Zinc Production
Zinc Production
Zinc is recovered from Cu-Pb-Zn polymetallic ores with 1-4% zinc as sulphides with silver, gold, cadmium and bismuth in them, with subsequent concentration using the froth flotation method, during which the concentrates with 50-60% zinc are also enriched by lead, copper and, sometimes, by pyrites, and then usually roasted in boiling bed to oxidize the zinc sulfide to zinc oxide. Sulfur dioxide gas, SO2, evolved during the process is utilized for sulphuric acid production. There are two ways for recovering zinc from ZnO. The first way consists of several pyrometallurgical processes that reduce zinc oxide sintering of the roasted concentrate for granulity and gas permeabilty and then distilling the metallic zinc from the resulting mix reducing using carbon (coke) at 1200-1300°C:
ZnO + C = Zn + CO
The distilled zinc is purified in segregation process during which the iron and lead impurities are separated, and 98.7% purity is achieved. More complex and expensive rectification methods may allow obtaining 99,995% of purity.
Electrolysis is the most common solution, during which the roasted concentrates are treated by sulphuric acid. Electrolysis of the obtained sulphates solution in tanks leaded or viniplasted inside is the following step. The purity of 99.95% is common for electrolytic method.