temperature 15-30% concentrated hexafluorosilicic acid undergoes similar reactions with chlorides, hydroxides, and carbonates of alkali and alkaline earth metals. Sodium hexafluorosilicate for instance may be produced by treating sodium chloride () by hexafluorosilicic acid: Heating sodium hexafluorosilicate gives silicon tetrafluoride: Uses The majority of the hexafluorosilicic acid is converted to aluminium fluoride and synthetic cryolite. These materials are central to the conversion of aluminium ore into aluminium metal. The conversion to aluminium trifluoride is described as: H2SiF6 + Al2O3 → 2 AlF3 + SiO2 + H2O Hexafluorosilicic acid is also converted to a variety of useful hexafluorosilicate salts. The potassium salt, Potassium fluorosilicate, is used in the production of porcelains, the magnesium salt for hardened concretes and as an insecticide, and the barium salts for phosphors. Hexafluorosilicic acid and the salts are used as wood preservation agents. Lead refining Hexafluorosilicic acid is also used as an electrolyte in the Betts electrolytic process for refining lead. Rust removers Hexafluorosilicic acid (identified as hydrofluorosilicic acid on the label) along with oxalic acid are the active ingredients used in Iron Out rust-removing cleaning products, which are essentially varieties of laundry sour. Niche applications H2SiF6 is a specialized reagent in organic synthesis for cleaving Si–O bonds of silyl ethers. It is more reactive for this purpose than HF. It reacts faster with t-butyldimethysilyl (TBDMS) ethers than triisopropylsilyl (TIPS) ethers. Treating concrete The application of hexafluorosilica acid to a calcium rich surface such as concrete will give that surface some resistance to acid attack. CaCO3 + H2O → Ca2+ + 2 OH− + CO2 H2SiF6 → 2 H+ + + 2 H2O → 6 F− + SiO2 + 4 H+ Ca2+ + 2 F− → CaF2 Calcium fluoride (CaF2) is an insoluble solid that is acid resistant. Natural salts Some rare minerals, encountered either within volcanic or coal-fire fumaroles, are salts of the hexafluorosilicic acid. Examples include ammonium hexafluorosilicate that naturally occurs as two polymorphs: cryptohalite and bararite. Safety Hexafluorosilicic acid can release hydrogen fluoride (HF) when evaporated, so it has similar risks. Inhalation of the vapors may cause lung edema. Like hydrogen fluoride, it attacks glass and stoneware. The LD50 value of hexafluorosilicic acid is 430 mg/kg. See also Ammonium fluorosilicate Sodium fluorosilicate Potassium fluorosilicate References Mineral acids Hydrogen compounds Nonmetal halides Hexafluorosilicates Fluoro complexes