Bauxite
Bauxite, an aluminium ore, is the world's main source of aluminium. It consists mostly of the minerals gibbsite Al(OH)3, boehmite γ-AlO(OH) and diaspore α-AlO(OH), mixed with the two iron oxides goethite and haematite, the clay mineral kaolinite and small amounts of anatase TiO2. In 1821 the French geologist Pierre Berthier discovered bauxite near the village of Les Baux in Provence, southern France.[1] In 1861, French chemist Henri Sainte-Claire Deville named the mineral "bauxite".[2]
Formation
Lateritic bauxites (silicate bauxites) are distinguished from karst bauxite ores (carbonate bauxites). The 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 clay layers – dispersed clays which were concentrated as the enclosing limestones gradually dissolved during chemical weathering.
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 depends 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 2009, Australia was the top producer of bauxite with almost one-third of the world's production, followed by China, Brazil, India, and Guinea. Although aluminium demand is rapidly increasing, known reserves of its bauxite ore are sufficient to meet the worldwide demands for aluminium for many centuries.[3] 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.
| Country | Mine production | Reserves | Reserve base | |
|---|---|---|---|---|
| 2010 | 2011 (est.) | |||
 Guinea | 17,400 | 18,000 | 7,400,000 | 8,600,000 |
 Australia | 68,400 | 67,000 | 6,200,000 | 7,900,000 |
 Vietnam | 80 | 80 | 2,100,000 | 5,400,000 |
 Jamaica | 8,540 | 10,200 | 2,000,000 | 2,500,000 |
 Brazil | 28,100 | 31,000 | 3,600,000 | 2,500,000 |
 Guyana | 1,760 | 2,000 | 850,000 | 900,000 |
 India | 18,000 | 20,000 | 900,000 | 1,400,000 |
 China | 44,000 | 46,000 | 830,000 | 2,300,000 |
 Greece | 2,100 | 2,100 | 600,000 | 650,000 |
 Iran | — | 500[5] | — | — |
 Suriname | 4,000 | 5,000 | 580,000 | 600,000 |
 Sierra Leone | 1,090 | 1,700 | 180,000 | ? |
 Kazakhstan | 5,310 | 5,400 | 160,000 | 450,000 |
 Venezuela | 2,500 | 4,500 | 320,000 | 350,000 |
 Russia | 5,480 | 5,800 | 200,000 | 250,000 |
 United States | 30[5] | N/A | 20,000 | 40,000 |
| Other countries | 2,630 | 2,600 | 3,300,000 | 3,800,000 |
| World total (rounded) | 209,000 | 220,000 | 29,000,000 | 38,000,000 |
In November 2010, Nguyen Tan Dung, the prime minister of Vietnam, announced that Vietnam's bauxite reserves might total 11000 Mt; this would be the largest in the world.[6]
Processing
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 sodium aluminate (the Bayer process). The aluminium compounds in the bauxite may be present as gibbsite(Al(OH)3), boehmite(AlOOH) or diaspore(AlOOH); the different forms of the aluminium component will dictate the extraction conditions. The undissolved waste, bauxite tailings, after the aluminium compounds are extracted contains iron oxides, silica, calcia, titania and some un-reacted alumina. After separation of the residue 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 in rotary kilns or fluid flash calciners to a temperature in excess of 1000oC. This aluminium oxide is dissolved at a temperature of about 960 °C in molten cryolite. 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, named after its American and French discoverers.
Prior to the invention of this process in 1886, 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.[7]
See also
References
- ↑ P. Berthier (1821) "Analyse de l'alumine hydratée des Beaux, département des Bouches-du-Rhóne" (Analysis of hydrated alumina from Les Beaux, department of the Mouths-of-the-Rhone), Annales des mines, 1st series, 6 : 531-534.
- ↑ Notes:
- In 1847, in the cumulative index of volume 3 of his series, Traité de minéralogie, French mineralogist Armand Dufrénoy listed the hydrated alumina from Les Beaux as "beauxite". (See: A. Dufrénoy, Traité de minéralogie, volume 3 (Paris, France: Carilian-Goeury et Vor Dalmont, 1847), p. 799.)
- In 1861, H. Sainte-Claire Deville named "bauxite" on p. 309, "Chapitre 1. Minerais alumineux ou bauxite" of: H. Sainte-Claire Deville (1861) "De la présence du vanadium dans un minerai alumineux du midi de la France. Études analytiques sur les matières alumineuses." (On the presence of vanadium in an alumina mineral from the Midi of France. Analytical studies of aluminum substances.), Annales de Chimie de de Physique, 3rd series, 61 : 309-342.
- ↑ "Bauxite and Alumina" (PDF). U.S. Geological Survey. p. 2. Retrieved 9 January 2014.
- ↑ "Bauxite and Alumina" (PDF). U.S. Geological Survey (Mineral Commodity Summaries). January 2012. p. 27. Retrieved August 1, 2012.
- 1 2 "World mineral statistics | MineralsUK". Bgs.ac.uk. Retrieved 2013-10-25.
- ↑ "Mining Journal - Vietnam’s bauxite reserves may total 11 billion tonnes". Retrieved 2010-11-28.
- ↑ "Aluminium versus aluminum Author: Michael Quinion, 1996–2011". Worldwidewords.org. 2006-01-23. Retrieved 2011-12-19.
Further reading
- Bárdossy, G. (1982): Karst Bauxites: Bauxite deposits on carbonate rocks. Elsevier Sci. Publ. 441 p.
- Bárdossy, G. and Aleva, G.J.J. (1990): Lateritic Bauxites. Developments in Economic Geology 27, Elsevier Sci. Publ. 624 p. ISBN 0-444-98811-4
- 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
- Hanilçi, N. (2013). Geological and geochemical evolution of the Bolkardaği bauxite deposits, Karaman, Turkey: Transformation from shale to bauxite. Journal of Geochemical Exploration
External links
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Wikimedia Commons has media related to Bauxite. |
- USGS Minerals Information: Bauxite
- Mineral Information Institute
"Bauxite". New International Encyclopedia. 1905.
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