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To get the gold to a very high level of purity (999 fine gold) it is sometimes processed further with aqua regia to effectively remove all the impurities. Aqua regia was also used for parting. It was made by adding sal ammoniac to nitric acid which produced a mixture of hydrochloric acid and nitric acid.
The fox in Basil Valentine's Third Key represents aqua regia, Musaeum Hermeticum, 1678. The third of Basil Valentine's keys (c. 1600) shows a dragon in the foreground and a fox eating a rooster in the background. The rooster symbolizes gold (from its association with sunrise and the sun's association with gold), and the fox represents aqua regia.
The resulting gold is 99.999% pure, and of higher purity than gold produced by the other common refining method, the Miller process, which produces gold of 99.5% purity. [ 1 ] [ 2 ] [ 3 ] For industrial gold production the Wohlwill process is necessary for highest purity gold applications.
Fulminating gold – a number of gold based explosives which "fulminate", or detonate easily. – gold hydrazide, formed by adding ammonia to the auric hydroxide. When dry, can explode on concussion. – an unstable gold carbonate formed by precipitation by potash from gold dissolved in aqua regia. Galena – lead(II) sulfide. Lead ore.
This method has been used since ancient times. In modern times, additional tests can be done. The trace will react in different ways to specific concentrations of nitric acid or aqua regia, thereby identifying the quality of the gold: 24 karat gold is not affected but 14 karat gold will show chemical activity.
Chloro(dimethyl sulfide)gold(I) is commercially available. It may be prepared by dissolving gold in aqua regia (to give chloroauric acid), followed by addition of dimethyl sulfide. [2] Alternatively, sodium tetrachloroaurate may be used as the source of gold(III). [3] The bromo analog, Me 2 SAuBr, has also been synthesized by a similar route. [4]
In 2010, US researchers discovered that an organic "aqua regia" in the form of a mixture of thionyl chloride SOCl 2 and the organic solvent pyridine C 5 H 5 N achieved "high dissolution rates of noble metals under mild conditions, with the added benefit of being tunable to a specific metal" for example, gold but not palladium or platinum. [11]
These exchanges led to a huge surplus of diamonds, during the recycling of the gold. Many refiners merely burned up the small "melee" diamonds, while others used an acid removal process known as aqua regia, (unless the gold buyers had physically removed the diamonds prior to melting the gold), to harmlessly remove the stones.