Aluminium is the third most abundant element in the earth's crust after oxygen and silicon. Because of its chemical reactivity, aluminium is never found in nature as an element but always in its oxidised form, as one of a selection of about 250 different minerals. The most prominent groups of such minerals are the silicates, and the products of their weathering, the clays. Other important compounds include the hydroxides, a group which includes bauxite, the base raw material for primary aluminium production.

Bauxite is generally extracted by open cast mining from strata, typically some 4-6 metres thick under a shallow covering of topsoil and vegetation. In most cases the topsoil is removed and stored.

Eighty percent of world bauxite production, mainly from large blanket type deposits is from surface mines, with the rest, mainly from Southern Europe and Hungary, from underground excavations.

On some surface deposits there is no overburden, and on others, the bauxite may be covered by more than 70 metres of rock and clay. Deposits that are hardened may require blasting in order to release the ore. Once the bauxite is loosened into manageable pieces it is generally loaded into trucks or railroad cars and transported to crushing or washing plants or to stockpiles.

Underground bauxite mines are used to exploit pockets or beds of deposit between layers of carbonic rock. Water in flow is a problem in most underground operations and dewatering shafts are often drilled before mining begins.

Unlike the base metal ores, bauxite does not require complex processing because most of the bauxite mined is of an acceptable grade or can be improved by a relatively simple and inexpensive process of removing clay. In many bauxites, clay is removed by some combination of washing, wet screening and cycloning, even by hand picking or sorting.

Top of page