Potassium dicyanoaurate is an
inorganic compound with formula K
2">u(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 (
2">u(CN)2sup>−) are generated on a large scale in the
extraction of gold from its ores.
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
Calcium cyanide is the inorganic compound with the formula Ca(CN)2. It is the calcium salt derived from hydrocyanic acid. It is a white solid, although the pure material is rarely encountered. It hydrolyses readily (even in moist air) to release ...
. The reaction for the dissolution of gold, the "Elsner Equation", is:
:4 Au + 8 KCN + O
2 + 2 H
2O → 4 K
2">u(CN)2+ 4 KOH
In this process, oxygen is the oxidant.
It can also be produced by reaction of gold(I) salts with excess potassium cyanide.
:AuCl + 2 KCN → K
2">u(CN)2 + KCl
Structure
:
Potassium dicyanoaurate is a salt. The dicyanoaurate anion is linear according to
X-ray crystallography
X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...
.
[ On the basis of ]infrared spectroscopy
Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or function ...
, the dicyanoaurate anion adopts a very similar structure in sodium dicyanoaurate (NaAu(CN)2).
Uses
Dicyanoaurate is the soluble species that is the focus of gold cyanidation
Gold cyanidation (also known as the cyanide process or the MacArthur-Forrest process) is a hydrometallurgical technique for extracting gold from low-grade ore by converting the gold to a water-soluble coordination complex. It is the most commonl ...
, the hydrometallurgical process for winning gold from dilute ores. In fact, sodium cyanide, not the potassium salt, is more widely used in commercial processes.
Aside from its major use as an intermediate in the extraction of gold, potassium dicyanoaurate is often used in gold plating
Gold plating is a method of depositing a thin layer of gold onto the surface of another metal, most often copper or silver (to make silver-gilt), by chemical or electrochemical plating. This article covers plating methods used in the modern elec ...
applications.
Related compounds
The compound containing gold(III) cyanide is also known: potassium tetracyanoaurate(III), K 4">u(CN)4 Its use is less common.
The potassium ion can be replaced with quaternary ammonium
In chemistry, quaternary ammonium cations, also known as quats, are positively charged polyatomic ions of the structure , R being an alkyl group or an aryl group. Unlike the ammonium ion () and the primary, secondary, or tertiary ammonium cations ...
cations as in tetrabutylammonium
Tetrabutylammonium is a quaternary ammonium cation with the formula (C4H9)4sup>+. It is used in the research laboratory to prepare lipophilic salts of inorganic anions. Relative to tetraethylammonium derivatives, tetrabutylammonium salts are mor ...
dicyanoaurate.
Safety
The ingestion of a gram quantities of potassium dicyanoaurate has led to death.
References
{{Cyanides
Cyanides
Aurates
Gold(I) compounds
Potassium compounds
Cyanometallates