Bauxite
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). In Europe and Jamaica, carbonate bauxites have been found above carbonate rocks (limestone and dolomite), where they were formed by the weathering either of intercalated clays or of clayey dissolution residues of the limestone.
The lateritic (silicate) bauxites occur in many countries of the tropical belt. They were formed by lateritization of various silicate rocks, such as granites, gneisses, basalts, syenite, clays, and shales. Compared with iron-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 aluminum content are frequently located below an iron-rich surface layer. The aluminum 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
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
ReferencesISBN links support NWE through referral fees
- Bardossy, Gyorgy, 1982. Karst Bauxites: Bauxite Deposits on Carbonate Rocks. Elsevier Science. ISBN 044499727X and ISBN 978-0444997272.
- Bardossy, Gyorgy, and G.J.J. Aleva, 1990. Lateritic Bauxites. Developments in Economic Geology 27, Elsevier. ISBN 0444988114 and ISBN 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 and ISBN 978-0873352338.
- Misra, Kula C., 2000. Understanding Mineral Deposits. Dordrecht, the Netherlands: Kluwer Academic Publishers. ISBN 0045530092 and ISBN 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 and ISBN 978-1405113175.
- Nesse, William D., 2000. Introduction to Mineralogy. Oxford, UK; New York, NY: Oxford University Press. ISBN 0195106911 and ISBN 978-0195106916.
External links
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