Sodium aluminium hexafluoride is an inorganic compound with formula Na₃ Al F₆. This white solid, discovered in 1799 by Peder Christian Abildgaard (1740–1801), occurs naturally as the mineral

cryolite Cryolite ( Na3 Al F6, sodium hexafluoroaluminate) is an uncommon mineral identified with the once-large deposit at Ivittuut on the west coast of Greenland, mined commercially until 1987. History Cryolite was first described in 1798 by Danish vete ...

and is used extensively in the industrial production of aluminium metal. The compound is the sodium (Na⁺) salt of the hexafluoroaluminate (AlF₆³⁻) ion.

Production

Most cryolite is manufactured by a variety of related pathways. One route entails combining

sodium aluminate Sodium aluminate is an inorganic chemical that is used as an effective source of aluminium hydroxide for many industrial and technical applications. Pure sodium aluminate (anhydrous) is a white crystalline solid having a formula variously given as ...

and hydrofluoric acid: :Na₃Al(OH)₆ + 6 HF → Na₃AlF₆ + 6 H₂O Other routes include: : : Often the

hexafluorosilicic acid Hexafluorosilicic acid is an inorganic compound with the chemical formula . Aqueous solutions of hexafluorosilicic acid consist of salts of the cation and hexafluorosilicate anion. These salts and their aqueous solutions are colorless. Hexafluo ...

, which is recovered from phosphate mining, is the precursor in a two-step process beginning with neutralization with ammonia to give

ammonium hexafluorosilicate Ammonium fluorosilicate (also known as ammonium hexafluorosilicate, ammonium fluosilicate or ammonium silicofluoride) has the formula (NH4)2SiF6. It is a toxic chemical, like all salts of fluorosilicic acid.Wiberg, E., Wiberg, N., and Holleman, A ...

: :H₃AlF₆ + 3NH₃ → (NH₄)₃AlF₆ :(NH₄)₃AlF₆ + 3NaOH → Na₃AlF₆ + 3NH₃ + 3H₂O The mineral form of sodium hexafluoroaluminate, which is called

, was mined at

Ivigtût Ivittuut (formerly, Ivigtût) (Kalaallisut: "Grassy Place") is an abandoned mining town near Cape Desolation in southwestern Greenland, in the modern Sermersooq municipality on the ruins of the former Norse Middle Settlement. Ivittuut is one of ...

on the west coast of Greenland until the deposit was depleted in 1987.

Use

The dominant application of synthetic

is as a

solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

(or flux) for electrolysis of aluminium oxides such as

bauxite Bauxite is a sedimentary rock with a relatively high aluminium content. It is the world's main source of aluminium and gallium. Bauxite consists mostly of the aluminium minerals gibbsite (Al(OH)3), boehmite (γ-AlO(OH)) and diaspore (α-AlO ...

. 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 Aluminium fluoride refers to inorganic compounds with the formula AlF3·''x''H2O. They are all colorless solids. Anhydrous AlF3 is used in the production of aluminium metal. Several occur as minerals. Occurrence and production Aside from anhydr ...

is used as that solvent. Unlike typical solutions, this one requires temperatures approaching 1000 °C to melt. Other uses include a whitener for enamels and an opacifier for glass.

Structure

It adopts a

perovskite Perovskite (pronunciation: ) is a calcium titanium oxide mineral composed of calcium titanate (chemical formula ). Its name is also applied to the class of compounds which have the same type of crystal structure as (XIIA2+VIB4+X2−3), known a ...

-like structure. The centers are nearly idealized

octahedra In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet a ...

. Na⁺ occupy both six- and distorted 8-coordinate sites.

Safety

The is 600 mg/kg for the comparable compound

. Cryolite is poorly soluble in water.

Related compounds

Chiolite Chiolite is a tetragonal-ditetragonal dipyramidal mineral, composed of sodium, fluorine, and aluminium. The name originates from the combination of the Greek words for snow (χιώυ) and stone (λίθος). It is an allusion to its similarity and ...

( ), another sodium fluoroaluminate.

References

External links

Chemical Land 21
{{fluorine compounds Aluminium complexes Fluoro complexes Sodium compounds Fluorometallates