GB640352A - Improvements in or relating to a method of recovering tin and the product resulting therefrom - Google Patents

Abstract

Tin is extracted from tin ores, wastes, stannic oxide, &c. by reducing the ore &c. to convert the tin into a form capable of reacting with an alkali metal hydroxide solution, and thereupon treating with the solution at a temperature of 75 DEG C. to the boiling-point to form sodium, potassium or lithium stannate without simultaneously dissolving substantial amounts of impurities. Reduction of the ore may be effected with carbon, coal, coke, lamp-black, carbon monoxide, natural gas, hydrogen, &c. at say, 760-1090 DEG C., avoiding appreciable fusion. High grade ores containing, say, 35-40 per cent tin may be first mixed with inert material such as the spent residues of the later leaching operation. If excessive sulphur is present, this may be partially or wholly removed by a previous roast. The reduced ore may be cooled in a non-oxidizing atmosphere. One mol. oxidizing agent, e.g. an alkali metal nitrate, nitrite, peroxide, hypochlorite, hydrogen peroxide, &c. may be used with 5-7 mols. alkali metal hydroxide used for the treatment of the ore, which may be such as to produce a liquid extract directly; alternatively a solid mass comprising alkali metal stannate crystals, to be subsequently extracted, may be produced. Tin may be recovered from the crystallized stannate by electrolysis, or from the oxide precipitated from a solution of the stannate. Specification 324,685 is referred to.