Bauxite

From Wikipedia, the free encyclopedia
Jump to navigation Jump to search
Bauxite with US penny for comparison
QEMSCAN mineral maps of bauxite ore-forming pisoliths
Bauxite in Les Baux-de-Provence, France
Bauxite with core of unweathered rock
Bauxite output in 2005
One of the world's largest bauxite mines in Weipa, Australia

Bauxite is a sedimentary rock with a relatively high aluminium content. It is the world's main source of aluminium. Bauxite consists mostly of the aluminium minerals gibbsite (Al(OH)3), boehmite (γ-AlO(OH)) and diaspore (α-AlO(OH)), mixed with the two iron oxides goethite and haematite, the aluminium clay mineral kaolinite and small amounts of anatase (TiO2) and ilmenite (FeTiO3 or FeO.TiO2).[1][2]

In 1821 the French geologist Pierre Berthier discovered bauxite near the village of Les Baux in Provence, southern France.[3] In 1861, French chemist Henri Sainte-Claire Deville named the substance "bauxite".[4]

Formation

Lateritic bauxites (silicate bauxites) are distinguished from karst bauxite ores (carbonate bauxites). The carbonate bauxites occur predominantly in Europe, Guyana, 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.[5] 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.

Numbers for 2010's total proven bauxite reserves x1,000 Mg[6]
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[7]
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[7] 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 11,000 Mt; this would be the largest in the world.[8]

Processing

Bauxite being loaded at Cabo Rojo, Dominican Republic, to be shipped elsewhere for processing; 2007
Bauxite being digested by washing with a hot solution of sodium hydroxide at 175 °C (347 °F) under pressure at National Aluminium Company, Nalconagar, India.

Bauxite is usually strip mined because it is almost always found near the surface of the terrain, with little or no overburden. As of 2010, approximately 70% to 80% of the world's dry bauxite production is processed first into alumina and then into aluminium by electrolysis.[9] 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 (1,760 °F) 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, and prior to the Deville process, aluminium ore was refined 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.[10]

Source of gallium

Bauxite is the main source of the rare metal gallium.[11]

During the processing of bauxite to alumina in the Bayer process, gallium accumulates in the sodium hydroxide liquor. From this it can be extracted by a variety of methods. The most recent is the use of ion-exchange resin[12]. Achievable extraction efficiencies critically depend on the original concentration in the feed bauxite. At a typical feed concentration of 50 ppm, about 15 % of the contained gallium is extractable[12]. The remainder reports to the red mud and aluminium hydroxide streams.[13]

See also

References

  1. ^ Geological Survey Professional Paper page b20[permanent dead link]
  2. ^ The Clay Minerals Society Glossary for Clay Science Project Archived 2016-04-16 at the Wayback Machine.
  3. ^ 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.
  4. ^ 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 aluminous substances.), Annales de Chimie et de Physique, 3rd series, 61 : 309-342.
  5. ^ "Bauxite and Alumina" (PDF). U.S. Geological Survey. p. 2. Retrieved 9 January 2014. 
  6. ^ "Bauxite and Alumina" (PDF). U.S. Geological Survey (Mineral Commodity Summaries). January 2012. p. 27. Retrieved August 1, 2012. 
  7. ^ a b "World mineral statistics | MineralsUK". Bgs.ac.uk. Retrieved 2013-10-25. 
  8. ^ "Mining Journal - Vietnam's bauxite reserves may total 11 billion tonnes". Archived from the original on 2011-06-16. Retrieved 2010-11-28. 
  9. ^ "BBC - GCSE Bitesize: Making aluminium". Retrieved 2018-04-01. 
  10. ^ "Aluminium versus aluminum Author: Michael Quinion, 1996–2011". Worldwidewords.org. 2006-01-23. Retrieved 2011-12-19. 
  11. ^ "Compilation of Gallium Resource Data for Bauxite Deposits Author: USGS" (PDF). Retrieved 2017-12-01. 
  12. ^ a b Frenzel, Max; Ketris, Marina P.; Seifert, Thomas; Gutzmer, Jens (March 2016). "On the current and future availability of gallium". Resources Policy. 47: 38–50. doi:10.1016/j.resourpol.2015.11.005. 
  13. ^ Moskalyk, R. R. (2003). "Gallium: the backbone of the electronics industry". Minerals Engineering. 16 (10): 921–929. doi:10.1016/j.mineng.2003.08.003. 

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

Retrieved from "https://en.wikipedia.org/w/index.php?title=Bauxite&oldid=846304746"
This content was retrieved from Wikipedia : http://en.wikipedia.org/wiki/Bauxite
This page is based on the copyrighted Wikipedia article "Bauxite"; it is used under the Creative Commons Attribution-ShareAlike 3.0 Unported License (CC-BY-SA). You may redistribute it, verbatim or modified, providing that you comply with the terms of the CC-BY-SA