Hexafluorosilicic acid

Sodium fluorosilicateHexafluorosilicic acid is an inorganic compound with the chemical formula (H3O)2SiF6 (also written as (H3O)2). It is a colorless liquid rarely encountered undiluted. Hexafluorosilicic acid has a distinctive sour taste and pungent smell. It is produced naturally on a large scale in volcanoes. It is manufactured as a coproduct in the production of phosphate fertilizers. The resulting hexafluorosilicic acid is almost exclusively consumed as a precursor to aluminum trifluoride and synthetic cryolite, which are used in aluminium processing. Salts derived from hexafluorosilicic acid are called hexafluorosilicates. Hexafluorosilicic acid is an inorganic compound with the chemical formula (H3O)2SiF6 (also written as (H3O)2). It is a colorless liquid rarely encountered undiluted. Hexafluorosilicic acid has a distinctive sour taste and pungent smell. It is produced naturally on a large scale in volcanoes. It is manufactured as a coproduct in the production of phosphate fertilizers. The resulting hexafluorosilicic acid is almost exclusively consumed as a precursor to aluminum trifluoride and synthetic cryolite, which are used in aluminium processing. Salts derived from hexafluorosilicic acid are called hexafluorosilicates. Hexafluorosilicic acid is generally assumed to consist of oxonium ions charge balanced by hexafluorosilicate dianions as well as water. In aqueous solution, the hydronium cation (H3O+) is traditionally equated with a solvated proton, and as such, the formula for this compound is often written as H2SiF6. Extending that metaphor, the isolated compound is then written as H2SiF6·2H2O, or (H3O)2SiF6.The situation is similar to that for chloroplatinic acid, fluoroboric acid, and hexafluorophosphoric acid. Hexafluorosilicate is an octahedral anion; the Si–F bond distances are 1.71 Å. Hexafluorosilicic acid is only available commercially as solution. The commodity chemical hydrogen fluoride is produced from fluorspar by treatment with sulfuric acid. As a by-product, approximately 50 kg of (H3O)2SiF6 is produced per tonne of HF owing to reactions involving silica-containing mineral impurities. (H3O)2SiF6 is also produced as a by-product from the production of phosphoric acid from apatite and fluorapatite. Again, some of the HF in turn reacts with silicate minerals, which are an unavoidable constituent of the mineral feedstock, to give silicon tetrafluoride. Thus formed, the silicon tetrafluoride reacts further with HF. The net process can be described as: