Process of recovering valuable components from red mud

摘要

Red mud, obtained by alkali treatment of bauxite, is treated to recover its constituents in a process which comprises slurrying the mud in water, passing in sulphur dioxide until the pH of the slurry is 3.5-6, separating the insoluble residue from the liquid, which contains the sodium values in the form of the bisulphite with possibly a little sulphite, suspending the residue in water and passing in sulphur dioxide until the pH is 1.5-2.3, separating the liquid from the insoluble residue, which is rich in iron and titanium oxides, heating the solution to drive off some of the sulphur dioxide until the pH is 2.5-3.0, thereby precipitating silica which is separated and recovered, and further heating the remaining solution to drive off more sulphur dioxide until the pH is above 3.5, to precipitate basic aluminium bisulphite, which is separated, dried, and calcined at 500-700 DEG C. to give alumina. The remaining solution may be added to a further portion of the initial red mud slurry. The evolved sulphur dioxide may be similarly recycled.