Bauxite

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

Bauxite with a U.S. penny

QEMSCAN mineral maps of bauxite ore-forming pisoliths

Bauxite with core of unweathered rock

Bauxite output in 2005

Bauxite is an aluminium ore and is the main source of aluminium. 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 recognised as containing aluminium and named by the French geologist Pierre Berthier in 1821.

Bauxite 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 (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 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.

Production trends

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 India. Although aluminium demand is rapidly increasing, known reserves of its bauxite ore are sufficient to meet the worldwide demands for aluminium for many centuries.^{[citation needed]} 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.

estimated Numbers for 2008's total proven bauxite reserves x1000 tonne

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	—	—
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

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.

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 becomes molten at a temperature of about 1000 °C, 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–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.

See also

• Alcoa
• Bauxite, Arkansas
• Rio Tinto Alcan
• United Company RUSAL

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

External links

• USGS Minerals Information: Bauxite
• Mineral Information Institute
•  "Bauxite". New International Encyclopedia. 1905. 
•  "Bauxite". Encyclopedia Americana. 1920.