ALUNITE ORE (EN: alum rock, alunite ore; DE: Alaunerz, Alunitschiefer; FR: mineral d'alunite; ES: mineral de alunite; RU: алунитовая руда) is the natural mineral formation, which comprises mainly the alunite (30-55%), quartz, chalcedony and opal (40-50% total), clay minerals (mainly kaolinite), and the small quantities of iron oxides, ilmenite, zircon, and other substances.
The alunite ores are the dense massive rocks (approximately 2700 kilograms per cubic metre). They are formed in the regions of the young volcanism as the result of the impact of the volcanic sulfurous gases and solutions, which are enriched with the sulfuric acid, on the country rocks. The deposits of the alunite ores are usually represented by the tabular or stock-like deposits. They appear as the result of the hydrothermal reworking of the acidic effusive rocks, and are accompanied by the forming of the fields of the secondary quartzites. The requirements of the industry for the quality of the alunite ores, which do not need the benefication, are: the content of the alunite in the ore is not less than 50%, the content of the clayish minerals, which is calculated as the kaolinite equivalent, is not more than 10%. In the ores, which are intended for the benefication, the content of the alunite is at least 25%, the recovery into the concentrate and the yield are at least 75%, the content within the concentrate is at least 75%, the content of the kaolinite is at most 5%. The alunite ores are the complex raw material, because it is possible the obtainment from them, besides the alumina, of the potassium sulfate (potassium fertilizers), of the sulfuric acid, and also of the vanadium and gallium.
The extraction of the alunite ores is usually performed by the open pit mining method. Their processing to the alumina is performed according to the so-called reductive method. Initially, the crushed and milled ore is subjected to the reductive roasting in the furnaces of the "fluidized bed", then it is processed according to the hydrochemical scheme. During this process, the alunite is leached, the aluminate solution is evaporated, and the aluminium hydroxide (hydrate of alumina), which has precipitated, is separated and calcined. The deposits of the alunite ores in the USSR are situated in the Azerbaijan SSR (Zaglikskoe), at the west of the Ukrainian SSR (Beganskoe, and others), at the Far East (Askumskoe, Shelikhovskoe, and others); such deposits are situated abroad in the USA (the Utah, Nevada, Colorado, Wyoming states), China, Australia, Iran, Mexico, Italy, Puerto Rico, India, Argentina, and other countries. In the USA, the forecasted reserves of the alunite ores are estimated at 1,413 million tonnes, reliably counted reserves are 252.5 million tonnes. Because of the limited reserves of the bauxites, the demand is growing for the alunite ores as the prospective raw material for the production of the alumina, potassium sulfate, sulfuric acid.
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