CA2105333A1 - Trihydrate clarification aid for the bayer process - Google Patents
Trihydrate clarification aid for the bayer processInfo
- Publication number
- CA2105333A1 CA2105333A1 CA002105333A CA2105333A CA2105333A1 CA 2105333 A1 CA2105333 A1 CA 2105333A1 CA 002105333 A CA002105333 A CA 002105333A CA 2105333 A CA2105333 A CA 2105333A CA 2105333 A1 CA2105333 A1 CA 2105333A1
- Authority
- CA
- Canada
- Prior art keywords
- alumina trihydrate
- slurry
- polymer
- mer units
- hydroxamated polymer
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F7/00—Compounds of aluminium
- C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
- C01F7/04—Preparation of alkali metal aluminates; Aluminium oxide or hydroxide therefrom
- C01F7/14—Aluminium oxide or hydroxide from alkali metal aluminates
- C01F7/144—Aluminium oxide or hydroxide from alkali metal aluminates from aqueous aluminate solutions by precipitation due to cooling, e.g. as part of the Bayer process
- C01F7/148—Separation of the obtained hydroxide, e.g. by filtration or dewatering
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Inorganic Chemistry (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
Abstract
Abstract of the Invention In a Bayer process for the production of alumina, the clarification of the alumina trihydrate slurry is improved by adding to the alumina trihydrate thickener feed slurry an anionic water-soluble hydroxamated polymer in an amount effective to improve the clarification of the slurry upon settlement.
Description
t. 3 3 SPECIFIÇATION
TechDiç~L~d of the Inyention ` The present invention is in the technical field of trihydrate clariFlcation, the settling of alumina trihydrate particles, in the Bayer process for the recovery of alumina from bauxite ore.
Back~ro~e Inyçntion In the Bayer proccss for the production of alumina, bauxite ore is pulverized, slurried in water, and then digested with caudic at elevated temperatures and pressures. The ~austic solution dissolves oxides of aluminum, forrning an aqueous sodium aluminate solution. The - caustic-insolub1e 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.
In rnore detail, the pulverized bauxite ore is fed to a slurry mixer where a water slurry is prepared. The slurry makeup wa~er is typically spent liquor (described below) and added caustic. This bauxite ore slurry i8 then diluted and passed through a digester or a series of digesters where about 98% of the total available alumina is released from the ore as caustic-soluble sodiusn aluminate. The digested slurry is then cooled to about 230 F, typically ` ` ` 2~33~
employing a series of flash tanks wherein heat and condensate are recovered. The aluminate liquor leaving the flashing operation contains from about I to about 20 weight percent solids, which solids consist of the insoluble residue that remains after, or is precipitated during, digestion. The coarser solid particles may be removed from the aluminate liquor with a "sand trap" cyclone. The finer solid particles are generally separated from the liquor first by settling and then by filtration, if necessary. The slurry of aluminate liquor and finer solids is normally first fed to the center well of a mud settler, or primary settler, where it is treated with a flocculant, and as thc mud settles, clarified sodium aluminate solution, referred to as "green" or -"pregnant" liquor, o-verflows a weir at the top. This overflow from the mud settling tank is passed to the subsequent process steps. If the aluminate liquor overflowing the settler contains an unacceptable concentration of suspended solids (at times from about 50 to about 500 mg of suspended solids per liter), it is then generally further clarified by filtration to give a filtrate with no more than about 10 mg suspended solids per liter of liquor.
Th~clarified sodium aluminate liquor is seeded with alumina trihydrate crystals to induce precipitation of alumina in tho form of alumina trihydrate, Al(OH),. Thc alumina trihydrate particles or crystals are then separated from the concentrated caustic liquor, and the remaining liquid phase, the spent liquor, is returned to the initial digestion step and employed as a digestant after reconstitution with caustic.
3 ~ 3 The treatment of the liquor collected after the primary settlement to remove any residual suspended solids before alumina trihydrate is recovered is refelTed to as a secondary clarification stage .
In another section of the Bayer circuit, the settled solids of the primary settler ("red mudn) are withdrawn from the bottom of the settler and passed through a countercurrent wæhing circuit for recovery of sodium aluminate and soda. As noted above, the red mud does not include any coarser particles removed prior lo feeding the slurry to the primary or mud settler.
In the recovery of alumina trihydrate as product in the Bayer process, or for use as precipitation secd, the alumina trihydrate crystals are generally separated from the liquor in which they are formed by settling andlor filtration. Coarse particles settle easily~ but fine particles settle slowly and to some extent are lost~product or, if recovered by filtration, $~1 blind the filters. The fine parhcles of alumina trihydrate which do not settle easily often flow over the top of the alumina trihydrate settler and are sent back to digestion with the spent liquor.
That alumina trihydrate is then digested and precipitated again in a second cycle through the Bayer process, lmnecessarily expending energy and reducing the alumina extraction capacity of the spent liquor.
Canadian Patent No. 825,234, October 1969, uses dextran, dextran sulfate and compositions therewith containing anionic salts to improve the flocculation and filtration of - . . , . - , . . .
;~ ) 3 3 alumina trihydrate from alkaline solutions thereof. U.S. Patent No. 5,041,269, August 1991, Moody et al., uses a flocculant for the recovery of alumina trihydrate crystals comprising a combination of dextran, or certain other polysaccharides, together with an anionic flocculant polymer including acrylic monomer.
It is an object of the present invention to provide a more effective separation of alumina trihydrate particles from aqueous alkaline media, particularly the fine alumina trihydrate particles, and particularly the separation thereof from the alkaline liquor in which they are formed in the Bayer process. It is an object of the present invention to provide a method whereby the suspended solids retained in the supernatant after settling of the alumina trihydrate from the alkaline liquor of the Bayer process are diminished. It is an object of the present invention to provide a more effective Bayer process wherein the separation of alumina trihydrate from the alkaline liquor is improved by an improved clarification of thç supernatant that forms above the settling, or settled, alumina trihydrate solids. These and other objects of the present invention a~e described in more detail below.
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The present invention provides a method for the improved clanfication of a Bayer process alumina trihydrate slurry comprising adding a water-solub1e anionic hydroxamated polymer to a Bayer process alumina trihydrate thickener feed slurry in an amount effective to improve the clarification of the slurry upon settlement. The present invention provides an irnproved Bayer process wherein the clarification of a Bayer process alumina trihydrate slurry is improved by adding to a Bayer process alumina trihydrate thickener feed slurry a water-soluble anionic hydroxamated polytner in an amount effective to improve the clarification of the slurry upon settlement.
Prçferre~ D~f t~~vention In the Bayer process digestion, the aqueous alkali~olution acquires a sodium aluminate content. ARer primary settlement and secondy~tion~ concentrated aluminate liquor (a supersat~sated solution) is ~eeded with al~ce precipitation. The precipitate settles and is then ~eparated from d further treated.
The precipitated alumina in the form of alumina trihydrate is difficult to separate from the concentrated caustic liquor. The finer crystalline material tends to settle slowly and gives poor supernatant clarities, which results in product or precipitation seed losses. Further, where .
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t3 3 recovery of the precipitate includes a filtration step, fine material causes filter blinding. The addition of the hydroxamated polyrner improves the supernatant clarity, reducing the amount of suspended solids, which are typically very fine suspended solids, in the supernatant upon settlement. The improved supernatant clarity minimizes alumina trihydrate losses and improves the subsequent supernatant filtration by reducing filter blinding, or eliminates the need for such subsequent supernatant filtration. It is also believed that lhe hydroxamated polymer clarification aid will improve the alumina-caustic liquor separation on a vacuum filter by forming a more porous filter cake.o4~ glq~
The liquor from v,rhich the alumina trihydrate crystals are to be separated in a commercial Bayer process is commonly referred to as the alumina trihydrate thickener feed, or alumina trihydrate thickener feed slurry. It is the feed to the Bayer circuit station at which the alumina trihytlrate crystab, after formation, are to be concentrated, or thickened, by settlement, afler which ~he supernatant and the alumina trihydrate crystals are separated. In a broader sense, an alumina~trihydrate thickener feed slurry is an alkaline aqueous slurry in which the solids are predominantly alumina trihytlrate crystals, prior to separation of solids and the aqueous phase by settlement and the liko.
The alumina trihydrate precipitate is usually recovered after settlement by filtration and washing of the settled phase afler supernalant removal, although it may be subjected to .
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settlement alone with removal of the supernatant. The recovered trihydrate crystals may then be treated by the usual processes, including calcination, which drives off the wa~er and is sufficient to burn off any organic residues, including the residues of the hydroxamated polymer. The supernatant (spent liquor) is recycled in the conventional manner to the digestion stage.
A commercial alumina trihydrate thickener feed is most commonly a caustic liquor having a pH from about 10 to above 14, a temperature between about 75 F and about 190 F
(from about 24 C to about 88 C), and an alumina trihydrate solids content of from about S to about 100 grams per liter of alumina trihydrate thickener feed slurry.
The alumina trihydrate thickener feed slurry to which the hydroxarnated polymer is added may have a concentration of dissolved organic components up to about 30 g/liter of slurry, and such a slurry typically has a concentration of dissolved organic components in the range of from about 0.1 to about S or 10 g/liter of slurry. The solids content of lhe alumina trihydrate thickener feed sluny outside of the alumina trihydrate solids generally is no more than about SO mlS (.OS grams), and the concentration of solids other than alumina trihydrate solids generally does not exceed a weight ratio of about 1:100 other solids to alumina trihydrate solids.
The alumina trihydrate crystals therefore comprise at least about 99 weight percent of the total solids in the alumina trihydrate thickener feed slurry to which the hydroxamated polymer is added.
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- . i , , . , The alkalinity of the alumina trihydrate thickener feed slurry can range from about 5 to about 400 g/liter of slurry, expressed as sodium carbonate. The alkalinity of alumina trihydrate thickener feed slurries typically are in the range of from about 50 to about 400 g/liter of slurry expressed as sodium carbonate, and often are within the range of from about 200 to about 400 g/liter of slurry expressed as sodium carbonate.
The process is generally carried out with the alumina trihydrate slurry at a temperature of at least about S0 C and often within the range of from about 60 C to about 80 C.
The addition of the hydroxamated polymer is made after precipitation has been induced and preferably while at lesst a significant portion of the alumina trihydrate solids remain suspended in the liquor, but it is possib1e to add it after some separation of alumina trihydrate solids has occurred as long as it is added before the final separation of alumina trihydrate residuals.
The hydroxarnated polymer should be added to the alumina trihydrate thickener feed slurry in an~mount effective to impro~re the clarification of the supernatant upon settlement. An improvcment in supernatant clarification is, of course, in comparison to supernatant clarification for the same ptocess parameters in the absence of the hydroxamated polymer.
The ef~ective amount of hydroxamated polymer can depend on the concentration of alumina trihydrate solids in the slurry, other slurry conditions, and the hydroxamated polymer's , ... . - .. , ... ,, ....... , . . ... - .... . , . :..... ... . . , ~ .
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anionic char~e density and molecular wei~ ht. The amount of the hydroxamated polymer added is usually in the range of from about 0.01 to about 20 mg/liter of slurry, preferably from about 0.05 to about 10 mg/liter of slurry, and more preferably from about 0.1 to about 5 mg/liter of slurry. Cornmonly less than about O.S mg/liter of slurry of polymer can be used.
The effective amount of hydroxamated pol)nner can be from about 0.0005 to about I
pound of hydroxamated polymer per ton of alumina trihydrate solids in the slurry, and in more preferred embodiment from about 0.005 to about 0.1 pound of hydroxamated polymer per ton of alumina,trihydrate solids in the slurry. About 0.1 pound per ton is the maximum needed under most conditions; and more than I pound per ton will oRen be unnecessary.
The hydoxamic polymer should be sufficiently stable under the process conditions used, the temperatures and caustic conditions described above.
Any water soluble h~rdroxamic polymer may be used, but the hydroxamic polymer is commonly a polymer conhining mer units with hydroxamic acid or salt pendant groups of the FormulaI ~
R' ~ C - C ~
FormulaI C = O
R" - N - O - R
3 ~
wherein R is hydrogen or a cation, and R' and R" are independently hydrogen or a substituent to carbon other than hydrogen, for instance a lower alkyl such as methyl.
The hydroxamic polymers, or hydroxamated poly ners, are well known in the art and can be prepared by post-polymerization derivatization from polymers containing pendant reactive groups, such as pendant ester groups, pendant amide groups, pendant anhydride groups, pendant nitrile groups and the like by the reaction thereof with hydroxylamine or its salt at a temperature within the range of from about 20 C to about 100 C for several hours. From about 1 to about 90 mole percent of the available pendant reactive groups of the precursor polymer may be replaced by hydroxamic groups in accordance with such procedures. Such post-polymerization derivatization may be carried out in a polymer solution or in a polymer-containing latex, including both water-continuous latices and water-in-oil latices (wherein the polymer is substantially associated with the dispersed aqueous phase). When two or more species of pendant reactiYe groups are present in the precursor polymer, the reaction with hydroxyl amine may favor ~Qne or more of such species over the other(s). The molecular weight of the hydroxamated polymer is dependent upon the molecular weight of the precursor polymer.
Hydtoxamic acid or salt-containing polymers of very high molecular weights can be prepared by using a watcr-in-oil latex of, t'or example, polyacrylamide or copolymers of acrylamide with acrylic acid or other suitable comonomers .
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Exemplaty of the polymers which may be hydroxamated for use in the present process include acrylic acid ester polymers, methacrylic acid ester polymers, crotonic acid ester polymers, and the like carboxylic acid ester polymers, such as polymers produced from the polymerization of methyl (meth)acrylate, ethyl (meth)acrylate, t-butyl (meth~acrylate, cyclohexyl (meth)acrylate, dimethyl aminoethyl (meth)acrylate, dimethyl aminoethyl (meth)acrylate, methyl crotonate, and the like type of carboxylic acid ester containing mer units, g¢nerally wherein the ester moiety is derived from a C"2 alcohol, and preferably wherein the ester moiety is derived from a C,.6 alcohol. The polymçrs which may be hydroxamated for use in the present proces~ also include polymers of maleic anhydride and esters thereof, pendant nitrile containing polyrners such as those produced from acrylonitrile, pendant amide containing polymers such as those produced from acrylamide, methacrylamide and the like. The hydroxamic acid or salt-containing polymer may be derived from homopolyrners, copolymers, terpolyrners, or polymers of more varied mer units. Hydroxamic polyrners are well known to those of ordinary ski11 in the art and are specifically disclosed, together with methods for their preparation, in U.S. Patent Nos. 3,34S,344, 4,480,067, 4,532,046, 4,536,296, and 4,587,306, and U.K. Patent Application 2171127, hereby incorporated hereinto by reference. Suitable hydroxylamine salt~ incluto the sulfate, sulfite, phosphate, perchlorate, hydrochloride, acetate, propionate, and the like.
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The hydroxamic acid or salt-containing polymer for use in the present process should generally have a weight average molecular weight within the range of from about 10,000 to about 50,000,000. The hydroxamated polymer preferably has a weight average molecular weight of at least aboutl million, preferably with an IV of from about 5 to about 40 dl/g.
The degree of hydroxarnation, that is, the concentration of mer units (polymer segments containing two adjacent backbone carbons) of the Formula I above, may vary from about I to about 90 mo1e percent, and preferably is within the range of from about 5 to about 75 mole percent, and most prcferably from about 10 to about 50 mole percent.
Since the alumina trihydrate thickener feed slurry is alkaline, the hydroxamated polymer in preferred embodiment is pr~dominantly anionic, although it can also contain nonionic or even a minor amount of cationic mer uniis, provided that the amount of any such cationic mer units is sufficicntly small so that the polymer retains an overa11 anionic nature and its water solublity.
The anionic mers other than the hydroxamic mer units (referred to herein as the "anionic mer units" unles~ expressly indicated otherwise) are generally carboxylic acids or sulphonic acids, and are usually deri~ed from acrylic acid (M) but can be derived from methacrylic acid (MAA) or a sulfoalkyl acrylamide, such as 2-sulfopropylacrylamide, or the other anionic monomers notcd abo~re. The hydroxamated polymer generally is comprised of from about I to about 99 mole percont, and preforably from about 15 to 90 mole percent, anionic mer units with :. , : , . . .. . .. . . . . . . .-. . ..
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- ~la~3.3 the balance being hydroxamic mer units, optionally together with nonionic mer units. More preferably the hydroxamated polymer is comprised of from about 25 to about 75 mole percent anionic mer units, the balance being hydroxamic mer units9 optionally together with nonionic mer units. In even more preferred embodiment, the hydroxarnated polyrner is comprised of from about 25 to about 75 mole percent anionic mer units, from about 10 to about 40 mole percent hydroxamic mer uni~s and from about 10 lo about 40 mole percent nonionic mer units.
The nonionic mer units are usually the polar (meth)acrylamide mer units (AcAm or methAcAm), but others may be used, for instance, mer units derived from vinyl acetate, vinyl pyrrolidone, butadiene, styrene, alkanolacrylamides such as methylol acrylamide and others.
` 14 .
Test Method The test method employed for evaluating Bayer process trihydrate clarification with and without a trihydrate clarification aid is as follows. A quantity of alumina trihydrate thickener feed sufficient for the desired number of comparative test runs is obtained fresh from a commercial Bayer circuit, and for each test run a 1000 ml sample thereof ("test sample") is charged to a 1000 ml graduated cylinder. The test samples are each plunged ten times to re-suspend the alumina trihydrate particles, then dosed with the trihydrate clarification aid being uscd, if any, and again plungcd ten times to disperse the trihydrate clarification aid in the alumina trihydrate thickener feed slurry. The plunging is accomplished using a stainless steel rod v~ith a paforated steel disk or rubber stopper attached to the end. The slurry is then leR
standing, without agitation, for a settlement time period of 30 minutes immedialely following the final plunging. At the end of the 30 minute settlement period, a samp1e of the supernate liquor is collected and the turbidity of such supernate sample is determined with a turbidity meter. The~urbidity of the supernate is inversely related to clarification efficiency. The alumina trihydrate thickener fced slurries so obtained fresh from a commercial Bayer circuit will contain from about 5 to about 100 grams of alumina trihydrate crystal per liter of slurry, and no more than about 50 mg of other solids per liter of slurry.
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ExamplQ I
The Test Method described above was employed to demonstrate the trihydrate clarification aid performance of a representative hydroxamated polymer according to the present invention. The polymer was an anionic, water-soluble terpolymer comprised of acrylic acid, acrylamide, and acrylhydroxamic mer units in the approximate mole ratios of 2:1:1, derived from the hydroxamation of a high molecular weight acrylic acid/acrylamide copolymer. The weight average molecular weight of the hydroxamated polyrner was about 10,000,000. The polymer dosage employed was 0.2 mg of polymer actiYes per liter of the slurry, and polyrner being added as a dilute aqueous solution. A blank or control in which no trihydrate clarification aid was used was also run as a comparison. The test results, in terms of supernatant turbidity ("NTU"), are set forth below in Table t.
T~ble 1 Dosage of Clarification Supernatant Turbidity ClariflCatiQn ~ id ~&/literl (NTU) none none 168 Hydroxamated Polyr;m.,r 0.2 118 The hydroxamated polymer employed in the present inven~ion is, as noted above, a water soluble polymer. The water solubility characteristics of the hydroxamated polymer preferably is defined in terms of the fluidity of its aqueous solutions. By "water soluble" is meant herein, and generally, that an aqueous solution of the polymer, at the polymer actives concentration at which it is charged to the aluminum trihydrate thickener feed slurry, is reasonably fluid, and preferably has a viscosity of no more than about 5,000 to 20,000 cps Brookfield, at a pH of between about 6 and about 14, and ambient room temperature (from about 23 to about 26 C.) The addition of the hydroxamated polymer in the form of a dilute aqueous solution facilitates a rapid dispersion of the polymer in the slurry. Such aqueous solutions of the hydroxamated polymer should not be overly viscous, but they also should not be so dilute that unnecessary volume of water is added to thc alumina trihydrate slurry. For most hydroxamated polymers, an aqueous solution containing from about 0.01 to about 0.5 weight percent of polymer actives is generally reasonable. To further facilitate the rapid dispersion of the hydroxamated polymer in the slurry, in preferrediembodiment the pol~ner is added to the alumina trihydrate thickener feed slurry as an alkaline aqueous solution, for instance having a pH of at least about 9, and more preferably at Ieast about 10, up to about a pH of about 14.
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The present invention provides a method for the improved clarification of a Bayer process alumina trihydrate slurry comprising adding to a Bayer process alumina trihydrate thickener feed slurry an anionic water-soluble hydroxamated polymer in an amount effective to improve the clarification of the slurry upon settlement. The present invention also provides an improved Bayer process for the production of alumina wherein bauxile ore is pulverized, slurried in water, and then digested with caustic at elevated temperatures and pressures, forming an aqueous sodium aluminate solution containing caustic-insoluble constituents, wherein the caustic-insoluble constituents are then substantially separated from the aqueous phase of the a~ueous sodium aluminate solution, and the sodium aluminate solution is then seeded with crystals of alumina trihydrate whereby a solid alumina trihydrate product is precipitated out of the solution, subjected to settlement (whereupon a supernatant is formed) and collected as product or recycled as precipitation seed. Such improved process is characterized by adding to the solution~aRer formation of the alumina trihydrate precipitate, and prior to the complete formation of the supernatant, a water-soluble anionic hydroxamated polymer in an amount effective to improve the clarification of the supernatant upon the settlement of the alumina ~rihydrate prccipitatc.
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In preferred embodiment, the alumina trihydrate thickener feed slurry or the solution has an alumina trihydrate solids content of from about 5 to about 100 grarns per liter of alumina trihydrate thickener feed slurry or the solution. In preferred embodiment, the alumina trihydrate crystals of the alumina trihydrate thickener feed slurry or the solution comprise at least about 99 weight percent of the total solids in the alumina trihydrate thickener feed slurry or the solution. -In preferred embodiment, the alumina trihydrate thickener feed slurry or the solution has an alkalinity of from about 5 to about 400 g/liter of the slurry or the solution, expressed as sodium carbonate. In preferred embodiment, the hydroxamated polyrner is added to the alumina trihydrate thickener feed slurry or the solution when the alumina trihydrate thickener feed slurry or the solution is at a temperature within the range of from about 60 C to about 80 C.
In preferred embodiment, the amount of the hydroxamated polymer added to the alumina trihydrate thickener feed slurry or the solution is in the range of from about 0.01 lo about 20 mg per liter of the slurry or the solution. In preferred embodiment, the amount of the hydroxamated polymer ad~ded to the alumina trihydrate thickener feed slurry or the solution is in the range of from about o.oc to about 10 mg per liter of the slurry or the solution. In preferred embodiment, the amount of the hydroxamated polymer added to the alumina trihydrate thickener feed slurry or the solution is in the range of from about 0.0005 to about I pound of the hydroxamated polymer per ton of alumina trihydrate solids in the slurry or the solution.
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, 3 .3 In preferred embodiment, the water soluble hydroxamic polymer is a polymer containing mer units of the Formula I
R' ~ C- C ~
Formulal C = O
R"- N- O - R
wherein R is hydrogen or a cation, and R' and R" are independently hydrogen or a substituent lo carbon other than hydrogen, for instance a lower alkyl such as methyl.
In preferred embodiment, the hydroxamated polymer has a weight average molecular weight within the range of from about 10,000 to about 50,000,000. In preferred embodiment, the hydroxamated polyrner has a weight a~rerage molecular weight of at least about I million. In preferred embodiment, the hydroxamated polymer has an Intrinsic Viscosity of from about S to about 40 dl/g. In preferred embodiment, the hydroxamated polymer is comprised of from about 2S to about,75 mole percent anionic mer units other than hydroxamic mer units, the balance being hydroxamic mer units, optionally together with nonionic mer units. In preferred embodiment, the hydroxarnate~d polyrner is comprised of from about 25 to about 75 mole percent anionic mer units other than hydroxamic mer units, from about 10 to about 40 mole percent hydroxamic mer units and from about 10 to about 40 mole percent nonionic mer units.
Industrial Applicabilitv of the lnvention The present invention is applicable to the Baye.r process for the production of alumina from bauxite ore.
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TechDiç~L~d of the Inyention ` The present invention is in the technical field of trihydrate clariFlcation, the settling of alumina trihydrate particles, in the Bayer process for the recovery of alumina from bauxite ore.
Back~ro~e Inyçntion In the Bayer proccss for the production of alumina, bauxite ore is pulverized, slurried in water, and then digested with caudic at elevated temperatures and pressures. The ~austic solution dissolves oxides of aluminum, forrning an aqueous sodium aluminate solution. The - caustic-insolub1e 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.
In rnore detail, the pulverized bauxite ore is fed to a slurry mixer where a water slurry is prepared. The slurry makeup wa~er is typically spent liquor (described below) and added caustic. This bauxite ore slurry i8 then diluted and passed through a digester or a series of digesters where about 98% of the total available alumina is released from the ore as caustic-soluble sodiusn aluminate. The digested slurry is then cooled to about 230 F, typically ` ` ` 2~33~
employing a series of flash tanks wherein heat and condensate are recovered. The aluminate liquor leaving the flashing operation contains from about I to about 20 weight percent solids, which solids consist of the insoluble residue that remains after, or is precipitated during, digestion. The coarser solid particles may be removed from the aluminate liquor with a "sand trap" cyclone. The finer solid particles are generally separated from the liquor first by settling and then by filtration, if necessary. The slurry of aluminate liquor and finer solids is normally first fed to the center well of a mud settler, or primary settler, where it is treated with a flocculant, and as thc mud settles, clarified sodium aluminate solution, referred to as "green" or -"pregnant" liquor, o-verflows a weir at the top. This overflow from the mud settling tank is passed to the subsequent process steps. If the aluminate liquor overflowing the settler contains an unacceptable concentration of suspended solids (at times from about 50 to about 500 mg of suspended solids per liter), it is then generally further clarified by filtration to give a filtrate with no more than about 10 mg suspended solids per liter of liquor.
Th~clarified sodium aluminate liquor is seeded with alumina trihydrate crystals to induce precipitation of alumina in tho form of alumina trihydrate, Al(OH),. Thc alumina trihydrate particles or crystals are then separated from the concentrated caustic liquor, and the remaining liquid phase, the spent liquor, is returned to the initial digestion step and employed as a digestant after reconstitution with caustic.
3 ~ 3 The treatment of the liquor collected after the primary settlement to remove any residual suspended solids before alumina trihydrate is recovered is refelTed to as a secondary clarification stage .
In another section of the Bayer circuit, the settled solids of the primary settler ("red mudn) are withdrawn from the bottom of the settler and passed through a countercurrent wæhing circuit for recovery of sodium aluminate and soda. As noted above, the red mud does not include any coarser particles removed prior lo feeding the slurry to the primary or mud settler.
In the recovery of alumina trihydrate as product in the Bayer process, or for use as precipitation secd, the alumina trihydrate crystals are generally separated from the liquor in which they are formed by settling andlor filtration. Coarse particles settle easily~ but fine particles settle slowly and to some extent are lost~product or, if recovered by filtration, $~1 blind the filters. The fine parhcles of alumina trihydrate which do not settle easily often flow over the top of the alumina trihydrate settler and are sent back to digestion with the spent liquor.
That alumina trihydrate is then digested and precipitated again in a second cycle through the Bayer process, lmnecessarily expending energy and reducing the alumina extraction capacity of the spent liquor.
Canadian Patent No. 825,234, October 1969, uses dextran, dextran sulfate and compositions therewith containing anionic salts to improve the flocculation and filtration of - . . , . - , . . .
;~ ) 3 3 alumina trihydrate from alkaline solutions thereof. U.S. Patent No. 5,041,269, August 1991, Moody et al., uses a flocculant for the recovery of alumina trihydrate crystals comprising a combination of dextran, or certain other polysaccharides, together with an anionic flocculant polymer including acrylic monomer.
It is an object of the present invention to provide a more effective separation of alumina trihydrate particles from aqueous alkaline media, particularly the fine alumina trihydrate particles, and particularly the separation thereof from the alkaline liquor in which they are formed in the Bayer process. It is an object of the present invention to provide a method whereby the suspended solids retained in the supernatant after settling of the alumina trihydrate from the alkaline liquor of the Bayer process are diminished. It is an object of the present invention to provide a more effective Bayer process wherein the separation of alumina trihydrate from the alkaline liquor is improved by an improved clarification of thç supernatant that forms above the settling, or settled, alumina trihydrate solids. These and other objects of the present invention a~e described in more detail below.
.; ., - . .. . , ~ . . , . . ... . . :i.. .. .
~, . : . - - .. . -: - . . .. . :
. . ~ .. .~
~ ~ ~3 J ~ 3 Disclosur~hQ~
The present invention provides a method for the improved clanfication of a Bayer process alumina trihydrate slurry comprising adding a water-solub1e anionic hydroxamated polymer to a Bayer process alumina trihydrate thickener feed slurry in an amount effective to improve the clarification of the slurry upon settlement. The present invention provides an irnproved Bayer process wherein the clarification of a Bayer process alumina trihydrate slurry is improved by adding to a Bayer process alumina trihydrate thickener feed slurry a water-soluble anionic hydroxamated polytner in an amount effective to improve the clarification of the slurry upon settlement.
Prçferre~ D~f t~~vention In the Bayer process digestion, the aqueous alkali~olution acquires a sodium aluminate content. ARer primary settlement and secondy~tion~ concentrated aluminate liquor (a supersat~sated solution) is ~eeded with al~ce precipitation. The precipitate settles and is then ~eparated from d further treated.
The precipitated alumina in the form of alumina trihydrate is difficult to separate from the concentrated caustic liquor. The finer crystalline material tends to settle slowly and gives poor supernatant clarities, which results in product or precipitation seed losses. Further, where .
- . - - - : :
.
t3 3 recovery of the precipitate includes a filtration step, fine material causes filter blinding. The addition of the hydroxamated polyrner improves the supernatant clarity, reducing the amount of suspended solids, which are typically very fine suspended solids, in the supernatant upon settlement. The improved supernatant clarity minimizes alumina trihydrate losses and improves the subsequent supernatant filtration by reducing filter blinding, or eliminates the need for such subsequent supernatant filtration. It is also believed that lhe hydroxamated polymer clarification aid will improve the alumina-caustic liquor separation on a vacuum filter by forming a more porous filter cake.o4~ glq~
The liquor from v,rhich the alumina trihydrate crystals are to be separated in a commercial Bayer process is commonly referred to as the alumina trihydrate thickener feed, or alumina trihydrate thickener feed slurry. It is the feed to the Bayer circuit station at which the alumina trihytlrate crystab, after formation, are to be concentrated, or thickened, by settlement, afler which ~he supernatant and the alumina trihydrate crystals are separated. In a broader sense, an alumina~trihydrate thickener feed slurry is an alkaline aqueous slurry in which the solids are predominantly alumina trihytlrate crystals, prior to separation of solids and the aqueous phase by settlement and the liko.
The alumina trihydrate precipitate is usually recovered after settlement by filtration and washing of the settled phase afler supernalant removal, although it may be subjected to .
- . ~
. ~ .. , . . ~ . , . . .. ~ . .-3 ~
settlement alone with removal of the supernatant. The recovered trihydrate crystals may then be treated by the usual processes, including calcination, which drives off the wa~er and is sufficient to burn off any organic residues, including the residues of the hydroxamated polymer. The supernatant (spent liquor) is recycled in the conventional manner to the digestion stage.
A commercial alumina trihydrate thickener feed is most commonly a caustic liquor having a pH from about 10 to above 14, a temperature between about 75 F and about 190 F
(from about 24 C to about 88 C), and an alumina trihydrate solids content of from about S to about 100 grams per liter of alumina trihydrate thickener feed slurry.
The alumina trihydrate thickener feed slurry to which the hydroxarnated polymer is added may have a concentration of dissolved organic components up to about 30 g/liter of slurry, and such a slurry typically has a concentration of dissolved organic components in the range of from about 0.1 to about S or 10 g/liter of slurry. The solids content of lhe alumina trihydrate thickener feed sluny outside of the alumina trihydrate solids generally is no more than about SO mlS (.OS grams), and the concentration of solids other than alumina trihydrate solids generally does not exceed a weight ratio of about 1:100 other solids to alumina trihydrate solids.
The alumina trihydrate crystals therefore comprise at least about 99 weight percent of the total solids in the alumina trihydrate thickener feed slurry to which the hydroxamated polymer is added.
.: - . , .
.
.
.
- . i , , . , The alkalinity of the alumina trihydrate thickener feed slurry can range from about 5 to about 400 g/liter of slurry, expressed as sodium carbonate. The alkalinity of alumina trihydrate thickener feed slurries typically are in the range of from about 50 to about 400 g/liter of slurry expressed as sodium carbonate, and often are within the range of from about 200 to about 400 g/liter of slurry expressed as sodium carbonate.
The process is generally carried out with the alumina trihydrate slurry at a temperature of at least about S0 C and often within the range of from about 60 C to about 80 C.
The addition of the hydroxamated polymer is made after precipitation has been induced and preferably while at lesst a significant portion of the alumina trihydrate solids remain suspended in the liquor, but it is possib1e to add it after some separation of alumina trihydrate solids has occurred as long as it is added before the final separation of alumina trihydrate residuals.
The hydroxarnated polymer should be added to the alumina trihydrate thickener feed slurry in an~mount effective to impro~re the clarification of the supernatant upon settlement. An improvcment in supernatant clarification is, of course, in comparison to supernatant clarification for the same ptocess parameters in the absence of the hydroxamated polymer.
The ef~ective amount of hydroxamated polymer can depend on the concentration of alumina trihydrate solids in the slurry, other slurry conditions, and the hydroxamated polymer's , ... . - .. , ... ,, ....... , . . ... - .... . , . :..... ... . . , ~ .
. . , . . ~ : ..... ~. . - . . . .
"' 3 ~
anionic char~e density and molecular wei~ ht. The amount of the hydroxamated polymer added is usually in the range of from about 0.01 to about 20 mg/liter of slurry, preferably from about 0.05 to about 10 mg/liter of slurry, and more preferably from about 0.1 to about 5 mg/liter of slurry. Cornmonly less than about O.S mg/liter of slurry of polymer can be used.
The effective amount of hydroxamated pol)nner can be from about 0.0005 to about I
pound of hydroxamated polymer per ton of alumina trihydrate solids in the slurry, and in more preferred embodiment from about 0.005 to about 0.1 pound of hydroxamated polymer per ton of alumina,trihydrate solids in the slurry. About 0.1 pound per ton is the maximum needed under most conditions; and more than I pound per ton will oRen be unnecessary.
The hydoxamic polymer should be sufficiently stable under the process conditions used, the temperatures and caustic conditions described above.
Any water soluble h~rdroxamic polymer may be used, but the hydroxamic polymer is commonly a polymer conhining mer units with hydroxamic acid or salt pendant groups of the FormulaI ~
R' ~ C - C ~
FormulaI C = O
R" - N - O - R
3 ~
wherein R is hydrogen or a cation, and R' and R" are independently hydrogen or a substituent to carbon other than hydrogen, for instance a lower alkyl such as methyl.
The hydroxamic polymers, or hydroxamated poly ners, are well known in the art and can be prepared by post-polymerization derivatization from polymers containing pendant reactive groups, such as pendant ester groups, pendant amide groups, pendant anhydride groups, pendant nitrile groups and the like by the reaction thereof with hydroxylamine or its salt at a temperature within the range of from about 20 C to about 100 C for several hours. From about 1 to about 90 mole percent of the available pendant reactive groups of the precursor polymer may be replaced by hydroxamic groups in accordance with such procedures. Such post-polymerization derivatization may be carried out in a polymer solution or in a polymer-containing latex, including both water-continuous latices and water-in-oil latices (wherein the polymer is substantially associated with the dispersed aqueous phase). When two or more species of pendant reactiYe groups are present in the precursor polymer, the reaction with hydroxyl amine may favor ~Qne or more of such species over the other(s). The molecular weight of the hydroxamated polymer is dependent upon the molecular weight of the precursor polymer.
Hydtoxamic acid or salt-containing polymers of very high molecular weights can be prepared by using a watcr-in-oil latex of, t'or example, polyacrylamide or copolymers of acrylamide with acrylic acid or other suitable comonomers .
Il :
,, , ~ . . , - ,, -~ ,. . . .......... .
.. .. - ..
Exemplaty of the polymers which may be hydroxamated for use in the present process include acrylic acid ester polymers, methacrylic acid ester polymers, crotonic acid ester polymers, and the like carboxylic acid ester polymers, such as polymers produced from the polymerization of methyl (meth)acrylate, ethyl (meth)acrylate, t-butyl (meth~acrylate, cyclohexyl (meth)acrylate, dimethyl aminoethyl (meth)acrylate, dimethyl aminoethyl (meth)acrylate, methyl crotonate, and the like type of carboxylic acid ester containing mer units, g¢nerally wherein the ester moiety is derived from a C"2 alcohol, and preferably wherein the ester moiety is derived from a C,.6 alcohol. The polymçrs which may be hydroxamated for use in the present proces~ also include polymers of maleic anhydride and esters thereof, pendant nitrile containing polyrners such as those produced from acrylonitrile, pendant amide containing polymers such as those produced from acrylamide, methacrylamide and the like. The hydroxamic acid or salt-containing polymer may be derived from homopolyrners, copolymers, terpolyrners, or polymers of more varied mer units. Hydroxamic polyrners are well known to those of ordinary ski11 in the art and are specifically disclosed, together with methods for their preparation, in U.S. Patent Nos. 3,34S,344, 4,480,067, 4,532,046, 4,536,296, and 4,587,306, and U.K. Patent Application 2171127, hereby incorporated hereinto by reference. Suitable hydroxylamine salt~ incluto the sulfate, sulfite, phosphate, perchlorate, hydrochloride, acetate, propionate, and the like.
.: ~
The hydroxamic acid or salt-containing polymer for use in the present process should generally have a weight average molecular weight within the range of from about 10,000 to about 50,000,000. The hydroxamated polymer preferably has a weight average molecular weight of at least aboutl million, preferably with an IV of from about 5 to about 40 dl/g.
The degree of hydroxarnation, that is, the concentration of mer units (polymer segments containing two adjacent backbone carbons) of the Formula I above, may vary from about I to about 90 mo1e percent, and preferably is within the range of from about 5 to about 75 mole percent, and most prcferably from about 10 to about 50 mole percent.
Since the alumina trihydrate thickener feed slurry is alkaline, the hydroxamated polymer in preferred embodiment is pr~dominantly anionic, although it can also contain nonionic or even a minor amount of cationic mer uniis, provided that the amount of any such cationic mer units is sufficicntly small so that the polymer retains an overa11 anionic nature and its water solublity.
The anionic mers other than the hydroxamic mer units (referred to herein as the "anionic mer units" unles~ expressly indicated otherwise) are generally carboxylic acids or sulphonic acids, and are usually deri~ed from acrylic acid (M) but can be derived from methacrylic acid (MAA) or a sulfoalkyl acrylamide, such as 2-sulfopropylacrylamide, or the other anionic monomers notcd abo~re. The hydroxamated polymer generally is comprised of from about I to about 99 mole percont, and preforably from about 15 to 90 mole percent, anionic mer units with :. , : , . . .. . .. . . . . . . .-. . ..
, , , , . . , , , , .. - .. .. - . : .
. . ... j. .. .. ., . ~ . ... . . , , . ~ . . . ..
- ~la~3.3 the balance being hydroxamic mer units, optionally together with nonionic mer units. More preferably the hydroxamated polymer is comprised of from about 25 to about 75 mole percent anionic mer units, the balance being hydroxamic mer units9 optionally together with nonionic mer units. In even more preferred embodiment, the hydroxarnated polyrner is comprised of from about 25 to about 75 mole percent anionic mer units, from about 10 to about 40 mole percent hydroxamic mer uni~s and from about 10 lo about 40 mole percent nonionic mer units.
The nonionic mer units are usually the polar (meth)acrylamide mer units (AcAm or methAcAm), but others may be used, for instance, mer units derived from vinyl acetate, vinyl pyrrolidone, butadiene, styrene, alkanolacrylamides such as methylol acrylamide and others.
` 14 .
Test Method The test method employed for evaluating Bayer process trihydrate clarification with and without a trihydrate clarification aid is as follows. A quantity of alumina trihydrate thickener feed sufficient for the desired number of comparative test runs is obtained fresh from a commercial Bayer circuit, and for each test run a 1000 ml sample thereof ("test sample") is charged to a 1000 ml graduated cylinder. The test samples are each plunged ten times to re-suspend the alumina trihydrate particles, then dosed with the trihydrate clarification aid being uscd, if any, and again plungcd ten times to disperse the trihydrate clarification aid in the alumina trihydrate thickener feed slurry. The plunging is accomplished using a stainless steel rod v~ith a paforated steel disk or rubber stopper attached to the end. The slurry is then leR
standing, without agitation, for a settlement time period of 30 minutes immedialely following the final plunging. At the end of the 30 minute settlement period, a samp1e of the supernate liquor is collected and the turbidity of such supernate sample is determined with a turbidity meter. The~urbidity of the supernate is inversely related to clarification efficiency. The alumina trihydrate thickener fced slurries so obtained fresh from a commercial Bayer circuit will contain from about 5 to about 100 grams of alumina trihydrate crystal per liter of slurry, and no more than about 50 mg of other solids per liter of slurry.
. .. , , , . . ~ . , . ,. .. : . . . . . .
ExamplQ I
The Test Method described above was employed to demonstrate the trihydrate clarification aid performance of a representative hydroxamated polymer according to the present invention. The polymer was an anionic, water-soluble terpolymer comprised of acrylic acid, acrylamide, and acrylhydroxamic mer units in the approximate mole ratios of 2:1:1, derived from the hydroxamation of a high molecular weight acrylic acid/acrylamide copolymer. The weight average molecular weight of the hydroxamated polyrner was about 10,000,000. The polymer dosage employed was 0.2 mg of polymer actiYes per liter of the slurry, and polyrner being added as a dilute aqueous solution. A blank or control in which no trihydrate clarification aid was used was also run as a comparison. The test results, in terms of supernatant turbidity ("NTU"), are set forth below in Table t.
T~ble 1 Dosage of Clarification Supernatant Turbidity ClariflCatiQn ~ id ~&/literl (NTU) none none 168 Hydroxamated Polyr;m.,r 0.2 118 The hydroxamated polymer employed in the present inven~ion is, as noted above, a water soluble polymer. The water solubility characteristics of the hydroxamated polymer preferably is defined in terms of the fluidity of its aqueous solutions. By "water soluble" is meant herein, and generally, that an aqueous solution of the polymer, at the polymer actives concentration at which it is charged to the aluminum trihydrate thickener feed slurry, is reasonably fluid, and preferably has a viscosity of no more than about 5,000 to 20,000 cps Brookfield, at a pH of between about 6 and about 14, and ambient room temperature (from about 23 to about 26 C.) The addition of the hydroxamated polymer in the form of a dilute aqueous solution facilitates a rapid dispersion of the polymer in the slurry. Such aqueous solutions of the hydroxamated polymer should not be overly viscous, but they also should not be so dilute that unnecessary volume of water is added to thc alumina trihydrate slurry. For most hydroxamated polymers, an aqueous solution containing from about 0.01 to about 0.5 weight percent of polymer actives is generally reasonable. To further facilitate the rapid dispersion of the hydroxamated polymer in the slurry, in preferrediembodiment the pol~ner is added to the alumina trihydrate thickener feed slurry as an alkaline aqueous solution, for instance having a pH of at least about 9, and more preferably at Ieast about 10, up to about a pH of about 14.
~ ' . . . ': . '. . ~ .
'' .',' ' , , ' ~ ' ~
The present invention provides a method for the improved clarification of a Bayer process alumina trihydrate slurry comprising adding to a Bayer process alumina trihydrate thickener feed slurry an anionic water-soluble hydroxamated polymer in an amount effective to improve the clarification of the slurry upon settlement. The present invention also provides an improved Bayer process for the production of alumina wherein bauxile ore is pulverized, slurried in water, and then digested with caustic at elevated temperatures and pressures, forming an aqueous sodium aluminate solution containing caustic-insoluble constituents, wherein the caustic-insoluble constituents are then substantially separated from the aqueous phase of the a~ueous sodium aluminate solution, and the sodium aluminate solution is then seeded with crystals of alumina trihydrate whereby a solid alumina trihydrate product is precipitated out of the solution, subjected to settlement (whereupon a supernatant is formed) and collected as product or recycled as precipitation seed. Such improved process is characterized by adding to the solution~aRer formation of the alumina trihydrate precipitate, and prior to the complete formation of the supernatant, a water-soluble anionic hydroxamated polymer in an amount effective to improve the clarification of the supernatant upon the settlement of the alumina ~rihydrate prccipitatc.
, . , . . . . , ~. , . ...... , . . .; ,,, -. -............ . . . .
. ~. . .
. ,.~
3 ~3 ~
In preferred embodiment, the alumina trihydrate thickener feed slurry or the solution has an alumina trihydrate solids content of from about 5 to about 100 grarns per liter of alumina trihydrate thickener feed slurry or the solution. In preferred embodiment, the alumina trihydrate crystals of the alumina trihydrate thickener feed slurry or the solution comprise at least about 99 weight percent of the total solids in the alumina trihydrate thickener feed slurry or the solution. -In preferred embodiment, the alumina trihydrate thickener feed slurry or the solution has an alkalinity of from about 5 to about 400 g/liter of the slurry or the solution, expressed as sodium carbonate. In preferred embodiment, the hydroxamated polyrner is added to the alumina trihydrate thickener feed slurry or the solution when the alumina trihydrate thickener feed slurry or the solution is at a temperature within the range of from about 60 C to about 80 C.
In preferred embodiment, the amount of the hydroxamated polymer added to the alumina trihydrate thickener feed slurry or the solution is in the range of from about 0.01 lo about 20 mg per liter of the slurry or the solution. In preferred embodiment, the amount of the hydroxamated polymer ad~ded to the alumina trihydrate thickener feed slurry or the solution is in the range of from about o.oc to about 10 mg per liter of the slurry or the solution. In preferred embodiment, the amount of the hydroxamated polymer added to the alumina trihydrate thickener feed slurry or the solution is in the range of from about 0.0005 to about I pound of the hydroxamated polymer per ton of alumina trihydrate solids in the slurry or the solution.
..... : j .- .. .. ;. . .
, . - . .. . . .. .
. ,, ,, - ~ , . . ~ ~ , . .
.. . . .
, 3 .3 In preferred embodiment, the water soluble hydroxamic polymer is a polymer containing mer units of the Formula I
R' ~ C- C ~
Formulal C = O
R"- N- O - R
wherein R is hydrogen or a cation, and R' and R" are independently hydrogen or a substituent lo carbon other than hydrogen, for instance a lower alkyl such as methyl.
In preferred embodiment, the hydroxamated polymer has a weight average molecular weight within the range of from about 10,000 to about 50,000,000. In preferred embodiment, the hydroxamated polyrner has a weight a~rerage molecular weight of at least about I million. In preferred embodiment, the hydroxamated polymer has an Intrinsic Viscosity of from about S to about 40 dl/g. In preferred embodiment, the hydroxamated polymer is comprised of from about 2S to about,75 mole percent anionic mer units other than hydroxamic mer units, the balance being hydroxamic mer units, optionally together with nonionic mer units. In preferred embodiment, the hydroxarnate~d polyrner is comprised of from about 25 to about 75 mole percent anionic mer units other than hydroxamic mer units, from about 10 to about 40 mole percent hydroxamic mer units and from about 10 to about 40 mole percent nonionic mer units.
Industrial Applicabilitv of the lnvention The present invention is applicable to the Baye.r process for the production of alumina from bauxite ore.
;~
,- ~ ., , , : :
~ ~ . ,, ,. , . :
, ,., ~: , -, . , , , ~
Claims (20)
1. A method for the improved clarification of a Bayer process alumina trihydrate slurry comprising adding to a Bayer process alumina trihydrate thickener feed slurry an anionic water-soluble hydroxamated polymer in an amount effective to improve the clarification of said slurry upon settlement.
2. The method of Claim 1 wherein said alumina trihydrate thickener feed slurry has an alumina trihydrate solids content of from about 5 to about 100 grams per liter of alumina trihydrate thickener feed slurry.
3. The method of Claim 1 wherein the alumina trihydrate crystals of said alumina trihydrate thickener feed slurry comprise at least about 99 weight percent of the total solids in said alumina trihydrate thickener feed slurry.
4. The method of Claim 1 wherein said alumina trihydrate thickener feed slurry has an alkalinity of from about 5 to about 400 g/liter of said slurry, expressed as sodium carbonate.
5. The method of Claim 1 wherein said hydroxamated polymer is added to said alumina trihydrate thickener feed slurry when said alumina trihydrate thickener feed slurry is at a temperature within the range of from about 60°C to about 80°C.
6. The method of Claim 1 wherein the amount of said hydroxamated polymer added to said alumina trihydrate thickener feed slurry is in the range of from about 0.01 to about 20 mg per liter of said slurry.
7. The method of Claim 1 wherein the amount of said hydroxamated polymer added to said alumina trihydrate thickener feed slurry is in the range of from about 0.05 to about 10 mg per liter of said slurry.
8. The method of Claim 1 wherein the amount of said hydroxamated polymer added to said alumina trihydrate thickener feed slurry is in the range of from about 0.0005 to about 1 pound of said hydroxamated polymer per ton of alumina trihydrate solids in said slurry.
9. The method of Claim 1 wherein said water soluble hydroxamic polymer is a polymer containing mer units of the Formula I
Formula I wherein R is hydrogen or a cation, and R' and R" are independently hydrogen or a substituent to carbon other than hydrogen.
Formula I wherein R is hydrogen or a cation, and R' and R" are independently hydrogen or a substituent to carbon other than hydrogen.
10. The method of Claim 1 wherein said hydroxamated polymer has a weight average molecular weight within the range of from about 10,000 to about 50,000,000.
11. The method of Claim 1 wherein said hydroxamated polymer has a weight average molecular weight of at least about 1 million.
12. The method of Claim 1 wherein said hydroxamated polymer has an intrinsic viscosity of from about 5 to about 40 dl/g.
13. The method of Claim 1 wherein said hydroxamated polymer is comprised of from about 25 to about 75 mole percent anionic mer units other than hydroxamic mer units, the balance being hydroxamic mer units, optionally together with nonionic mer units.
14. The method of Claim 1 wherein said hydroxamated polymer is comprised of from about 25 to about 75 mole percent anionic mer units other than hydroxamic mer units, from about 10 to about 40 mole percent hydroxamic mer units and from about 10 to about 40 mole percent nonionic mer units.
15. An improved Bayer process for the production of alumina wherein bauxite ore is pulverized, slurried in water, and then digested with caustic at elevated temperatures and pressures, forming an aqueous sodium aluminate solution containing caustic-insoluble constituents, wherein said caustic-insoluble constituents are then substantially separated from the aqueous phase of said aqueous sodium aluminate solution, and wherein sodium aluminate solution is then seeded with crystals of alumina trihydrate whereby a solid alumina trihydrate product is precipitated out of said solution and subjected to settlement, whereupon a supernatant is formed, and said aluminum trihydrate precipitate is collected as product or recycled as precipitation seed, characterized by adding to said solution after at least the formation of said alumina trihydrate precipitate, and prior to the complete formation of said supernatant, a water-soluble anionic hydroxamated polymer in an amount effective to improve the clarification of said supernatant upon said settlement of said alumina trihydrate precipitate.
16. The method of Claim 15 wherein said solution at the time when said hydroxamic polymer is added has an alumina trihydrate solids content of from about 5 to about 100 grams per liter and said alumina trihydrate solids comprise at least about 99 weight percent of the total solids in said solution.
17. The method of Claim 15 wherein the amount of said hydroxamated polymer added to said solution is in the range of from about 0.01 to about 20 mg per liter of said solution.
18. The method of Claim 15 wherein the amount of said hydroxamated polymer added to said solution is in the range of from about 0.0005 to about 1 pound of said hydroxamated polymer per ton of alumina trihydrate solids in said solution.
19. The method of Claim 15 wherein said hydroxamated polymer has a weight average molecular weight of at least about 1 million.
20. The method of Claim 15 wherein said hydroxamated polymer has an intrinsic viscosity of from about 5 to about 40 dl/g and is comprised of from about 25 to about 75 mole percent anionic mer units other than hydroxamic mer units, the balance being hydroxamic mer units, optionally together with nonionic mer units.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US94429092A | 1992-09-14 | 1992-09-14 | |
| US07/944,290 | 1992-09-14 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2105333A1 true CA2105333A1 (en) | 1994-03-15 |
Family
ID=25481143
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002105333A Abandoned CA2105333A1 (en) | 1992-09-14 | 1993-09-01 | Trihydrate clarification aid for the bayer process |
Country Status (4)
| Country | Link |
|---|---|
| AU (1) | AU667390B2 (en) |
| CA (1) | CA2105333A1 (en) |
| GB (1) | GB2270519B (en) |
| IE (1) | IE76299B1 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9068776B2 (en) | 2009-10-30 | 2015-06-30 | Suncor Energy Inc. | Depositing and farming methods for drying oil sand mature fine tailings |
| US9404686B2 (en) | 2009-09-15 | 2016-08-02 | Suncor Energy Inc. | Process for dying oil sand mature fine tailings |
| US9909070B2 (en) | 2009-09-15 | 2018-03-06 | Suncor Energy Inc. | Process for flocculating and dewatering oil sand mature fine tailings |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0602900B1 (en) * | 1992-12-14 | 1997-03-12 | Nalco Chemical Company | Trihydrate crystal modification in the bayer process |
| AU669284B2 (en) * | 1993-06-02 | 1996-05-30 | Nalco Chemical Company | Use of hydroxamic acid containing polymers to improve filtration of settler overflow in Kelly filters in the Bayer process |
| US5601726A (en) * | 1994-06-06 | 1997-02-11 | Cytec Technology Corp. | Hydroxameted polymers in the bayer process to reduce solids |
| US5539046A (en) * | 1994-11-04 | 1996-07-23 | Cytec Technology Corp. | Blends of hydroxamated polymer emulsions with polyacrylate emulsions |
| AU720125B2 (en) * | 1995-11-07 | 2000-05-25 | Cytec Technology Corp. | Reduction of impurities in bayer process alumina trihydrate |
| WO2006093588A1 (en) | 2005-02-25 | 2006-09-08 | Cytec Technology Corp. | Water-in-oil-in water emulsions of hydroxamated polymers and methods for using the same |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4767540A (en) * | 1987-02-11 | 1988-08-30 | American Cyanamid Company | Polymers containing hydroxamic acid groups for reduction of suspended solids in bayer process streams |
-
1993
- 1993-09-01 CA CA002105333A patent/CA2105333A1/en not_active Abandoned
- 1993-09-02 GB GB9318210A patent/GB2270519B/en not_active Expired - Fee Related
- 1993-09-03 AU AU46114/93A patent/AU667390B2/en not_active Withdrawn - After Issue
- 1993-09-13 IE IE930677A patent/IE76299B1/en not_active Application Discontinuation
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9404686B2 (en) | 2009-09-15 | 2016-08-02 | Suncor Energy Inc. | Process for dying oil sand mature fine tailings |
| US9909070B2 (en) | 2009-09-15 | 2018-03-06 | Suncor Energy Inc. | Process for flocculating and dewatering oil sand mature fine tailings |
| US10590347B2 (en) | 2009-09-15 | 2020-03-17 | Suncor Energy Inc. | Process for flocculating and dewatering oil sand mature fine tailings |
| US9068776B2 (en) | 2009-10-30 | 2015-06-30 | Suncor Energy Inc. | Depositing and farming methods for drying oil sand mature fine tailings |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9318210D0 (en) | 1993-10-20 |
| IE930677A1 (en) | 1994-03-23 |
| IE76299B1 (en) | 1997-10-08 |
| AU4611493A (en) | 1994-03-24 |
| GB2270519A (en) | 1994-03-16 |
| GB2270519B (en) | 1996-03-20 |
| AU667390B2 (en) | 1996-03-21 |
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