Method for the removal of iron from sodium aluminate liquors resulting from alkaline attack on alumina-monohydrate-containing bauxite

摘要

A process for eliminating iron from supersaturated sodium aluminate solutions obtained from the alkaline attack according to the Bayer process of the monohydrate bauxite including successively the steps of grinding and eventually of desilicatation in the presence of an aliquot of decomposed liquor, then attack at a temperature higher than 200 DEG C., usually between 240 DEG and 270 DEG C., of the said crushed and eventually desilicatated bauxite by the remaining fraction of the decomposed liquor, to make the alumina hydrate soluble and to form at the end of the attack an insoluble suspension of the residue or red mud in the supersaturated sodium aluminate liquor which, after cooling and dilution, is decanted to separate the mud or insoluble residues from the supersaturated liquor destined to be decomposed in the presence of seeds after filtration, characterized by the fact that at the end of the attack, during the cooling of the suspension achieved by decreasing the pressure in the reactors, one injects in the said suspension at a temperature higher than 140 DEG C. a small quantity of a mixture containing calcium.