Sodium cyanide is the inorganic compound with the formula NaCN. This highly toxic salt is used mainly in gold mining but have other niche applications. It is also called cyanogran.

Production and chemical properties

Sodium cyanide is produced by treating the weak acid hydrogen cyanide with sodium hydroxide:

HCN + NaOH → NaCN + H₂O

Worldwide production was estimated at 500,000 tons in the year 2006. In former times, it was prepared by the Castner-Kellner process involving the reaction of sodium amide with carbon at elevated temperatures.

NaNH₂ + C → NaCN + H₂

As the salt is derived from a weak acid, NaCN readily undergoes hydrolysis: the moist solid emits small amounts of hydrogen cyanide, which smells like bitter almonds (not everyone can smell it—the ability thereof is due to a genetic trait). Sodium cyanide reacts rapidly with strong acids to release hydrogen cyanide. This dangerous process represents a significant risk associated with cyanide salts.It is detoxified most efficiently with hydrogen peroxide:

NaCN + H₂O₂ → NaOCN + H₂O

Applications

Cyanide mining

Sodium cyanide is mainly used to extract gold and other precious metals in mining. This application takes advantage of the high affinity of gold(I) for cyanide, which induces gold metal to oxidize and dissolve in the presence of air and water.

4 Au + 8 NaCN + O₂ + 2 H₂O → 4 Na[Au(CN)₂] + 4 NaOH

Very few alternative methods exist for this extraction process.

Chemical feedstock

Several commercially significant chemical compounds are derived from cyanide, including cyanuric chloride, cyanogen chloride, and many nitriles. In organic synthesis, cyanide, which is classified as a strong nucleophile, is used to prepare nitriles, which occur widely in many specialty chemicals, including pharmaceuticals.

Niche uses

Being highly toxic, sodium cyanide is used to kill or stun rapidly such as in illegal cyanide fishing and by entomologists as a killing agent in collecting jars.

Toxicity

Cyanide salts are among the most rapidly acting of all known poisons. Cyanide is a potent inhibitor of respiration, acting on mitochondrial cytochrome oxidase and hence blocking electron transport. This results in decreased oxidative metabolism and oxygen utilization. Lactic acidosis then occurs as a consequence of anaerobic metabolism.

References

See also

• Summitville mine
• Cyanide

External links

• Institut national de recherche et de sécurité (1997). " Cyanure de sodium. Cyanure de potassium". Fiche toxicologique n° 111, Paris:INRS, 6pp. (PDF file, in French)
• International Chemical Safety Card 1118
• Hydrogen cyanide and cyanides (CICAD 61)
• National Pollutant Inventory - Cyanide compounds fact sheet
• NIOSH Pocket Guide to Chemical Hazards
• CSST (Canada)
• Sodium cyanide hazards to fish and other wildlife from gold