Sodium hexafluoroaluminate

Sodium aluminium hexafluoride
Names
	Other names Sodium fluoroaluminate; Cryolite; Kryolite; Aluminate(3-), hexafluoro-, trisodium, (OC-6-11)-
Identifiers
CAS Number	13775-53-6 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:39289 ;
ChemSpider	11431435 ;
PubChem CID	159692;
CompTox Dashboard (EPA)	DTXSID90872955 ;
	InChI InChI=1S/Al.6FH.3Na/h;61H;;;/q+3;;;;;;;3+1/p-6 Key: REHXRBDMVPYGJX-UHFFFAOYSA-H ; InChI=1/Al.6FH.3Na/h;61H;;;/q+3;;;;;;;3+1/p-6/rAlF6.3Na/c2-1(3,4,5,6)7;;;/q-3;3*+1 Key: REHXRBDMVPYGJX-ZWHJLPLDAC;
	SMILES [Na+].[Na+].[Na+].F[Al-3](F)(F)(F)(F)F;
Properties
Chemical formula	Na3AlF6
Molar mass	209.94 g/mol
Appearance	white powder
Density	2.9 g/cm3, solid
Melting point	950 °C (1,740 °F; 1,220 K)
Boiling point	decomposes
Solubility in water	0.04% (20°C)
Vapor pressure	essentially 0
Hazards
	Lethal dose or concentration (LD, LC):
LDLo (lowest published)	900 mg/kg (rabbit, oral)
	NIOSH (US health exposure limits):
PEL (Permissible)	TWA 2.5 mg/m3
REL (Recommended)	TWA 2.5 mg/m3
IDLH (Immediate danger)	250 mg/m3 (as F)
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Sodium aluminium hexafluoride is the inorganic compound with the formula Na₃ Al F₆. This white solid, discovered by José Bonifácio de Andrada e Silva, occurs naturally as the mineral cryolite and is used extensively in the industrial production of aluminium metal. The compound consists of the sodium (Na⁺) salt of hexafluoroaluminate (AlF₆³⁻).

Production

Most cryolite is manufactured from aluminium oxides, hydrofluoric acid, and sodium hydroxide or the equivalent reagent hexafluorosilicic acid:^[3]

6 NaOH + Al₂O₃ + 12 HF → 2 Na₃AlF₆ + 9 H₂O

It was mined as cryolite 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 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.^[4]

Safety

Cryolite is poorly soluble in water, which mitigates problems. The LD₅₀ = 600 mg/kg for the comparable compound aluminium trifluoride.^[3]

References

^ ^a ^b ^c ^d NIOSH Pocket Guide to Chemical Hazards. "#0559". National Institute for Occupational Safety and Health (NIOSH).
^ "Fluorides (as F)". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
^ ^a ^b J. Aigueperse, P. Mollard, D. Devilliers, M. Chemla, R. Faron, R. Romano, J. P. Cuer, "Fluorine Compounds, Inorganic" in Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005.doi:10.1002/14356007.a11_307
^ http://www.mineralszone.com/minerals/cryolite.html

External links

[PGCH-1] NIOSH Pocket Guide to Chemical Hazards. "#0559". National Institute for Occupational Safety and Health (NIOSH).

[2] "Fluorides (as F)". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).

[Ullmann-3] J. Aigueperse, P. Mollard, D. Devilliers, M. Chemla, R. Faron, R. Romano, J. P. Cuer, "Fluorine Compounds, Inorganic" in Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005.doi:10.1002/14356007.a11_307

[4] ttp://www.mineralszone.com/minerals/cryolite.html

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