Zinc concentrate

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.