Bauxite

Detail of the external structure of this rock, appreciating the presence of iron oxide.

Bauxite is a sedimentary rock with a relatively high aluminum content. It is the main source of aluminum in the world. Bauxite consists mainly of the aluminum minerals gibbsite (Al(OH)₃), boehmite (γ-AlO(OH)), and diaspore (α-AlO(OH)), mixed with two oxides of iron, goethite and hematite, aluminum clay minerals, kaolinite, and small amounts of anatase (TiO₂) and ilmenite (FeTiO₃ or FeO.TiO ₂).

It can be both soft and hard, composed of hydrated aluminum oxides. It originates as a residue produced by the chemical weathering of a wide range of rocks commonly rich in clay. Some bauxites have a more complex origin and can be reprocessed chemical precipitates. Commonly forms in the tropics in hot and humid climate zones.

Bauxite received its name in reference to the city of Les Baux, in Provence (France), where the geologist Pierre Berthier identified it in 1821 and named it bauxite, his name in French.

Appearance, composition and chemistry

Abandoned bauxite mine in Gánt, Hungary.

Bauxite can have various colors, including pink, red, cream, brown, gray and yellow. When it is reddish, it is due to iron oxides. The structure is also variable and can be porous, compact, stratified, structureless, pisolithic, or with shell-like structures. Other bauxites preserve the original rock structure and are pseudomorphic.

In a simplified way, the chemistry of bauxite can be expressed in the following formula:

AlOX(OH)3− − 2X{displaystyle AlO_{X}(OH)_{3-2X}}}

where X can be a number between 0 and 1.

Training

Bauxite with non-tempered rock core

Numerous grading schemes for bauxite have been proposed but, until 1982, there was no consensus.

Vadász (1951) distinguished lateritic bauxites (silicate bauxites) from karst mineral bauxites (carbonate bauxites):

• Carbonate bauxites occur predominantly in Europe, Guyana, Suriname and Jamaica on carbonated rocks (limestone and dolomite), where they were formed by lateritic meteorization and residual accumulation of intercalated clay layers - scattered clays that concentrated as the wrapping limes gradually dissolved during chemical meteorization.
• Lateritic bauxites are mostly found in the tropic countries. They were formed by lateritization of several silicate rocks such as granite, gneis, basalt, sienite, and schist. Compared to iron-rich laterites, the formation of bauxites depends even more on intense weather conditions in a place with very good drainage. This allows the dissolution of the caolinite and the precipitation of the gibbsita. The areas with the highest aluminum content are often below a surface layer of ferruginous. Aluminum hydroxide in the laterite deposits of bauxite is almost exclusively gibbsita.

In the case of Jamaica, a recent soil analysis showed elevated levels of cadmium, suggesting that the bauxite originates from Miocene volcanic ash deposits from episodes of significant volcanism in Central America.

Mining

Production of bauxite in 2005, as a percentage of Australian production.

It is the main aluminum ore used by the industry. Bauxite is generally extracted by an open pit mining system, approximately 4 to 6 meters deep. Between 85 and 95% of the bauxite mined is used in aluminum production. There are numerous bauxite deposits, mainly in tropical and subtropical regions, and also in Europe. Some of the main countries where bauxite is mined are Brazil, Jamaica, and Australia. The iron content in bauxites raises the cost of aluminum production, so iron-rich bauxites are undesirable for aluminum production.

"From this bauxitic clay, high-grade bauxite can be obtained by eliminating the clayey fraction and recovering the gibbsite aggregates, by washing and sieving. These aggregates contain 59% Al2 O3 and 3% SiO2 and 4.5% Fe2 O3•

in Colombia, in an area of 1000km2, between the departments of Cauca and Valle, it is estimated at 750'000,000 tons of bauxftic clay on a dry basis that would allow the extraction of 93'750,000 tons of gibsftic aggregates".

Total proven reserves and bauxite production in 2019. Numbers represent x1,000 tons

Country	Mining production		Reservations	Reserve base
	2019	2020 (est.)
Australia	105 000	110 000	5 100 000	-
ChinaChina	70 000	60 000	1 000	-
GuineaGuinea	67 000	82 000	7 400 000	-
BrazilBrazil	34 000	35 000	2 700 000	-
India	23 000	22 000	660 000	-
IndonesiaIndonesia	17 000	23 000	1 200 000	-
Jamaica	9 020	7 700	2 000 000	-
Kazakhstan Kazakhstan	5 800	5 800	160 000	-
Russia Russia	5 570	6 100	500 000	-
Saudi ArabiaSaudi Arabia	4 050	4 000	190 000	-
VietnamVietnam	4 000	4 000	3 700 000	-
MalaysiaMalaysia	900	500	170 000	-
Other countries	12 000	11 000	4 900 000	-
Total world (rounded)	358 000	371 000	30 000	-