sulfateioniin

The sulfate ion, SO4^2−, is an inorganic polyatomic anion derived from sulfuric acid by loss of two protons. In Estonian, the term is sulfateioniin. In this ion, sulfur is in the +6 oxidation state and is surrounded by four oxygen atoms in a tetrahedral arrangement.

Resonance among the four S−O bonds makes them equivalent, with each bond order about 1.5. In aqueous solution, sulfate exists as SO4^2− and is a weak base; it can be protonated to bisulfate (HSO4−) under strongly acidic conditions.

Sulfate occurs in nature in minerals such as gypsum (CaSO4·2H2O) and kieserite (MgSO4). Seawater contains sulfate at relatively high concentrations, and industrially it is recovered or produced from sulfuric acid reactions and by processing sulfates and metal oxides.

Sulfate forms a wide range of salts with metals and nonmetals. It is used in fertilizers (for example, ammonium sulfate), in pigments and detergents, and as a chemical reagent. Insoluble sulfate salts such as barium sulfate are widely used as contrast agents in medicine due to their radiopacity.

Safety and environmental notes: sulfate salts generally have low acute toxicity, but inhaled dust can irritate the airways. Large discharges can affect water quality and aquatic life. Sulfate is a persistent anion in the environment and formation is linked to industrial processes and atmospheric sulfuric acid production.