Recovery of Zinc from Dross

Abstract

During galvanising of iron and steel articles, there is some direct solution of iron in the molten zinc while iron salts adhering to the metal surface are reduced by the molten zinc, with the liberation of iron, which then forms an alloy with zinc. Such an alloy of iron and zinc containing entrapped zinc is called dross and sinks to the bottom of the galvanising bath. In general experience, for every 100 tons of zinc consumed, about 24 tons form dross. During contact with the Posts and Telegraphs Department, Government of India, concerning aluminising, it was reported by them that about 35 percent of the quantity of zinc consumed there in galvanising telegraphic stories is lost as dross which fetches only 60% of the price of virgin zinc. With zinc at Rs.1100/- per ton and dross at Rs.140/- nearly. The possibility of recovering zinc from galvanising dross were explored in the National Metallurgical Laboratory with special reference to this report by Posts and Telegraphs Department. It is obvious that the cost of recovery of zinc from dross should not exceed the monetary loss incurred in direct disposal of dross, otherwise generally contains about 96 percent zinc, one third of which is present in its elementary form. The shortage of zinc in India emphasises the need to recover zinc from dross.