A process for crystallising out impurities from Bayer process liquors.

摘要

The present invention relates to a process for the removal by crystallisation of crystallisable impurities from the liquors produced during the production of alumina from bauxite using the Bayer process. The process comprises evaporating in the absence of the simultaneous addition of steam some of the water present in the liquor until the concentration of sodium hydroxide therein is equivalent to from 350 to 600 g/l expressed as Na2CO3, and holding the evaporated liquor at a temperature and for a time sufficient to allow a significant proportion of the crystallisable impurities to crystallise out, wherein there is added during the process an amount of a synthetic flocculant sufficient to assist in the crystallising morphology of at least some of the crystallisable impurities in the liquor.