Zinc sulphate is recovered from solutions containing zinc and magnesium sulphates by adding powdered calcium carbonate and heating the solution to 65-95 DEG C. to precipitate zinc as basic carbonate, which precipitate is removed and dissolved in sulphuric acid to produce zinc sulphate solution free from magnesium sulphate the initial sulphate solution may be obtained from sulphuric acid solutions of effluent muds containing zinc and magnesium hydroxide and calcium sulphate, produced by treating spent liquid from viscose coagulating and hot stretching baths with lime, according to an example, an effluent mud was treated with spent hot stretching bath acid containing sulphuric acid and zinc sulphate. Ferrous iron was oxidized with chlorine, sodium hypochlorite or diebromate and the ferric iron precipitated with powdered chalk. The resulting slurry of calcium sulphate containing zinc and magnesium sulphates in solution was filtered and the solution reacted with powdered chalk at 80-95 DEG C. while passing steam into the liquid. The basic zinc carbonate precipitate was separated and treated with sulphuric acid such as that obtained as canal liquor. The solution of zinc sulphate was filtered from the residue. Specifications 467,500 [Group IV] and 678,462 are referred to.
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