PRECIPITATION OF GIBBSITE FROM A BAYER LIQUOR

摘要

A Bayer liquor is produced by dissolving bauxite in hot caustic soda. The liquor is cooled so that it is supersaturated, and seed crystals of gibbsite are added to the liquor (16). At the same time at least part of the liquor is subjected to intense ultrasonic irradiation (34) such as to cause cavitation, preferably by passing liquor and seed crystals (28) through a recirculation duct (30). The ultrasound increases the proportion of fines by breaking up any crystal agglomerates and also by generating crystal nuclei, and also removes fouling from crystal surfaces. The precipitation process is consequently more effective. If ultrasound is applied when measurements indicate that there are insufficient fines in the liquor, this improves the consistency of the precipitation process.