Bauxites


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Bauxites

 

rock consisting basically of hydrates of alumina and iron oxides, with an admixture of other mineral components. The basic chemical component of bauxite is alumina (Al2O3) and the constant constituent is iron oxide (Fe2O3). The most harmful admixture is silica (SiO2). Other admixtures may be titanium dioxide (TiO2), calcium oxide (CaO), magnesium oxide (MgO), manganese oxide (MnO), phosphorous pentoxide (P2O5), and others.

The color of bauxite is various shades of red (from rose to dark red) and gray (from greenish-gray to dark gray, almost black). The density varies from 2,900 kg per m3 to 3,500 kg per m3, depending on the iron oxide content. Hardness of the densest varieties ranges up to 6 on the mineralogical scale. The structure of bauxite is dense (jasper-like), pisolitic, oolitic, porous, or friable (ocherous). The rock-forming minerals are monohydrates of alumina, namely diaspore and boehm-ite, and a trihydrate, gibbsite (hydrargillite), with admixtures of the hydroxide and iron oxide mineral groups (goethite, hydrogoethite, hydrohematite, and others), kao-linite, chlorites, calcite, halloysite, and others. Depending on the type of rock-forming minerals, three types of bauxite are distinguished: (1) monohydrate, containing alumina in a monohydrate form (diaspore, boehmite), (2) trihydrate, containing alumina in the trihydrate form (gibbsite), and (3) mixed, in which there are both forms. The formation of bauxite deposits is mainly connected with the processes of lateritic weathering of alkaline, acidic, and occasionally basic rocks, or with the sedimentation process in ocean and lake basins of large quantities of alumina, which is present in transferable molecule solutions and sols.

According to generic signs, bauxite deposits are divided into two basic kinds: (1) platform deposits, connected with horizontal continental sediments; and (2) deposits of geosynclinal regions, confined to coastline sediments.

The alumina content of commercial bauxites ranges from 28 percent to 60 percent, and more. The silicous ratio (relation of alumina to silica) in bauxite used to get aluminum must not be lower than 2.1 to 2.6. Bauxite’s greatest importance is as a raw material for the derivation of aluminum. Bauxites are also used in the production of paints, artificial abrasives, as flux (in the iron and steel industry), and as sorbents for cleansing oil products of various impurities. In addition aluminous cement is obtained from bauxite through agglutination or smelting, and synthetic corundum is obtained from smelting in electric furnaces. Bauxite rocks of low iron content with a heat-resistance of 1770° C to 1900° C are used to make high-alumina refractory material.

In the USSR large bauxite deposits are distributed in the Urals (Sverdlovsk Oblast, Bashkir ASSR), in the Kazakh SSR (particularly the Turgai bauxite region), in Western and Eastern Siberia (particularly Altai Krai, Krasnoiarsk Krai, and others), Leningrad and Arkhangel’ Oblasts, and others. Of the foreign socialist countries Hungary, China, and Rumania have the largest reserves of bauxite.

Of the capitalist and developing countries the following particularly stand out by the size of their explored bauxite reserves: Jamaica, Guyana, Surinam, and Brazil in the Americas; Ghana and Guinea in Africa; France in Europe; and India in Asia; large bauxite formations have been discovered in the Australian Union. The total yield of bauxite in capitalist and developing countries was 2.7 million tons (t) in 1937, 21.4 million t in 1960, 29.2 million t in 1965, and 35.7 million t in 1967 (see Table 1).

With the over 13–fold growth of the bauxite yield from 1937 to 1967 came sharp changes in its geographic distribution; in 1937 the share of the Western European countries was 46 percent and of the Americas 44 percent, while in 1967 it was, correspondingly, already 13.3 percent and 61 percent. Jamaica, where large deposits of bauxite were explored only in the years of World War II, moved into first place. The share of the African countries and of the Australian Union is growing. The exploitation of the basic bauxite deposits in capitalist and developing countries is controlled by a few powerful companies of the leading capitalist countries (largely by US monopolies in Jamaica, Surinam, and

Table 1. Bauxite extraction in capitalist and developing countries (in tons)
Country193711966196719682
1 Data for territories is calculated for present-day borders
2 Estimate
Total2,674,00031,182,00035,715,000
North America432,00012,075,00012,638,000
 Haiti362,000460,000477,000
 Dominican Republic818,0001,092,0001,008,000
 United States432,0001,825,0001,690,0001,687,000
 Jamaica9,070,0009,396,0008,757,000
South America768,0008,188,0009,147,000
 Brazil9,000250,000302,000227,000
 Guyana367,0003,348,0003,380,0003,723,000
 Surinam392,0004,590,0005,465,0005,659,000
Western Europe1,233,0004,452,0004,744,000
 Greece137,0001,383,0001,687,0001,764,000
 Italy387,000255,000242,000216,000
 France691,0002,810,0002,813,0002,713,000
 Federal Republic of Germany4,0004,0002,0003,000
Asia233,0002,405,0002,601,000
 India15,000750,000790,000951,000
 Indonesia199,000700,000912,000879,000
 Malaysia19,000955,000899,000798,000
 Africa2,235,0002,349,000
 Ghana352,000350,000285,000
 Republic of Guiana1,608,0001,665,0001,814,000
 Sierra Leone275,000334,000421,000
Australia8,0001,827,0004,236,0004,957,000

Guyana; in France, largely by the French companies Pechiney and Ugine; in Ghana, by British aluminum companies; and so on), in whose hands is concentrated the commanding portion of the aluminum industry of the capitalist world.

REFERENCES

Boksity, ikh mineralogiia i genezis. Moscow, 1958.
Kratkii kurs mestorozhdenii poleznykh iskopaemykh. Edited by S. A. Vakhromeev. Moscow, 1967.
Rozin, M. S. Geografiia poleznykh iskopaemykh kapitalisticheskikh i razvivaiushchikhsia stran. Moscow, 1966.

M. S. ROZIN

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