GB580987A - Improvement in and relating to the recovery and utilization of tin - Google Patents

Abstract

Metallic tin is extracted from ores containing cassiterite (stannic oxide) or from sulphide ores, by the electrolysis, after purification, of a solution of alkali metal stannates or thiostannates formed by the fusion of the ore with caustic alkalies. After fusion, with preliminary roasting if necessary to remove sulphides, the ore is disintegrated and freed from excess alkali, which is subsequently re-used, by washing with water. A second wash with water recovers most of the stannates in solution together with a large number of other metallic impurities which are precipitated, either hot or cold, by addition of hydrogen sulphide or solution of sodium or potassium sulphides, any soluble polysulphides being destroyed if necessary by the addition of a sulphite. The tin is precipitated as stannic acid by treatment of the hot solution with carbon dioxide or sodium bicarbonate solution and washed to remove carbonates, whilst the residual carbonate solution is treated with lime to precipitate siliceous impurities and recover the caustic alkali for re-use in the fusion. The stannic acid is then dissolved in caustic electrolyte from the cell to maintain the stannate concentration in the bath, iron anodes being used. The Specification also refers to the use of mixtures of sodium and potassium salts, and to the use of potassium stannate and hydroxide in the cell and sodium hydroxide in the preliminary fusion. In processes for use with tin-sulphide ores, the sulphide may either be fused with caustic alkali to produce thiostannate, the pure tin sulphide being precipitated by carbon dioxide and redissolved, or the sulphur may be removed as already stated, by roasting, and the material thereafter treated to produce stannic acid. Chemical equations and figures of temperatures, efficiencies &c. are given in the Specification.