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Cobalt (pronounced /koʊbɔːlt/) is a hard, lustrous, grey metal, a chemical element with symbol Co and atomic number 27. Although cobalt-based colors and pigments have been used since ancient times for making jewelry and paints, and miners have long used the name kobold ore for some minerals, the free metallic cobalt was not prepared and discovered until 1735 by Georg Brandt.

Cobalt is found in various metallic-lustered ores for example cobaltite (CoAsS), but it is produced as a by-product of copper and nickel mining. The copper belt in the Democratic Republic of the Congo and Zambia yields most of the worldwide mined cobalt.

Cobalt is used in the preparation of magnetic, wear-resistant, and high-strength alloys. Cobalt blue (cobalt(II) aluminate, CoAl2O4) gives a distinctive deep blue color to glass, ceramics, inks, paints, and varnishes. Cobalt-60 is a commercially important radioisotope, used as a tracer and in the production of gamma rays for industrial use.

Cobalt is an essential trace-element for all multicellular organisms as the active center of coenzymes called cobalamins. These include vitamin B-12 which is essential for mammals. Cobalt is also an active nutrient for bacteria, algae, and fungi, and may be a necessary nutrient for all life.

Characteristics
Cobalt is a ferromagnetic metal. Pure cobalt is not found in nature, but compounds of cobalt are common. Small amounts of it are found in most rocks, soil, plants, and animals. It is the element of atomic number 27. The Curie temperature is 1388 K, and the magnetic moment is 1.6–1.7 Bohr magnetons per atom. In nature, it is frequently associated with nickel, and both are characteristic minor components of meteoric iron. Mammals require small amounts of cobalt which is the basis of vitamin B12. Cobalt-60, an artificially produced radioactive isotope of cobalt, is an important radioactive tracer and cancer-treatment agent. Cobalt has a relative permeability two thirds that of iron. Metallic cobalt occurs as two crystallographic structures: hcp and fcc. The ideal transition temperature between hcp and fcc structures is 722 K, but in practice, the energy difference is so small that random intergrowth of the two is common.

History
Cobalt compounds have been used for centuries to impart a rich blue color to glass, glazes, and ceramics. Cobalt has been detected in Egyptian sculpture and Persian jewelry from the third millennium BC, in the ruins of Pompeii (destroyed AD 79), and in China dating from the Tang dynasty (AD 618–907) and the Ming dynasty (AD 1368–1644)[2]. Cobalt glass ingots have been recovered from the Uluburun shipwreck, dating to the late 14th century BC.

Swedish chemist Georg Brandt (1694–1768) is credited with isolating cobalt circa 1735. He was able to show that cobalt was the source of the blue color in glass, which previously had been attributed to the bismuth found with cobalt. The word cobalt is derived from the German kobalt, from kobold meaning "goblin", a term used for the ore of cobalt by miners. The first attempts at smelting the cobalt ores to produce cobalt metal failed, yielding cobalt(II) oxide instead. Also, because the primary ores of cobalt always contain arsenic, smelting the ore oxidized into the highly toxic and volatile oxide As4O6, which was inhaled by workers.

During the 19th century, cobalt blue was produced at the Norwegian Blaafarveværket (70–80% of world production), led by the Prussian industrialist Benjamin Wegner.

In 1938, John Livingood and Glenn Seaborg discovered cobalt-60. This isotope was famously used at Columbia University in the 1950s to establish parity violation in beta decay.

Occurrence
Cobalt occurs in copper and nickel minerals and in combination with sulfur and arsenic in the sulfidic cobaltite (CoAsS), safflorite (CoAs2) and skutterudite (CoAs3) minerals. The mineral cattierite is similar to pyrite and occurs together vaesite in the copper deposits in the Katanga Province.If the sulfides come in contact with the atmosphere weathering starts transforming the minerals by oxidation. The products of the oxidation are for example pink erythrite ('cobalt glance': Co3(AsO4)2·8H2O) and sphaerocobaltite (CoCO3).

Production

Cobalt ore
Cobalt output in 2005
World production trendCobalt is not found as a native metal but generally found in the form of ores. Cobalt is usually not mined alone, and tends to be produced as a by-product of nickel and copper mining activities. The main ores of cobalt are cobaltite, erythrite, glaucodot, and skutterudite.

In 2005, the copper deposits in the Katanga Province (former Shaba province) of the Democratic Republic of the Congo was the top producer of cobalt with almost 40% world share, reports the British Geological Survey. The problematic political situation in the Congo influences the price of cobalt significantly, best example was the Shaba crisis in 1978.

There are several methods which can be used to separate cobalt from copper and nickel. They depend on the concentration of cobalt and the exact composition of the used ore. The first possible separation step is the froth flotation of the ore, in which special surfactants yield in an enrichment of cobalt. The following roasting of the ores can be conducted in a way that the cobalt sulfide is oxidized to the cobalt sulfate, while the copper and the iron are oxidized to the oxide. The leaching with water extracts the sulphate together with the arsenates. The residues are further leached with sulfuric acid yielding a solution of copper sulfate. They also present iron nickel and cobalt salts can be precipitated by chlorine or hypochloride. If the copper is not produced by leaching and electrowinning but by the pyrometallurgic process, the cobalt can be leached from the slag of the copper smelter.[11]

All the above mentioned processes yield copper compounds which are transformed into the cobalt oxide Co3O4. The reduction to the metal is done either by the aluminothermic reaction or reduction with carbon in a blast furnace.