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Bauxite with core of unweathered rock


Bauxite is the most important aluminium ore. It consists largely of the minerals gibbsite Al(OH)3, boehmite γ-AlO(OH), and diaspore α-AlO(OH), together with the iron oxides goethite and hematite, the clay mineral kaolinite and small amounts of anatase TiO2. It was named after the village Les Bauxmarker in southern France, where it was first discovered in 1821 by the geologist Pierre Berthier.

Bauxite formation

Lateritic bauxites (silicate bauxites) are distinguished from karst bauxites (carbonate bauxites). The early discovered carbonate bauxites occur predominantly in Europe and Jamaicamarker above carbonate rocks (limestone and dolomite), where they were formed by lateritic weathering and residual accumulation of intercalated clays or of clayey dissolution residues of the limestone.

The lateritic bauxites occur in many countries of the tropical belt. They were formed by lateritization (see laterite) of various silicate rocks such as granite, gneiss, basalt, syenite and shale. Compared with iron-rich laterites, the formation of bauxites demands even more intense weathering conditions with a very good drainage. This enables dissolution of kaolinite and precipitation of gibbsite. Zones with highest aluminium content are frequently located below a ferruginous surface layer. The aluminium hydroxide in the lateritic bauxite deposits is almost exclusively gibbsite.

Production trends

Bauxite output in 2005


In 2007, Australia was one of the top producers of bauxite with almost one-third world share, followed by China, Brazil, Guinea, and Jamaica. Although aluminium demand is rapidly increasing, known reserves are sufficient to meet the needs for a considerable length of time. Increased aluminium recycling, which has the advantage of lowering the energy costs of production, will help extend bauxite reserves.

The following table is ranked by total proven bauxite reserves.

(x1000 tonne, Numbers for 2008 estimated)
Country Mine production Reserves Reserve base
2007 2008
18,000 18,000 7,400,000 8,600,000
62,400 63,000 5,800,000 7,900,000
30 30 2,100,000 5,400,000
14,600 15,000 2,000,000 2,500,000
24,800 25,000 1,900,000 2,500,000
1,600 1,600 700,000 900,000
19,200 20,000 770,000 1,400,000
30,000 32,000 700,000 2,300,000
2,220 2,200 600,000 650,000
4,900 4,500 580,000 600,000
4,800 4,800 360,000 450,000
5,900 5,900 320,000 350,000
6,400 6,400 200,000 250,000
NA NA 20,000 40,000
Other countries 7,150 6,800 3,200,000 3,800,000
World total (rounded) 202,000 205,000 27,000,000 38,000,000
Source: U.S. Geological Survey, Mineral Commodity Summaries, January 2009

Processing

Bauxite being loaded at Cabo Rojo, Dominican Republic, to be shipped elsewhere for processing; 2007.


Bauxite is strip mined (surface mining) because it is found at the surface, with little or no overburden. Approximately 95% of the world's bauxite production is processed into alumina and then aluminium. Bauxites are typically classified according to their intended commercial application: metallurgical, abrasive, cement, chemical and refractory.

Bauxites are heated in pressure vessels with sodium hydroxide solution at 150–200 °C through which aluminium is dissolved as aluminate (Bayer process). After separation of ferruginous residue (red mud) by filtering, pure gibbsite is precipitated when the liquid is cooled and seeded with fine grained aluminium hydroxide. Gibbsite is converted into aluminium oxide by heating. This is molten at approx. 1000 °C by addition of cryolite as a flux and reduced to metallic aluminium by a highly energy-consumptive electrolytic process (the Hall-Héroult process).

References

  • Bardossy, G. (1982): Karst Bauxites. Bauxite deposits on carbonate rocks. Elsevier Sci. Publ. 441 p.
  • Bardossy, G. and Aleva, G.J.J. (1990): Lateritic Bauxites. Developments in Economic Geology 27, Elsevier Sci. Publ. 624 p. ISBN 0-444-988


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