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: The slurry subjected to aggregation processing by a line mixer is supplied to a slurry feed member via a slurry supply passage and then fed radially outward from slurry fed outlets within a sedimentation tank. Therefore, liquid flow hardly takes place below the slurry feed member and the settling velocity of the solid is increased. The slurry feed member is arranged close to the boundary face of the thickened slurry zone, and thus the settling distance of the solid is shortened. Accordingly, the residence time of the solid is shortened to a great extent. In addition, the sedimentation tank can be constructed to be sealed and solid-liquid separation can be also performed under the pressurized state.

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: An aqueous slurry of about 100-1000 centipoises viscosity suspending about 200-2000 g/l of aluminum hydroxide particles smaller than 5 .mu.m is spray-dried, and the dried powders are calcined to obtain alumina powders. The alumina powders have a sharp particle size distribution, being suitable for electronic, abrasive and refractory applications.

Abstract: In the production of alumina from aluminous ores containing alumina trihydrate and alumina monohydrate comprising a first-stage digestion by digesting alumina trihydrate from a slurry of the ores and a caustic solution and separating the resulting slurry into a caustic aluminate solution and an insoluble residue, and a second-stage digestion by digesting alumina monohydrate from a slurry of the insoluble residue separated in the first-stage digestion and a caustic solution, the present invention provides an improvement wherein scale formation onto a preheater for the slurry in the second-stage digestion is completely or substantially prevented and reduction in heat transfer coefficient of heat transfer surface is remarkably lowered. The improvement is attained by setting up a desilication reaction zone in the course of the first-stage digestion, whereby the slurry introduced into said zone is subjected to desilication reaction treatment.

Abstract: A highly efficient process for producing metallic gallium from a gallium containing alkali aluminate solution circulating in the Bayer process is disclosed. The process comprises subjecting an alkali aluminate solution to electrolysis, said solution being obtained by (1) cooling an alkali aluminate solution after the aluminum hydroxide separation step in the Bayer process in the presence or absence of at least one, as a seed, alkali salt of an element selected from vanadium and phosphorus, or complexes containing the alkali salt, in order to precipitate crystals of impurities containing vanadium, phosphorus, etc.

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.

Abstract: Impurities such as organic substances, i.e. sodium oxalate and inorganic impurities, i.e.

Abstract: A process for the removal of sulfur oxides from exhaust gases by absorbing with a slurry of red mud containing calcium ion which comprises the steps of:(1) contacting an exhaust gas containing sulfur oxides of not higher than about 100.degree. C. with a slurry of red mud containing calcium ion led from the next step (2) to take up sulfur oxides in the gas until pH of the slurry becomes in the range of 4.3 to less than 6 while maintaining the molar fraction of SO.sub.4.sup.-- to total SO.sub.2 in the slurry within the said pH range at 0.05 to 0.7; and then,(2) contacting the treated gas with a fresh slurry of red mud containing calcium ion to further take up sulfur oxides in the gas while maintaining the concentration of NaHSO.sub.3 in the slurry at not more than about 8 g/l.

Abstract: In the production of alumina from bauxite by the Bayer process, the present invention provides an improvement for effectively and economically removing organic substances from a circulating alkali aluminate solution by contacting the aluminate solution containing organic substances with molecular oxygen gas or a molecular oxygen-containing gas in the presence of copper ions as a catalyst at an elevated temperature, thereby oxidizing the organic substances, adding a chemical substance to the resulting aluminate solution which reacts with copper ions to deposit a water-insoluble precipitate, and separating the precipitate from the solution, and recycling the precipitate as a copper source to the above-mentioned wet oxidation procedure.

Abstract: In the production of alumina from aluminous ores by the Bayer process, the present invention provides an improvement for effectively and economically recovering caustic components consisting essentially of sodium aluminate from aluminum hydroxide cakes as seed classified from the product aluminum hydroxide by washing the seed with a washing liquor having a substantially saturated concentration of sodium oxalate and little content of caustic and then removing organic substances such as sodium oxalate from the washed seed by secondly washing said seed with hot water, thereby recovering caustic components without the dissolution of sodium oxalate from the seed into the recovered caustic solution and attaining the removal of sodium oxalate contaminant with high efficiency.

Abstract: In a process for extracting alumina from alumina-containing ores on a two-stream system by individually preheating a slurry of alumina-containing ores and an aqueous alkali solution each in preheaters of indirectly heating, mixing the preheated slurry with the preheated aqueous alkali solution, and extracting alumina from the ores in a digester of either the heating type involving the direct injection of live steam or the heat-insulated type, the alumina is extracted from the ores by preparing the slurry of alumina-containing ores with water or a diluted aqueous alkali solution, such as from the drain obtained by recovering steam from an evaporator for cooling the slurry resulting from extraction, and utilizing the recovered steam in preheating the slurry of the alumina-containing ores or decomposition solution or both, preheating the slurry of alumina-containing ores, and mixing the preheated slurry with an aqueous alkali solution preheated as another stream as the decomposition solution.