Production of alumina

Claim 1

A process for extraction of alumina and soda from bauxite having a high silica content, which includes the steps: (a) grinding the bauxite, and mixing the ground bauxite with a sodium aluminate liquor; (b) digesting the mixture of step (a) at elevated temperature and pressure; (c) separating red mud solids as slurry or filter cake, containing sodium aluminosilicates, from the liquor product of step (b); (d) mixing the separted red mud solids with a strong caustic soda solution the soda concentration in the reactng mixture being in the range 9 to 20% Na 2 O, and the caustic to alumina ratio being greater than 4 with sufficient lime to achieve a stoichiometric ratio with respect to the silica in the mud in the range of 1.8 to 2.2; (e) digesting the product of step (d) at a temperature in the range of 260° to 320° C. and under pressure of 4 to 9 MPa to dissolve soda and alumina values; the amount of caustic solution used in step (d) being such that the final A/C, of the digested liquor product of step (e) is in the range of 0.15 to 0.2.