Abstract: A process for producing aluminum fluoride particles having a smooth surface, comprising the steps of adding aluminum fluoride seed crystals to a super-saturated solution of aluminium fluoride; allowing aluminum fluoride particles to be precipitated under heating and agitation; collecting the aluminium fluoride particles by filtration; and drying them, wherein: a super-saturated solution of aluminium fluoride containing 0.6 to 1.3 wt % of fluosilicic acid which is preferably obtained by reacting aluminum hydroxide with fluosilicic acid in an [Al(OH).sub.3 /H.sub.2 SiF.sub.6 ] molar ratio of 1.80 to 1.90 is used as the crystallization mother liquor.

Abstract: The present invention allows the reproduction of a crystalline aluminum hydroxide having a high particle strength and a high purity which can find wide application such as abrasive from a supersaturated sodium aluminate solution which is being recycled in the production of aluminum hydroxide or lithographic printing plate. In a process for the purification of aluminum hydroxide which comprises the hydrolysis reaction of a supersaturated solution of sodium aluminate to crystallize aluminum hydroxide, the improvement which comprises the steps of keeping the temperature of a suspension formed by mixing a mother liquor having a total caustic soda concentration of from 50 to 700 g/l and an aluminum concentration or from 0 to 300 g/l with crystalline aluminum hydroxide at a range of from 10.degree. C. to 200.degree. C. for at least 1 to 48 hours, mixing the suspension with the supersaturated solution of sodium aluminate, and then causing the crystallization reaction at the crystallization reaction temperature.

Abstract: A process is provided for making K.sub.2 SO.sub.4 3Al.sub.2 O.sub.3 4S0.sub.3 +xH.sub.2 O or Na.sub.2 SO.sub.4 3Al.sub.2 O.sub.3 4SO.sub.3 +xH.sub.2 O where x is a number from 4 to 12, which is used as a pigment. Sulfuric acid, one of a sulfate salt or a hydroxide of either potassium or sodium and one of a sulfate of aluminum or a hydroxide of aluminum are inputted into a crystallizer and reacted to form either Al.sub.2 (SO.sub.4).sub.3 K.sub.2 SO.sub.4 +24H.sub.2 O or Al.sub.2 (SO.sub.4).sub.3 Na.sub.2 SO.sub.4 +24H.sub.2 O. A fluid flow containing either Al.sub.2 (SO.sub.4).sub.3 K.sub.2 SO.sub.4 +24H.sub.2 O or Al.sub.2 (SO.sub.4).sub.3 Na.sub.2 SO.sub.4 +24H.sub.2 O is drawn off from the crystallizer and transferred into a pigment reactor where it is subjected to a temperature of about 200.degree. C. and a pressure ranging from 120 to 350 pounds per square inch so as to result in the production of either basic potassium aluminum sulfate K.sub.2 SO.sub.4 3Al.sub.2 O.sub.3 4SO.sub.3 +xH.sub.

Abstract: A process for making ink which begins with a leach liquor of Al.sub.2 (SO.sub.4).sub.3 +K.sub.2 SO.sub.4 +Fe.sub.2 SO.sub.4 and other sulfates that are introduced to a surface-cooled crystallizer that drops the Al.sub.2 (SO.sub.4).sub.3 +18H.sub.2 O which is removed from the leach liquor. The leach liquor is then supplied with a mixture which includes K.sub.2 SO.sub.4 into a simple crystallization and evaporation unit to drop Al.sub.2 (SO.sub.4).sub.3 +K.sub.2 SO.sub.4 +24H.sub.2 O. A pressure of 250 PSI and a temperature of 200.degree. C. are then applied in a discrete continuous process that yield a basic sodium or sodium/potassium aluminum sulfate and excess sodium sulfate or sodium/potassium. The excess sodium sulfate or sodium/potassium sulfate is returned to the simple crystallization and evaporation unit. The basic potassium aluminum sulfate (BKAS) and/or basic sodium aluminum sulfate (BNaAS) Na.sub.2 SO.sub.4, 3Al.sub.2 O.sub.3, 4SO.sub.3, 9H.sub.2 O is used as a filler in the making of ink.

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 producing phase-pure, monodispersed, single crystal alpha-alumina particles of controlled size and shape comprises the steps of providing an aluminum hydrous oxide precursor and a glycol solution, dispersing said precursor in said glycol solution to create a suspension, heating and stirring said suspension in a closed pressure vessel to produce alpha-alumina particles, cooling said suspension, and removing said alpha-alumina particles from said solution. Additionally nucleation seeds may be added to the solution. Control of size is a function of seeding concentration, and control of morphology is a function of stirring rate.

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: A method of making activated alumina includes beginning with a leach liquor of potassium and aluminum sulphates that is subjected to a surface-cooled crystallizer with a heat-exchanger input temperature of 160.degree. F. and a surface-chilled temperature of 60.degree. F. Crystals of aluminum sulphate are precipitated and recrystalized by evaporation in a vacuum and at an elevated temperature. Purified crystals of aluminum sulphate are then dried at 50.degree.-60.degree. C. The dried aluminum sulphate crystals are then dehydrated at 400.degree.-450.degree. C. after a rise rate of 50.degree.-60.degree. C. per minute to drive off most of the water. A roasting and recalcination step at 1000.degree. C.-1050.degree. C. after a rise rate of 50.degree.-60.degree. C. per minute is used drive off the sulphate. The remaining alumina is smelted by electrolysis for aluminum.

Abstract: A method of manufacturing aluminum fluoride anhydride by means of a wet method. This method is featured in that a seed crystal of AlF.sub.3.3H.sub.2 O containing not more than 5% of fine particle 40 .mu.m or less in diameter is added into the super-saturated solution of aluminum fluoride in such a ratio that the total surface area of the seed crystal is in the range of 40-100 m.sup.2 per 1 kg of AlF.sub.3.3H.sub.2 O to be precipitated until an initial concentration of the super-saturated solution is reduced to 1.6%. The initial concentration of the super-saturated solution is adjusted to 8 to 15%. Resultant slurry is heated under agitation, thereby precipitating in batch-wise large AlF.sub.3.3H.sub.2 O particles which are then separated, dried and dehydrated.

Abstract: A process for the precipitation of aluminum trihydroxide from a supersaturated sodium aluminate solution, comprising the steps of(a) supplying a stream of supersaturated sodium aluminate solution and a first stream of aluminum trihydroxide particles as seed particles to a first reaction circuit,(b) maintaining the sodium aluminate stream containing the stream of seed particles in the first reaction circuit under conditions mainly resulting in precipitation and agglomeration of aluminum trihydroxide,(c) passing the stream thus obtained to a second reaction circuit in which the stream is maintained under conditions mainly resulting in precipitation and growth of aluminum trihydroxide particles,(d) passing the stream obtained in the second reaction circuit to a separation/classification unit to separate the stream into a first aluminum trihydroxide product stream comprising the coarser particle size portion, a second aluminum trihydroxide product stream comprising the finer particle size portion and a spent liqu

Abstract: A method of making activated alumina includes beginning with a leach liquor of potassium and aluminum sulphates that is subjected to a surface-cooled crystallizer with a heat-exchanger input temperature of 160.degree. F. and a surface-chilled temperature of 60.degree. F. to 80.degree. F. Crystals of aluminum sulphate are precipitated and recrystalized by evaporation in a vacuum and at an elevated temperature. Purified crystals of aluminum sulphate are then dried at 50.degree.-60.degree. C. The dried aluminum sulphate crystals are then dehydrated at 400.degree.-450.degree. C. after a rise rate of 10.degree.-20.degree. C. per minute to drive off most of the water. A roasting and recalcination step at 900.degree. C.-950.degree. C. after a rise rate of 10.degree.-20.degree. C. per minute is used drive off the sulphate. The remaining alumina is useful as a high-grade catalyst.

Abstract: A process is disclosed for treating used aluminum chlorofluoride catalyst either alone or mixed with organics. It involves forming a solution of the catalyst in water or an aqueous acid and then adjusting the pH and/or composition of the aqueous phase formed to precipitate compounds containing the aluminum and/or fluorine.

Abstract: Aluminum and fluorine are recovered from fluorine containing waste materials from the production of aluminum metal (FCWM) as ALF.sub.2 OH hydrate by a process comprising: leaching FCWM with dilute sulphuric acid at a pH value within the range of 0-3; if needed adding aluminum in an acid soluble form; adjusting the pH value of the aqueous phase to a value within the range 3.7-4.1 at the end of the leaching period by addition of a caustic aqueous solution; precipitating silica at a temperature not exceeding 60.degree. C.; separating the reaction mixture into a solid phase containing precipitated silica and non-soluble residues of the FCWM and a purified solution; and precipitating AlF.sub.2 OH hydrate from the purified solution at a temperature within the range 90.degree.-100.degree. C. and at a pH value not exceeding about 4.1 by controlled continuous addition of an aqueous caustic solution. Reducing and/or non-oxidizing operating conditions are maintained during all these process steps. The precipitated AlF.

Abstract: A process for the production of an aluminum hydroxide with rounded grain surfaces. An alkaline solution of a specific composition derived from the Bayer process is inoculated and adsorptively precipitated with an aluminum hydroxide with a specific grain distribution. The aluminum hydroxide obtained according to the new process is especially suitable for the flameproof finishing of polyesters.

Abstract: A process for the production of an aluminum hydroxide with rounded grain surfaces. An alkaline solution of a specific composition derived from the Bayer process is inoculated and adsorptively precipitated with an aluminum hydroxide with a specific grain distribution. The aluminum hydroxide obtained according to the new process is especially suitable for the flameproof finishing of polyesters.

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 process is disclosed for forming compacted silver nitrate bodies. A feed silver nitrate solution is introduced into an evaporative crystallizer (10). Steam is provided to a steam jacket (30) to heat the solution in the crystallizer (10) and form a slurry comprising silver nitrate crystals. The crystallizer (10) has an agitator (20) to mix the slurry and promote crystal growth. Slurry density is maintained within a desired range by controlling the rate of steam flow to the steam jacket (30) via a control valve (34). Slurry containing silver nitrate crystals is withdrawn from the crystallizer (10) and introduced to a centrifuge separator (78), for separating and drying the crystals. The separated, dried crystals are further dried by contact with an airstream and fall into a hopper (88). The crystals flow from the hopper into a translucent feed tube (96) and then into a roll compactor (100) that compacts the crystals to form the compacted silver nitrate bodies.

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 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 method of manufacture including bringing seed and aluminum hydroxide together in an aqueous medium and hydrothermally digesting for producing boehmite at the expense of the aluminum hydroxide.

Abstract: In a process for precipitating alumina hydrate from a stream of Bayer process liquor, wherein the stream is first divided into a major portion and a minor portion, the minor portion fed to an agglomeration stage and seeded with fine seed to induce precipitation and formation of a slurry, and the major portion cooled and charged with coarse seed and directed to a growth stage to induce formation of alumina hydrate product, the steps of: separating solids from the minor portion after formation of the slurry; cooling, to a temperature of between about 45.degree. C. and about 60.degree. C., the liquid remaining after separating solids from the slurry formed in the agglomeration stage; adding an amount of coarse seed to the remaining liquid to generate a slurry of fresh hydrate nuclei; and recombining the slurry of fresh hydrate nuclei with the major portion of the stream.

Abstract: Methods are described for preparing aluminum nitride of controllable morphology for ceramic and heat conduction applications. The methods comprise forming spherical particles or flakes of an intermediate, RAlNH, followed by heating the spheres or flakes of RAlNH at elevated temperatures to produce high purity aluminum nitride of corresponding morphology. Spheres of RAlNH are formed by (i) freezing a suspension of RAlNH in a liquid medium and thawing, by (ii) aging the suspension, or by (iii) dissolving RAlNH in a liquid medium and precipitating it. Flakes are formed by freezing a suspension of RAlNH in a liquid medium and removing frozen medium from the frozen suspension.

Abstract: An improved process for precipitating alumina from Bayer process liquors is disclosed. The process involves dividing an incoming pregnant liquor stream into a minor portion of about 10 to about 25% by volume of the total incoming pregnant liquor stream, and directing that stream into a series of small tanks where the minor stream is permitted to agglomerate. Fine aluminum hydroxide seed having a median particle size of between about 30 and about 60 microns is added to this stream. The slurry resulting from the agglomeration stage is then directed to a set of larger vessels in which the growth stage will take place. At this point, the remaining portion of the pregnant liquor is combined with the slurry resulting from the agglomeration stage. A coarse seed charge of about 150 to about 600 grams/liter of seed having a median particle size of between about 80 and about 100 microns is charged into the second set of vessels.

Abstract: Process for the production of a short-prismatic aluminum hydroxide by decomposing a supersaturated sodium aluminate liquor. The product can be used as a pigment and filler in the paper industry, as a flame-retardant filler in plastics and as a white pigment in paints and enamels.

Abstract: A method of modifying crystal structure of alumina trihydrate crystallizing from saturated Bayer liquors, which method includes the treatment of the saturated Bayer liquors with a crystal modifying amount of a polysaccharide, preferably a dextran.

Abstract: An improved process for precipitating alumina from Bayer process liquors is disclosed. The process involves dividing an incoming pregnant liquor stream into a minor portion of about 10 to about 25% of the total incoming pregnant liquor stream, and directing that stream into a series of small tanks where the minor stream is permitted to agglomerate. Fine aluminum hydroxide seed having a median particle size of between about 30 and about 60 microns is added to this stream. The slurry resulting from the agglomeration stage is then directed to a set of larger vessels in which the growth stage will take place. At this point, the remaining portion of the pregnant liquor is combined with the slurry resulting from the agglomeration stage. A coarse seed charge of about 150 to about 600 grams/liter of seed having a median particle size of between about 80 and about 100 microns is charged into the second set of vessels. This improved process helps to increase the yield of a strong coarse aluminum trihydroxide product.

Abstract: The invention involves a method for making uniformly sized particles from solid compounds. First, a suitable solid compound is dissolved in a suitable solvent. Then, a precipitating liquid is infused, precipitating non-aggregated particles with substantially uniform mean diameter. The particles are then separated from the solvent. Depending on the solid compound and the desired particle size, the parameters of temperature, ratio of non-solvent to solvent, infusion rate, stir rate, and volume can be varied according to the invention. The precipitating liquid may be aqueous or non-aqueous, depending upon the relative solubility of the compound and the desired suspending vehicle.

Abstract: A process for obtaining essentially cone-shaped aluminum chloride granules free of fines from a gas current containing aluminum chloride, comprising contacting said gas current with a surface whose temperature is below about 70.degree. C. to deposit the aluminum chloride thereon in the form of cone-shaped granules and then heating said surface for a time and at a temperature sufficient to detach said granules from said surface; and the essentially cone-shaped product of such process.

Abstract: Methods are described for preparing aluminum nitride of controllable morphology for ceramic and heat conduction applications. The methods comprise forming spherical particles or flakes of an intermediate, RA1NH, followed by heating the spheres or flakes of RA1NH at elevated temperatures to produce high purity aluminum nitride of corresponding morphology. Spheres of RA1NH are formed by (i) freezing a suspension of RA1NH in a liquid medium and thawing, by (ii) aging the suspension, or by (iii) dissolving RA1NH in a liquid medium and precipitating it. Flakes are formed by freezing a suspension of RAINH in a liquid medium and removing frozen medium from the frozen suspension.

Abstract: A process is disclosed for the control of the particle form of aluminum hydroxide crystals precipitated from an alkali metal aluminate solution which comprises either the use of certain monohydric and polyhydric alcohols or controlling the caustic concentration of the sodium aluminate solution or a combination whereby particles shapes may be produced principally comprising acicular form or principally comprising lamellar form, depending upon the caustic concentration of the alkali metal hydroxide and the vol. % of the alcohol.

Abstract: Solid aluminum hydroxide compositions having improved solubility, stability and filterability are formed by adding at least a stoichiometric amount of a solid base to a concentrated solution of an aluminum salt (about 8.3% Al.sub.2 O.sub.3 or higher) and stirring vigorously. The base used has an alkali metal, alkali earth metal, or other metallic cation, and does not contribute an anion other than hydroxide to the solution. Particularly suitable bases are carbonate and bicarbonate.

Abstract: Disclosed is generally spherical aluminum hydroxide particles comprised of solid crystals of aluminum hydroxide, the crystals extending radially outwardly from a central core region and having a shape selected from lamellar and acicular, the particle density ranging from 0.3 to 2.5 gms/cc.

Abstract: A process for producing a solid, cold-water soluble, sulfate containing aluminum chloride composition suitable for use as a waste water clarifying agent comprising introducing alkali aluminate, sulfuric acid, hydrochloric acid and hydrated aluminum oxide into a spray drier and recovering the resulting solid product.

Abstract: A system is disclosed for the purification of a caustic solution to remove impurities therefrom comprises: bringing the caustic solution into contact under pressure with the outside of a plurality of porous hollow fibers each having at least one open end and coated with a semipermeable membrane and collecting purified solution from the open ends of the hollow fibers. In a preferred embodiment, the filtering medium comprises porous hollow polysulfone fibers coated with a semipermeable sulfonated polysulfone membrane.

Abstract: The invention concerns a process for the precipitation of aluminium hydroxide by seeding in two phases, which is intended to produce at a high level of productivity alumina with large grains, referred to as `sandy coarse`, by precipitation in a succession of tanks in cascade relationship of a supersaturated solution of sodium aluminate coming from alkaline attack on bauxite in accordance with the BAYER process. The process comprises three stages:in the first agglomeration stage, the supersaturated aluminate liquor is introduce into the tank, with an equivalent amount of terms of Na.sub.2 O of between 110 and 175 g/liter, at a temperature of between 65.degree. and 80.degree. C.

Abstract: Substantially pure boehmite is produced by heating an aqueous sodium aluminate solution to a temperature of about 115.degree.-145.degree. C., preferably about 120.degree.-130.degree. C., treating the heated solution with alumina seed material and separating a boehmite precipitate from the solution. A particularly preferred seed material is boehmite gel.

Abstract: A process for the production of aluminum trihydroxide having a controlled median diameter of less than 4 microns, with a unimodal distribution and minimum deviation. The process comprises grinding aluminum trihydroxide until the aluminum trihydroxide has a specific BET surface area of at least 8 m.sup.2 /g, adding the ground aluminum trihydroxide to a sodium aluminate solution, and then decomposing the solution to precipitate aluminum trihydroxide having the required median diameter.

Abstract: Disclosed is a process for producing finely divided dispersions of metal oxides and/or metal hydroxides. A supersaturated sodium aluminate liquor containing dissolved aluminum hydroxide is seeded with particles of at least one metal oxide and/or metal hydroxide. The liquor is subjected to predetermined crystallization conditions to form a crystallized solid. The crystallized solid is then separated from the liquor and dried.

Abstract: Finely divided alumina, recovered from the dust recovery systems of alumina hydrate calcination facilities, is employed as seed for the precipitation of alumina hydrate from pregnant Bayer process liquors. The finely divided alumina dust can either be used as seed in as-is condition, or, if desired, agglomerated to coarse and strong particles prior to use as seed. Agglomeration is accomplished by combining the dust in a predetermined weight ratio with alumina trihydrate seed under controlled conditions. The process allows the utilization of an otherwise undesirable and unacceptable by-product of alumina hydrate calcination.

Abstract: The present invention relates to a method for producing a polyaluminium hydroxide complex of a chloride and sulphate type in solid form, an aqueous solution of the polyaluminium hydroxide complex being admixed with at least one water-miscible organic solvent having 1-4 C, the weight ratio of the aqueous solution to the solvent being at least 1:0.70, preferably 1:1-2, to crystallize the complex.The method provides a highly stable, amorphous crystalline product.

Abstract: A process is provided wherein metal granules coated with a polymerizable oil are heated, while being mechanically mixed, to a polymerizing temperature to convert the oil coating to a varnish and the varnish coating thereafter heated to a higher temperature to decompose at least partially the varnish to carbon, thereby producing a carbon coating strongly bonded to the metal granules. The temperatures employed are below the melting point of the metal granules. The coating is preferably applied to magnesium, aluminum or alloys thereof for use as addition agents in steel, e.g., desulfurizing or deoxidizing agents, and may contain fine particles of at least one calcium compound.

Abstract: A system for the precipitation of Al(OH).sub.3 from green liquor is provided which comprises process and apparatus for feeding the green liquor into the bottom of a chamber containing a supersaturated solution of alumina and Al(OH).sub.3 seed particles. The flow of green liquor into the bottom of the chamber is maintained at a rate sufficient to suspend the seed particles in the chamber with minimum turbulence so that the liquor is in approximately plug flow. As Al(OH).sub.3 precipitates on the seed particles, the particles grow larger and gradually move to the bottom of the chamber where they are removed. The solution, somewhat depleted with respect to Al.sub.2 O.sub.3, overflows the chamber to return to the process.

Abstract: In a gradient process of growing crystals from liquid media, the need for mechanical seed holders is eliminated in that a solvent is used which at the instantaneous temperature and under the instantaneous pressure employed in the growing process has a density which is equal or approximately equal to the density of the crystal or crystals which is or are being grown.

Abstract: Process for recovering coarsely crystalline alumina hydrate from bauxite according to the Bayer process wherein, in the presence of fine seed crystals, agglomerates are initially formed in a supersaturated sodium aluminate solution at 80.degree. to 65.degree. C. The agglomerates are then conducted through a first cascade of crystallizers and, after cooling to 55.degree. to 45.degree. C., through a second crystalizer cascade. A crystal suspension is extracted from the last crystallizer of the second crystallizer cascade and fractionated into fine seed crystals and coarse product crystals.

Abstract: An improved precipitation system is provided for the Bayer process production of alumina hydrate. In order to produce coarse and strong alumina hydrate at high yield, supersaturated Bayer process sodium aluminate liquor is seeded with a relatively small seed charge in a first precipitator at a relatively low temperature and the produced slurry is transferred to a second precipitator where without additional seeding, the solids content of the slurry is allowed to increase to about 250-700 g/l by accumulating solids in the line until the desired solids content is reached. After a suitable residence time, a coarse, strong product hydrate can be recovered in yields of or exceeding 80 g/l based on the alumina (Al.sub.2 O.sub.3) content of the supersaturated sodium aluminate liquor subjected to precipitation.

Abstract: Process for the preparation of high purity alumina containing less than 0.1 weight percent of residual chlorine starting from impure aluminum chloride solutions, which process comprises a crystallization step to provide aluminum chloride hexahydrate crystals having a diameter of from about 400 to about 4000 micrometers in the presence of hydrochloric acid; washing the aluminum chloride hexahydrate crystals so obtained with pure hydrochloric acid; and pyrohydrolyzing the washed crystals of aluminum chloride hexahydrate at a temperature of from about 700.degree. to about 1300.degree. C., in which pyrohydrolysis a gas is forced through a layer of the washed aluminum chloride hexahydrate so as to remove the gaseous reaction products while obviating any possible movement of the solid by the gas, the process particularly producing transition aluminas simultaneously having a specific surface area greater than 100 m.sup.2 /g and a chlorine content less than 0.1 weight percent.

Abstract: Oxide refractory materials (for example, alumina-zirconia mixtures) can be cast to have an extremely fine crystal structure by casting them onto a non-reactive, non-melting particulate solid cooling media of a material other than that of the oxide refractory material (for example, steel spheres having a size ranging from about 5 to about 60 mm). By using steel spheres as the cooling media, the spheres can be removed from the solidified material with a magnet. The solidified material, when crushed and graded, has exceptional utility as an extremely tough abrasive grain.

Abstract: Aqueous aluminum sulfate solution is hydrolyzed at temperatures above about 300.degree. C. to produce a basic aluminum sulfate product that is readily purified and converted to Al.sub.2 O.sub.3.

Abstract: Coarse grains of aluminum hydroxide having high resistance to disintegration to powder in a calcination step are continuously produced from a supersaturated sodium aluminate solution of the Bayer process through(1) a first precipitation step of adding recycle seed aluminum hydroxide to a supersaturated sodium aluminate solution having a molar ratio of Na.sub.2 O as caustic soda to Al.sub.2 O.sub.3 in solution of less than 1.8 supplied to a precipitation tank of substantially complete mixing type in a ratio of 30-150 kg of the recycle seed to 1 m.sup.3 of the solution, thereby partially decomposing the seed-added solution until the molar ratio of the solution reaches 2.0-2.4 while keeping the solution at 65.degree.-80.degree. C.

Abstract: Coarse grains of aluminum hydroxide are economically produced in a high yield from sodium aluminate solution by dividing supersaturated sodium aluminate solution being prepared by the Bayer process and having a molar ratio of Na.sub.2 O as caustic soda to Al.sub.2 O.sub.3 in solution of less than 1.8 into two streams, adding a portion of recycle seed aluminum hydroxide and fine grains of aluminum hydroxide as seed to one of the streams of sodium aluminate solution, partially decomposing the sodium aluminate solution until the molar ratio of the sodium solution reaches 1.8-2.6, adding to the resulting partially decomposed sodium aluminate slurry the other stream of sodium aluminate solution, which has been cooled to a temperature low enough to lower the temperature of the partially decomposed sodium aluminate slurry by at least 3.degree. C.