Sulfur
Sulfur, or Sulphur, a nonmetallic chemical element. It is relatively abundant and widely distributed in nature. As a mineral, sulfur occurs both in elemental, or native, form (chemically uncombined) and in combination with other elements. Elemental sulfur has been known since ancient times and is the brimstone mentioned in the Bible. Because it is a vital part of most proteins, sulfur is present in virtually all plants and animals. Astronomers have detected sulfur in the sun and other stars, and the element has been found in certain meteorites.
Sulfur can exist in a number of forms, or allotropes, which differ from one another somewhat in physical properties and appearance. The most familiar form is rhombic sulfur, a yellow odorless, brittle solid that ignites readily in air and burns with a blue flame. When rhombic sulfur is slowly heated almost to the melting point, it changes to another allotrope, monoclinic sulfur. Plastic, or amorphous, sulfur is a rubbery allotrope that occurs when liquid sulfur us poured into cold water. After a few days, plastic sulfur changes back to ordinary rhombic sulfur.
Chemically, sulfur is active and combines with most other elements, especially when heated. Two major groups of sulfur-containing compounds—sulfides and sulfates—include a number of important minerals.
The more common sulfides include iron pyrites (iron disulfide); chalcocite (copper sulfide, a chief ore of copper); cinnabar (red mercuric sulfide, the main ore of mercury); and sphalerite (zinc sulfide). Hydrogen sulfide, a poisonous gas with the odor of rotten eggs, is produced in nature by decaying plant and animal matter. Among the principal sulfates are gypsum and anhydrite.
Coal, petroleum, and natural gas often have high content of sulfur. In coal and petroleum the sulfur occurs in the form of various organic (carbon-containing) compounds. In natural gas, it occurs chiefly as hydrogen sulfide. Burning a fuel containing sulfur produces sulfur dioxide, a highly irritating gas that is a major source of air pollution. Sulfur is usually removed from natural gas and petroleum fuels, but it is generally impractical to remove sulfur from coal. Many coal-fired power plants therefore use devices called scrubbers that remove sulfur dioxide from the combustion gases produced in burning the coal.
Occurrence and ProductionThe major source of sulfur are deposits of native sulfur, natural gas and petroleum rich in sulfur, and iron pyrites. Native sulfur occurs in underground deposits in volcanic regions and in association with large underground formations of salt called salt domes. Deposits of native sulfur are mined by the Frasch process. Sulfur is obtained from sulfur-rich natural gas and petroleum as a by-product and is referred to as recovered sulfur.
The leading producers of sulfur are the United States, Canada, Turkmenistan, China, and Poland. Most of the production of the United States consists of native sulfur from Texas and Louisiana and recovered sulfur from Texas and several other states.
UsesThe making of sulfuric acid—one of the most useful of all industrial chemicals—accounts for more than 80 per cent of the sulfur used in the United States. Other compounds made from sulfur include carbon disulfide, important in the manufacture of cellulose fibers; sulfur chloride, a versatile industrial liquid; and sulfur dioxide, useful as a bleaching agent and in the pulp and paper industries. Elemental sulfur is used in rubber vulcanization, as a fungicide, and in certain medicines.
Symbol: S. Atomic number: 16. Atomic weight: 32.07. Specific gravity: rhombic, 2.07; monoclinic, 1.957. Melting point: rhombic, 235.0 F. (112.8 C); monoclinic, 246.2 F. (119.0 C). Boiling point: 832.3 F. (444.6 C). There are four stable isotopes: S-32, S-33, S-34, and S-36. Sulfur belongs to Group VI_A of the Periodic Table and may have a valence of +2, +4, or +6.