fluorosilicate

Fluorosilicate is a term used for compounds that contain the hexafluorosilicate anion SiF6^2−, and for related fluorosilicic acid species. The most common salts are sodium fluorosilicate (Na2SiF6), potassium fluorosilicate (K2SiF6), and ammonium fluorosilicate ((NH4)2SiF6). Fluorosilicic acid is the aqueous form, also known as fluosilicic acid, with the formula H2SiF6. These substances are primarily encountered as fluoride sources in various practical applications.

Chemically, the hexafluorosilicate ion is six-coordinate silicon with an octahedral geometry, surrounded by six fluorine ligands. In aqueous solutions, fluorosilicate species arise from the hydrolysis or reaction of silicon fluorides, forming H2SiF6 and related ions. The fluorosilicate anion can pair with different cations to give stable crystalline salts, which are soluble in water to varying degrees depending on the counterion.

Preparation and production methods typically involve the reaction of fluorinating agents with silica-bearing materials, followed by neutralization or crystallization to yield the desired fluorosilicate salt. Fluorosilicic acid can be produced by hydrolysis of silicon tetrafluoride in aqueous media, and it can be neutralized to form salts such as Na2SiF6 or K2SiF6.

Uses of fluorosilicate compounds are dominated by fluoride delivery. They are employed as sources of fluoride in water fluoridation programs in some regions and are used in certain dental care products as a fluoride additive. Some industrial applications also leverage fluorosilicate salts as fluoride sources or for specialized chemical processes. Safety considerations include the corrosive and toxic potential of fluorinating agents and fluoride-bearing solutions; appropriate handling, storage, and regulatory limits on fluoride exposure are important.

See also: fluoride compounds, fluoridation, hexafluorosilicate.