each year in the fumes from processing galvanized scrap due to the severe separation problems involved with this waste arising. Zinc dusts and zinc oxides collected from smelting and refining fumes and zinc drosses produced zinc alloys are best recycled as pure zinc oxide or zinc dust or zinc chemicals. Zinc oxide is the most important zinc chemical, and is produced from zinc wastes by one of three process:
(i) Reduction of galvanisers ash with coke or anthracite in a rotating kiln (Waeltz kiln). The zinc vapour is oxidized at the lower end of the kiln and resulting zinc oxide collected from the fumes in a baghouse.
(ii) Melting metallic zinc scrap in a horizontal retort and the resulting zinc vapour oxidized to zinc oxide on contact with air.
(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).