(iii) Dissolving impure zinc oxide wastes in acid followed by solution purification precipitation of zinc carbonate and calcinations to ZnO. Zinc sulphate is made solely from zinc residues low in chloride content by leaching with sulphuric acid. This is followed by solution purification and cementation precipitation of copper, nickel, and cadmium by addition of zinc dust. Manganese and iron are removed by oxidation and the resulting solution evaporated to yield the monohydrate (ZnSO4•H2O).