Potassium dicyanoaurate

Potassium dicyanoaurate (or potassium gold cyanide) is an inorganic compound with formula K[Au(CN)2]. It is a colorless to white solid that is soluble in water and slightly soluble in alcohol. The salt itself is often not isolated, but solutions of the dicyanoaurate ion ([Au(CN)2]−) are generated on a large scale in the extraction of gold from its ores.[3]

Potassium dicyanoaurate
Names
IUPAC name
Potassium dicyanoaurate(I)
Other names
potassium cyanoaurate[1]
potassium gold cyanide
potassium gold dicyanide
Identifiers
3D model (JSmol)
6235525
ChEBI
ChemSpider
ECHA InfoCard 100.034.303
EC Number
  • 237-748-4
37363
UNII
UN number 1588
  • InChI=1S/2CN.Au.K/c2*1-2;;/q2*-1;2*+1
    Key: XTFKWYDMKGAZKK-UHFFFAOYSA-N
  • ionic form: [C-]#N.[C-]#N.[K+].[Au+]
  • coordination form: N#C[Au-]C#N.[K+]
Properties
KAu(CN)2
Molar mass 288.101 g/mol
Appearance white crystal[1]
Density 3.45 g/cm3[1]
Boiling point decomposes
140 g/L[1]
Structure
Rhombohedral, hR54, No. 148
R3
a = 0.728 nm, b = 0.728 nm, c = 2.636 nm
1.2099 nm3
9
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 toxic
GHS labelling:
GHS05: CorrosiveGHS06: ToxicGHS09: Environmental hazard
Warning
H290, H300, H310, H315, H317, H318, H330, H410
P260, P264, P273, P280, P284, P301+P310
Related compounds
Other anions
 Potassium argentocyanide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Production

In mining of gold from dilute sources, gold is selectively extracted by dissolution in aqueous solutions of cyanide, provided by dissolving sodium cyanide, potassium cyanide and/or calcium cyanide. The reaction for the dissolution of gold, the "Elsner Equation", is:

4 Au + 8 KCN + O2 + 2 H2O → 4 K[Au(CN)2] + 4 KOH

In this process, oxygen is the oxidant.[4]

It can also be produced by reaction of gold(I) salts with excess potassium cyanide.

AuCl + 2 KCN → K[Au(CN)2] + KCl

Structure
dicyanoaurate is a rod-shaped anion.

Potassium dicyanoaurate is a salt. The dicyanoaurate anion is linear according to X-ray crystallography.[3] On the basis of infrared spectroscopy, the dicyanoaurate anion adopts a very similar structure in sodium dicyanoaurate (NaAu(CN)2).[5]

Uses

Dicyanoaurate is the soluble species that is the focus of gold cyanidation, the hydrometallurgical process for winning gold from dilute ores. In fact, sodium cyanide, not the potassium salt, is more widely used in commercial processes.[6]

Aside from its major use as an intermediate in the extraction of gold, potassium dicyanoaurate is often used in gold plating applications.

The compound containing gold(III) cyanide is also known: potassium tetracyanoaurate(III), K[Au(CN)4]. Its use is less common.

The potassium ion can be replaced with quaternary ammonium cations as in tetrabutylammonium dicyanoaurate.[7]

Safety

The ingestion of gram quantities of potassium dicyanoaurate has led to death.[8]

References
  1. Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. p. 4.82. ISBN 978-1439855119.
  2. Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.
  3. Rosenzweig, A.; Cromer, D. T. (1959). "The Crystal Structure of KAu(CN)2". Acta Crystallographica. 12 (10): 709–712. doi:10.1107/S0365110X59002109.
  4. Treatment of Ores Containing Reactive Iron Sulphides. Multi Mix Systems
  5. Chadwick, B.M.; Frankiss, S.G. (1976). "Vibrational Spectra and Structures of Some Dicyanoaurate(I) Complexes". Journal of Molecular Structure. 31 (1): 1–9. Bibcode:1976JMoSt..31....1C. doi:10.1016/0022-2860(76)80113-5.
  6. Rubo, Andreas; Kellens, Raf; Reddy, Jay; Steier, Norbert; Hasenpusch, Wolfgang (2006). "Alkali Metal Cyanides". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.i01_i01.
  7. Stender, Matthias; Olmstead, Marilyn M.; Balch, Alan L.; Rios, Daniel; Attar, Saeed (2003). "Cation and Hydrogen Bonding Effects on the Self-Association and Luminescence of the Dicyanoaurate Ion, Au(CN)2−". Dalton Transactions (22): 4282. doi:10.1039/b310085e.
  8. Wright, I. H.; Vesey, C. J. (September 1986). "Acute poisoning with gold cyanide". Anaesthesia. 41 (9): 936–939. doi:10.1111/j.1365-2044.1986.tb12920.x. PMID 3022615.
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