Production and supply of sodium cyanide

摘要

The term cyanide is used in reference to a group of compounds containing the (CN)-radical, wherein the carbon is triple bonded to the nitrogen. Most often this term refers to hydrogen cyanide (HCN) or one of the simple alkali metal cyanides such as sodium cyanide (NaCN), potassium cyanide (KCN) or calcium cyanide (Ca(CN)_2). Sodium cyanide is the most widely used type of cyanide by the precious metal mining industry, though Ca(CN)_2 and KCN are used in select locations.Sodium cyanide was first prepared in 1834 by heating Prussian blue (a mixture of cyanogen compounds of iron) and sodium carbonate and then extracting sodium cyanide from the cooled mixture using alcohol. Today, almost all sodium cyanide is produced by reacting hydrogen cyanide with sodium hydroxide (NaOH) and evaporating off the water. This is often called the neutralization-wet process.HCN + NaOH -> NaCN + H_2OThe wet process typically uses 50 percent (by weight) NaOH and purified anhydrous hydrogen cyanide (liquid or vapour). Substituting another alkali metal hydroxide for the NaOH produces the corresponding alkaline metal cyanide (use KOH to yield KCN for example). The HCN may be sourced as a by-product of an acrylonitrile process or from a stand-alone on-purpose HCN plant. The former ties NaCN availability to the acrylonitrile market; the latter does not connect supply directly to the acrylonitrile market. On-purpose HCN processes include the BMA (Blausaure-Methan-Ammoniak) process whereby methane or propane is reacted with ammonia over a platinum catalyst; the Andrussow process whereby methane and ammonia are reacted over a catalyst in the presence of air; and the Shawinigan process whereby hydrocarbon gas is passes through super-heated carbon. Plants that produce NaCN from byproduct HCN are located in many countries including Australia, Brazil, China, Japan, Russia, South Korea, the UK, and the US. On-purpose HCN units for the production of metal cyanide are located in may countries as well, including Australia, France, Germany, South Africa and the US.