Cobalt: the essentials

Cobalt is a brittle, hard, silver-grey transition metal with magnetic properties similar to those of iron (ferromagnetic). Cobalt is present in meteorites. Ore deposits are found in Zaire, Morocco and Canada. The isotope cobalt-60 (60Co) is an artificially produced isotope used as a source of γ rays (its high energy radiation is useful for sterilisation in medicine and of foods). Cobalt salts colour glass a beautiful deep blue colour. Cobalt compounds are important catalysts in a number of industrial processes. Cobalt is required in small amounts for life and is the only metal found in vitamins (cobalt is the critical component of vitamin B12.

Table: basic information about and classifications of cobalt.

Cobalt: historical information

Cobalt was discovered by Georg Brandt at 1735 in Sweden. Origin of name: from the German word "kobald" meaning "goblin" or evil spirit.

Minerals containing cobalt were of value to the early civilisations of Egypt and Mesopotamia for colouring glass deep blue.

Cobalt was announced to be an element by Georg Brandt about 1739 (or possibly 1735). He had been trying to demonstrate that the blue colour of glass was because of a new element, cobalt, rather than bismuth, an element often found in the same locations as cobalt.

Cobalt: physical properties

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Cobalt: orbital properties

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Isolation

Isolation: it is not normally necessary to make cobalt in the laboratory as it is available readily commercially. Many ores contain cobalt but not many are of economic importance. These include the sulphides and arsenides linnaeite, Co3S4, cobaltite, CoAsS, and smaltite, CoAs2. Industrially, however, it is normally produced as a byproduct from the produstion of copper, nickel, and lead.

Normally the ore is "roasted" to form a mixture of metals and metal oxides. Treatment with sulphuric acid leaves metallic copper as a residue and disolves out iron, cobalt, and nickel as the sulphates. Iron is obtained by precipitation with lime (CaO) while cobalt is produced as the hydroxide by precipitation with sodium hypochlorite (NaOCl)

2Co2+(aq) + NaOCl(aq) + 4OH-(aq) + H2O → 2Co(OH)3(s) + NaCl(aq)

The trihydroxide Co(OH)3 is heated to form the oxide and then reduced with carbon (as charcoal) to form cobalt metal.

2Co(OH)3 (heat) → Co2O3 + 3H2O

2Co2O3 + 3C → Co + 3CO2

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cobalt atomic number