The bauxite is a rock of aluminous continental deterioration or residual rock or otherness. Of varied structure, it contains in variable proportions of the hydrates of Alumine, Kaolinite, Silice and Oxyde S of Fer which confer its characteristic red coloring to him.

Its specific minerals are the alumina hydrates like the polymorphic of (Bayerite and Gibbsite, monoclinical) and those of Hello (OH) (diaspore and Boehmite, orthorhombic). This otherness is regarded as ore of Aluminum only if its total silica content does not cross a variable threshold according to the costs of the process of extraction of alumina (proceeded Bayer), then of the transformation of aluminum alumina by electrolysis. In general, these limiting contents silica do not exceed 8% and to in no case cannot exceed 15%, value for which the alumina hydrates are unstable with the profit of the Kaolinite. By dismantling, this residual rock gives rise to various other rocks of the sedimentary type that it is in seamen circle or continental, even underground by racking in their substrate carbonated by dissolution of the latter (Aramonite).

History

The bauxite was discovered by the chemist Pierre Berthier in 1821 close to the village of the Beam-of-Provence (near to Avignon in France). He discovered bauxite by seeking iron ore for the account of Lyons industrialists.

He gave him the name of alumina ground of the Beams . The name was transformed into beauxite by Armand Dufrénoy in 1847 then in bauxite by Henry Holy-Claire Deville in 1861.

Composition of the ores

General composition

One distinguishes two types of bauxite: bauxite of karst and lateritic bauxite. They consist of minerals of the family of the hydroxides and aluminum oxides, the hydroxides and iron oxides, titanium minerals, argillaceous minerals.

Aluminum oxides and hydroxides

  • the Bayerite α Al (OH) 3 and the Gibbsite γ Al (OH) 3 (also called hydrargillite ) (Monoclinical S). They are present often in lateritic bauxites (bauxite with gibbsite of the Jamaica), one finds them with other aluminum hydroxides in bauxite of karst.

  • the Boehmite : γ Hello (OH) (orthorhombic). Boehmite very present in bauxites of karst is associated with another hydroxide.
  • the Diaspore : α Hello (OH) (orthorhombic)
  • the Corundum : α Al2O3 (trigonal with network rhomboedric)

Iron hydroxides and oxides

Most frequent are:

One also finds the Magnétite (Fe3O4), the Maghémite (γ Fe2O3).

To see:

  • crystalline Structures of the hydroxides oxy-hydroxides and iron oxides

Because of the presence of these iron minerals, the bauxite had been regarded a long time at the XIXe century as an iron ore too high-grade in aluminum to be used.

Titanium minerals

Titanium is mainly present in the form of TiO2 ( Rutile , Anatase , brookite ).

Clay

Concentrated at the base and the top of the layers of bauxite, one frequently finds Kaolinite Al2Si2O5 (OH) 4 often associated with boehmite and the gibbsite, minerals which derive from it by hydrolysis in continental environment or return there by silicification progressing since the sedimentary cover of the ore.

Production

Evolution of the production

(A) 1886: starting of the manufacture of aluminum by the proceeded Héroult-Hall.

Starting

The extraction of bauxite in an industrial way began in 1860 in the French department from the Var. Until 1913, the France was the principal producer, followed by the the United States. Following the First World War, the United States became the first producer.

The period 1920-1939

This period is marked by a diversification of the sources with the emergence of new countries in Europe and of the Caribbean zone to the detriment of the production of the United States.

The period 1950-1990

This period shows almost the disappearance of the historical producers: North America and Europe. The French production ceases with the beginning of the year 1990. On the other hand, Africa and especially Australia become major producers.

(b) Mainly Greece and France. French production ceasing with the 1990.
beginning of the year (c) Mainly the Jamaica and to a lesser extent the Brazil.
(d) Mainly the Guinea.

External bond

  • http://www.mindat.org/min-575.html

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