Abstract: The present invention provides a process for producing aluminum hydroxide with little contamination by silica at a high yield, while suppressing losses of consumed alumina and alkaline components. The process comprises the steps of mixing a first alumina-containing slurry with a preheated alkaline aqueous solution, extracting alumina from the mixture, separating a dissolution residue from the mixture to obtain a solution, mixing the solution with a second alumina-containing slurry, extracting alumina from the mixture, and precipitating aluminum hydroxide after a desilication treatment.

Abstract: A process for treating an alumina monohydrate-based bauxite by high temperature caustic digestion includes the steps of introducing alumina trihydrate into the digested slurry at a temperature of less than 200° C., in order to obtain an aluminate liquor at atmospheric pressure having an alumina/caustic weight ratio between 1.20 and 1.30, and diluting the resultant aluminate liquor to result in a caustic concentration between 160 and 175 g Na2O/liter. After settling and filtration, the resulting supersaturated liquor undergoes a further dilution before or during a crystallization step. The alumina trihydrate product is filtered from the spent liquor, which is concentrated and recycled.

Abstract: A process for the manufacture of coarse aluminum hydroxide via the Bayer Process. The process involves the decomposition of a supersaturated alkaline aluminate liquor in a two stage precipitation process having an agglomeration stage and a growth stage. The agglomeration stage takes place in agglomeration tanks, where the liquor is seeded with fine aluminum hydroxide to induce precipitation and formation of a suspension, followed by a growth stage, where the suspension is seeded with a coarse aluminium hydroxide. Typically, the feed of the supersaturated alkaline aluminate liquor is split over a first agglomeration tank at a higher liquor temperature of 70° to 100° C. and a second agglomeration tank or one or more of a series of second agglomeration tanks at a lower liquor temperature of 50° to 80° C.

Abstract: Process for treating alumina monohydrate-based bauxite by high-temperature caustic digestion characterized in the following series of operations:

Abstract: The present invention comprises a method for reducing the viscosity of the settled mud or underflow of a raked thickener thereby reducing the torque necessary to move the rake blade through the settled mud. The method includes the step of delivering a viscosity modifier to the settled mud and in front of the rake blade by pumping the viscosity modifier down the rake arm to an area in front of the rake blade. The method also includes an improved rake mechanism that includes a means for delivering viscosity modifier to the settled mud and in front of the rake blade. The present invention also includes a method for increasing the rate of consolidation of flocculated solids in a slurry.

Abstract: A process of recovering alumina from a pregnant Bayer process liquor by crystallisation after adding to the liquor a crystallisation modifier characterised in that the crystallisation modifier comprises: (a) a polyalkoxylated non-ionic surfactant, (b) a surfactant, or precursor thereof, which is not a polyalkoxylated non-ionic surfactant and (c) water. In a further aspect of the invention the composition may contain water but preferably contains substantially no water. Preferred compositions for the crystallisation modifier for use in this process contain a surfactant blend which consists essentially only of the polyalkoxylated non-ionic surfactant (a) and the surfactant (b) or precursor thereof. The process consistently gives excellent improvement in crystal size without decreased yield. Specifically the process results in a reduction in the percentage of undersized crystals.

Abstract: The invention concerns a process that uses an ion exchanger resin to recover the sodium contained in industrial alkaline waste and, in particular, in the "red mud" and sodium effluents coming from the manufacture of aluminum hydrate according to the Bayer process. It includes putting the alkaline resins (1), usually "red mud" in the form of an aqueous suspension in contact with an RH.sup.+ type cationic resin, preferably, a carboxylic resin to attach the sodium selectively and quantitatively to the resin (5) and then to extract it quantitatively in the form of NaOH (8) by displacement using a lime suspension (6), preferably, lime milk. The resin (9), after attaching the calcium, is then regenerated for reuse at the beginning of the process (2) by elution of the calcium as CaCl.sub.2 (12) with a diluted hydrochloric acid solution (10).

Abstract: The present invention is directed to improvements in the Bayer mining process, used for the recovery of alumina from bauxite ore. Water-continuous emulsion polymers are advantageously used to improve the clarification, filtration and scale control of red-mud containing liquors generated during the Bayer process. Preferred polymers are high molecular weight poly(methyl acrylate/acrylic acid), poly(methyl acrylate), poly(vinyl acetate/acrylic acid/methyl acrylate) and a combination of a high molecular weight poly(methyl acrylate/acrylic acid) with a lower molecular weight poly(methyl acrylate/acrylic acid).

Abstract: A process is described for removing dissolved silica from an alkaline solution containing sodium aluminate, e.g. a Bayer process solution. The process comprises contacting the alkaline solution with a slowly stirred bed of particles comprising coarse silica sand or a mixture of coarse silica sand and particles of sodalite, whereby the dissolved silica is precipitated out of solution to form a precipitation of desilication product dispersed in the solution and separating the desilication product solids from the alkaline solution to obtain a desilicated alkaline solution.

Abstract: A process for reducing the level of colloidal iron in a Bayer process stream comprises intermixing an amidoxime polymer with a Bayer process stream and separating the resultant polymer-iron complex to provide purified sodium aluminate solution.

Abstract: The present invention is directed to the clarification of red mud-containing liquors generated in the Bayer process for the recovery of alumina from bauxite ore with a combination of high molecular weight emulsion polymer and lower molecular weight emulsion polymers. The invention is also a method for the same purpose utilizing a methyl acrylate emulsion homopolymer.

Abstract: Processes for spray drying water-soluble and water-swellable vinyl-addition polymer-containing dispersions, emulsions and microemulsions to obtain substantially dry water-soluble or water-swellable polymer particles, compositions of substantially dry water-soluble or water-swellable polymer particles, methods of agglomerating spray-dried polymer particles, and methods of using spray-dried polymer particles and agglomerates in water-treating, mining, paper, food processing, soil conditioning, solution thickening, biotechnological, and oil recovery applications are disclosed.

Abstract: A method for improving the flocculation of suspended solids in a Bayer process liquor in a primary settler stage. The method includes the step of adding to a primary settler feed a composition including water-continuous polymer, said polymer being hydrolyzable in a Bayer process liquor to an acid form, said acid form being an active red mud flocculent. A novel emulsion, and a polymerization technique for obtaining high molecular weight emulsions are also disclosed.

Abstract: Processes for improving solids/liquids separation efficiency in the Bayer process are disclosed, wherein solids are flocculated with hydroxamated polymers and centrifuged.

Abstract: A new and improved method for inhibiting the precipitation of sodium oxalate crystals in a Bayer process liquor is provided. In an embodiment, the method comprises the step of adding to the Bayer process liquor, after red mud separation, a minor effective amount of a liquor oxalate stabilizer selected from hydrocarbon-substituted amine oxide compounds and/or hydrocarbon-substituted betaine compounds.

Abstract: Process of sodium oxalate purification of sodium aluminate solutions resulting from alkaline attack of bauxites according to the Bayer process, comprising:precipitation of said sodium oxalate in at least a fraction of the pre-decomposed sodium aluminate solution, by means of an agent that destabilizes the supersaturation state of the sodium oxalate, or deoxalation initiator,separation of the oxalate, precipitated with the destabilizing agent in the form of an insoluble residue, and the purified sodium aluminate solution which is then recycled as the leaching liquor, characterized in that the destabilizing agent or deoxalation initiator, placed in contact with the sodium aluminate solution, is a salt other than an oxalate, a metal oxide, a metal hydroxide, or a mixture thereof, said destabilizing agent remaining insoluble and chemically inert with respect to the reaction medium, and in that, after regeneration if any, it is recycled to the top of the process as the deoxalation initiator.

Abstract: Process for the production of aluminium hydroxide by digesting bauxite with alkali solution and precipitating aluminium hydroxide from the digestion solution, comprising:a combining bauxite and alkali solution having a caustic concentration of at least 180 grams per liter expressed as sodium carbonate and digesting partly the bauxite in the combined product in a first digestion step at relatively low temperature,b separating reaction product obtained in step a into a liquid phase and a solids/liquid slurry,c combining liquid phase and solids/liquid slurry obtained in step b and digesting the combined product in a second digestion step at relatively high temperature,d releasing heat from the reaction product obtained in step c to preheat liquid phase obtained in step b,e separating the reaction product obtained in step d into a supersaturated sodium aluminate solution and undissolved material,f precipitating aluminium hydroxide from the supersaturated sodium aluminate solution obtained in step e and separating

Abstract: Processes for improving solids/liquids separation efficiency in the Bayer process are disclosed, wherein Bayer process streams are treated with calcium or magnesium salts, flocculated with carboxylic acid or salt group-containing polymers, and centrifuged.

Abstract: A method for flocculation of red mud in Bayer Process streams utilizing a fatty acid or fatty acid ester free latex polymer flocculant. Preferred fatty acid free emulsifiers useful for the preparation of such flocculants are obtained by reacting ethylene and/or propylene oxide with a reagent selected from the group consisting of ethylene diamine, ethanol and ethylene glycol.

Abstract: Methods of reducing foam in Bayer process liquor are provided, said methods comprising adding a composition to the Bayer process liquor that comprises a tri(alkoxy alkyl) phosphate and a hydroxyl group containing carrier.

Abstract: A method for the preparation of new semi-crystalline, porous inorganic oxide compositions possessing uniform framework-confined mesopores in the range 2.0-10.0 nm. The method uses an interaction between various nonionic polyethylene oxide based surfactants (N.degree.) and neutral inorganic oxide precursors (I.sup..quadrature.) at ambient reaction temperatures. The materials formed exhibit a disordered assembly of worm-like channels of regular diameter owing to the specific mechanism of self-assembly, producing highly stable materials and particles incorporating large numbers of the channels. This (N.degree. I.degree.) templating approach introduces several new concepts to mesostructure synthesis. The application of the low-cost, non-toxic and biodegradable surfactants and ambient reaction temperatures, introduces environmentally clean synthetic techniques to the formation of mesostructures. Recovery of the template can be achieved through solvent extraction where the solvent may be water or ethanol.

Abstract: The processing of bauxite in the Bayer Process results in the formation of titanaceous, siliceous, and other scale on equipment and apparatus such that a great deal of time and effort is spent in order to maintain the process at its height efficiency by reducing or eliminating the same. The scale is treated, reduced, altered, etc., according to the present invention by the use of hydroxamated polymers having weight average molecular weights ranging from about 1,000 to less than about 10,000.

Abstract: The processing of bauxite in the Bayer Process results in the formation of titanaceous, siliceous, and other scale on equipment and apparatus such that a great deal of time and effort is spent in order to maintain the process at its height efficiency by reducing or eliminating the same. The scale is treated, reduced, altered, etc., according to the present invention by the use of hydroxamated polymers having weight average molecular weights of over about 10,000.

Abstract: Sodium oxalate is precipitated from spent Bayer process liquor by mixture with a low total alkalinity (TA) sodium oxalate seed solution that has been treated with two or more adsorbents to remove organic poisons from the sodium oxalate. The adsorbents are preferably two different adsorbents selected from activated carbon, ESP dust, calcium oxide and magnesium oxide. Surprisingly, combination treatments with activated carbon and ESP dust are most effective even though ESP dust alone has little effect on oxalate removal.

Abstract: The invention comprises a process for improved flocculation of Bayer process red mud-containing slurry. The improvement comprises adding to the red mud-containing liquor a hydroxymethyl diphosphonic acid polymer optionally in addition to the conventional flocculant. The polymer is added to the red mud-containing liquor in an amount sufficient to reduce the concentration of suspended solids in the supernatant phase and/or increase the rate of sedimentation.

Abstract: Processes for reducing the level of impurities in alumina trihydrate produced in the Bayer process are disclosed, wherein alumina trihydrate-containing process streams are flocculated with hydroxamated polymers and centrifuged.

Abstract: Improved process for fluidifying flocculated aqueous suspensions of red muds in the production of alumina from bauxite by the Bayer process, which consists:in dissolving bauxite using sodium hydroxide;then, in decanting and in washing the red muds formed in order to separate them from the alumina in successive vats, while recycling the washing waters upstream;and finally, in eliminating the red muds thus treated;and in which a flocculant (F) consisting of a polyacrylamide of molecular weight greater than ten million is introduced into the suspension of one of the successive vats;wherein a dispersing agent (D) formed by an anionic acrylic acid polymer of molecular weight lower than fifty thousand is added simultaneously with said flocculant (F) to the suspension in the same vat.

Abstract: The present invention is a method for producing alumina trihydrate with a low silica content from Gibbsite-containing bauxite of low reactive silica content. The present method involves two desilication steps: one step before extraction of alumina from the bauxite, i.e., a pre-desilication, and an additional desilication step following alumina extraction, i.e., a post-desilication. The present method comprises the steps of:(a) heating a suspension of ground bauxite in an aqueous solution comprising sodium hydroxide at a temperature greater than 80.degree. C.; and(b) increasing the sodium hydroxide concentration of the suspension from (a); and(c) heating the suspension from (b) at a temperature greater than 80.degree. C.; and(d) diluting the suspension from (c) with an aqueous solution; and(e) heating the suspension from (d) at a temperature greater than 80.degree. C., affording a suspension comprising a supersaturated, desilicated sodium aluminate liquor and insoluble solid.

Abstract: A process for eliminating iron from supersaturated sodium aluminate solutions obtained from the alkaline attack according to the Bayer process of the monohydrate bauxite including successively the steps of grinding and eventually of desilicatation in the presence of an aliquot of decomposed liquor, then attack at a temperature higher than 200.degree. C., usually between 240.degree. and 270.degree. C.

Abstract: There is disclosed a method for improving the brightness level of aluminum hydroxide removed from a caustic solution. The method comprises:(a) pre-filtering the solution to remove contaminants therefrom; and (b) contacting the filtered solution with an adsorbent consisting essentially of a calcined compound having the formula: A.sub.w B.sub.x (OH).sub.y C.sub.z.nH.sub.2 O wherein A represents a divalent metal cation selected from the group consisting of: Mg.sup.2+, Ni.sup.2+, Fe.sup.2+, Ca.sub.2+ and Zn.sup.2+ ; B represents a trivalent metal cation selected from the group consisting of: Al.sup.3+, Fe.sup.3+ and Cu.sup.3+ ; C represents a mono- to tetravalent anion selected from the group consisting of: OH.sup.-, Cl.sup.-, Br.sup.-, NO.sub.3.sup.- CH.sub.3 COO.sup.-, C.sub.2 O.sub.4.sup.2-, CO.sub.3.sup.2-, SO.sub.4.sup.2-, PO.sub.4.sup.3-, Fe(CN).sub.6.sup.3- and Fe(CN).sub.6.sup.4- ; and w, x, y, z and n satisfy the following: 0<z.ltoreq.x.ltoreq.4.ltoreq.w.ltoreq. 1/2 y and 12.gtoreq.n.gtoreq.

Abstract: Red mud bauxite residue produced in the Bayer Process is treated in a plurality of centrifuges and repulp tanks to successively wash and dewater the red mud. A final centrate liquor is obtained in a first upstream centrifuge stage which is rich in alumina and caustic values for respective recovery and reuse. The concentrated red mud cake produced in the final downstream washing/centrifuge step is low in caustic and alumina concentration permitting environmentally friendly disposal. The concentrated red mud cake is reslurried and mixed with bauxite sand for disposal in a dry stacking impoundment area.

Abstract: The filtration rate of Bayer Process primary settler overflow and/or the flocculation in the initial stages of the washer train in the Bayer Process are improved by contacting the settler feed stream or the feed stream to the first stages of the washer train first with a) a lower molecular weight polymer which contains hydroxamic acid and/or salt groups and then with b) a mixture of an anionic polymer and a second, higher molecular weight polymer which contains hydroxamic acid groups.

Abstract: Bauxite that is to be used in the Bayer process for the recovery of alumina is washed with aqueous wash liquor having a caustic content of at least 50 g/l and which comprises aqueous caustic from the alumina recovery circuit of the Bayer process and, after removing organic material from the wash liquor, the wash liquor is included in the digestion stage, the separation stage or the alumina recovery circuit of the Bayer process.

Abstract: A process for the production of aluminum hydroxide from an alumina-containing ore comprising, in a process for the production of aluminum hydroxide involving extraction of alumina from an alumina-containing ore by an aqueous alkaline solution, supplying a slurry containing the alumina-containing ore at a high solid content which is prepared from a small amount of an alkaline solution together with an aqueous alkaline solution which is so preheated to a temperature that a preheated temperature is enough high to have a temperature after the mixing with the slurry which is higher than an extraction temperature of alumina, simultaneously or after the mixing them, to an extraction apparatus comprising of a tube reactor, extracting alumina from the alumina-containing ore under extraction conditions of a temperature of 120.degree.-160.degree. C.

Abstract: The invention comprises a process for improved flocculation of Bayer process red mud-containing slurry. The improvement comprises adding to the red mud-containing liquor a phosphonic acid polymer optionally in addition to the conventional flocculant. The polymer is added to the red mud-containing liquor in an amount sufficient to reduce the concentration of suspended solids in the supernatant phase and/or increase the rate of sedimentation.

Abstract: A process is disclosed for the production of alumina by the Bayer process, including a precipitation process having an agglomeration stage and a growth stage in which the precipitation slurry is passed through a multiplicity of growth tanks. In the agglomeration stage, the precipitation slurry is maintained at a temperature of about 75.degree. C. to 85.degree. C. In the growth stage, the agglomeration slurry is cooled by about 1.degree. C. to 3.degree. C. in each growth tank of the multiplicity of growth tanks as compared to an adjacent previous growth tank. The temperature of the precipitation slurry leaving the final precipitator is preferably about 55.degree. C.

Abstract: Water soluble polymer flocculants are formed from monomers derived from ethylenically unsaturated dibasic carboxylic acids of formula (I) where R.sup.1 =H and R.sup.2 =COOH or R.sup.1 =COOH and R.sup.2 =H. Flocculants are provided for use in Bayer process liquors which are copolymers of acids of formula (I) with ethylenically unsaturated copolymerisable monomer and which have molecular weight above 300,000. Preferably the polymer is a terpolymer of dibasic acid, monobasic and polymerisable termonomer. A particularly preferred flocculant is formed from at least 10 mol % maleic acid with acrylic acid and acrylamide as comonomers and is used preferably for flocculation of red mud in the primary settler and/or the various red mud washing stages.

Abstract: A composition comprising a blend of an inverse emulsion of a hydroxamated polymer and a second inverse emulsion of a second polymer selected from the group consisting of alkali metal (meth)acrylate homopolymers, ammonium (meth)acrylate homopolymers, and copolymers of the (meth)acrylates with (alk)acrylamides, wherein the molar ratio of hydroxamated polymer to said second polymer in the emulsion is within the range of about 99:1 to 15:85 when the second polymer is an alkali metal (meth)acrylate homopolymer or copolymer and is within the range of about 99:1 to 58:42 when said second polymer is an ammonium (meth)acrylate homopolymer or copolymer. Processes for removing suspended solids from Bayer alumina process streams using these compositions are also provided.

Abstract: Alginic acid is used in combination with high molecular weight synthetic water soluble polymers to flocculate red mud from Bayer process liquors. Superior clarity of supernatant liquor is achieved using the process of the invention.

Abstract: Organic impurities are removed from Bayer process liquors using a polymer which contains vinylamine and/or vinylformamide.

Abstract: Siliceous materials produced by thermally treating spent Bayer process liquors are obtained in modified form when produced in the presence of polymeric quaternary ammonium compounds, polyamine polymers, copolymers of acrylic acid and acrylamide, and polyacrylamides. These modified siliceous materials possess morphologies which confer upon them a reduced tendency to deposit on surfaces throughout the process.

Abstract: The invention purpose is a process to obtain gel to elaborate Zeolite 4A, to be used in detergents due to its capacity for calcium absortion; the process lies on the obtention of an alkaline aluminum solution starting from bauxite provided by tank 3 which is attacked in digestor 1 with sodium hydroxide provided by tank 4, with a concentration of 11% minimum, with a filtration of the reacting mass and a purification 13 before the gel formation step in whose reactor 14 is also introduced an alkaline solution of SiO2 to obtain by agitation and temperature a gel which is treated in a crystallizer 15, cooling and concentrating the crystalline mass in 16, filtered in 17, and passed to a dryer 20 from where the product Zeolite 4A passes to storage 21. Bauxite residues are attacked with boiling sulphuric acid in reactor 9, filtering the resulting mass in 11 to recycle the silica and to recover the metal sulphates in solution for using them in water treatments.

Abstract: A secondary polishing process for Bayer Process liquors suspension is described. The polishing process uses a combination of bio-polymers, particularly such bio-carbohydrates as dextran, with an inert insoluble solid, such as a filter aid, to treat the primary red mud settler overflow, then clarifying these treated overflow liquors in a secondary clarifier. Results provide for from 0-20 milligrams per liter suspended solids, often from 0-5 ppm suspended solids, and may make sand filter or Kelly filter operation an option in the Bayer Process.

Abstract: A method for inhibiting the precipitation of sodium oxalate crystals in a Bayer process liquor. The method comprises the step of adding to the Bayer process liquor, after red mud separation and immediately prior to crystallization of alumina trihydrate, or during crystallization of alumina trihydrate, or during classification of alumina trihydrate, an effective amount of a cationic, surface active, alkylammonium salt compound.

Abstract: A method for defoaming a Bayer process liquor, the method comprising the steps of adding to the Bayer process liquor an effective amount of an antifoam/defoamer composition comprising a polyether surfactant and a polyhydric alcohol fatty acid ester.

Abstract: Siliceous materials produced by thermally treating Bayer process liquors are obtained in modified form when produced in the presence of ammonium, aromatic amine, and amine compounds, or compounds bearing ammonium, aromatic amine or amine moieties, such as N-propylamine, pyridine and tetramethylammonium hydroxide. These modified siliceous materials possess morphologies which confer upon them a reduced tendency to deposit on surfaces throughout the process.

Abstract: The invention concerns the production of aluminum trihydrate crystal by the Bayer process, by digesting ground bauxite, filtering off the red mud, cooling the filtrate, and crystallizing out the dissolved aluminum hydroxide as gibbsite. Before and/or during the crystallization, polyglycerines of the general formula H--(OCH.sub.2 CHOH--CH.sub.2).sub.n --OH, where n is an integer equal to or greater than 3, are added.

Abstract: A process for improving the flocculation of suspended solids in a Bayer process liquor in a primary settler stage. The method includes the step of adding to a primary settler feed from about 1 to about 100 parts per million of a composition including a non-inverted, water-continuous polymer, said polymer being hydrolyzable in a Bayer process liquor to an acid form, said acid form being an active red mud flocculant.

Abstract: A method for defoaming a Bayer process liquor, the method comprising the steps of adding to the Bayer process liquor an effective amount of an antifoam/defoamer composition comprising a water-soluble polypropylene glycol having an average molecular weight of from about 200 to about 600 daltons.

Abstract: A process for improved flocculation of Bayer process red mud-containing liquor uses a conventional water soluble anionic flocculant to form a red mud phase and a supernatant from the red mud-containing liquor, the supernatant containing suspended solids. The process is characterized by the addition of a water soluble clarification aid in addition to the conventional flocculant, wherein the clarification aid is pullulan, lactan, zooglan, rhamsan, or combinations thereof. The clarification aid is added to the red mud-containing liquor in an amount sufficient to reduce the concentration of suspended solids in the supernatant.