The most widely used industrial processes are: electrolytic and
it is very widespread and it requires concentrates with limited impurities. The process includes the following steps:
The roasting of the concentrates to oxidize sulfides in huge molds. Inside the catalysis towers the resulting sulfur dioxide is transformed into sulfuric acid, a very important by-product.
Stripping: the oxides obtained are attacked by a sulfuric solution, which dissolves Zinc, the other metals and all impurities.
Cleansing and electrolysis: this particular step separates the impurities and serves to recuperate all associated metals such as Cadmium. Zinc sulfide is sent to the electrolysis cells where aluminum cathodes and Lead anodes are immersed. Because of the flow of electrical current, Zinc is deposited on the cathodes where it is subsequently removed by a machine and melt into ingots with 99.995 percent purity.
The Thermal Process:
the process starts from the roasting of the concentrates as well, which are transformed into agglomerate oxides; this process gives them the necessary hardness to be utilized in blast surfaces of the Imperial Smelting type. This step allows for the recovery of the sulfuric acid. Inside the blast furnaces the Zinc oxides are reduced by the carbon monoxide produced by the combustion of the coke. Zinc reaches a higher temperature than its boiling point; it is thus carried by the fumes and captured by a rainfall of molten Lead. With the subsequent cooling and because of the difference in specific weight, a layer of Zinc separates from the Lead, thus the resulting metal is Zinc with more than 1 percent of impurities such as Pb and Cd.
The next thermal refining is carried out by the distilment of Zinc. Thanks to the different boiling points of the residual metals, it allows for the separation of Zinc from Lead and
Second Melting: the principal raw materials used are Mattes, Zinc Fine Ashes, Zinc Scraps, fabrication discards, cutouts and old Zinc sheets. Zinc Oxides, Zinc Powders and Zinc Ingots are obtained through thermal melting: ingots are mostly used in the production of brass and in the galvanising of steel.