GB203798A - Method of manufacture of alumina from sulphate of aluminium - Google Patents

Abstract

Alumina is obtained in a form soluble in acids by heating crude aluminium sulphate with solid, liquid or gaseous reducing agents to a dark red heat. Sulphuretted hydrogen sulphur dioxide and sulphur are among the products. When sulphuretted hydrogen is employed as the reducing agent sulphur is liberated in considerable quantity. Sulphur may be used as a solid reducing agent in conjunction with reducing gases and the issuing gases containing sulphuretted hydrogen can be again used for reduction of a new charge. The aluminium sulphate may be heated in hydrogen at 500 DEG C. in an externally-heated oven. The charge is preferably moved in counter current against the hydrogen. Or the charge may be internally heated by admitting oxygen, air, chlorine or the like to the hydrogen, but not in such amount as to destroy the reducing character of the gases. Or the sulphate may be conveyed upwards in an upright channel containing pipes of ferrosilicon or of iron coated with silica or of a metal not attacked by sulphuretted hydrogen while a stream of a mixture of hydrogen, sulphuretted hydrogen, and nitrogen which have been pre-heated in the tubes is passed downwards against the sulphate. Air is admitted at the top where the alumina leaves. A revolving furnace can also be employed and if required a pressure different from atmospheric pressure may be used. The heating of the sulphate in hydrogen may be effected in presence of chlorine, or hydrochloric acid to cause the volatilization of the iron as chloride. Specification 895/79 is referred to.ALSO:Alumina is obtained in a form soluble in acids by treating crude aluminium sulphate with solid liquid or gaseous reducing agents to a dark red heat. Sulphuretted hydrogen sulphur oxide and sulphur are among the products. When sulphuretted hydrogen is employed as the reducing agent, sulphur is liberated in considerable quantity. Sulphur may be used as a solid reducing agent in conjunction with reducing gases, and the issuing gases containing sulphuretted hydrogen can be again used for reduction of a new charge. The iron may be removed by treating the product with dilute acids. The aluminium sulphate may be made by calcining kaolin at 800 DEG C., adding sulphuric acid, heating to render silica insoluble, leaching, and crystallizing or evaporating to dryness. The aluminium sulphate may be heated in hydrogen at 500 DEG C. in an externally-heated oven. The charge is preferably moved in counter-current against the hydrogen. Or the charge may be internally heated by admitting oxygen, air, chlorine, or the like to the hydrogen, but not in such amount as to destroy the reducing character of the gases. Or the sulphate may be conveyed upwards in an upright channel containing pipes of ferrosilicon or of iron coated with silica or of a metal not attacked by sulphuretted hydrogen while a stream of a mixture of hydrogen, sulphuretted hydrogen, and nitrogen which have been pre-heated in the tubes, is passed downwards against the sulphate. Air is admitted at the top where the alumina leaves. A revolving furnace can also be employed, and if required, a pressure different from atmospheric pressure may be used. The iron in the product may be removed by weak acid or by a solution of iron or aluminium chloride or by heating with chlorine, sulphur chloride, carbon chloride, or the like. Or the iron can be converted into sulphide by means of sulphur or sulphuretted hydrogen and then removed by acids. The heating of the sulphate in hydrogen may be effected in presence of chlorine or hydrochloric acid to cause the volatilization of the iron as chloride. Specification 895/79 is referred to.