sulfur

Sulfur is a chemical element with the symbol S and atomic number 16. It is a nonmetal and one of the most abundant elements on Earth, occurring widely in minerals, fossil fuels, and volcanic gases as sulfur compounds. Elemental sulfur is a bright yellow solid at room temperature.

Its physical properties include a melting point of 115.21°C and a boiling point of 444.6°C, a density of about 2.07 g/cm3 in the solid state, and relative insolubility in water. Sulfur exists in several allotropes; the most common crystalline forms are orthorhombic alpha-sulfur and monoclinic beta-sulfur. When molten, sulfur can form long polymer chains, producing "plastic sulfur" upon rapid cooling.

Occurrence and production: Native sulfur occurs in volcanic regions and hot springs. Much sulfur is obtained as a byproduct of refining offshore oil and gas or roasting sulfide ores. Global production is concentrated in a few countries.

Uses: The largest consumer is sulfuric acid, produced by the contact process and used in fertilizer manufacture, mineral processing, and chemical synthesis. Other applications include vulcanization of rubber, pigments, pharmaceuticals, and catalysts. Sulfur compounds such as sulfates and sulfides are widely encountered in industry and the environment.

Biological role: Sulfur is an essential element for life, incorporated into the amino acids cysteine and methionine and into various coenzymes and vitamins. Microorganisms participate in the global sulfur cycle through reduction of sulfates and oxidation of sulfides.

Safety: Elemental sulfur is of relatively low toxicity, but inhalation of sulfur dust can irritate the respiratory tract. Burning sulfur releases sulfur dioxide, a toxic gas that can cause respiratory problems and acid rain.