Cyanidation


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cyanidation

[‚si·ə·nə′dā·shən]
(chemistry)
Joining of cyanide to an atom or molecule.
(metallurgy)

Cyanidation

 

(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).

REFERENCES

Maslenitskii, I. N., and L. V. Chugaev. Metallurgiia blagorodnykh metallov. Moscow, 1972.
Osnovy metallurgii, vol. 5. Moscow, 1968.
References in periodicals archive ?
In Malaysia, limited published research exists on the health impacts of cyanidation on communities near gold mining operations.
This indicates that in order to grow well on media contaminated with gold cyanidation tailing, the three plant species need additional organic matter, such as compost used in this study.
The remaining materials of the amalgamation and cyanidation processes that are in the form of sludge still contain mercury, gold and other heavy metals are generally disposed to agricultural lands and water bodies.
One unconnected, but important point is there is generally good correlation between the fire assay and cyanidation extraction data.
It is noteworthy that simple floatation of the 75 micron grind produced a concentrate with more than 95% of the gold from the sample, and floatation followed by ultra-fine grinding of the resulting concentrate before cyanidation may be the simplest way to increase final cyanide gold recovery.
The 3,500 tpd cyanidation circuit at the La Encantada Silver Mine is expected to be completed by February 2009.
Bottle roll cyanidation tests conducted by the Minerals Engineering Centre at Dalhousie University returned gold recoveries ranging from 95.
It is important to recognise that hydromet-allurgical treatment of gold ores predated the discovery of cyanidation.
Cyanidation tests on all of the samples indicate that greater than 95% of the gold was extracted into solution after 48 hours;
These results were achieved by testing a master composite representing mineralized material from the Meio and Serra zones of the Project using gravity concentration followed by carbon-in-leach (CIL) cyanidation of the gravity tails.
The oxidized solids will be treated with limestone and lime at elevated temperatures to facilitate silver recovery, prior to conventional precious metal recovery by carbon-in-leach cyanidation, carbon stripping, and electrowinning.