Bauxite

From formulasearchengine
Jump to navigation Jump to search

{{#invoke:Hatnote|hatnote}}

Bauxite with US penny for comparison
QEMSCAN mineral maps of bauxite ore-forming pisoliths
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 aluminum. 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 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 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.)
Template:Country data Guinea 17,400 18,000 7,400,000 8,600,000
Template:Country data Australia 68,400 67,000 6,200,000 7,900,000
Template:Country data Vietnam 80 80 2,100,000 5,400,000
Template:Country data Jamaica 8,540 10,200 2,000,000 2,500,000
Template:Country data Brazil 28,100 31,000 3,600,000 2,500,000
Template:Country data Guyana 1,760 2,000 850,000 900,000
Template:Country data India 18,000 20,000 900,000 1,400,000
Template:Country data China 44,000 46,000 830,000 2,300,000
Template:Country data Greece 2,100 2,100 600,000 650,000
Template:Country data Iran 500[3]
Template:Country data Suriname 4,000 5,000 580,000 600,000
Template:Country data Sierra Leone 1,090 1,700 180,000 ?
Template:Country data Kazakhstan 5,310 5,400 160,000 450,000
Template:Country data Venezuela 2,500 4,500 320,000 350,000
Template:Country data Russia 5,480 5,800 200,000 250,000
Template:Country data United States 30[3] N/A 20,000 40,000
Other countries 2,630 2,600 3,300,000 3,800,000
World total (rounded) 209,000 220,000 29,000,000 38,000,000

In November 2010, Nguyen Tan Dung, the prime minister of Vietnam, announced that Vietnam's bauxite reserves might total 11000Mt; 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 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 after its American and French discoverers in 1886.

Prior to the Hall–Héroult process, 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

Template:Wikipedia books

References

Further reading

  • 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
  • Grant, C; lalor, G and Vutchkov, M (2005) Comparison of bauxites from Jamaica, the Dominican Republic and Suriname. Journal of Radioanalytical and Nuclear Chemistry p. 385-388 Vol.266, No.3
  • Hanilçi, N. (2013).Geological and geochemical evolution of the Bolkardaği bauxite deposits, Karaman, Turkey: Transformation from shale to bauxite. Journal of Geochemical Exploration

External links

Template:Sister

Template:Ores Template:Industry country lists