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Joining of cyanide to an atom or molecule.



(also cyanide process), in hydrometallurgy, a method of extracting metals, chiefly gold and silver, from ores and concentrates by dissolving them selectively in solutions of alkali-metal cyanides. Selective dissolution is achieved with a weak concentration of the solution (0.03 to 0.3 percent cyanide), in order that there be little interaction with other constituents in the ore. Gold and silver dissolve in a cyanide solution when the water contains dissolved oxygen; increasing the solution’s concentration intensifies the process. To avoid decomposition of the cyanides, 0.005 to 0.02 percent of a protective alkali, such as lime or caustic soda, is added to the solution.

The theory of cyanidation processes is based on the laws of the kinetics of dissolution at inhomogeneous surfaces (with cathode depolarization by oxygen) and the kinetics of the diffusion of metals (with the simultaneous diffusion of the cyanide and oxygen). Of great importance are the regularities of the interaction of reagents with minerals that take into account the minerals’ composition and structure.

Two cyanidation methods are used in industry. The first involves the percolation of solutions through a layer of finely crushed ore or sand and the agitation of the pulp along with intensive aeration. Gold and silver are often precipitated from solution with zinc dust. The second method, which is currently being developed, is sorption cyanidation, which combines the processes of leaching out and recovering the dissolved gold and silver from a pulp by sorption with anionites or activated charcoals. This method is effective for processing ore slimes that are difficult to filter.

The recovery rate of gold by the cyanidation of pulp ranges between 90 and 96 percent, using 0.25 to 3 kg of sodium cyanide per ton and 0.5 to 5 kg of protective alkali per ton.

The dissolution of gold and silver in cyanide solutions was first investigated by P. R. Bagration (1843) and was further studied by F. Eisner (Germany, 1846) and M. Faraday (1856). It was introduced into industrial practice in the early 1890’s (patents by J. S. MacArthur and the brothers R. W. Forrest and W. Forrest of Great Britain in 1887 and 1888).


Maslenitskii, I. N., and L. V. Chugaev. Metallurgiia blagorodnykh metallov. Moscow, 1972.
Osnovy metallurgii, vol. 5. Moscow, 1968.
References in periodicals archive ?
Today, however, cyanidation methods, also known as carbon in leach, have been used extensively in gold extraction, and these methods have a detrimental impact on the ecosystem.
For the month of April 2014, the dual circuit mill averaged 2,297 tpd (984 tpd in cyanidation and 1,314 tpd in flotation) compared to the first quarter average of 1,609 tpd (735 tpd in cyanidation and 874 tpd in flotation).
At almost all of the ASGM, the amalgamation process followed by cyanidation process are common methods used to recover as much gold as possible from gold ore [2].
the "Company" or "First Majestic") is pleased to announce that the Company's new 1,000 tonnes per day (tpd) cyanidation circuit at its Del Toro Silver Mine in Zacatecas, Mexico began initial production of silver dore bars on November 20, 2013.
Pressure oxidation (POX) of the pyrite/arsenopyrite concentrate is required to extract the contained gold by cyanidation.
The outcome from the programme suggests the resource could be economically treated using standard Gravity Concentration / Carbon in leach (CIL) cyanidation technology.
To maximize the recovery of all precious metals the Company is now working with the metallurgical lab to further develop an encompassing recovery process which will include both cyanidation recovery as well as the silver-lead process.
Meanwhile, local environmental groups are protesting the use of cyanide in the mining procedures that call for crushing, grinding, pressure oxidation, and CIL cyanidation at the Barrick Gold Pueblo Viejo mine.
Some 90 percent of gold mines around the world employ cyanidation to harvest their loot.
Cyanidation as a chemical method for leaching of gold was studied in 1880s by John Steward MacArthur and due to instant good results, it eventually replaced chlorination processing.
The majority of the samples were sieved in the laboratory into six size fractions and the coarser fractions were analysed for gold by cyanidation which should extract all the oxidised gold in the sample and by fire assay which analyses total gold.
2]) and arsenopyrite (FeAsS) minerals are oxidized to liberate gold which can be efficiently recovered in the subsequent cyanidation stage.