Cobalt

Cobalt: the essentials

 Brief description: cobalt is a brittle, hard, transition metal with magnetic properties similar to those of iron. Cobalt is present in meteorites. Ore deposits are found in Zaire, Morocco and Canada. Cobalt-60 (⁶⁰Co) is an artificially produced isotope used as a source of γ rays (high energy radiation). Cobalt salts colour glass a beautiful deep blue colour.

Marmite, which we all eat here in England and which is what makes us English, is a source of vitamin B₁₂, actually a compound containing cobalt. The equivalent, but altogether blander, in Australia is Vegemite. Marmite is available in the USA. Try mixing it with peanut butter.

This sample is from The Elements Collection, an attractive and safely packaged collection of the 92 naturally occurring elements that is available for sale.

Cartoon by Nick D Kim (nearingzero.net, used by permission).

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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