GB868928A - Process for the manufacture of alumina enabling the use of the low blast-furnace - Google Patents

Abstract

Alumina is obtained from siliceous bauxite by heating said bauxite together with carbon and iron pyrites in a low blast furnace to which a blast of oxygenated air is admitted to maintain a zone at 1750-1850 DEG C. in the furnace, through which the charge passes to form a molten Al2O3-Al2S3 slag and a ferro silicon alloy, separating said slag from said alloy and hydrolysing the aluminium sulphide therein. The product is a mixture of crystalline and amorphous alumina. In the example, dilute hydrochloric acid was used for hydrolysis. If desired iron may be added to the charge to retain in the furnace sulphur liberated in the lower parts thereof. The bauxite may be presulphurised with sulphur-containing gases, e.g. hydrogen sulphide, by bringing the bauxite into contact in a separate plant with gases evolved from the furnace; thereafter the purified gases may be burnt and the combustion products used to preheat the furnace blast.ALSO:Ferrosilicon is produced inter alia in the production of alumina, by heating siliceous bauxite together with carbon and iron pyrites in a low blast furnace to which a blast of oxygenated air is admitted to maintain a zone at 1750-1850 DEG C. in the furnace, through which the charge passes to form a molten Al2O3-Al2S3 slag (which is separated for processing) and ferrosilicon. The blast preferably contains 50-70% by volume of oxygen. If desired iron may be added to the charge to retain in the furnace sulphur liberated in the lower parts thereof. The bauxite may be presulphurized with sulphur-containing gases, e.g. hydrogen sulphide, by bringing the bauxite into contact in a separate plant with gases evolved from the furnace; thereafter the purified gases may be burnt and the combustion products used to preheat the furnace blast.