Uses and properties
Gold/Silver Mining Industry
The gold and silver mining industry is the world's main cyanide consumer. Sodium cyanide is the most efficient complexing agent for dissolving finely distributed gold and silver particles from the ore.
Sodium cyanide is also used in the selective flotation of sulphidic ores. Cyanide is used as "depressant": by rendering the sulphidic ore particles hydrophilic they are prevented from reacting with the "collectors". This allows the separation of the metals like lead, zinc, copper, molybdenum and iron selectively.
Sodium cyanide is required to introduce the CN-group into organic substances as a basis for developing in a wide variety of products in pharmacy, compound structures chemistry and polymer chemistry. Not only in inorganic reactions but also in organic chemistry, particularly alkali cyanides play an important role. Organic halogen compounds react with alkali cyanides in water or polar aprotic solvents, like dimethylsulfoxide or dimethyl formamide, to form nitriles which can be further processed to carboxylic acids, amides, esters and amines.
In the electroplating industry, sodium and potassium cyanide are used to produce the required heavy metal or precious metal cyanide complexes for brass, zinc, copper, gold, and silver electrodeposition. Potassium cyanide is used in the electroplating industry to produce plated jewellery and other gold-plated items.
lkali cyanides not only serve to produce the required heavy metal cyanide complexes, but they are also used in formulating the cyanidic electrolytes themselves. As a result of this it is possible to deposit the much less noble zinc together with the more noble copper from brass baths in the form of an alloy containing 67 - 74% Cu. Excellent throwing power, simplicity in operating the plating bath and insensibility to impurities are additional criteria of electrolytes containing cyanides which have proven themselves especially effective in electroplating of iron and steel. Particularly in these cases, the improved scattering power is a guarantee for more uniform covering and no corrosion problems. In cases where the highest plating quality is required, cyanide pre-treatment and degreasing bath are still in use even today, especially since attempts to employ other strong complexing agents instead of cyanides have failed because of insurmountable waste water problems.
Another type of surface refinement is the hardening of parts of steel. Cyanides release carbon on to the surface of the material being treated at relatively low temperatures. They are nevertheless stable enough to permit simple process control even at high temperatures. As a result, it is possible to attain surface qualities that are characterized by extremely high strength and resistance to abrasion. These qualities are required, for example, in engine parts subject to high stresses (crankshafts, inlet and exhaust valves, camshafts, etc.).
Voluntary Code of Practice, September 2002