Ammonia → Ammonium thiosulfate

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The present invention accomplishes its desired objects by broadly providing an improved process of preparing a metallic sulphate from mixing of the corresponding metallic sulphide concentrates with ammonium sulphate and heating the mixture to yield the metallic sulphate, evolved sulphur, sulphur dioxide, ammonia, and water. The improvement comprises heating the mixture by directly contacting the mixture with products of combustion of a heating fuel. The metallic sulphate may initially be added before heating to the mixture of the corresponding metallic sulphide and ammonium sulphate to inhibit the development of semi-fluid conditions in the reaction of the metallic sulphide concentrates with the ammonium sulphate. Heating may be done at a temperature between about 150° C. and 480° C., and a diluent gas may additionally be added to the products of combustion. A raw fuel gas may be also added above the mixture being heated and the volatile sulphur, sulphur dioxide and ammonia may be subsequently dissolved in water in an absorption tower to produce solutions of ammonium thiosulphate and ammonia hydroxide.

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