GB693612A - Improvements in process for improving slags and dross - Google Patents

Abstract

In order to facilitate the extraction of alumina from slags, an agent is added, in powdered, granular, liquid or gaseous state, to alter the composition of the slag under such conditions that the mass remains molten, cooling being effected slowly. The additional agent may be preheated in order to assist in maintaining the molten condition of the mass, or may be combustible or of such a composition as to combine with one or other of the constituents of the slag or of the other added agents to produce an exothermic reaction; such substances comprise calcium sulphide, iron sulphide, calcium carbide, silicon, aluminium, magnesium, carbon, hydrogen, and hydrocarbons. Air or oxygenated air can be blown through the molten mass to combine with any sulphur present as calcium sulphide, the air and the evolved sulphur dioxide aiding in causing complete mixing. To ensure complete mixing of the mass and so to facilitate the reactions, manganese, titanium, sodium, potassium, barium, or calcium, or their oxides, sulphides, or halides can be added. In a slag comprising alumina, lime and silica, ferrous oxide is added to combine with any free silica or to displace it from combination with alumina and lime and so reduce the amount of insoluble silico-aluminates present; the ferrous oxide may be added in the form of rolling-mill scale. Iron pyrites may be added instead of ferrous oxide so that, by blowing, oxidation is effected and additional heat produced. Gypsum may be employed in conjunction with the pyrites as an oxidizing agent. If a self-pulverizing product is desired, the percentage of ferrous oxide added is less than four times the ratio between the lime and silica.ALSO:In order to facilitate the extraction of alumina from slags, an agent is added, in powdered, granular, liquid or gaseous state, to alter the composition of the slag under such conditions that the mass remains molten, cooling being effected slowly. The additional agent may be preheated in order to assist in maintaining the molten condition of the mass, or may be combustible or of such a composition as to combine with one or other of the constituents of the slag or of the other added agents to produce an exothermic reaction; such substances comprise calcium sulphide, iron sulphide, calcium carbide, silicon, aluminium, magnesium, carbon, hydrogen, and hydrocarbons. Air or oxygenated air can be blown through the molten mass to combine with any sulphur present as calcium sulphide, the air and the evolved sulphur dioxide aiding in causing complete mixing. To ensure complete mixing of the mass and so to facilitate the reactions, manganese, titanium, sodium, potassium, barium, or calcium, or their oxides, sulphides, or halides can be added. In a slag comprising alumina, lime, and silica, ferrous oxide is added to combine with any free silica or to displace it from combination with alumina and lime and so reduce the amount of insoluble silico-aluminates present; the ferrous oxide may be added in the form of rolling-mill scale. Iron pyrites may be added instead of ferrous oxide, so that, by blowing, oxidation is effected and additional heat produced. Gypsum may be employed in conjunction with the pyrites as an oxidizing agent. If a self-pulverizing product is desired, the percentage of ferrous oxide added is less than four times the ratio between the lime and silica.