Production of Zinc From Sulfide Ore

More than 90% of the zinc production occurs from sulfide ores. Zinc metal is produced from ore concentrate by pyrometallurgical or electrolytic techniques. Nowadays the latter are dominant. Both methods, utilizing ore as raw material, constitute the primary processes, while methods working up zinc scrap are secondary. 

The concentrate of zinc ore is roasted at 900-1000°C, according to the reaction 2ZnS -I- 30, 2ZnO -i- 2SO, 

The roasting is often carried out in so-called fluidized beds, giving a very intimate contact between soHd partides and gas, which reduces the amount of air for the roasting to a minimum. The gas will be rich in SOj and suitable for recovery. Sulfides normally contain small amounts of mercury, arsenic, selenium and tellurium. To remove these toxic impurities, sophisticated methods have been developed. This has been necessary because of the risk that they would otherwise enter the food chain. 

About 80% of the world s production of zinc is based on electrolytic methods. The roasted concentrate is dissolved in sulfuric acid. Impurities such as Cu, Co and Cd are removed from the solution by adding zinc dust. The precipitation reactions are exemphfied by 

The purified solution is electrolyzed with lead anodes and aluminum cathodes. To use aluminum as cathode material is artful. As a result of the passive layer on the aluminum surface, the precipitated zinc has low adherence to the cathode and can be shaved off as sheets after the electrolysis. 

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