Aluminum Company of America

Paul J The

Chanakya Misra

J Finley Bush

Alan Pearson

Thinnalur J Sivakumar

Fred S Williams

William A Nigro

Richard H Goheen

William V Felix

A process for producing aluminum hydroxide including the steps of:

Process for producing aluminum hydroxide of improved whiteness

A process for producing aluminum hydroxide product having an improved level of whiteness is disclosed. In the process, a caustic solution having dissolved aluminum hydroxide is subjected to purification to remove color producing humate material. Purification includes passing the caustic solution through a semi-permeable membrane. The solution purified of humate material is treated to precipitate aluminum hydroxide therefrom.

Bayer process for producing aluminum hydroxide having improved whiteness

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.

Process for lowering level of contaminants in Bayer liquor by membrane

A process for cleaning lime having undesirable levels of contaminants, particularly manganese oxide, is disclosed. The process includes leaching the contaminants from the lime with an aqueous means, preferably spent Bayer liquor, to form a slurry containing said impurities and cleaned lime. The cleaned lime is then removed from the slurry containing the contaminants.

Lime cleaning process to remove manganese oxide

Wet oxidation of organic contaminants in aqueous sodium aluminate solutions is enhanced when a heated and oxygenated solution is passed through a packed bed containing a metal packing member that is chemically inert to sodium aluminate solutions at elevated temperatures. Process temperature is about 180.degree.-300.degree. C. and oxygen partial pressure is at least about 345 kPa. The packed bed has a packing surface of at least 100 square meters per cubic meter bed volume and preferably at least 50% free space.

Lowering organic contaminant content in a sodium aluminate solution by

A process for the purification of spent liquor from an alumina precipitation stage is disclosed wherein the spent liquor is first contacted with 50 volume % or less ethanol to form a sodium oxalate precipitate and the, after removal of the sodium oxalate precipitate is contacted with over 50 volume % of ethanol extraction fluid to separate the mixture into a first layer comprising the ethanol and at least a portion of the caustic from the spent liquor and a second layer which comprises the remainder of the spent liquor. The spent liquor may then be subjected to a further precipitation to recover further alumina. The spent liquor remaining may be further treated in subsequent extraction steps to concentrate and dispose of undesirable impurities remaining.

Recovery of aluminum from spent liquor

A process for removing organic contaminants from a mineral ore such as bauxite. The ore is washed with an aqueous solution containing caustic soda, sodium carbonate or mixtures thereof in an amount up to about 80 g/l total alkali content (expressed as sodium carbonate equivalent). The ore is preferably washed at a temperature of about 95.degree. C. for about 5 hours with a solution containing about 20 g/l total alkali content. In a preferred embodiment, the ore is separated from a rinse solution containing degradation products of organic contaminants, and the washed ore is then dissolved in a caustic solution to produce Bayer process liquor. This process provides a means to reduce the organic carbon concentration in Bayer process liquor, with resultant increase in productivity of the Bayer process.

Removal of organic contaminants from bauxite and other ores

A process is disclosed which provides for the removal of sodium oxalate compounds from a Bayer-type process liquor, after prior precipitation of aluminum hydroxide, which comprises: treating the liquor with ethanol in an amount up to 50 vol. % of the liquor to form a first layer comprising the ethanol and at least a portion of the caustic in the liquor, and a second layer comprising the liquor; and filtering at least the liquor layer to recover a sodium oxalate precipitate. Preferably, the liquor is concentrated to provide a caustic concentration of at least 200 and, most preferably, about 250 grams per liter total caustic (measured as sodium carbonate).

Process for the removal of sodium oxalate compounds from Bayer spent

A Bayer process solution is filtered through a bed of particles of a granular substance containing Fe.sub.2 O.sub.3 to remove copper and zinc species from the solution. The particles preferably have an Fe.sub.2 O.sub.3 content of about 40 to 100% by weight. For more effective removal of zinc, the particles are coated with a metal sulfide, preferably zinc sulfide.

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Murrysville, PA, United States of America

Paul J The