Bauxites

(Map) Bauxites

BAUXITES (from the name of the Les Baux place, at the south of France, where their depositions have been discovered for the first time * EN: bauxite; DE: Bauxite; FR: bauxites; ES: bauxitas; RU: бокситы) are the aluminium ore, which is consisting mainly of the aluminium hydroxides, iron oxides and hydroxides, and clayish minerals.

The main ore-forming minerals of the bauxites are: diaspore, boehmite, gibbsite, goethite, hydrogoethite, hydrohematite, kaolinite, chamosite, chlorites, rutile, anatase, ilmenite, alumino-goethite, alumino-hematite, siderite, calcite, micas. According to appearance, bauxites are very diverse. Their colour is usually red, reddish-brown, less often gray, white, yellow, black. They distinguish the bauxites: according to the aggregation state, dense (stony), porous, earthy, loose, and clay-like; according to the structural features, clastic (pelite, sandstone, gritstone, conglomerate), and concretions (oolite, pisolite, bean); according to the texture, colloform (homogeneous, layered, and so on). Because of the different porosity, the density of the bauxites varies from 1800 (the loose bauxites) to 3200 kilograms per cubic metre (the stony bauxites).

According to the prevalent mineral composition, they distinguish the bauxites: mono-hydroxide, formed with the diaspore, boehmite; tri-hydroxide, formed with the gibbsite; of the mixed composition, formed with the diaspore-boehmite, boehmite-gibbsite. There also exist the more fractional sub-divisions of bauxites, depending on the mineral composition: chamosite-boehmite, chamosite-gibbsite, gibbsite-kaolinite, goethite-chamosite-boehmite, kaolinite-boehmite, and others. According to the conditions of the forming, bauxites are divided mainly into the laterite (residual) varieties, and the redeposited (sedimentary) varieties. Bauxites have formed themselves either as the result of the deep chemical processing (laterization) of the alumino-silicate rocks under the conditions of the humid tropical climate (the lateritic bauxites), or as the result of the transfer of the products from the lateritic weathering, and of their redeposition (the sedimentary bauxites). Depending on the tectonic situation, they distinguish the bauxites of the craton and geosynclinal regions, and also the bauxites of the oceanic islands. Bauxites form tabular and lenticular bodies with varying thickness, and according to the projection onto the horizontal plane, the depositions of the linear, isometric, and irregular shape. Not rarely, the depositions consist of several (according to the vertical cross section) lenses. The quality of the lateritic bauxites is usually high, while the sedimentary bauxites may be from the high-grade quality (for example, the North-Ural deposits), to the substandard quality (the Bokson deposit within Buryatia).

Bauxites are the main ore for the extraction of alumina (Al2O3) and aluminium; they are used within the abrasive industry (electro-corundum), within the ferrous metallurgy (flux during the smelting of the open-hearth steel); the low-iron bauxites are used for the obtainment of the high-alumina mullitized refractories, of the fast-hardening alumina cements, and so on. Bauxites are the complex raw materials; they contain Ga, and also Fe, Ti, Cr, Zr, Nb, rare earth elements. Within the USSR, the requirements for the quality of the extracted (marketable) bauxites are determined by the GOST governmental standard, and also by the contractual conditions between the suppliers and consumers. According to the classification from the active GOST 972-74 standard, bauxites are divided into the 8 marks, depending on the weight ratio between the contents of alumina and silica (the so named silicon module). For the lowest mark (B-6, II grade), the silicon module must not be less than 2, with the content of alumina at least 37%; for the high-grade bauxites (B-0, B-00), the silicon module is more than 10, with the content of alumina 50% and more. The special grades and marks of bauxites have their own fields of usage within the industry.

They extract bauxites using the opencast, less often underground methods. The choice of the technological scheme for the processing of bauxites depends on their composition. The production of aluminium from bauxites is performed through 2 stages: at the first stage, they obtain alumina using the chemical methods, and at the second stage, they isolate the pure metal from alumina, using the method of electrolysis within the melt of the fluoride salts of aluminium. During the obtainment of alumina, they use mainly the hydrochemical Bayer method, the sintering method, and the combined Bayer-sintering method (parallel and serial variants). The schematic diagram of the Bayer process includes the treating (leaching) of the finely grinded bauxites with the concentrated sodium hydroxide solution, as the result of which alumina goes into the solution in the form of the sodium aluminate (NaAl3O2). Out of the aluminate solution, which has been purified of the red sludge, they precipitate the aluminium hydroxide (alumina). They process the low-quality bauxites using more complicated method, namely, using the sintering method, during which they sinter the three-component charge (the mixture of the grinded bauxite with limestone and soda) at the temperature of 1250 degrees Celsius within the rotating kilns. They leach the sinter, which has been obtained, with the circulating alkaline solution of the low concentrations. They separate and filter the hydroxide, which has been precipitated. The parallel combined Bayer-sintering scheme prescribes the simultaneous processing of the high-quality and low-grade (high-silicon) bauxites at the single industrial plant. The sequential combined scheme of this method includes the processing of bauxites into alumina first by the Bayer method, and later the additional extraction of alumina from the red sludges using the method of their sintering with limestone and soda. The major bauxite-bearing regions (see the Map) are located within the European part of the USSR, at the Ural mountains, and within Kazakhstan.

Within the European part, they are known within the Arkhangelsk province of the Russian Federation (Iksinskoe, and others), at the Middle (Vezhayu-Vorykvinskoe, and others) and Southern Timan (Timsherskoe, Puzlinskoe, and others), within the Leningrad (Tikhvinskoe) and Belgorod (Vislovskoe, and others) provinces of the Russian Federation. At the Ural mountains, the deposits of bauxites are being developed within the Sverdlovsk (Severouralsk bauxite-bearing region) and Chelyabinsk (South Ural deposits) provinces of the Russian Federation. Within the limits of the Northern Kazakhstan, the depositions of bauxites are concentrated within the Kostanay (Krasnooktyabrskoe deposit, Belinskoe, Ayatskoe, Eastern Ayatskoe, and other deposits) and Turgay (Eastern Turgay group of deposits) provinces of the Kazakh SSR. Within the eastern Siberia, bauxites are available within the region of the Chadobetskoe uplift near the Angara river, and within the eastern Sayan (Boksonskoe deposit).

The most ancient bauxites within the USSR are known at the Boksonskoe deposit (pre-Cambrian, Vendian). The bauxites of the North Ural group are associated with the depositions of the Middle Devonian, the Middle Timan bauxites are associated with the depositions of the Middle and Upper Devonian. The bauxites of the Iksinskoe and Vislovskoe deposits are embedded within the depositions of the Lower Carboniferous, the deposits of the Northern Kazakhstan have formed themselves during the Cretaceous and Paleogene time, and are youngest.

There have the large reserves of bauxites China (the deposits within the Shandong, Henan, Gansu, Yunnan, Liaoning, Shaanxi, and other provinces), Hungary (the Halimba, Nirad, Iskasentdёrd, Gant, and other deposits), Yugoslavia (the Vlasenica, Drnis, Lika plateau, Biela Lipa, Obrovac, Niksic, Bijelo Polyana deposits), the deposits of bauxites are also known within the Romania, Vietnam, and North Korea.

Within the industrially developed capitalistic and developing countries, the reserves of bauxites by the start of the 1982 amounted to approximately 22 billion tonnes, including the proven reserves of 13.5 billion tonnes. The major reserves of bauxites are accounted for the territories of the developing countries, namely, approximately 75% (16.7 billion tonnes), including the proven reserves of approximately 75% (10.1 billion tonnes). Within the developed countries, the deposits of the high quality bauxites are known in the form of the laterite covers on the territory of Australia; their share within the total reserves is approximately 20%. The major part of the bauxite deposits is situated on the poorly researched territories of the countries within the tropical belt, and because of this fact, it is assumed, that the tendency of the faster growth of reserves in comparison with extraction will preserve itself.

During the 1974, there has been created the International Association of the bauxite-extracting countries (International Bauxite Association). There have entered initially into its structure Australia, Guinea, Jamaica, Guyana, Suriname, and Yugoslavia, and later Ghana, Haiti, and the Dominican Republic. There also have the significant reserves of bauxites Brazil, Greece, India, Turkey, USA, France.

The extraction of bauxites within the industrially developed capitalistic and developing countries during the 1981 has amounted to 73.0 million tonnes, including 40.9 within the developing countries, and 32.12 within the industrially developed countries. There holds the 1st place in the extraction of bauxites Australia, then Guinea, Jamaica, Suriname, Brazil, Guyana. During the prospective future, the greatest increase of the productive capacities for the extraction of bauxites is expected within Australia, Guinea, and Brazil. According to the forecasts (80-ies - 90-ies), the absolute majority of the alumina industrial plants will be built within the bauxite-extracting countries, and the volume of the external commerce dealing with bauxites, which at the start of the 80-ies has amounted to approximately 35 million tonnes, will grow with the relatively slow tempos.

See also the "Aluminium industry" article.