Bauxite

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A sample of bauxite, placed next to a penny.
Bauxite showing a core of unweathered rock.

Bauxite is an important ore of aluminum, composed mainly of aluminum oxide and hydroxide minerals. It was named after the village Les Baux-de-Provence in southern France, where it was first discovered in 1821 by geologist Henri Rouvère. Bauxites have a range of commercial applications, such as for the production of aluminum metal and aluminum-based chemicals, abrasives, cements, and refractory materials.

Contents

Composition

Bauxite consists predominantly of minerals such as gibbsite (Al(OH)3), boehmite (AlO(OH)), and diaspore (AlO(OH)), as well as lesser amounts of clays (such as kaolinite), silt, and iron oxides and hydroxides. It may also contain small amounts of anatase (TiO2).

Formation

Bauxite is a laterite,[1] formed by the intense weathering of surface rocks. In the geosciences, lateritic bauxites (silicate bauxites) are distinguished from karst bauxites (carbonate bauxites). In Europe and Jamaica, carbonate bauxites have been found above carbonate rocks (limestone and dolomite), where they were formed by the weathering either of intercalated clays or of clayey dissolution residues of the limestone.

The lateritic (silicate) bauxites occur in many countries of the tropical belt. They were formed by lateritization of various aluminum silicate rocks, such as granites, gneisses, basalts, syenite, clays, and shales. Compared with iron-rich laterites, the formation of bauxites demands even stronger weathering conditions with a very good drainage. This enables dissolution of kaolinite and precipitation of gibbsite. Zones with highest aluminum content are frequently located below an iron-rich surface layer. The aluminum hydroxide in the lateritic bauxite deposits is almost exclusively gibbsite.

Processing

The bulk of the world's bauxite production is processed into alumina (aluminum oxide) and then into aluminum. In the Bayer process, bauxites are heated in pressure vessels with sodium hydroxide solution at 150-200 °C. As a result, the aluminum in the ore is dissolved as aluminate, and the iron-rich residue (red mud) is separated by filtering. The liquor is then cooled, and pure gibbsite is precipitated by seeding with fine-grained aluminum hydroxide. Gibbsite is converted into aluminum oxide by heating. This product is molten at approximately 1000 °C by adding cryolite (Na3AlF6) as a flux, and it is reduced to metallic aluminum by an electrolytic process called the Hall-Héroult process.

World bauxite mine production, reserves, and reserve base

(x1000 tonne, Numbers for 2001 estimated)
Country 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
People's Republic of 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

See also

Notes

  1. A laterite is a surface formation in hot, wet tropical areas. The rock is enriched in iron and aluminum and develops by intensive, long-lasting weathering of the underlying parent rock.

References

  • Bardossy, Gyorgy. 1982. Karst Bauxites: Bauxite Deposits on Carbonate Rocks. Elsevier Science. ISBN 044499727X
  • Bardossy, Gyorgy, and G.J.J. Aleva. 1990. Lateritic Bauxites. Developments in Economic Geology 27, Elsevier. ISBN 0444988114
  • Kogel, Jessica Elzea, Nikhil C. Trivedi, James M. Barker, and Stanley T. Krukowski (editors), 2006. Industrial Minerals & Rocks: Commodities, Markets, and Uses, Seventh Edition. Littleton, CO: Society for Mining, Metallurgy, and Exploration. ISBN 0873352335
  • Misra, Kula C., 2000. Understanding Mineral Deposits. Dordrecht, the Netherlands: Kluwer Academic Publishers. ISBN 0045530092
  • Moon, Charles J., Michael E.G. Whateley, and Anthony M. Evans (editors), 2006. Introduction to Mineral Exploration, Second Edition. Malden, MA: Blackwell Publishing. ISBN 1405113170
  • Nesse, William D. 2000. Introduction to Mineralogy. Oxford, UK; New York, NY: Oxford University Press. ISBN 0195106911

External links

All links retrieved January 9, 2013.

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