GB440486A - Improved manufacture of pure alumina - Google Patents

Abstract

Siliceous aluminiferous materials such as clay, kaolin, or leucite are treated with sulphurous acid, the solution obtained is decomposed by heating, preferably by means of steam, the raw alumina thus precipitated is desulphurized by calcination at a temperature below 900 DEG C., say at 450--550 DEG C., and then brought into solution as aluminate by soda lye, the aluminate solution being decomposed to obtain pure alumina. If dilute solutions of aluminium sulphite are used, their decomposition by means of steam together with prolonged boiling of the solution gives a raw alumina containing very little sulphur, and the calcination step may advantageously be carried out in the presence of inert or reducing gases, for instance in a current of hydrogen. Residual sulphur compounds may be removed by alkaline agents before the treatment with soda lye. The Specification as open to inspection under Sect. 91 comprises also the following subject-matter. The raw alumina need not be calcined, but may be boiled in a solution of sodium or calcium chloride to remove sulphur, and residual sulphur be removed by caustic lime, soda, or ammonia; and decomposition of the sulphite p solution may be effected at 75--95 DEG C., when the raw alumina is to be calcined, and the calcined alumina may be dissolved in weak aluminate lye at 20--50 DEG C., preferably with admission of air. This subject-matter does not appear in the Specification as accepted.