Sodium hexafluoroaluminate

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Sodium aluminium hexafluoride
Sodium aluminium hexafluoride unit cell
Sodium aluminium hexafluoride unit cell
Names
Other names
Sodium fluoroaluminate
Cryolite
Kryolite
Aluminate(3-), hexafluoro-, trisodium, (OC-6-11)-
Identifiers
CAS Number
  • 13775-53-6 checkY
3D model (JSmol)
ChEBI
ChemSpider
InChI
  • InChI=1S/Al.6FH.3Na/h;6*1H;;;/q+3;;;;;;;3*+1/p-6 checkY
    Key: REHXRBDMVPYGJX-UHFFFAOYSA-H checkY
  • InChI=1/Al.6FH.3Na/h;6*1H;;;/q+3;;;;;;;3*+1/p-6/rAlF6.3Na/c2-1(3,4,5,6)7;;;/q-3;3*+1
    Key: REHXRBDMVPYGJX-ZWHJLPLDAC
  • [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
0.04% (20°C)[1]
Vapor pressure essentially 0
Hazards
GHS labelling:[3]
GHS08: Health hazardGHS07: Exclamation markGHS09: Environmental hazard
Signal word
 Danger
H332, H372, H411
Precautionary statements
 P260
Lethal dose or concentration (LD, LC):
LDLo (lowest published)
 900 mg/kg (rabbit, oral)[2]
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 2.5 mg/m3[1]
REL (Recommended)
 TWA 2.5 mg/m3[1]
IDLH (Immediate danger)
 250 mg/m3 (as F)[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N  (what is checkY☒N ?)
Infobox references

Sodium aluminium hexafluoride is an inorganic compound with formula Na3AlF6. This white solid, discovered in 1799 by Peder Christian Abildgaard (1740–1801),[4][5] 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 (AlF63−) ion.

Production[]

Most cryolite is manufactured by a variety of related pathways. One route entails combining sodium aluminate and hydrofluoric acid:[6]

Na3Al(OH)6 + 6 HF → Na3AlF6 + 6 H2O

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:

H3AlF6 + 3 NH3 → (NH4)3AlF6
(NH4)3AlF6 + 3 NaOH → Na3AlF6 + 3 NH3 + 3 H2O

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.[7]

Solubility[]

Cryolite is poorly soluble in water. The LD50 is 600 mg/kg for the comparable compound aluminium trifluoride.[6]

References[]

  1. ^ a b c d 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).
  3. ^ GHS: GESTIS 001900
  4. ^ (Staff) (1799). "Norwegische Titanerze und andre neue Fossilien" [Norwegian titanium ores and other new minerals]. Allgemeine Journal der Chemie (in German). 2: 502. "Zugleich theilte er … wie gefrorne Salzlauge schmilzt." (At the same time he also communicated a report on an especially white, spar-like mineral [that had been] brought a few years ago from Greenland to Denmark. According to one of the investigations undertaken regarding it, it consisted of alumina and hydrofluoric acid. A compound of which no similar example has yet occurred in the mineral realm. It has received the name "cryolite" because it melts like frozen brine before the [flame of a] blowpipe.)
  5. ^ Abildgaard, P. C. (1800). "Om Norske Titanertser og om en nye Steenart fra Grönland, som bestaaer af Flusspatsyre og Alunjord" [On Norwegian titanium ores and on a new mineral from Greenland, which consists of hydrofluoric acid and alumina]. Det Kongelige Danske Videnskabers-Selskabs (The Royal Danish Scientific Society). 3rd series (in Danish). 1: 305–316. [From p. 312] Han har kaldt denne grönlandske Steen Kryolith eller Iissteen formedelst dens Udseende, og fordi den smelter saa meget let for Blæsröret. (He has named this Greenlandic stone cryolite or ice stone on account of its appearance, and because it melts so easily under a blowpipe.)
  6. ^ a b Aigueperse, Jean; Mollard, Paul; Devilliers, Didier; Chemla, Marius; Faron, Robert; Romano, René; Cuer, Jean Pierre (2000). "Fluorine Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a11_307.
  7. ^ http://www.mineralszone.com/minerals/cryolite.html

External links[]

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