was shown to have zinc in its active site. The digestive enzyme carboxypeptidase became the second known zinc-containing enzyme in 1955. Production Mining and processing Zinc is the fourth most common metal in use, trailing only iron, aluminium, and copper with an annual production of about 13 million tonnes. The world's largest zinc producer is Nyrstar, a merger of the Australian OZ Minerals and the Belgian Umicore. About 70% of the world's zinc originates from mining, while the remaining 30% comes from recycling secondary zinc. Commercially pure zinc is known as Special High Grade, often abbreviated SHG, and is 99.995% pure. Worldwide, 95% of new zinc is mined from sulfidic ore deposits, in which sphalerite (ZnS) is nearly always mixed with the sulfides of copper, lead and iron. Zinc mines are scattered throughout the world, with the main areas being China, Australia, and Peru. China produced 38% of the global zinc output in 2014. Zinc metal is produced using extractive metallurgy. The ore is finely ground, then put through froth flotation to separate minerals from gangue (on the property of hydrophobicity), to get a zinc sulfide ore concentrate consisting of about 50% zinc, 32% sulfur, 13% iron, and 5% . Roasting converts the zinc sulfide concentrate to zinc oxide: 2ZnS + 3O2 ->[t^o] 2ZnO + 2SO2 The sulfur dioxide is used for the production of sulfuric acid, which is necessary for the leaching process. If deposits of zinc carbonate, zinc silicate, or zinc-spinel (like the Skorpion Deposit in Namibia) are used for zinc production, the roasting can be omitted. For further processing two basic methods are used: pyrometallurgy or electrowinning. Pyrometallurgy reduces zinc oxide with carbon or carbon monoxide at into the metal, which is distilled as zinc vapor to separate it from other metals, which are not volatile at those temperatures. The zinc vapor is collected in a condenser. The equations below describe this process: ZnO + C ->[950^oC] Zn + CO ZnO + CO ->[950^oC] Zn + CO2 In electrowinning, zinc is leached from the ore concentrate by sulfuric acid and impurities are precipitated: ZnO + H2SO4 -> ZnSO4 + H2O Finally, the zinc is reduced by electrolysis. 2ZnSO4 + 2H2O -> 2Zn + O2 + 2H2SO4 The sulfuric acid is regenerated and recycled to the leaching step. When galvanised feedstock is fed to an electric arc furnace, the zinc is recovered from the dust by a number