The Production and Uses of Zinc
The Metal used for Galvanising, Paints, Brass and other Alloys
Mar 28, 2008
Zinc is the fourth most widely used metal in the world. It has been used for more than 3000 years in the important alloy, brass, but was only isolated in its pure form about 200 years ago. In the UK, the first zinc smelter was built in Bristol in 1737 by William Champion, who, it is said, gained his information by travelling throughout Europe dressed in rags.
Zinc Ores
Brass was made as long ago as 1600BC by heating copper with a whitish mineral known as calamine. This mineral is impure zinc carbonate and is one of the ores used today to extract zinc. Other ores used are marmatite (zinc iron sulfide) and zinc blende (zinc sulfide).
Sintering
The process of extraction begins with sintering. Crushed ore is strongly heated while air is passed through it. This burns the sulphur in the ores, forming sulphur dioxide which is used to manufacture sulphuric acid as a valuable side-product. The resulting porous solid is essentially zinc oxide which is taken to be smelted in the next stage, the blast furnace.
Blast Furnace
The oxide is mixed with coke and fed into the top of the furnace where it is blasted with air at 1000 degrees Celsius. The coke is burned to form carbon monoxide which reacts with the zinc oxide forming zinc and carbon dioxide. The zinc is formed as a vapour which is then cooled to 550 degrees in a spray of molten lead. The zinc is then separated from the lead while they are both molten.
Galvanised Steel
There are two main uses for zinc. Over half of the zinc used globally is used in galvanising steel. Steel is coated with a layer of zinc, either by dipping it into molten zinc or by electrolysis. The zinc protects the steel in two ways. First it forms a thin layer of zinc oxide on its surface, preventing further corrosion. Second, if it is scratched through to the steel, the zinc corrodes first, because it is a more reactive metal than the steel. Galvanised steel is used as a cheap material for roofs and other construction.
Brass and Other Alloys
The other use of zinc is in alloys. Brass is still an important alloy because it is hard and corrosion resistant. Its colour and shine give it an important ornamental use. Its strength and electrical conductivity make it useful in electrical plugs. Zinc based alloys are also used in die-casting because they have a lower melting point than copper or steel and can be forced into steel dies to set without shrinking.
Zinc Compounds
Zinc oxide is added to the rubber in tyres, in ointments to prevent bacteria and fungi from reproducing, as a sunscreen and in paints. Zinc sulfide is used in fluorescent lights, TV screens and luminous dials.
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