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Cobalt is a silver-white magnetic metal, with the chemical symbol ‘Co’ and an atomic number of 27. It is found in a chemically combined form in the earth’s crust, and is obtained when mining nickel, lead, silver, copper and iron. Copper has been used since ancient times due to its blue hue, but it is now mainly used as an alloy in the engineering industries, as well as in sectors like healthcare.
Properties of Cobalt
Cobalt is a bluish-white, lustrous, hard and brittle metal. It is a ferromagnetic, weakly reducing metal that is protected from oxidation by a passivating oxide film. The metal is chemically active and forms many compounds. It stays magnetic to the highest temperature of all the magnetic elements, with a Curie point of 1121 degrees C.
Historical Use of Cobalt
The use of cobalt has been tracked back to ancient times to color ceramics and glass. Cobalt coloring of ceramics has been around for roughly 2600 years, with evidence of cobalt-containing glazes having been found in Ancient Egyptian tombs. Chinese pottery from Tang and Ming dynasties were also found to contain the blue colors made from cobalt-containing minerals. The earliest recorded use of colbalt is the archaic form “kobelt” in Agricola’s Bermannus in 1530. As well as its many other uses, cobalt is still used by artists today as cobalt salts, which produce vivid shades of blue in porcelain, glass, pottery and tiles.
As an element, cobalt was first isolated in 1730 by the chemist Georg Brandt. He was interested in a dark blue ore from some copper workings, but eventually realized that it contained an unrecognised metal. His claim that he discovered a new type of metal was disputed for years by other chemists, due to the new element being a compound of iron and arsenic, but it was eventually recognised as its own element.
Mining
Most cobalt is acquired as a by-product of nickel refining, as well as the mining and smelting of copper. Cobalt can also be obtained from the main cobalt ores of cobaltite, glaucodot, erythrite, and skutterudite. The supply of cobalt greatly depends up the supply and demand of both nickel and copper due to it generally being produced as a by-product. Methods to extract from copper and nickel, include froth flotation and leaching the slag from coper smelting. In froth flotation, the surfactants bind to ore components. Roasting then converts ores to cobalt sulfate, and copper and iron become oxidized. When water is leached, the sulfates and arsenates are extracted, and the residues can be further leached with sulfuric acid to make solutions of copper sulfate. The products are transformed into cobalt oxide, which is reduced to metal by an aluminothermic reaction, or by reduction with carbon in a blast furnace.
Modern Uses of Cobalt
Three of the main uses of cobalt are as a metal alloy, for electroplating and in batteries.
Alloys of cobalt make up half of global cobalt use each year. Cobalt alloys are widely used for aircraft engine parts, as the high temperature strength is an important factor. When cobalt is alloyed with nickel and aluminum, it can be made into powerful magnets. These magnets are used in hearing aids, microphones and compasses.
Due to its appearance, hardness and resistance to corrosion, cobalt is often used in electroplating. Electroplating applies a layer of material to an object to give it a pleasing aesthetic or protective quality. By adding cobalt to a material, rusting can be prevented.
Cobalt is used in lithium-ion batteries as part of lithium cobalt oxide (LiCoO2). The battery is composed of cobalt oxide layers, with lithium between them. Nickel batteries, which include nickel-cadmium and nickel metal hydride, also contain cobalt to help with the oxidation of nickel in the battery.
Biological Uses of Cobalt
As well as being used in industry, cobalt also has a few uses in biology and medicine. Cobalt is a trace element and has been found to be an active site of vitamin B12. In large doses cobalt can be carcinogenic, but in small doses it can be given as a salt to treat mineral deficiencies.
Cobalt-60 is a radioactive isotope, which is an important source of gamma-rays. It can easily be produced with a predictable quantity and high activity by bombarding cobalt with neutrons. Cobalt 60 is widely used as a cancer treatment, as well as a tracer and for radiotherapy. Cobalt-60 is also useful in sterilization, being used to sterilize medical supplies.
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