GB141688A - Improvements in the electrolytic treatment of ores containing zinc and other metals - Google Patents

Abstract

A precipitate obtained by adding zinc dust, with or without a copper salt, to sulphate solutions prepared from ores containing zinc and cadmium, with or without copper and cobalt, is treated for the recovery of cadmium, zinc, and, if present, copper, in the following manner. If substantially free from cobalt, the precipitate is oxidized and leached with sufficient dilute sulphuric acid to dissolve a maximum of zinc and cadmium and a minimum of copper. From the residue the copper is recovered by smelting or otherwise. Alternatively, the precipitate, oxidation of which is guarded against, may be leached with sufficient acid to dissolve the zinc, the residue being then oxidized and further treated to dissolve the cadmium. In either case, the solution containing the cadmium is treated with zinc dust in quantity insufficient for complete precipitation of the cadmium, which is thus obtained free from zinc. In this treatment, the solution should be slightly acid and air should be excluded as much as possible; about 1/2 gr. of cadmium per litre should remain after precipitation. A further treatment of the solution in a second vat with excess of zinc, and preferably in the presence of about 1/2 gr. of copper per litre, gives a zinc solution which is added to the purified ore solution, and a precipitate which can be used again in the first vat. The precipitated cadmium is roasted and dissolved in dilute sulphuric acid or spent electrolyte. Copper is removed by excess of the cadmium precipitate, metallic cadmium, or cadmium oxide, and the solution, then containing about 100 gr. cadmium per litre, is electrolyzed. After electrolysis, the solution should contain 60 gr. of acid per litre. An alternative method of separating the zinc from the cadmium consists in agitating the solution with zinc oxide or hydrate at 60 DEG C. for some time, and then cooling to 35 DEG C. so as to precipitate the zinc as basic sulphate. When the original precipitate contains cobalt, it is oxidized and leached with zinc sulphate solution or just sufficient dilute sulphuric acid to dissolve out most of the cadmium and cobalt, and the residue is then treated as in the first case. The solution of cadmium and cobalt is treated with zinc dust as described above so as to obtain zinc-free cadmium, which is added to that obtained from the residue above mentioned, and a solution of zinc and cobalt, from which a pigment may be prepared, for instance by adding sodium carbonate and drying and heating the precipitate.