bauxite

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For more information on bauxite, visit Britannica.com.

A rock mainly comprising minerals that are hydrous aluminum oxides. These minerals are gibbsite, boehmite, and diaspore. The major impurities in bauxite are clay minerals and iron oxides. Bauxite is a weathering product of aluminous rock that results from intense leaching in tropical and subtropical areas, a process called laterization. Bauxite deposits are generally found on plateaus in stable areas where they had sufficient geologic time to form and were protected from erosion. See also Aluminum.

Bauxite is the primary ore of aluminum. The two types of bauxites that are used commercially as aluminum ores are laterite and karst. Lateritic bauxites constitute more than three-fourths of the world's bauxite resources. Karstic bauxites are formed on a carbonate terrain and are concentrated in sinkholes and solution depressions on the surface of carbonate rocks. See also Laterite.

Bauxite used to produce alumina is called metallurgical grade; approximately 90% of the world's production is for this purpose. Other major uses are in refractories, abrasives, chemicals, and aluminous cements. The compositional requirements are much more rigid for these uses. The alumina content must be higher, and the iron, silica, and titanium contents significantly lower, than for metallurgical-grade bauxite. World resources of bauxite are many tens of billions of tons, so an adequate supply is assured for hundreds of years.

The major ore of aluminium, usually occurring as a form of clay which results from the weathering of tropical rocks. Its main constituents are aluminous laterite and hydrous aluminium oxides. Australia, Brazil, and Jamaica are major producers.

Environment

Weathered surface deposits.

Amorphous to microcrystalline. Usually massive; broken surfaces often have a pisolitic texture (a small-scale conglomerate of little spherical brown masses in a lighter matrix); more often like hard clay. Tiny white crystals may lie in the small pisolitic geodes.

White or gray to dark red-brown. Luster dull; hardness 1-3, specific gravity 2.0-2.5. Crumbly to compact.

Bauxite is an omnibus term (like wad, limonite, and gummite), widely accepted and used to describe a mixture of more or less hydrated aluminum oxides, but not used as a proper mineral name. The specific minerals are gibbsite (Al[OH] ₃ ), boehmite (AlO[OH]), and diaspore (HAlO ₂ ). In the common mixture any crystals will be microscopic and probably indistinguishable; thus the word is still useful.

Infusible and insoluble; colored blue when moistened with cobalt nitrate and heated by the blowpipe flame.

Much like a clay, though most bauxite is perhaps a little harder than the usual clays. The pisolitic types are easier to spot.

Bauxite is the mined source of aluminum. It is a secondary mineral resulting from the leaching of silica from clay minerals, clayey limestones, or low-silica igneous rocks, commonly under conditions of tropical weathering. This explains the geographical distribution of aluminum ores, most of which are found in the tropics, and some of which (as in Provence, France) are probably residual from earlier geological periods when climates were different. Abundant in Jamaica; in Brazil, Surinam, and French Guiana in South America; in Alabama, Georgia, and Arkansas in the U.S.; and in Europe at Le Baux, France, and in Hungary.

• Mineral compounds

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.

Contents 1 Bauxite formation 2 Production trends 3 Processing 4 See also 5 Notes 6 References 7 External links

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 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.

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 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^[1]

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[2]	—	—
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.^[3]

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.^[4]

See also

	Book: Aluminium
Wikipedia books are collections of articles that can be downloaded or ordered in print.

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

Notes

1. ^ "Bauxite and alumina" (PDF). http://minerals.usgs.gov/minerals/pubs/commodity/bauxite/mcs-2009-bauxi.pdf. Retrieved 2011-12-19. 
2. ^ http://www.bgs.ac.uk/mineralsuk/commodity/world/home.html
3. ^ "Mining Journal - Vietnam’s bauxite reserves may total 11 billion tonnes". http://www.mining-journal.com/exploration--and--development/vietnams-bauxite-reserves-may-total-11-billion-tonnes. Retrieved 2010-11-28. 
4. ^ "Aluminium versus aluminum Author: Michael Quinion, 1996–2011". Worldwidewords.org. 2006-01-23. http://www.worldwidewords.org/articles/aluminium.htm. Retrieved 2011-12-19. 

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
• 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

External links

Wikimedia Commons has media related to: Bauxite

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

v t e Ore minerals, mix of minerals and ore deposits Ores Oxides Cassiterite (tin) Chromite (chromium) Hematite (iron) Ilmenite (titanium) Magnetite (iron) Uraninite (uranium) Sulfides Acanthite (silver) Chalcopyrite (copper) Chalcocite (copper) Cinnabar (mercury) Galena (lead) Pentlandite (nickel) Sphalerite (zinc) Other Bauxite (aluminium) Scheelite (tungsten) Ore deposit types Banded iron formation Carbonate hosted lead zinc ore deposits Heavy mineral sands Iron oxide copper gold Kambalda type komatiitic nickel ore deposits Lateritic nickel Magmatic nickel-copper-iron-PGE deposits Porphyry copper Sedimentary exhalative deposits Volcanogenic massive sulfide

v t e Lists of countries by industrial output rankings Metallurgy Aluminum Al2O3 Bauxite Bismuth Copper Gold Iron ore Manganese Steel Tin Uranium production reserves Zinc Mineral Antimony Bentonite Feldspar Fluorite Salt Emissions CO2 per capita GDP per Greenhouse gas per capita Other Cement Motor vehicles Lists by country List of international rankings List of top international rankings by country

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Dansk (Danish)
n. - bauxit

Nederlands (Dutch)
bauxiet

Français (French)
n. - bauxite

Deutsch (German)
n. - Bauxit

Ελληνική (Greek)
n. - βωξίτης

Italiano (Italian)
bauxite

Português (Portuguese)
n. - bauxita (f) (Miner.)

Русский (Russian)
боксит

Español (Spanish)
n. - bauxita

Svenska (Swedish)
n. - bauxit

中文（简体）(Chinese (Simplified))
铁矾土, 铁铝氧石

中文（繁體）(Chinese (Traditional))
n. - 鐵礬土, 鐵鋁氧石

한국어 (Korean)
n. - 보크사이트(알루미늄 원광)

日本語 (Japanese)
n. - ボーキサイト

العربيه (Arabic)
‏(الاسم) هيدروكسيد الألمنيوم‏

עברית (Hebrew)
n. - ‮מחצב המהווה חומר-גלם לאלומיניום‬

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