BENTONITE, bentonite clays (from the name of the Fort Benton city, within the Montana state, within the USA, within the region of which this clay has been uncovered for the first time * EN: bentonite, bentonite clay, mineral soap; DE: Bentonit; FR: bentonite; ES: bentonita; RU: бентонит) are the clays, which are consisting mostly of the minerals of the montmorillonite group (less often palygorskite) and which disperse themselves within water up to the colloidal state.

Bentonite possesses the increased binding ability, high capacity of the exchangeable bases, high sorptive and catalytic activity. Besides montmorillonite, there may exist as the impurity within bentonite the hydromicas, kaolinite, palygorskite, cristobalite, zeolites, and other minerals. The alkaline bentonites distinguish themselves by the high plasticity and by the swelling capacity (approximately by 8 times). There are distinguished 3 industrial-genetic types of the deposits of bentonite: hydrothermal-metasomatic, volcanogenic-sedimentary, and terrigenous-sedimentary. The first two types have been formed as the result of the hydrothermal metasomatism, or of the underwater conversion of the volcanic ashes, tuffs, and other volcanogenic and volcanogenic-sedimentary rocks; the third type comprises the redeposition and diagenetic alterations of the products of water erosion of the crusts of weathering, and of the de-crystallization of the colloid-dispersive products. The colour of the slightly altered bentonites ranges from white to light-green and light-blue, becoming during their weathering creamy, and later yellow, red, or brown. Bentonite is fatty and soap-like for the touch. Within the USSR, the clays of the bentonite type have the local (within the Caucasus, Central Asia) names, namely, askangel, gilyabi, gumbrin, kil.

They widely use bentonite within the national economy: within the mining-extracting industry, for the preparation of the drilling fluids; within the foundry production, as the binding and plasticizing additives for the obtainment of the molding mixtures, and for the facing of the furnaces by the fireclay bricks; within the ferrous metallurgy, for the pelletizing of the finely dispersed concentrate of the iron ore; within the ceramic production, for providing the high strength to the porcelain, faience, and electroceramic products; within the building industry, for the production of the high quality expanded clay; within the food industry, for the cleaning of the drinking water, beer, juices, syrups; within the medicine and pharmacology, for the manufacturing of the tablets, pastes, creams, powders; within the agriculture, for the improvement of the soil structure, as the carrier of the major nutritional substances. They use the activated bentonite as the catalyst during the cracking of petroleum, and as the adsorbent during the purification of the products of the petroleum processing, and so on. The requirements for bentonite within the USSR are limited to the determination of the dispersion, disintegration within water, binding and adsorptive abilities. The GOST 3226-77 "Clays for molding" standard regulates the quality of the bentonites, which are used within the foundry production. The requirements of the numerous consumers of bentonite are described within the OST sectoral standards and technical conditions (for example, the TU 39-044-74 "Bentonite clays as the raw material for the preparation of the drilling fluids").

Within the USSR, there are known 24 deposits of bentonite with the balance reserves, which have been explored according to the industrial categories (447.3 million tonnes, 1982). Besides this, 234.4 million tonnes of bentonite have been accounted for within the balance list of the reserves according to the S2 category. The reserves of the Cherkassy deposit amount to 104.7 million tonnes.

There are being developed 12 deposits (the annual extraction has been 2854 thousand tonnes during the 1981; the methods are underground and open pit). Abroad, the deposits of bentonite are known within the USA (Black Hills, Sanders Defiance), Canada, Great Britain, and other countries. The largest producer and main exporter of bentonite is the USA, the annual extraction is more than 4.2 million tonnes (1981); there has been extracted within Greece 419.5 thousand tonnes, within Japan 400 thousand tonnes, within Italy 230.8 thousand tonnes, within Argentina 145 thousand tonnes, within Spain 110 thousand tonnes (1978). The worldwide extraction (without the socialistic countries) is more than 6 million tonnes (1981).