any of the natural mineral formations containing native sulfur in concentrations that make extraction technically feasible and economically profitable. Sulfur ores are classified according to the composition of the enclosing rock and include limestone-calcite (more than 90 percent of world production), calcitic dolomite, clay, gypsum, opalite, and quartzite ores. The principal minerals that make up sulfur ores are native sulfur, calcite, dolomite, gypsum, anhydrite, celestite, quartz, chalcedony, opal, clay minerals, pyrite, and alunite. Depending on the structure and texture of the ores, which determine the ores’ technical properties, distinctions are made between, for example, ores containing crystal aggregates and those with finely disseminated sulfur particles. Sulfur ores containing more than 25 percent sulfur are considered rich, those containing 10 to 25 percent are classified as intermediate, and those with 5 to 10 percent are considered lean. Useful by-products of the ores include limestones (flotation wastes, used for liming soils), celestite, pyrite, and alunite. Harmful substances in the ores include organic matter (bitumens), As, and Se.
Deposits of sulfur ores can occur as sheetlike, lenticular, or pocket formations and can be simple or complex (with rock in-terbeds). Deposits can vary in extent from tens of centimeters to tens of meters. The major genetic and industrial type of deposit is that formed by infiltration and metasomatism in the sulfates of sedimentary strata and caprock formations over salt domes. Aside from ores, sulfur and sulfur compounds can also be obtained from pyrites, from the hydrogen sulfide in natural gas, and from the wastes (tailings) from the concentration of chalco-pyrite and other sulfide ores. Other sources include bituminous sandstones, anhydrite and gypsum, the sulfur gases of furnaces used in metallurgy and in the coking of heavy residual bottoms of crude oil, and petroleum containing sulfur. All sources exclusive of ores are known collectively as sulfur-bearing raw materials.
Sulfur is extracted from sulfur ores by a mining process (10–20 percent of world production) and a geotechnological process (90–80 percent). In the former, sulfur ores are mined in quarries or, much less frequently, in underground shafts. The ores are then concentrated by flotation with the production of a sulfur concentrate, from which crude, or lump, sulfur is obtained using special furnaces, kettles, and autoclaves. The crude sulfur is then purified to yield refined sulfur. In the geotechnological process, the sulfur is melted from sulfur ores at the deposit site using superheated water (Frasch process). A hole is bored from the ground surface to the deposit. Three pipes are then lowered: one for the water at 165°–170°C, one for air, and one for conveying the molten sulfur to the surface. In 1973, world production of sulfur through this process exceeded 10 million tons.
World reserves of native sulfur at the beginning of 1973 were estimated at 871.5 million tons, not including reserves of the socialist countries. Most sulfur ores (approximately 76 percent) are concentrated in Iraq (335 million tons), the United States (150 million tons of extractive reserves), Chile (100 million tons), and Mexico (80 million tons). Large deposits of sulfur ores are known to exist in Poland (Tarnobrzeg and Grzybów deposits). In the USSR, there are deposits of sulfur ores in Cis-carpathia (Rozdol deposit), in Kuibyshev Oblast (Vodino and Kamennodol’skoe deposits), in Turkmenia (Gaudrak deposit), and on Kamchatka (Maletoivaiamsk deposit).
World production of sulfur, excluding the socialist countries, from sulfur ores in 1973 was 15–16 million tons, including 9.1 million tons in the United States, 900,000 tons in Mexico, and 250,000 tons in Iraq. Of the total production in 1972, approximately 27 percent (excluding the socialist countries) came from native sulfur, 38 percent from natural gas and petroleum, 19 percent from pyrites, and 16 percent from other types of sulfur-containing raw materials.
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A. S. SOKOLOV