Sodium hexafluoroaluminate
Sodium aluminium hexafluoride is an inorganic compound with formula NaAlF. This white solid, discovered in 1799 by Peder Christian Abildgaard (1740–1801), occurs naturally as the mineral cryolite and is used extensively in the industrial production of aluminium metal. The compound is the sodium (Na) salt of the hexafluoroaluminate (AlF) ion. Production. Most cryolite is manufactured by a variety of related pathways. One route entails combining sodium aluminate and hydrofluoric acid: Often the hexafluorosilicic acid, which is recovered from phosphate mining, is the precursor in a two-step process beginning with neutralization with ammonia to give ammonium hexafluorosilicate: The  mineral form of sodium hexafluoroaluminate, which is called cryolite, was mined at Ivigtût on the west coast of Greenland until the deposit was depleted in 1987. Use. The main application of synthetic cryolite is as a solvent (or flux) for electrolysis of aluminium oxides such as bauxite. The conversion of aluminium oxides into metallic aluminium requires that the metal ions be dissolved so that they can accept the electrons provided in the electrolysis cell. A mixture of cryolite and some aluminium trifluoride is used as that solvent. Unlike typical solutions, this one requires temperatures approaching 1000 °C to melt . Sodium aluminium hexafluoride is also used as a pesticide. Other uses include a whitener for enamels and an opacifier for glass. Solubility. Cryolite is poorly soluble in water. The is 600 mg/kg for the comparable compound aluminium trifluoride.