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Aluminium Oxide

Bauxite is the usual source of aluminium compounds for electrolysis. It was first discovered at Les Baux in France, though the French mines are now exhausted. Significant quantities of bauxite are mined in Jamaica, Australia and India, with some mining in North and South America.

The ecological disruption caused by mining has been one of the issues facing the aluminium industry. For more information on this see the issues section.

In order to obtain pure aluminium oxide from bauxite, sodium hydroxide is used. This is one of the two major products from the electrolysis of sodium chloride solution ("brine"), the other product being chlorine. Click here for more information on chlorine manufacture.

Cryolite

Aluminium oxide is dissolved in sodium aluminium fluoride ("cryolite") for electrolysis. Cryolite is made using sodium aluminate and hydrogen fluoride, the latter being generated from the mineral fluorspar (rich in calcium fluoride) and sulphuric acid.

Fluorspar (sometimes referred to as fluorite) is usually 60-80% calcium fluoride. The mineral is crushed, and then a floatation technique is used to separate the calcium fluoride from other materials present. Reaction with the acid also produces calcium sulphate ("gypsum") used in the making of cement and plaster.
photo: fluorspar mineral


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