Calcium cyanide is the

inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

Ca(CN)₂. It is the

calcium Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

derived from hydrocyanic acid. It is a white solid, although the pure material is rarely encountered. It slowly hydrolyses in solution or moist

air An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

to release hydrogen cyanide and is very

toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subst ...

Preparation

Solutions of calcium cyanide can be prepared by treating

calcium hydroxide Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca( OH)2. It is a colorless crystal or white powder and is produced when quicklime ( calcium oxide) is mixed with water. Annually, approxim ...

with

hydrogen cyanide Hydrogen cyanide (formerly known as prussic acid) is a chemical compound with the chemical formula, formula HCN and structural formula . It is a highly toxic and flammable liquid that boiling, boils slightly above room temperature, at . HCN is ...

. Solid calcium cyanide is produced commercially by heating

calcium cyanamide Calcium cyanamide, also known as Calcium carbondiamide, Calcium cyan-2°-amide or Calcium cyanonitride is the inorganic compound with the formula CaCN2. It is the calcium salt of the cyanamide () anion. This chemical is used as fertilizer and is c ...

with

sodium chloride Sodium chloride , commonly known as Salt#Edible salt, edible salt, is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. It is transparent or translucent, brittle, hygroscopic, and occurs a ...

. The reaction is incomplete. The product is only of 50% purity, other components being sodium cyanide,

, and carbon. Because of the carbon impurity, the solid is black, hence material is often called black cyanide.

Reactivity

At temperatures around 600 °C, calcium cyanide converts to calcium cyanamide:"Production of Hydrocyanic Acid" ''United States Patent Office.'' 1933.(accessed April 22, 2012). :Ca(CN)₂ → CaCN₂ + C It is suspected that this reaction is one step in the conversion of calcium carbide with nitrogen gas. The ratio of calcium cyanide to calcium cyanamide is sensitive to the presence of alkali metal halides, such as sodium chloride. Calcium cyanide hydrolyzes upon acidification to form

: :Ca(CN)₂ + 2H⁺ → Ca²⁺ + 2HCN Calcium cyanide reacts with ammonium carbonate to give produce ammonium cyanide: :Ca(CN)₂ + (NH₄)₂CO₃ → 2NH₄CN + CaCO₃

Uses

Calcium cyanide is used almost exclusively in the mining industry. It serves as an inexpensive source of

cyanide In chemistry, cyanide () is an inorganic chemical compound that contains a functional group. This group, known as the cyano group, consists of a carbon atom triple-bonded to a nitrogen atom. Ionic cyanides contain the cyanide anion . This a ...

in many leaching or vat operation to obtain precious metals such as

gold Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...

and

silver Silver is a chemical element; it has Symbol (chemistry), symbol Ag () and atomic number 47. A soft, whitish-gray, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. ...

from their ores."Use of Cyanide for the Gold Industry" ''International Cyanide Management Code for the Use of Cyanide in the Gold .'' 2011. http://www.cyanidecode.org/cyanide_use.php (accessed April 22, 2012).

Safety

Like other cyanide salts, this compound is highly toxic and its use is strictly regulated.

References

External links

Hydrogen Cyanide and Cyanide Salts (CASRN Various)
{{Calcium compounds Cyanides

Cyanide In chemistry, cyanide () is an inorganic chemical compound that contains a functional group. This group, known as the cyano group, consists of a carbon atom triple-bonded to a nitrogen atom. Ionic cyanides contain the cyanide anion . This a ...

Gold mining