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Bauxite with an American penny
Bauxite with core of unweathered rock

Bauxite is the most important aluminium ore. This form of rock consists mostly of the minerals gibbsite Al(OH)3, boehmite γ-AlO(OH), and diaspore α-AlO(OH), in a mixture with the two iron oxides goethite and hematite, the clay mineral kaolinite, and small amounts of anatase TiO2. Bauxite was named after the village Les Baux in southern France, where it was first recognized as containing aluminum and named by the French geologist Pierre Berthier in 1821.

Contents

Bauxite formation

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 and residual accumulation of intercalated clays or by clay dissolution residues of the limestone.

The lateritic bauxites are found mostly in the countries of the tropics.They were formed by lateritization (see laterite) of various silicate rocks such as granite, gneiss, basalt, syenite, and shale. In comparison with the iron-rich laterites, the formation of bauxites demands even more intense weathering conditions in a location with very good drainage. This enables the dissolution of the kaolinite and the precipitation of the 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 of the world's production, followed by China, Brazil, Guinea, and Jamaica. Although aluminium demand is rapidly increasing, known reserves of its bauxite ore are sufficient to meet the worldwide demands for aluminum for many centuries, Increased aluminium recycling, which has the advantage of lowering the cost in electric power in producing aluminum, will considerably extend the world's 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
 Guinea 18,000 18,000 7,400,000 8,600,000
 Australia 62,400 63,000 5,800,000 7,900,000
 Vietnam 30 30 2,100,000 5,400,000
 Jamaica 14,600 15,000 2,000,000 2,500,000
 Brazil 24,800 25,000 1,900,000 2,500,000
 Guyana 1,600 1,600 700,000 900,000
 India 19,200 20,000 770,000 1,400,000
 China 30,000 32,000 700,000 2,300,000
 Greece 2,220 2,200 600,000 650,000
 Iran - 500[1] - -
 Suriname 4,900 4,500 580,000 600,000
 Kazakhstan 4,800 4,800 360,000 450,000
 Venezuela 5,900 5,900 320,000 350,000
 Russia 6,400 6,400 200,000 250,000
 United States 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 usually strip mined (surface mining) because it is almost always found near the surface of the terrain, with little or no overburden. Approximately 95% of the world's bauxite production is processed first into alumina, and then into aluminum by electrolysis. Bauxite rocks are typically classified according to their intended commercial application: metallurgical, abrasive, cement, chemical, and refractory.

Usually, bauxite ore is heated in a pressure vessel along with a sodium hydroxide solution at a temperature of 150 to 200 Celsius. At these temperatures, the aluminum is dissolved as an aluminate (the Bayer process). After separation of ferruginous residue (red mud) by filtering, pure gibbsite is precipitated when the liquid is cooled, and then seeded with fine-grained aluminium hydroxide. The gibbsite is usually converted into aluminum oxide, Al2O3, by heating. This mineral becomes molten at a temperature of about 1000 Celsius, when the mineral cryolite is added as a flux. Next, this molten substance can yield metallic aluminium by passing an electric current through it in the process of electrolysis, which is called the Hall-Heroult process after its American and French discoverers in 1886.

Before Hall and Heroult discovered their process that uses cryolyte and electricity, aluminum was separated from its ore - in small quantities - by heating the ore with metallic sodium or potassium in a vacuum. However, those two metals were themselves produced by electrolysis, and the entire procedure was quite complicated and expensive. The Hall-Heroult process greatly simplified the process of refining aluminum and made it economical to produce aluminum from bauxite in very large quantities.

Notes

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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1911 encyclopedia

Up to date as of January 14, 2010
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From LoveToKnow 1911

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Simple English

Bauxite is the main ore of aluminium. It is mostly aluminium oxide.

Bauxite is the most important aluminium ore. It is largely made up 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 Baux-de-Provence in southern France, where it was first discovered in 1821 by geologist Pierre Berthier.

Bauxite information

There are two main kinds of bauxite ores: carbonate bauxites (karst bauxites), and silicate bauxites (lateritic bauxites). Carbonate bauxites were discovered earlier, and occur mainly in Europe and Jamaica above carbonate rocks such as limestone and dolomite.

The lateritic bauxites occur in many countries of the tropical belt. They were formed from various silicate rocks such as granite, gneiss, basalt, syenite, and shale.

Forming bauxite demands intense weathering conditions with very good drainage. Bauxite deposits with highest aluminium content are frequently located below an iron-bearing surface layer. In lateritic bauxite, the aluminum hydroxide contained in lateritic bauxite deposits is almost entirely a form called gibbsite.


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