A process for the preparation of aluminium hydroxide with improved white color

摘要

Aluminium hydroxide of high whiteness is produced by (i) heating aluminium hydroxide obtained from the Bayer process to a temperature of 300 to 700 °C, (ii) dissolving the soluble fraction of the thus obtained activated product at 85 to 275 °C in aqueous sodium hydroxide to form a sodium aluminate liquor 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 to 50 to 80 °C and seeding with crystallized aluminium hydroxide to induce further crystallization, and (v) separating, washing and drying the produced aluminium hydroxide crystals.