Zinc concentrate is a semi-processed intermediate product used in the production of zinc metal and zinc alloys, which is the result of a flotation process after the zinc ore has been mined and milled. The zinc ore contains 1-15% zinc whereas the concentrate typically contains approximately 55% zinc, 6.5% iron and 32% sulfur together with other elements at much lower levels.
By percentage, zinc concentrate normally contains zinc sulfide (80% to 85%), iron sulfide (7.0% to 12%), lead sulfide (3.0% to 5.0%) silica (2.5% to 3.5%), and cadmium sulfide (0.35% to 0.41%).
The zinc production process involves roasting the concentrate at approximately 950 °C. When the right temperature is reached oxidation of the zinc, iron and sulfur occurs. The sulfur can be collected and turned into commercial grade sulfuric acid (H2SO4).
The iron and zinc then oxidises, and having been reduced to a powdered form is diluted with sulfuric acid, neutralised, and then filtered to remove contaminants.
The refined solution is then electrolysed in a cell fitted with a lead anode and an aluminium cathode. In this process the zinc is deposited on the cathode from which it is later stripped off. It is then sent to a foundry where it takes its final form as either zinc metal (99.95% pure zinc), or zinc alloy together with copper, aluminium or magnesium. The zinc is cast into various forms, normally ingots or plates, with weights from 9 kg to 4 tons.
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