 Mining and processing
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| There are zinc mines throughout the world, with the largest producers being China, Australia and Peru. In 2005, China produced almost one-fourth of the global zinc output, reports the British Geological Survey. Mines and refineries in Europe
include Umicore in Belgium, Tara, Galmoy and Lisheen in Ireland, and Zinkgruvan in Sweden. Zinc metal is produced using extractive metallurgy. Zinc sulfide (sphalerite) minerals are concentrated using the froth
flotation method and then usually roasted using pyrometallurgy to oxidise the zinc sulfide to zinc oxide. The zinc oxide is
leached in several stages of increasingly stronger sulfuric acid (H2SO4). Iron is usually rejected as Jarosite or goethite, removing other impurities at the same time. The final purification uses zinc
dust to remove copper, cadmium and cobalt. The metal is then extracted from the solution by electrowinning as cathodic deposits. Zinc cathodes can be directly cast or alloyed with aluminium.
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| Electrolyte solutions must be very pure for electrowinning to be at all efficient. Impurities can change the decomposition
voltage enough to where the electrolysis cell produces largely hydrogen gas rather than zinc metal.
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| There are two common processes for electrowinning the metal, the low current density process, and the Tainton high current
density process. The former uses a 10% sulfuric acid solution as the electolyte, with current density of 270-325 amperes per
square meter. The latter uses 22-28% sulfuric acid solution as the electrolyte with current density of about 1000 amperes
per square meter. The latter gives better purity and has higher production capacity per volume of electrolyte, but has the
disadvantage of running hotter and being more corrosive to the vessel in which it is done. In either of the electrolytic processes,
each metric ton of zinc production expends about 3900 kWh (14 MJ) of electric power
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| There are also several pyrometallurgical processes that reduce zinc oxide using carbon, then distill the metallic zinc from the resulting mix in an atmosphere of carbon monoxide. These include the Belgian-type
horizontal-retort process, the New Jersey Zinc continuous vertical-retort process, and the St. Joseph Lead Company's electrothermal
process. The Belgian process requires redistillation to remove impurities of lead, cadmium, iron, copper, and arsenic. The New Jersey process employs a fractionating column, which is absent in the Belgian process, that separates the individual
impurities, where they can be sold as byproducts. The St. Joseph Lead Company process heats the zinc oxide/coke mixture by
passing an electric current through it rather than by coal or gas fire.
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| Another pyrometallurgical process is flash smelting. Then zinc oxide is obtained, usually producing zinc of lesser quality
than the hydrometallurgical process. Zinc oxide treatment has much fewer applications, but high grade deposits have been successful
in producing zinc from zinc oxides and zinc carbonates using hydrometallurgy.
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