or recovery of alumina trihydrate crystals as product
in the Bayer process, or for use as precipitation seed, is generally achieved by
settling, cyclones, filtration and/or a combination of these techniques. Coarse
particles settle easily, but fine particles settle slowly. Typically, plants will use two
or three steps of settling in order to classify the trihydrate particles into different size
distributions corresponding to product and seed. In particular, in the final step of
classification a settling vessel is often used to capture and settle the fine seed
particles. Within the settling steps of the classification system, flocculants can be
used to enhance particle capture and settling rate.
The overflow of the last classification stage is returned to the process
as spent liquor. This spent liquor will go through heat exchangers and evaporation
and eventually be used back in digestion. As a result, any trihydrate particles
reporting to the overflow in this final settling stage will not be utilized within the
process for either seed or product. Effectively such material is recirculated within
the process, creating inefficiencies. Therefore, it is important to achieve the lowest
possible concentration of solids in the overflow of the last stage of classification to
maximize the efficiency of the process.
As described for example in U .S. Pat. No. 5,041,269, conventional
technology employs the addition of synthetic water soluble polyacrylate flocculants
and/or dextran flocculants to improve the settling characteristics of the alumina
trihydrate particles in the classification process and reduce the amount of solids in
the spent liquor. While various flocculants are often used in the trihydrate
classification systems of Bayer plants, it is highly desirable to reduce as far as
possible, the loss of solids with the spent liquor.
Thus there is clear need and utility for a method of improving the
classification and flocculation of precipitated alumina trihydrate in the Bayer
process. Such improvements would enhance the efficiency of the production of
alumina from bauxite ore.
The art described in this section is not intended to constitute an
admission that any patent, publication or other information referred to herein is
"prior art" with respect to this invention, unless specifically designated as such. In
addition, this section should not be construed to mean that a search has been made or
that no other pertinent information as defined in 37 CFR §1.56(a) exists. Additional
features and advantages are described herein, and will be apparent from, the
following Detailed Description.
Brief Summary of the Invention
The invention relates to a method for improving the Bayer process
for the production of alumina from bauxite ore. The invention concerns the use of
cross-linked polysaccharides, specifically cross-linked dextran or cross-linked
dihydroxypropyl cellulose to improve the performance of unit operations within the
Bayer process, in particular to enhance the settling of fine alumina trihydrate
crystals. The cross linked cellulose comprises covalently cross-linked mixed
cellulose ether containing predominantly 2,3-dihydroxypropyl ethers. It may also
comprise ethylsulfonate ethers. Key characteristic of such cross-linked cellulose
ether are the presence of 2,3-dihydroxylpropyl groups and the covalent cross-linking
achieved under homogenous reaction conditions resulting in significant viscosity
increases of the in water dissolved polymer. A surprisingly unique characteristic of
the so prepared dihydroxypropyl ethers is their capability to enhance the flocculation
of aluminum trihydrate solids from a highly alkaline, pregnant process liquors in the
Bayer process.
Detailed Description of the Invention
The following definitions are provided to determine how terms used
in this application, and in particular how the claims, are to be construed. The
organization of the definitions is for convenience only and is not intended to limit
any of the definitions to any particular category.
"Consisting Essentially of means that the methods and compositions
may include additional steps, components, ingredients or the like, but only if the
additional steps, components and/or ingredients do not materially alter the basic and
novel characteristics of the claimed methods and compositions.
"Dextran" is a polysaccharide characterized as being an a-D-1,6
glucose-linked glucan with side chains 1-3 linked to the backbone units of the
polysaccharide.
"Dihydroxypropyl cellulose" means a cellulose derivative with the
addition of 1,2-dihydroxypropyl ether group to the cellulose backbone.
"Hydrocyclone" means a device to classify, separate or sort particles
in a liquid suspension based on the ratio of their centripetal force to fluid resitance,
in particular for dense and coarse particles, and low for light and fine particles, they
often have a cylindrical section at the top where liquid is being fed tangentially and
a conical base, and they often have two exits on the axis: the smaller on the bottom
(for underflow) and a larger one at the top (for overflow), generally the underflow is
the denser or coarser fraction, while the overflow is the lighter or finer fraction.
"Liquor" or "Bayer liquor" means a caustic, liquid medium that has
run through a Bayer process in an industrial facility.
"Polysaccharide" means a polymeric carbohydrate having a plurality
of repeating units comprised of simple sugars the C-O-C linkage formed between
two such joined simple sugar units in a polysaccharide chain is called a glycosidic
linkage, and continued condensation of monosaccharide units will result in
polysaccharides, common polysaccharides are amylose and cellulose, both made up
of glucose monomers, polysaccharides can have a straight chain or branched
polymer backbone including one or more sugar monomers, common sugar
monomers in polysaccharides include glucose, galactose, arabinose, mannose,
fructose, rahmnose, and xylose.
"Slurry" means a mixture comprising a liquid medium within which
fines (which can be liquid and/or finely divided solids) are dispersed or suspended,
when slurry is sparged, the tailings remain in the slurry and at least some of the
concentrate adheres to the sparge bubbles and rises up out of the slurry into a froth
layer above the slurry, the liquid medium may be entirely water, partially water, or
may not contain any water at all.
"Surfactant" is a broad term which includes anionic, nonionic,
cationic, and zwitterionic surfactants. Enabling descriptions of surfactants are
stated in Kirk-Othmer, Encyclopedia of Chemical Technology, Third Edition,
volume 8, pages 900-912, and in McCutcheon's Emulsifiers and Detergents, both of
which are incorporated herein by reference.
"Thickener" or "Settler" means a vessel used to effect a solid-liquid
separation of a slurry, often with the addition of flocculants, the vessel constructed
and arranged to receive a slurry, retain the slurry for a period of time sufficient to
allow solid portions of the slurry to settle downward (underflow) away from a more
liquid portion of the slurry (overflow), decant the overflow, and remove the
underflow. Thickener underflow and thickener overflow are often passed on to
filters to further separate solids from liquids.
In the event that the above definitions or a description stated
elsewhere in this application is inconsistent with a meaning (explicit or implicit)
which is commonly used, in a dictionary, or stated in a source incorporated by
reference into this application, the application and the claim terms in particular are
understood to be construed according to the definition or description in this
application, and not according to the common definition, dictionary definition, or the
definition that was incorporated by reference. In light of the above, in the event that
a term can only be understood if it is construed by a dictionary, if the term is defined
by the Kirk-Othmer Encyclopedia of Chemical Technology, 5th Edition, (2005),
(Published by Wiley, John & Sons, Inc.) this definition shall control how the term is
to be defined in the claims.
At least one embodiment of the invention is directed towards a
process for extracting alumina trihydrate comprises the digestion of pretreated
bauxite ore in an alkaline liquor to produce a slurry of red mud solids and aluminate
in suspension in the alkaline liquor then decanting the red mud solids from the
alkaline liquor suspension to produce the decanting liquor; the passing of said
decanting liquor through security filtration to remove all solids, precipitation and
production of a slurry containing alumina trihydrate solids which then are
flocculated and settled with the addition of a cross-linked polysaccharide. Larger
trihydrate particles are put through the calcination process to produce purified
alumina while finer particles are re-used as seed for the precipitation process.
In at least one embodiment the preferred flocculant of the trihydrate
solids in the process is a crosslinked polysaccharide. Preferred polysaccharides
include dextran and dihydroxypropyl cellulose. The flocculant is added in the range
of 0.1 to 100 ppm. The most preferred dose range for the flocculant is 0.3 to 20 ppm.
The cross linked cellulose can comprise covalently cross-linked mixed cellulose
ether containing 2,3-dihydroxypropyl ethers.
In at least one embodiment the cross linked cellulose is predominantly 2,3-
dihydroxypropyl ethers. In at least one embodiment the cross linked
polysaccharide/cellulose also comprises ethylsulfonate ethers. Key characteristic of
such cross-linked cellulose ether are the presence of 2,3-dihydroxylpropyl groups.
In at least one embodiment the reagent used to convert cellulose to
dihydroxypropyl cellulose is glycidol. Another suitable reagents is 3-chloro-l,2-
propanediol.
In at least one embodiment the dihydroxypropyl cellulose is further
modified to contain additional anionic charge. This may be accomplished by
reacting the dihydroxypropyl cellulose with sodium vinylsulfonate and/or sodium
chloroacetate.
In at least one embodiment the cross-linkages in the ethylsulfonated
dihydroxypropyl cellulose are formed at least in part by reaction with a reagent such
as epichlorohydrin, divinylsulfone, glycerol diglycidyl ether, polyethyleneglycol
diglycidyl ether, neopentylglycol diglycidyl ether, resorcinol diglycidyl ether, 1,2-
dichloroethane, N.N-methylene bisacrylamide, and 1,4-benzoquinone, and any
combination thereof. The cross-linking agents produce bonds between the individual
polymer chains of ethylsulfonated dihydroxypropyl cellulose that are stable in
aqueous alkaline media. Ether linkages as produced by epichlorohydrin or
diglyccidyl ethers belong to these group of bonds.
In at least one embodiment the cross-linked polysaccharide is
dextran. In at least one embodiment the cross-linked dihydroxypropyl cellulose is
produced by addition of dextran or dihydroxypropyl cellulose to an alkaline solution
containing sodium hydroxide, potassium hydroxide, or other alkali metals or water
soluble alkaline earth metal hydroxide, to provide a causticized polymer solution
having a pH in the range of 11 to 14. The causticized polysaccharide is then reacted
with an appropriate bifunctional cross-linking agent.
As described at least in U.S. Pat. Nos. 6,726,845, 6,740,249,
3,085,853, 5,008,089, 5,041,269, 5,091,159, 5,106,599, 5,346,628 and 5,716,530
and Australian Patents 5310690 and 737191, dextran itself has previously been used
in the Bayer Process.
However, by cross-linking the dextran or dihydroxypropyl cellulose
chains (or for that matter, other suitable polysaccharides), superior and unexpected
improvements are observed in the activity of cross-linked material when compared
to conventional polysaccharides or the uncross-linked analog. Prior art uses of
polysaccharides are impaired by the fact that increasing dosages of polysaccharides
in Bayer liquor result in superior flocculation only up to a maximum dosage. After
the maximum dosage has been reached, further addition of such polysaccharide
material typically produces no further performance improvement. When the crosslinked
polysaccharides are used and in particular when cross-linked dextran is used,
superior performance (not possible at any dose rate using conventional
polysaccharides) can be achieved. Surprisingly the maximum performance of crosslinked
dextran is superior to the maximum performance using conventional dextran
at any dose. Additionally, for cross-linked polysaccharides, the dose at which
continued addition results in no further performance benefits is increased.
Furthermore, when the polysaccharide is cross-linked an unexpected 50% increase
in effectiveness has been observed. For example, a composition comprising 5%
cross-linked dextran will perform at least as well as a 10% composition of dextran,
and in some cases better.
U.S. Pat. Nos. 5,049,612 and 4,339,331 teach that in mining
applications such as sulfide ore flotation, it was found that the performance of
starch, a traditional flotation depressant, can be improved after cross-linking. So
while it is true that cross-linked polysaccharides have been used in mining
applications such as in U .S. Pat. Nos. 5,049,612 and 4,339,331, it is quite
unexpected that in Bayer process applications, the activity of dextran would be
significantly improved after cross-linking. Furthermore, the ability of cross-linked
polysaccharides to have up to or at least a 50% improvement in performance or to
increase the maximum effective dosage of polysaccharides is unexpected and novel.
In at least one embodiment the mass ratio of a general cross linking
reagent/polysaccharide can be varied between, but is not limited to, about 0 to 0.2.
Specifically, for epichlorohydrin as the cross linking reagent, the ratio can be varied
between, but is not limited to, 0 to 0.1, most preferably 0.005 to 0.08. Appropriate
cross-linking is achieved as measured by an increase in the solution viscosity of at
least 10% above the original solution viscosity.
In at least one embodiment the composition is added to liquor in a
trihydrate classification circuit of said alumina trihydrate production process. The
composition can be added to said liquor at one or more locations in a Bayer process
where solid-liquid separation occurs.
In at least one embodiment the composition can be added to said
liquor at one or more locations in a Bayer process where it inhibits the rate of
nucleation of one or more alumina hydrate crystals in said process.
In at least one embodiment the composition can be added to said
liquor at one or more locations in a Bayer process where it reduces the rate of scale
formation in said process.
In at least one embodiment the composition can be added to said
liquor at one or more locations in a Bayer process where it facilitates red mud
clarification in the process.
In at least one embodiment the composition can be added in
combination with or according to any of the compositions and methods disclosed
US Patent 8,252,266.
EXAMPLES
The foregoing may be better understood by reference to the following
examples, which are presented for purposes of illustration and are not intended to
limit the scope of the invention.
Example 1:
50 gram of cellulose (dissolving wood pulp, bahia pulp, Solucell 350,
disintegrated on a Retsch mill with a 1mm screen) was charged to a 1500 ml
cylindrical reaction flask equipped with an overhead stirrer in the form of a double
helix. The cellulose was suspended in 800 gram of 2-methyl-2-butanol and the
reaction flask was closed. The suspension was kept at ambient temperature and
deoxygenated with a bottom nitrogen purge while the stirrer rotated at 250 rpm. The
bottom nitrogen purge was kept for 30 minutes. At this point the bottom nitrogen
purge was changed to top nitrogen blanket and 69.1 gram of a 25% sodium
hydroxide solution was added to the suspended cellulose fiber slurry. The cellulose
slurry was continuously stirred and the temperature was gradually increased from
ambient to 80°C over a period of 60 minutes. 69 g of glycidol (Aldrich) was added at
a feed rate of 1 ml/minute to the stirred alkalized cellulose slurry. The temperature
of the slurry was kept at 80°C and controlled by heating or cooling. The mixture was
kept at temperature for another 20 minutes. At this point 14 gram of a solution of
sodium vinylsulfonate (Aldrich) was added to the warm (80°C) and stirred mixture
at a feed rate of 1 ml/minute. After completed addition the mixture was stirred at
80°C for another 60 minutes. A product sample taken at this point was completely
water-soluble. The slurried mixture of the alkalized cellulose ether was neutralized
with acetic acid (approximately 29.5 g) against phenolphthalein (pink to clear). The
crude 2,3-dihydroxypropyl-ethylsulfonated cellulose was isolated as a moist filter
cake from the reaction slurry via filtration. The filter cake was dried in a tow step
process. Most of the organic volatiles were removed in a once through air, drying
oven at 60°C over a period of 60 minutes. The reaming water in the crude cellulose
ether was evaporated at 0.01 mmHg and a temperature not exceeding 25°C over a
period of 46 hours. 150 grams of a crude dry product were isolated containing 24%
sodium acetate and 76% 2,3-dihydroxypropyl-ethylsulfonated cellulose. A 2%
solution of the crude, dry cellulose ether had a viscosity of 36 cps (30 rpm, 22°C,
spindle LS62).
EXAMPLE 2:
43 gram of cellulose (dissolving wood pulp, Toba Pulp Lestari,
Tobacell EUC 94, disintegrated on a Retsch mill with a 1mm screen) was charged
to a 1500 ml cylindrical reaction flask equipped with an overhead stirrer in the form
of a double helix. The cellulose was suspended in 800 gram of 2-methyl-2-propanol
and the reaction flask was closed. The suspension was kept at ambient temperature
and deoxygenated with a bottom nitrogen purge while the stirrer rotated at 250 rpm.
The bottom nitrogen purge was kept for 30 minutes. At this point the bottom
nitrogen purge was changed to top nitrogen blanket and 59.5 gram of a 25% sodium
hydroxide solution was added to the suspended cellulose fiber slurry. The cellulose
slurry was continuously stirred and the temperature was gradually increased from
ambient to 80°C over a period of 60 minutes. 59 g of glycidol (Aldrich) was added at
a feed rate of 1 ml/minute to the stirred alkalized cellulose slurry. After completed
addition the mixture was stirred at 80°C for another 60 minutes. A product sample
taken at this point was virtually free of suspended solids. The slurried mixture of the
alkalized cellulose ether was neutralized with acetic acid (approximately 22.6 g)
against phenolphthalein (pink to clear). The crude 2,3-dihydroxypropyl cellulose
was isolated as a moist filter cake from the reaction slurry via filtration. The filter
cake was dried in a tow step process. Most of the organic volatiles were removed in
a once through air, drying oven at 60°C over a period of 60 minutes. The reaming
water in the crude cellulose ether was evaporated at 0.01 mmHg and a temperature
not exceeding 25°C over a period of 16 hours. 117.3 grams of a crude dry product
were isolated containing 26% sodium acetate and 74% 2,3-dihydroxypropyl
cellulose. A 2% solution of the crude, dry cellulose ether had a viscosity of 36 cps
(30 rpm, 22°C, spindle LS62).
EXAMPLE 3;
8 g of a crude 2,3-dihydroxypropyl-ethylsulfonated cellulose
prepared as in example 1 and with a viscosity of 35 cps (2%, 30 rpm, 23°C, spindle
LS62) was dissolved in 92 g of water. 1.02 g (or as indicated in below table) of a
50% solution of NaOH was added to the mixture and the resulting solution was
vigorously stirred with an overhead caged impeller at 2000 rpm until the mixture
was homogeneous, approximately 2 minutes. 0.527 g (or as indicated in below
table) of epichloprohydrin (Fluka) was added to the mixture and the resulting
solution was again vigorously stirred with an overhead caged impeller at 2000 rpm
until the mixture was homogeneous, approximately for 5 minutes. The mixture was
allowed to rest over night for 16 hours to form a continuous cross-linked gel. The
reaction crude was diluted to 2%, neutralized with acetic acid against
phenolphthalein and inhibited against microbial degradation with a non-oxidizing
biocide such as Kathon®. The so prepared solutions of the cross-linked 2,3-
dihydroxypropyl-ethylsulfonated cellulose are suitable as coagulants and flocculants
for aluminum trihydrate in the Bayer process.
Table 1:
EPI epichlorohydrin
AGU anhydrous glucose monomer unit of 2,3-dihydroxypropylethylsulfonated
cellulose
NaOH sodium hydroxide
The cross-linking reaction of ethylsulfonated dihydroxypropyl
cellulose was explored in detail either with ethylsulfonated dihydroxypropyl
cellulose, dihydroxypropyl cellulose, or hydroxyethyl cellulose. Insights learned
during the reactions between a cross-linking agent and either dihydroxypropyl
cellulose or hydroxyethyl cellulose could be directly transferred to the cross-linking
of ethylsulfonated dihydroxypropyl cellulose. A tabular summary of relevant
reactions is shown below in tables 2 and 3.
Tab e 2:
Tab e 2:
The results of the examples are as follows:
1. The dihydroxypropyl cellulose ether has as DS (degree of substitution,
number of dihydroxypropyl groups per monomeric glucose unit in the
cellulose chain) in the range of 0.5 to 3.0.
The preferred DS of the dihydroxypropyl cellulose ether is in the range
of 1.5 to 2.5.
The dihydroxypropyl cellulose ether can have in addition to the DS in the
range of 1.5 to 2.5 a MS (multiple degree of substitution, average number
of dihydroxypropyl groups per single hydroxide appendage on the
monomeric glucose unit in the cellulose chain) of greater or equal to 1.
The dihydroxypropyl cellulose ether has anionic substituents.
The dihydroxypropyl cellulose ether has anionic substituents were the
DS of the anionic component is greater then 0 and less then 0.5.
The preferred anionic substituent on the dihydroxypropyl cellulose ether
is a ethylsulfonate group.
The dihydroxypropyl ethylsulfonated cellulose has been cross-linked
under homogeneous or heterogeneous conditions.
The cross-linkage between the individual dihydroxypropyl
ethylsulfonated cellulose ether is of covalent nature.
The cross-linking of the dihydroxypropyl ethylsulfonated cellulose ether
had the effect of increasing its molecular weight and its solution
viscosity.
The dihydroxypropyl ethylsulfonated cellulose had before cross-linking a
Brookfield viscosity in the range of 10 to 100 cps at 30 rpm, 20°C, and
2% actives content and after cross-linking a Brookfield viscosity in the
range of 200 to 3000 cps at 30 rpm, 20°C, and 2%.
11. The cross-linked dihydroxypropyl ethylsulfonated cellulose is capable of
enhancing the flocculation of aluminum trihydrate solids from pregnant
process liquors in the Bayer process.
While this invention may be embodied in many different forms, there
are described in detail herein specific preferred embodiments of the invention. The
present disclosure is an exemplification of the principles of the invention and is not
intended to limit the invention to the particular embodiments illustrated. All patents,
patent applications, scientific papers, and any other referenced materials mentioned
herein are incorporated by reference in their entirety. Furthermore, the invention
encompasses any possible combination of some or all of the various embodiments
described herein and/or incorporated herein. In addition the invention encompasses
any possible combination that also specifically excludes any one or some of the
various embodiments described herein and/or incorporated herein.
The above disclosure is intended to be illustrative and not exhaustive.
This description will suggest many variations and alternatives to one of ordinary
skill in this art. All these alternatives and variations are intended to be included
within the scope of the claims where the term "comprising" means "including, but
not limited to". Those familiar with the art may recognize other equivalents to the
specific embodiments described herein which equivalents are also intended to be
encompassed by the claims.
All ranges and parameters disclosed herein are understood to
encompass any and all subranges subsumed therein, and every number between the
endpoints. For example, a stated range of " 1 to 10" should be considered to include
any and all subranges between (and inclusive of) the minimum value of 1 and the
maximum value of 10; that is, all subranges beginning with a minimum value of 1
more, (e.g. 1 to 6.1), and ending with a maximum value of 10 or less, (e.g. 2.3 to
9.4, 3 to 8, 4 to 7), and finally to each number 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10
contained within the range. All percentages, ratios and proportions herein are by
weight unless otherwise specified.
This completes the description of the preferred and alternate
embodiments of the invention. Those skilled in the art may recognize other
equivalents to the specific embodiment described herein which equivalents are
intended to be encompassed by the claims attached hereto.

Claims
1. A method of producing alumina utilizing a Bayer process, the method
comprises the step of adding to a liquor or slurry of the Bayer process, a
composition containing one or more ethylsulfonated cross-linked polysaccharides.
2. The method of claim 1 wherein the cross-linked polysaccharides, comprises
a reaction product made by cross-linking dextran or dihydroxypropyl cellulose or
polysaccharides with a cross linking agent to form a cross-linked molecule.
3. The method of claim 1 wherein the cross-linked polysaccharide is
dihydroxypropyl cellulose and the number of dihydroxypropyl groups per
monomeric glucose unit in the cellulose chain) in the range of 0.5 to 3.0.
4. The method of claim 1 wherein the cross-linked polysaccharide has been
reacted with a sufficient amount of sodium vinylsulfonate or sodiumchloroacetate to
impart to the polysaccharide one or more anionic substituent regions.
5. The method of claim 3 wherein the dihydroxypropyl cellulose is the reaction
product of reacting cellulose with 3-chloro-l,2-propanediol.
6. The method of claim 3 wherein the dihydroxypropyl ethylsulfonated
cellulose before cross-linking had a Brookfield viscosity in the range of 10 to 100
cps at 30 rpm, 20°C, and 2% actives content and after cross-linking a Brookfield
viscosity in the range of 200 to 3000 cps at 30 rpm, 20°C, and 2%.
7. The method of claim 1 wherein the composition is added to said liquor at one
or more locations and thereby inhibits the rate of nucleation of one or more alumina
trihydrate crystals in said process.
8. The method of claim 1 wherein the composition is added to said liquor at one
or more locations and thereby reduces the rate of scale formation in said process.
9. The method of claim 1 wherein the composition is added to said liquor at one
or more locations to facilitate red mud clarification in said process.
10. The method of claim 1 wherein the composition addition improves the yield
of alumina trihydrate sequestration from an alumina trihydrate process by adding the
composition to said liquor of said process.
11. The method of claim 10 wherein the crosslinking agent is selected from the
group consisting of: epichlorohydrin, dichloroglycerols, divinyl sulfone, bisepoxide,
phosphorus oxychloride, trimetaphosphates, dicarboxylic acid anhydride, N,N'-
methylenebisacrylamide; 2,4,6-trichloro-s-triazine, and any combination thereof.
12. The method of claim 1 wherein the cross-linked polysaccharides, comprises
a reaction product made by cross-linking one of: scleroglucan, dextran,
dihydroxypropyl cellulose, and any combination thereof with a cross linking agent
to form a cross-linked molecule.