Anthracite

ANTHRACITE (from the Greek word "anthrakitis" (the type of coal) * EN: anthracite, hard coal; DE: Anthrazit; FR: anthracite, ES: antracita; RU: антрацит) is mineral coal with the highest degree of coalification (metamorphism). The colour is grayish-black and black-gray, the lustre is metallic, the streak on the surface of the unglazed porcelain is velvety black. It does not sinter. It has the high density of organic mass (1500-1700 kilograms per cubic metre) and electrical conductivity. The hardness on the Mohs scale is 2.0-2.5. Under the microscope, within the thin polished sections, anthracite is slightly translucent; within the reflected light, the helificiated components are pleochroic from the bright white and yellow-white to light gray and gray colours; it is anisotropic. The transition of mineral coals into anthracite, as the result of metamorphism, proceeded gradually; within the USSR (GOST 21489-76), the boundary between them is defined according to the reflective ability of vitrinite (see the "Vitrinite group" article) within the oil immersion (for anthracite, R0 is 2.5%). The content of carbon within the organic mass of anthracite is 94-97%, of hydrogen is 1-3%, the specific heat of combustion is: Qsdaf is 33.8-35.2 megajoules per kilogram, Qjr is 23.9-31.0 megajoules per kilogram.

The greatest quantity of anthracite has formed itself as the result of the regional metamorphism during the submerging of the coal-bearing strata into the region of the increased temperatures and pressures. The role of the thermal and contact metamorphism in the formation of anthracite is limited, depends on the thickness of the magma bodies, on their type, on the depth of introduction, on the distances from them to the coals, which have been subjected to heat impact. The temperature during the formation of anthracite within the conditions of the regional metamorphism was, apparently, within the range of 350-550 degrees Celsius, which, together with the change of the pressure, with peculiarities of the source material, and with other causes, has led to the formation of anthracite with various properties.

In a number of previously active classifications, anthracites were sub-divided into the marks PA (semi-anthracites) and A (anthracites). Within the newly introduced government standards on the classification of coals and anthracite of the major basins and deposits of the USSR, the mark PA is not provided. The classification parametres, which are adopted within the standards, are: the Vdaf yield of volatile substances, and the Vobdaf volumetric yield of volatile substances. For anthracite of the major basins, the Vobdaf is 0.22 cubic metres per kilogram, the Vdaf is less than 8% within the Donetsk basin, and less than 9% within the Gorlovka basin. There has been adopted as additional parameter within the Donetsk basin the indicator of the Qsdaf heat of combustion, less than 35.2 megajoules per kilogram. Within the USSR, anthracites have been identified within the Donetsk (major reserves), Gorlovka, Tunguska, Taimyr basins, and also within the coal basins and at the deposits of the Urals and Magadan province of the RSFSR. The availability of the highly metamorphosed coals, including anthracite, is known within the Kuznetsk, Pechora, Uzgen basins, at the Kugitang deposit (Turkmen SSR). The proven geological reserves of anthracite within the USSR (1980) are more than 14 billion tonnes; the annual extraction is more than 60 million tonnes, including within Donbas 99.3% of the total volume of extraction of anthracite. The greatest quantity of mines, which are extracting anthracite, belong to the productive consortia "Donbassantratsit", "Rostovugol", "Gukovugol", "Torezantratsit", "Shahterskantratsit", "Sverdlovantratsit". The productive capacity of individual mines is 3 million tonnes per year and more.

Anthracite is widely used as the high quality smokeless energetic fuel, and also as the technological raw material within the ferrous and non-ferrous metallurgy, chemical, electrical industry, and within the series of other industries, which are associated with the products of processing of anthracite. There are important for technological purposes the increased mechanical and thermal stability of anthracite, its electrical conductivity, and low yield of volatile substances. The major non-fuel areas of usage are: the production of thermo-anthracite, carbon-graphite blocks, electrodes, electrical corundum, carbides of calcium and silicon, thermo-graphite, microphone powder, the usage for the sintering of iron ores, burning of carbonatic rocks for technological purposes. Despite the relatively low rate of consumption of anthracite for technological purposes (from 0.12 to 7%, depending on the type of industry), the requirements to its quality in comparison with the fuel-energetic usage are the highest. Even relatively small deterioration of certain properties of anthracite often negatively impacts the quality of industrial products.