Abstract
Rotating disc electrodes were used to study the kinetics of cementation of copper using zinc discs over a wide range of Cu(I) concentration (0.15–1.57 mM)), free cyanide (0–10 mM), pH (pH8–11) and temperature (20–50°C). By modelling the speciation of the Cu(I) species in the solution, it is able to postulate that Cu(CN) 2 − is the electrochemical active species responsible for the cementation process. By increasing the free cyanide concentration or the solution pH within the above ranges, the concentration of this species decreases dramatically, thus causing the cementation rate to drop significantly. Under the test conditions, the cementation process is controlled by a kinetic step, with an activation energy of 31.8 kJ/mol. By selecting a high free cyanide concentration and a high pH, gold can be selectively cemented from a gold-copper mixture using zinc, leaving copper completely behind in the solution.
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