A natural mixture of hydrated aluminium oxide minerals produced by the weathering of rocks in hot, humid climates in which more soluble constituents are leached out. It is the chief ore of aluminium.
Bauxite is an aluminium ore which consists largely of the Al minerals gibbsite Al(OH)3, boehmite and diaspore AlOOH, together with the iron oxides goethite and hematite, the clay mineral kaolinite and small amounts of anatase TiO2.
Formation
In geosciences lateritic bauxites (silicate bauxites) are distinguished from karst bauxites (carbonate bauxites). The early discovered carbonate bauxites occur predominantly in Europe and Jamaica above carbonate rocks (limestone and dolomite), where they were formed by lateritic weathering either of intercalated clays or of clayey dissolution residues of the limestone.
The lateritic bauxites occur in many countries of the tropical belt. The aluminium hydroxide in the lateritic bauxite deposits is almost exclusively gibbsite.
World Bauxite Mine Production, Reserves, and Reserve Base
(x1000 tonne) Mine production Reserves Reserve base 2000 2001 ------------------------------------------------------------------- Australia 200–800 53,500 3,800,000 7,400,000 Brazil 14,000 14,000 3,900,000 4,900,000 PR China 9,000 9,200 720,000 2,000,000 Guinea 15,000 15,000 7,400,000 8,600,000 Guyana 2,400 2,000 700,000 900,000 India 7,370 8,000 770,000 1,400,000 Jamaica 11,100 13,000 2,000,000 2,500,000 Russia 4,200 4,000 200,000 250,000 Suriname 3,610 4,000 580,000 600,000 United States NA NA 20,000 40,000 Venezuela 4,200 4,400 320,000 350,000 Other countries 10,800 10,200 4,100,000 4,700,000 ------------------------------------------------------------------- World total (rounded) 135,000 137,000 24,000,000 34,000,000 (Numbers for 2001 estimated)Processing
Approx.
Bauxites are heated in pressure vessels with sodium hydroxide solution at 150-200 °C through which aluminium is dissolved as aluminate (Bayer-Process).
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