Abstract: An improved process for preparing a metallic sulphate in a reaction zone from mixing of the corresponding metallic sulphide concentrates with ammonium sulphate and heating. Heating preferably includes directly contacting the mixture with products of combustion of a heating fuel at temperatures between about 150.degree. C and about 480.degree. C. The products of combustion may be diluted with a gas, and the metallic sulphate of the corresponding metallic sulphide may be initially mixed with the mixture to inhibit the development of semi-fluid conditions in the reaction of the metallic sulphide concentrates with ammonium sulphate.