Patent ID: 6827923
Filing Date: 2004-12-07
Classification: C01F,C01P,C09C

Abstract:
A process for the production of aluminium hydroxide of high whiteness, comprising the steps of(i) heating aluminium hydroxide obtained from the Bayer process having an average particle size of 20 to 200 &mgr;m to a temperature of 300 to 700Â° C. to form activated aluminum hydroxide; (ii) dissolving the soluble fraction of the activated aluminium hydroxide at 85 to 275Â° C. in an aqueous solution containing sodium hydroxide to form a sodium aluminate liquor having a molar ratio of Na2O:Al2O3 of 1.40 to 2.4 and containing an undissolved residue of very fine boehmite; (iii) filtering said sodium aluminate liquor to obtain a clear solution of sodium aluminate supersaturated with respect to dissolved alumina; (iv) cooling said clear solution of sodium aluminate to 50 to 80Â° C., and seeding with previously crystallized aluminium hydroxide to induce further crystallization and keeping at 50 to 80Â° C. for a period of time sufficient to achieve crystallization of a substantial amount of aluminium hydroxide; and (v) separating, washing and drying the produced aluminium hydroxide crystals.