Bauxite

This article is about the ore. For the town in Arkansas, see Bauxite, Arkansas.
Bauxite with US penny for comparison
QEMSCAN mineral maps of bauxite ore-forming pisoliths
Bauxite in Les Baux-de-Provence, France
Bauxite with core of unweathered rock
Bauxite output in 2005
One of the world's largest bauxite mines in Weipa, Australia

Bauxite, an aluminium ore, is the world's main source of aluminium. It consists mostly of the minerals gibbsite Al(OH)3, boehmite γ-AlO(OH) and diaspore α-AlO(OH), mixed with the two iron oxides goethite and haematite, the clay mineral kaolinite and small amounts of anatase TiO2. Bauxite was named by the French geologist Pierre Berthier in 1821 after the village of Les Baux in Provence, southern France, where he discovered it and was the first to recognize that it contained aluminium.

Formation

Lateritic bauxites (silicate bauxites) are distinguished from karst bauxite ores (carbonate bauxites). The 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 clay layers – dispersed clays which were concentrated as the enclosing limestones gradually dissolved during chemical weathering.

The lateritic bauxites are found mostly in the countries of the tropics. They were formed by lateritization of various silicate rocks such as granite, gneiss, basalt, syenite, and shale. In comparison with the iron-rich laterites, the formation of bauxites depends even more on 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.

In the case of Jamaica, recent analysis of the soils showed elevated levels of cadmium, suggesting that the bauxite originates from recent Miocene ash deposits from episodes of significant volcanism in Central America.

Production trends

In 2009, Australia was the top producer of bauxite with almost one-third of the world's production, followed by China, Brazil, India, and Guinea. Although aluminium demand is rapidly increasing, known reserves of its bauxite ore are sufficient to meet the worldwide demands for aluminium for many centuries.[1] Increased aluminium recycling, which has the advantage of lowering the cost in electric power in producing aluminium, will considerably extend the world's bauxite reserves.

Numbers for 2010's total proven bauxite reserves x1,000 tonne[2]
Country Mine production Reserves Reserve base
2010 2011 (est.)
 Guinea17,40018,0007,400,0008,600,000
 Australia68,40067,0006,200,0007,900,000
 Vietnam80802,100,0005,400,000
 Jamaica8,54010,2002,000,0002,500,000
 Brazil28,10031,0003,600,0002,500,000
 Guyana1,7602,000850,000900,000
 India18,00020,000900,0001,400,000
 China44,00046,000830,0002,300,000
 Greece2,1002,100600,000650,000
 Iran—500[3]——
 Suriname4,0005,000580,000600,000
 Sierra Leone 1,090 1,700 180,000 ?
 Kazakhstan5,3105,400160,000450,000
 Venezuela2,5004,500320,000350,000
 Russia5,4805,800200,000250,000
 United States30[3]N/A20,00040,000
Other countries2,6302,6003,300,0003,800,000
World total (rounded)209,000220,00029,000,00038,000,000

In November 2010, Nguyen Tan Dung, the prime minister of Vietnam, announced that Vietnam's bauxite reserves might total 11000 Mt; this would be the largest in the world.[4]

Processing

Bauxite being loaded at Cabo Rojo, Dominican Republic, to be shipped elsewhere for processing; 2007
Bauxite being digested by washing with a hot solution of sodium hydroxide at 175°C under pressure at National Aluminium Company, Nalconagar, India.

Bauxite is usually strip mined because it is almost always found near the surface of the terrain, with little or no overburden. Approximately 70% to 80% of the world's dry bauxite production is processed first into alumina, and then into aluminium by electrolysis as of 2010. 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 °C. At these temperatures, the aluminium 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 aluminium oxide, Al2O3, by heating. This mineral is dissolved at a temperature of about 960 °C in molten cryolite. 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–Héroult process, named after its American and French discoverers.

Prior to the invention of this process in 1886, elemental aluminium was made by heating ore along with elemental sodium or potassium in a vacuum. The method was complicated and consumed materials that were themselves expensive at that time. This made early elemental aluminium more expensive than gold.[5]

See also

References

  1. ↑ "Bauxite and Alumina" (PDF). U.S. Geological Survey. p. 2. Retrieved 9 January 2014.
  2. ↑ "Bauxite and Alumina" (PDF). U.S. Geological Survey (Mineral Commodity Summaries). January 2012. p. 27. Retrieved August 1, 2012.
  3. ↑ 3.0 3.1 "World mineral statistics | MineralsUK". Bgs.ac.uk. Retrieved 2013-10-25.
  4. ↑ "Mining Journal - Vietnam’s bauxite reserves may total 11 billion tonnes". Retrieved 2010-11-28.
  5. ↑ "Aluminium versus aluminum Author: Michael Quinion, 1996–2011". Worldwidewords.org. 2006-01-23. Retrieved 2011-12-19.

Further reading

External links

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