Comalco Aluminum Limited

Ian L Grayson

Pearson J Cresswell

Andrew H Smith

A process for recovery of valuable products from Bayer process red mud comprises the steps: (a) digesting red mud with sulphur dioxide in the presence of water to dissolve soda, alumina and silica therein; (b) heating the product of step (a), with or without prior removal of insolubles, to selectively precipitate silica, and removing solids including the precipitated silica, to produce a liquor containing soda and alumina; (c) causticizing the liquor to precipitate calcium sulphite; and (d) separating the precipitated calcium sulphite from the liquor to produce calcium sulphite and sodium aluminate solution as products. In a preferred embodiment calcium sulphite produced in step (c) is calcined to regenerate lime and sulphur dioxide for recycle to the liquor causticization and red mud digestion stages respectively, and sodium aluminate produced in step (d) is returned to the Bayer process.

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Burwood, Australia

Ian L Grayson