Bauxite

This article is about the ore. For town in Arkansas, see Bauxite, Arkansas.

Bauxite with a US Cent

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 Baux-de-Provence in southern France, where it was first discovered in 1821 by geologist Pierre Berthier.

Contents 1 Bauxite information 2 Production trends 3 Processing 4 Supply 5 Aluminocrete or Alcrete 6 See also 7 References 8 External links

Bauxite information

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 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 2005, Australia was the top producer of bauxite with almost one-third world share, followed by Guinea, Brazil and China, reports the British Geological Survey.

(x1000 tonne, Numbers for 2001 estimated)

Country	Mine production		Reserves	Reserve base
	2000	2001
Australia	53,800	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

Processing

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 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 liquor 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).

Supply

According to The Recycler\'s Handbook By The EarthWorks Group (1990), Earth\'s bauxite reserves will run out in 400-500 years. However Lester Brown has suggested bauxite could run out within 69 years based on an extremely conservative extrapolation of 2% growth per year.Brown, Lester Plan B 2.0, New York: W.W. Norton, 2006. p. 109

Aluminocrete or Alcrete

Aluminocrete or AlcreteSoils at James Cook University, Cairns Qld is a type of soil deposit, rich in aluminium. It is generally found in tropical regions, where the parent material is rapidly weathered because of high rainfall and high ambient temperatures. In these conditions, more mobile elements are leached out of the soil, leaving the relatively insoluble Al³⁺ ions behind. A hard, nearly impermeable crust, called a duricrust, may form on or near the surface of such soils. Duricrusts of aluminium-rich soils are called alcrete, or aluminocrete. Alcrete deposits with extremely high concentrations of aluminium are known as bauxite.

See also

• Aluminum in Africa

References

This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (May 2007)

• Bardossy, G. (1882): 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 0-444-98811-4

External links

• USGS Minerals Information: Bauxite
• Mineral Information Institute

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