Difference between revisions of "Bauxite" - New World Encyclopedia
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[[Image:Bauxite with unweathered rock core. C 021.jpg|thumb|250px|Bauxite with core of unweathered rock]] | [[Image:Bauxite with unweathered rock core. C 021.jpg|thumb|250px|Bauxite with core of unweathered rock]] |
Revision as of 21:55, 23 February 2007
Bauxite is an aluminum ore. It consists largely of the aluminum minerals gibbsite Al(OH)3, boehmite and diaspore AlOOH, 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-de-Provence in southern France, where it was first discovered in 1821 by geologist Henri Rouvère.
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 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.
World bauxite mine production, reserves, and reserve base
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 |
Processing
Approx. 95% of the world bauxite production is processed into 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 liquor is cooled and seeded with fine grained aluminium hydroxide. Gibbsite is converted into aluminium oxide by heating. This is molten at approximately 1000 °C by addition of cryolite as a flux and reduced to metallic aluminum by a very energy-consumptive electrolytic process (Hall-Héroult process).
See also
ReferencesISBN links support NWE through referral fees
- Bardossy, Gyorgy, 1982. Karst Bauxites: Bauxite Deposits on Carbonate Rocks. Elsevier Science. ISBN 044499727X (ISBN-13: 978-0444997272).
- Bardossy, Gyorgy, and G.J.J. Aleva, 1990. Lateritic Bauxites. Developments in Economic Geology 27, Elsevier. ISBN 0444988114 (ISBN-13: 978-0444988119).
- 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 (ISBN-13: 978-0873352338).
- Misra, Kula C., 2000. Understanding Mineral Deposits. Dordrecht, the Netherlands: Kluwer Academic Publishers. ISBN 0045530092 (ISBN-13: 978-0045530090).
- 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 (ISBN-13: 978-1405113175).
- Nesse, William D., 2000. Introduction to Mineralogy. Oxford, UK; New York, NY: Oxford University Press. ISBN 0195106911 (ISBN-13: 978-0195106916).
External links
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