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Study of gold leaching in oxygenated solutions containing cyanide-copper-ammonia using a rotating quartz crystal microbalance

Zheng, J., Ritchie, I.M., La Brooy, S.R. and Singh, P. (1995) Study of gold leaching in oxygenated solutions containing cyanide-copper-ammonia using a rotating quartz crystal microbalance. Hydrometallurgy, 39 (1-3). pp. 277-292.

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Gold and copper often occur together in ores, an occurence which creates processing difficulties since cyanide solutions are not selective for gold. Although it has been shown that ammoniacal cyanide solutions can leach gold selectively, little practical use has been made of this finding since the mechanism is not yet understood and strategies for optimisation have not been fully developed.

This paper describes a kinetic study of one part of this system, namely the dissolution of gold in oxygenated solutions containing mixtures of cyanide-ammonia-copper. The rates were measured using a rotating quartz crystal microbalance. The results confirm that the dissolution of gold in alkaline cyanide solutions proceeds at a lower rate than expected as a result of a blocking film on the gold surface. The addition of copper(I) to the cyanide solutions retards the leaching rate by an amount which increases as the copper content increases. However, this is not just because there is less free cyanide present. A speciation calculation shows that the copper is in some way involved in the dissolution reaction. In contrast, the addition of ammonia to the cyanide leaching solution causes the rate to progressively decrease, ultimately reaching an ammonia concentration above which there is no further decrease in leaching rate. Electrochemical measurements showed that the ammonia has greatly suppressed the anodic half-reaction.

The final gold leach system to be investigated was one containing oxygen, cyanide, copper(I) and ammonia, the latter two components being maintained at a fixed ratio of 1:4 while varying the copper to cyanide ratio from approximately 1:6 to l:2. However, for a total cyanide concentration of 0.032 M and ammonia concentration of about 0.04 M, the rate starts to increase. It is presumably in this region that selective leaching of gold from copper occurs.

Item Type: Journal Article
Murdoch Affiliation(s): School of Mathematical and Physical Sciences
Publisher: Elsevier BV
Copyright: © 1995 Published by Elsevier B.V.
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