Difference between revisions of "Bauxite" - New World Encyclopedia

From New World Encyclopedia
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Bauxite is a [[laterite]], a rock formed from intense weathering environments such as found in richly forested, humid, tropical climates.
 
Bauxite is a [[laterite]], a rock formed from intense weathering environments such as found in richly forested, humid, tropical climates.
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From "laterite":
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'''Laterite''' is a surface formation in hot and wet tropical areas which is enriched in iron and aluminum and develops by intensive and long lasting [[weathering]] of the underlying [[parent rock]]. Nearly all kinds of rocks can be deeply decomposed by the action of high rainfall and elevated temperatures. The percolating rain water causes dissolution of primary rock [[minerals]] and decrease of easily soluble elements as [[sodium]], [[potassium]], [[calcium]], [[magnesium]] and [[silicon]]. This gives rise to a residual concentration of more insoluble elements predominantly [[iron]] and [[aluminum]].
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Laterites consist mainly of the minerals [[kaolinite]], [[goethite]], [[hematite]] and [[gibbsite]] which form in the course of weathering. Moreover, many laterites contain [[quartz]] as relatively stable relic mineral from the parent rock. The [[iron oxides]] [[goethite]] and [[hematite]] cause the red-brown color of laterites.
  
 
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"Bauxite is a naturally occurring, heterogeneous material composed primarily of one or more aluminum hydroxide minerals, plus various mixtures of silica, iron oxide, titania, aluminosilicate, and other impurities in minor or trace amounts.  The principal aluminum hydroxide minerals found in varying proportions with bauxites are gibbsite and the polymorphs boehmite and diaspore.  Bauxites are typically classified according to their intended commercial application:  abrasive, cement, chemical, metallurgical, refractory, etc.  The bulk of world bauxite production (approximately 85%) is used as feed for the manufacture of alumina via a wet chemical caustic leach method commonly known as the Bayer process.  Subsequently, the majority of the resulting alumina produced from this refining process is in turn employed as the feedstock for the production of aluminum metal by the electrolytic reduction of alumina in a molten bath of natural or synthetic cryolite (Na3AlF6), the Hall-Héroult process."
 
"Bauxite is a naturally occurring, heterogeneous material composed primarily of one or more aluminum hydroxide minerals, plus various mixtures of silica, iron oxide, titania, aluminosilicate, and other impurities in minor or trace amounts.  The principal aluminum hydroxide minerals found in varying proportions with bauxites are gibbsite and the polymorphs boehmite and diaspore.  Bauxites are typically classified according to their intended commercial application:  abrasive, cement, chemical, metallurgical, refractory, etc.  The bulk of world bauxite production (approximately 85%) is used as feed for the manufacture of alumina via a wet chemical caustic leach method commonly known as the Bayer process.  Subsequently, the majority of the resulting alumina produced from this refining process is in turn employed as the feedstock for the production of aluminum metal by the electrolytic reduction of alumina in a molten bath of natural or synthetic cryolite (Na3AlF6), the Hall-Héroult process."
 
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Revision as of 03:53, 2 March 2007

A sample of bauxite, placed next to a penny.
Bauxite showing a core of unweathered rock.

Bauxite is an important ore of aluminum. It was named after the village Les Baux-de-Provence in southern France, where it was first discovered in 1821 by geologist Henri Rouvère.

Composition

Bauxite is composed of aluminum oxide and hydroxide minerals such as gibbsite (Al(OH)3), boehmite (AlO(OH)), and diaspore (AlO(OH)), as well as clays (such as kaolinite), silt, and iron oxides and hydroxides. It may also contain small amounts of anatase (TiO2).

7777777777 Bauxite is a laterite, a rock formed from intense weathering environments such as found in richly forested, humid, tropical climates.

From "laterite": Laterite is a surface formation in hot and wet tropical areas which is enriched in iron and aluminum and develops by intensive and long lasting weathering of the underlying parent rock. Nearly all kinds of rocks can be deeply decomposed by the action of high rainfall and elevated temperatures. The percolating rain water causes dissolution of primary rock minerals and decrease of easily soluble elements as sodium, potassium, calcium, magnesium and silicon. This gives rise to a residual concentration of more insoluble elements predominantly iron and aluminum.

Laterites consist mainly of the minerals kaolinite, goethite, hematite and gibbsite which form in the course of weathering. Moreover, many laterites contain quartz as relatively stable relic mineral from the parent rock. The iron oxides goethite and hematite cause the red-brown color of laterites.

77777777777 888888888888

"Bauxite is a naturally occurring, heterogeneous material composed primarily of one or more aluminum hydroxide minerals, plus various mixtures of silica, iron oxide, titania, aluminosilicate, and other impurities in minor or trace amounts. The principal aluminum hydroxide minerals found in varying proportions with bauxites are gibbsite and the polymorphs boehmite and diaspore. Bauxites are typically classified according to their intended commercial application: abrasive, cement, chemical, metallurgical, refractory, etc. The bulk of world bauxite production (approximately 85%) is used as feed for the manufacture of alumina via a wet chemical caustic leach method commonly known as the Bayer process. Subsequently, the majority of the resulting alumina produced from this refining process is in turn employed as the feedstock for the production of aluminum metal by the electrolytic reduction of alumina in a molten bath of natural or synthetic cryolite (Na3AlF6), the Hall-Héroult process." 88888888888

Formation

In the geosciences, 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 either 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 granites, gneisses, basalts, syenite, clays and shales. Compared with Fe-rich laterites the formation of bauxites demands even stronger weathering conditions with a very good drainage. This enables dissolution of kaolinite and precipitation of gibbsite. Zones with highest Al contents are frequently located below a feruginous surface layer. The aluminium hydroxide in the lateritic bauxite deposits is almost exclusively gibbsite.

Processing and applications

Approximately 95 percent of the world's bauxite production is processed into aluminum. Bauxites are typically classified according to their intended commercial application: metallurgical, abrasive, cement, chemical, and refractory.

In the Bayer process, bauxites are heated in pressure vessels with sodium hydroxide solution at 150-200 °C. As a result, the aluminum in the ore is dissolved as aluminate. The ferruginous (iron-rich) residue (red mud) is separated by filtering, and pure gibbsite is precipitated when the liquor is cooled and seeded with fine-grained aluminum hydroxide. Gibbsite is converted into aluminum oxide by heating. This product is molten at approximately 1000 °C by addingcryolite as a flux, and it is reduced to metallic aluminum by a very energy-consumptive electrolytic process called the Hall-Héroult process.

World bauxite mine production, reserves, and reserve base

(x1000 tonne, Numbers for 2001 estimated)
Country Mine production Reserves Reserve base
2000 2001
Australia 200–800 53,500 3,800,000 7,400,000
Brazil 14,000 14,000 3,900,000 4,900,000
People's Republic of China 9,000 9,200 720,000 2,000,000
Guinea 15,000 15,000 7,400,000 8,600,000
Guyana 2,400 2,000 700,000 900,000
India 7,370 8,000 770,000 1,400,000
Jamaica 11,100 13,000 2,000,000 2,500,000
Russia 4,200 4,000 200,000 250,000
Suriname 3,610 4,000 580,000 600,000
United States NA NA 20,000 40,000
Venezuela 4,200 4,400 320,000 350,000
Other countries 10,800 10,200 4,100,000 4,700,000
World total (rounded) 135,000 137,000 24,000,000 34,000,000

See also

References
ISBN links support NWE through referral fees

  • Kogel, Jessica Elzea, Nikhil C. Trivedi, James M. Barker, and Stanley T. Krukowski (editors), 2006. Industrial Minerals & Rocks: Commodities, Markets, and Uses (Seventh Edition). Littleton, CO: Society for Mining, Metallurgy, and Exploration. ISBN 0873352335 and ISBN 978-0873352338.
  • Moon, Charles J., Michael E.G. Whateley, and Anthony M. Evans (editors), 2006. Introduction to Mineral Exploration (Second Edition). Malden, MA: Blackwell Publishing. ISBN 1405113170 and ISBN 978-1405113175.

External links

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