cyanide process

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cyanide process

or

cyanidation,

method for extracting goldgold,
metallic chemical element; symbol Au [Lat. aurum=shining dawn]; at. no. 79; at. wt. 196.96657; m.p. 1,064.43°C;; b.p. 2,808°C;; sp. gr. 19.32 at 20°C;; valence +1 or +3.
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 from its ore. The ore is first finely ground and may be concentrated by flotation; if it contains certain impurities, it may be roasted. It is then mixed with a dilute solution of sodium cyanide (or potassium or calcium cyanide) while air is bubbled through it. The gold is oxidized and forms the soluble aurocyanide complex ion, Au(CN)2−1. (Silver, usually present as an impurity, forms a similar soluble ion.) The solution is separated from the ore by methods such as filtration, and the gold is precipitated by adding powdered zinc. The precipitate usually contains silver, which is also precipitated, and unreacted zinc. The precipitate is further refined, e.g., by smelting to remove the zinc and by treating with nitric acid to dissolve the silver. The cyanide process was developed (1887) by J. S. MacArthur and others in Glasgow, Scotland. It is now the most important and widely used process for extracting gold from ores.

cyanide process

[′sī·ə‚nīd ‚präs·əs]
(metallurgy)
Process of dissolving powdered gold and silver ores in a weak solution of sodium cyanide or potassium cyanide; the precious metals are precipitated from solution by zinc. Also known as cyanidation.