Choice and surface preparation of the cathode used for electrowinning of manganese metal

Abstract

A series of different materials as cathodes have been used to deposit Electrolytic Manganese Metal (EMM) from aqueous bath containing 100g/l manganese sulphate, 150g/l ammonium sulphate and 0.1 to 0.2 g/l SO2 in a diaphragm cell. National Metallurgical Laboratory in its bench scale as well as in 8kg/day, 16kg/day and 50kg/day EMM in the Manganese Pilot Plant has tried aluminium copper, ordinary steel, 17% chromium steel and 18.8 stainless steel sheet with 2% Mo as cathodes for the above purpose. It is found that it requires surface preparation for successful economic deposition. Ultimately 316 stainless steel with 18% Cr, 8% Ni and 2% Mo sheet is found to be the most suitable cathode material for electrolysis of manganese metal. Before introducing in the diaphragm cell it is well polished and alkaline cleaned and dried. The minute amount of silicate or silica or silica which remains on it does not inhibit the deposition bur greatly facilitates stripping. Moreover it has very good elasticity so that it can be flexed to a great extent in time of stripping. It is highly resistant to sulphuric acid-ammonium sulphate solution so that cathodes made of it can be treated in anolyte with no etching. It does not warp due to hammering and corrode by the spray above the solution level in the electrolytic cell.