Bauxite

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Bauxite with US penny for comparison BauxiteUSGOV.jpg
Bauxite with US penny for comparison
QEMSCAN mineral maps of bauxite ore-forming pisoliths Qemscan pisoliths.png
QEMSCAN mineral maps of bauxite ore-forming pisoliths

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 (FeO(OH)) and haematite (Fe2O3), the aluminium clay mineral kaolinite (Al2Si2O5(OH)) and small amounts of anatase (TiO2) and ilmenite (FeTiO3 or FeO.TiO2). [1]

Contents

In 1821 the French geologist Pierre Berthier discovered bauxite near the village of Les Baux in Provence, southern France. [2] [ non-primary source needed ]

Formation

Bauxite with core of unweathered rock Bauxite with unweathered rock core. C 021.jpg
Bauxite with core of unweathered rock

Numerous classification schemes have been proposed for bauxite but, as of 1982, there was no consensus. [3]

Vadász (1951) distinguished lateritic bauxites (silicate bauxites) from karst bauxite ores (carbonate bauxites): [3]

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.

Bauxite output in 2005 2005bauxite.png
Bauxite output in 2005
One of the world's largest bauxite mines in Weipa, Australia Weipa-bauxite-mine.jpg
One of the world's largest bauxite mines in Weipa, Australia

Australia is the largest producer of bauxite, followed by China. [4] In 2017, China was the top producer of aluminium with almost half of the world's production, followed by Russia, Canada, and India. [5] Although aluminium demand is rapidly increasing, known reserves of its bauxite ore are sufficient to meet the worldwide demands for aluminium for many centuries. [6] 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.

2017 total proven bauxite reserves x1,000 Mg [4]
CountryMine productionReserves
Guinea 45,0007,400,000
Australia 83,0006,000,000
Vietnam 2,0003,700,000
Brazil 36,0002,600,000
Jamaica 8,1002,000,000
China 68,0001,000,000
Indonesia 3,6001,000,000
Guyana 1,500850,000
India 27,000830,000
Russia 5,600500,000
Greece 1,800250,000
Saudi Arabia 3,900210,000
Kazakhstan 5,000160,000
Malaysia 1,000110,000
United States W [lower-alpha 1] 20,000
Other countries9,0303,200,000
World total (rounded)300,00030,000,000
  1. Withheld to avoid disclosing company proprietary data

In November 2010, Nguyen Tan Dung, the prime minister of Vietnam, announced that Vietnam's bauxite reserves might total 11,000 Mt (11 trillion kg); this would be the largest in the world. [7]

Processing

Bauxite being loaded at Cabo Rojo, Dominican Republic, to be shipped elsewhere for processing; 2007 CaboRojoDRBauxite.jpg
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. [8] 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 (300 to 390 °F). 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 1,000 °C (1,830 °F). 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. [9]

Source of gallium

Bauxite is the main source of the rare metal gallium. [10]

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. [11] Achievable extraction efficiencies critically depend on the original concentration in the feed bauxite. At a typical feed concentration of 50 ppm, about 15 percent of the contained gallium is extractable. [11] The remainder reports to the red mud and aluminium hydroxide streams. [12]

See also

Related Research Articles

Aluminium Chemical element with atomic number 13

Aluminium is a chemical element with the symbol Al and atomic number 13. It is a silvery-white, soft, non-magnetic and ductile metal in the boron group. By mass, aluminium makes up about 8% of the Earth's crust, where it is the third most abundant element and also the most abundant metal. Occurrence of aluminium decreases in the Earth's mantle below, however. The chief ore of aluminium is bauxite. Aluminium metal is highly reactive, such that native specimens are rare and limited to extreme reducing environments. Instead, it is found combined in over 270 different minerals.

Hydroxide family of the hydroxide salts

Hydroxide is a diatomic anion with chemical formula OH. It consists of an oxygen and hydrogen atom held together by a covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, a ligand, a nucleophile, and a catalyst. The hydroxide ion forms salts, some of which dissociate in aqueous solution, liberating solvated hydroxide ions. Sodium hydroxide is a multi-million-ton per annum commodity chemical. A hydroxide attached to a strongly electropositive center may itself ionize, liberating a hydrogen cation (H+), making the parent compound an acid.

Sodium hydroxide Chemical compound with formula NaOH

Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations Na+
and hydroxide anions OH
.

Aluminium oxide Chemical compound with formula Al2O3

Aluminium oxide (IUPAC name) or aluminum oxide (American English) is a chemical compound of aluminium and oxygen with the chemical formula Al2O3. It is the most commonly occurring of several aluminium oxides, and specifically identified as aluminium(III) oxide. It is commonly called alumina and may also be called aloxide, aloxite, or alundum depending on particular forms or applications. It occurs naturally in its crystalline polymorphic phase α-Al2O3 as the mineral corundum, varieties of which form the precious gemstones ruby and sapphire. Al2O3 is significant in its use to produce aluminium metal, as an abrasive owing to its hardness, and as a refractory material owing to its high melting point.

Aluminium hydroxide chemical compound

Aluminium hydroxide, Al(OH)3, is found in nature as the mineral gibbsite (also known as hydrargillite) and its three much rarer polymorphs: bayerite, doyleite, and nordstrandite. Aluminium hydroxide is amphoteric in nature, i.e., it has both basic and acidic properties. Closely related are aluminium oxide hydroxide, AlO(OH), and aluminium oxide or alumina (Al2O3), the latter of which is also amphoteric. These compounds together are the major components of the aluminium ore bauxite.

Gibbsite form of aluminium hydroxide, mineral

Gibbsite, Al(OH)3, is one of the mineral forms of aluminium hydroxide. It is often designated as γ-Al(OH)3 (but sometimes as α-Al(OH)3.). It is also sometimes called hydrargillite (or hydrargyllite).

Cryolite perovskite, halide mineral (as opposed to the chemical compound)

Cryolite (Na3AlF6, sodium hexafluoroaluminate) is an uncommon mineral identified with the once-large deposit at Ivittuut on the west coast of Greenland, depleted by 1987.

The Bayer process is the principal industrial means of refining bauxite to produce alumina (aluminium oxide) and was developed by Carl Josef Bayer. Bauxite, the most important ore of aluminium, contains only 30–60% aluminium oxide (Al2O3), the rest being a mixture of silica, various iron oxides, and titanium dioxide. The aluminium oxide must be purified before it can be refined to aluminium metal.

Diaspore hydroxide mineral

Diaspore, also known as diasporite, empholite, kayserite, or tanatarite, is an aluminium oxide hydroxide mineral, α-AlO(OH), crystallizing in the orthorhombic system and isomorphous with goethite. It occurs sometimes as flattened crystals, but usually as lamellar or scaly masses, the flattened surface being a direction of perfect cleavage on which the lustre is markedly pearly in character. It is colorless or greyish-white, yellowish, sometimes violet in color, and varies from translucent to transparent. It may be readily distinguished from other colorless transparent minerals with a perfect cleavage and pearly luster—like mica, talc, brucite, and gypsum— by its greater hardness of 6.5 - 7. The specific gravity is 3.4. When heated before the blowpipe it decrepitates violently, breaking up into white pearly scales.

Boehmite hydroxide mineral

Boehmite or böhmite is an aluminium oxide hydroxide mineral, a component of the aluminium ore bauxite. It is dimorphous with diaspore. It crystallizes in the orthorhombic dipyramidal system and is typically massive in habit. It is white with tints of yellow, green, brown or red due to impurities. It has a vitreous to pearly luster, a Mohs hardness of 3 to 3.5 and a specific gravity of 3.00 to 3.07. It is colorless in thin section, optically biaxial positive with refractive indices of nα = 1.644 - 1.648, nβ = 1.654 - 1.657 and nγ = 1.661 - 1.668.

The Deville process was the first industrial process used to produce alumina from bauxite.

Sodium aluminate chemical compound

Sodium aluminate is an inorganic chemical that is used as an effective source of aluminium hydroxide for many industrial and technical applications. Pure sodium aluminate (anhydrous) is a white crystalline solid having a formula variously given as NaAlO2, NaAl(OH)4 (hydrated), Na2O·Al2O3, or Na2Al2O4. Commercial sodium aluminate is available as a solution or a solid.
Other related compounds, sometimes called sodium aluminate, prepared by reaction of Na2O and Al2O3 are Na5AlO4 which contains discrete AlO45− anions, Na7Al3O8 and Na17Al5O16 which contain complex polymeric anions, and NaAl11O17, once mistakenly believed to be β-alumina, a phase of aluminium oxide.

Lepidocrocite hydroxide mineral

Lepidocrocite, also called esmeraldite or hydrohematite, is an iron oxide-hydroxide mineral. Lepidocrocite has an orthorhombic crystal structure, a hardness of 5, specific gravity of 4, a submetallic luster and a yellow-brown streak. It is red to reddish brown and forms when iron-containing substances rust underwater. Lepidocrocite is commonly found in the weathering of primary iron minerals and in iron ore deposits. It can be seen as rust scale inside old steel water pipes and water tanks.

Carl Josef Bayer was an Austrian chemist who invented the Bayer process of extracting alumina from bauxite, essential to this day to the economical production of aluminium.

Aluminium hydroxide oxide or aluminium oxyhydroxide, AlO(OH) is found as one of two well defined crystalline phases, which are also known as the minerals boehmite and diaspore. The minerals are important constituents of the aluminium ore, bauxite.

Laterite A soil and rock type rich in iron and aluminium

Laterite is a soil and rock type rich in iron and aluminium and is commonly considered to have formed in hot and wet tropical areas. Nearly all laterites are of rusty-red coloration, because of high iron oxide content. They develop by intensive and prolonged weathering of the underlying parent rock. Tropical weathering (laterization) is a prolonged process of chemical weathering which produces a wide variety in the thickness, grade, chemistry and ore mineralogy of the resulting soils. The majority of the land area containing laterites is between the tropics of Cancer and Capricorn.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated.

Bauxite tailings Waste product from the production of alumina

Bauxite tailings, also known as bauxite residue, red mud, red sludge, or alumina refinery residues (ARR), is a highly alkaline waste product composed mainly of iron oxide that is generated in the industrial production of alumina. It is important to differentiate between the alkaline waste generated in the Bayer process and the tailings generated during the mining of bauxite. This article specifically covers the alkaline waste generated when operating the Bayer process. The scale of production makes the waste product an important one, and issues with its storage are reviewed and every opportunity is explored to find uses for it.

Compounds of aluminium class of chemical compounds

Aluminium (or aluminum) combines characteristics of pre- and post-transition metals. Since it has few available electrons for metallic bonding, like its heavier group 13 congeners, it has the characteristic physical properties of a post-transition metal, with longer-than-expected interatomic distances. Furthermore, as Al3+ is a small and highly charged cation, it is strongly polarizing and aluminium compounds tend towards covalency; this behaviour is similar to that of beryllium (Be2+), an example of a diagonal relationship. However, unlike all other post-transition metals, the underlying core under aluminium's valence shell is that of the preceding noble gas, whereas for gallium and indium it is that of the preceding noble gas plus a filled d-subshell, and for thallium and nihonium it is that of the preceding noble gas plus filled d- and f-subshells. Hence, aluminium does not suffer the effects of incomplete shielding of valence electrons by inner electrons from the nucleus that its heavier congeners do. Aluminium's electropositive behavior, high affinity for oxygen, and highly negative standard electrode potential are all more similar to those of scandium, yttrium, lanthanum, and actinium, which have ds2 configurations of three valence electrons outside a noble gas core: aluminium is the most electropositive metal in its group. Aluminium also bears minor similarities to the metalloid boron in the same group; AlX3 compounds are valence isoelectronic to BX3 compounds (they have the same valence electronic structure), and both behave as Lewis acids and readily from adducts. Additionally, one of the main motifs of boron chemistry is regular icosahedral structures, and aluminium forms an important part of many icosahedral quasicrystal alloys, including the Al–Zn–Mg class.

References

  1. The Clay Minerals Society Glossary for Clay Science Project Archived 2016-04-16 at the Wayback Machine
  2. 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 credits Berthier with naming "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.
  3. 1 2 Bárdossy, G. (1982). Karst Bauxites. Amsterdam: Elsevier. p. 16. ISBN   978-0-444-99727-2.
  4. 1 2 U.S. Geological Survey, Mineral Commodity Summaries, January 2018 (PDF). U.S. Geological Survey. 2018. pp. 30–31.
  5. https://minerals.usgs.gov/minerals/pubs/commodity/aluminum/mcs-2017-alumi.pdf
  6. "Bauxite and Alumina" (PDF). U.S. Geological Survey. p. 2. Retrieved 9 January 2014.
  7. "Mining Journal - Vietnam's bauxite reserves may total 11 billion tonnes". Archived from the original on 2011-06-16. Retrieved 2010-11-28.
  8. "BBC - GCSE Bitesize: Making aluminium". Archived from the original on 2018-02-25. Retrieved 2018-04-01.
  9. Michael Quinion (2006-01-23). "Aluminium versus aluminum". Worldwidewords.org. Retrieved 2011-12-19.
  10. "Compilation of Gallium Resource Data for Bauxite Deposits Author: USGS" (PDF). Retrieved 2017-12-01.
  11. 1 2 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.
  12. 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