IMPROVEMENTS IN ALUMINA PLANTS

摘要

A process for the production of alumina by the Bayer process includes a precipitation process having an agglomeration stage and a growth stage. In the agglomeration stage, selected process parameters are controlled to limit the bound soda content of the slurry, whilst still maintaining conditions for high yield. In the growth stage, selected process parameters are controlled to controll the soda pick-up during growth so that a continuous decrease of soda content is obtained. Preferably, the growth stage is divided into a number of separate precipitation vessels and the temperature drop from one precipitator to the next is from 1 to 3 DEG C. The temperature of the liquor leaving the final precipitator is preferably about 55 DEG C. The agglomeration stage is preferably operated at 75 - 85 DEG C. Apparatus suitable for use in the method is also described.