What is Cyanide
What is Cyanide?
Cyanide is a chemical made up of carbon and nitrogen. The common types of cyanide are: sodium cyanide, calcium cyanide and potassium cyanide, which are white solids and have a bitter almond-like odor in damp air. Hydrogen cyanide is a colorless gas form of cyanide which also has a faint, bitter almond-like odor that some people are unable to detect due to a genetic trait.
Cyanide is produced from industrial sources and occurs naturally in over a thousand plant species. It is present in almonds, lima beans, spinach and cassava root, a common food source in tropical countries. In fact, it is formed, excreted and degraded naturally by both plants and animals. Cyanide is also produced in the human body and exhaled in extremely low concentrations with each breath.
It is a hazardous substance which, in concentrated amounts, can be very harmful to humans and animals. Progressively higher cyanide intake causes unconsciousness and respiratory failure, requiring immediate medical attention. The effect on the human body is based on the concentration, route and duration of exposure.
Cyanide does not cause cancer and is not bio-accumulative in animals or fish. It can be effectively destroyed with no long term impacts. Cyanide gas evaporates quickly in open spaces such as the outdoors. Sunlight alone will break down cyanide when exposed to air and in surface water. Like other chemicals used by industry, cyanide can be managed safely to protect people and the environment.
Cyanide Usage
Cyanide has been widely used by industry for over a century. Globally approximately 1.27 million tonnes of cyanide are produced annually. Of this total, about 87 percent is used to produce basic industrial and consumer items, such as plastics, adhesives, cosmetics, fire retardants, pharmaceuticals, foods and anti-caking additives. Thirteen percent is used to produce cyanide reagents for mineral processing to recover gold, copper, zinc and silver. Given its industry applications, elimination of cyanide usage within the gold mining industry would not eliminate the need for industrial use of cyanide.
Cyanide is integral to the production of gold. Gold typically occurs at very low concentrations in rocks – less than 10 grams per ton. At these concentrations, the use of water-based chemical extraction processes is the only economically viable method of extracting gold from ore.
Although chemical replacements for cyanide have been investigated for decades, it is still the most effective chemical known for the extraction of gold and silver from rock. Cyanide is used in ore processing at many of Barrick’s operations, based on proven safe practices and processes.
Cyanide is supplied to the gold mining industry in a variety of physical and chemical forms, including solid briquettes, flake cyanide and liquid cyanide. Sodium cyanide comes in either briquette or liquid form, whereas calcium cyanide is supplied in flake or liquid form. Barrick uses sodium cyanide at its operations.
Process:
Water is added to cyanide to create a solution of sodium cyanide.
A weak solution is mixed with ore to dissolve the gold.
The leachate, or cyanide-gold solution, is collected and the gold is recovered.
A noble metal, gold is not soluble in water. Cyanide stabilizes the gold molecule in solution, in combination with an oxidant, such as oxygen. The liquid cyanide solution is then recycled and reused to extract more gold. Even at mines where ore requires the use of roasting or bio-oxidizing, cyanide is still used as a second step in the process of gold extraction.
The form of cyanide reagent chosen for use is dictated by safety considerations, availability, means of transport, distance from source and cost. Large operations close to manufacturing facilities typically prefer liquid cyanide for operator safety considerations. Smaller and more remote operations use solid forms of cyanide to avoid transporting liquids over long distances and to minimize costs.