GB697283A - Improvements in processes for the manufacture of alumina - Google Patents

Abstract

Material intended for the extraction of alumina by concentrated alkaline lyes is produced by introducing ferrous or ferroso-ferric oxide into a siliceous aluminous starting material, e.g. bauxite, in quantity at least sufficient to fix, as a product insoluble under extraction conditions, the silica which would otherwise combine with the alumina or the base metal of the alkaline lyes, and calcining at a temperature sufficient to ensure the combination of the silica and the said oxide. Alternatively, in the preparation of material intended for the extraction of alumina by water or dilute alkaline lyes, ferrous or ferroso-ferric oxide is added to a siliceous aluminous material, e.g. schist, clay, clinkers or slag, which either contains lime or to which lime, say as calcium carbonate, is added, in amount indicated above, allowing also for the silica which would otherwise combine with the lime, and calcining as before, e.g. at 1300-1400 DEG C in a neutral atmosphere. Material capable of forming ferrous or ferroso-ferric oxide in situ, e.g. ferric oxide, or alkali metal or alkaline earth metal ferrite, may alternatively be used, especially when the aluminous materials treated contain reducing agents, e.g. sulphides present in the slag. The iron oxides, whether simple or compound, may be added to the aluminous material in a state of fusion, e.g. slag as discharged from iron blast furnaces.