METHOD FOR PRODUCING ALUMINA FROM LOW GRADE ALUMINIUM-CONTAINING RAW MATERIAL

摘要

The invention relates to metallurgy, in particular, acid methods for producing alumina, and can be used for processing a low grade aluminium-containing raw material. The method for producing alumina comprises treating aluminium-containing raw material with hydrochloric acid forming chloride slurry, separating the slurry and recovering a chloride solution, salting out of aluminium chloride hexahydrate from the chloride solution using calcium chloride, and thermal decomposition of the aluminium chloride hexahydrate thus producing alumina. In order to improve the quality of alumina and to reduce energy consumption, the chloride slurry is neutralised using calcium oxide to a pH of 1.6-2.2, and following the salting out of aluminium chloride hexahydrate, the mother liquor is evaporated stepwise during which process alkali metal chlorides are selectively crystallized and calcium chloride is recovered in the form of crystals and/or a concentrated aqueous solution, whereby part of the calcium chloride is recycled into the salting out of aluminium chloride hexahydrate.