bauxite

[After Les Baux, a commune of southeast France.]

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.

This article is about the ore. For the 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 in southern France, where it was first discovered in 1821 by the geologist Pierre Berthier.

Contents 1 Bauxite formation 2 Production trends 3 Processing 4 References 5 External links

Bauxite formation

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 2007, Australia was one of the top producers of bauxite with almost one-third world share, followed by China, Brazil, Guinea, and Jamaica. Although aluminium demand is rapidly increasing, known reserves are sufficient to meet the needs for a considerable length of time. Increased aluminium recycling, which has the advantage of lowering the energy costs of production, will help extend bauxite reserves.

The following table is ranked by total proven bauxite reserves.

(x1000 tonne, Numbers for 2008 estimated)

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
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

Source: U.S. Geological Survey, Mineral Commodity Summaries, January 2009

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Processing

Bauxite being loaded at Cabo Rojo, Dominican Republic, to be shipped elsewhere for processing; 2007.

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 alumina and then 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 liquid 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).

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

Wikimedia Commons has media related to: Bauxite

• USGS Minerals Information: Bauxite
• Mineral Information Institute

v • d • e Ore minerals and ore deposits Ore minerals Oxides Cassiterite (tin) · Chromite (chromium) · Hematite (iron) · Ilmenite (titanium) · Magnetite (iron) Sulfides Argentite (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

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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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