Sulfates

Sulfates refer to a family of chemical compounds that contain the sulfate anion, SO4^2−. In inorganic chemistry, the term most often denotes salts and esters of sulfuric acid (H2SO4). The sulfate ion features a central sulfur atom in oxidation state +6, bonded to four oxygen atoms in a tetrahedral arrangement, with resonance among S–O bonds that distributes the charge.

Sulfates form a wide range of salts, including calcium sulfate (CaSO4), sodium sulfate (Na2SO4), and magnesium sulfate (MgSO4). Solubility varies among sulfates: some are highly soluble in water, while others are sparingly soluble or practically insoluble (for example, calcium sulfate and barium sulfate). Many sulfates occur naturally and are important industrially.

Natural minerals include gypsum (CaSO4·2H2O) and anhydrite (CaSO4), which differ by hydration; barite (BaSO4) and celestine (SrSO4) are notable sulfate minerals. Other hydrated forms include kieserite (MgSO4) and epsomite (MgSO4·7H2O).

Uses and applications are broad. Fertilizers commonly employ ammonium sulfate ((NH4)2SO4) and gypsum as soil amendments. Sodium sulfate serves in detergents and the glass industry, while calcium and barium sulfates have roles in construction materials and medical imaging, respectively. Sulfates are also generated and consumed in the production of sulfuric acid, a central chemical in many industries.

Environmental and health considerations include the presence of sulfates in natural waters, where high levels can affect taste and cause laxative effects. In the environment, oxidation of sulfide minerals can lead to sulfuric acid formation, contributing to acid mine drainage; in anaerobic settings, sulfate-reducing bacteria produce sulfide, influencing sulfur cycles in ecosystems.