Cathodic processes in the leaching and electrochemistry of covellite in mixed sulfate–chloride media |
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Authors: | M S Lee M J Nicol P Basson |
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Affiliation: | (1) Department of Advanced Materials Science & Engineering, Mokpo National University, Chonnam, 534-729, Korea;(2) Extractive Metallurgy, Murdoch University, South Street, Murdoch, WA, 6150, Australia;(3) BHPBilliton, Johannesburg Technology Centre, Randburg, South Africa |
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Abstract: | The cathodic processes that occur on a covellite (CuS) surface in mixed sulfate–chloride solutions in the absence and presence
of copper(II) ions have been studied using potentiostatic transients and cyclic voltammetry at rotating disk electrodes in
the potential range 0.3–0.7 V (versus SHE). This range is relevant to the oxidative leaching of this copper mineral in sulfate
and chloride lixiviants. Variations in the concentrations of sulfate and chloride ions had a small effect on the cathodic
reduction of covellite in the potential range of 0.5–0.3 V, although the presence of chloride ion resulted in a significant
increase in the anodic current on the reverse sweep. On the other hand, addition of copper(II) ions resulted in enhanced cathodic
currents and subsequent anodic currents in both sulfate and chloride solutions due to reduction of covellite to an undefined
reduced copper sulfide species. Reduction of copper(II) to copper(I) ions becomes the preferred cathodic reaction as the concentration
of chloride ions increases, becoming mass transport controlled at a rotating disc electrode at potentials below about 0.4 V.
Potentiostatic measurements at potentials negative to the mixed potential in acidic chloride solutions have shown that reduction
of copper(II) ions is reversible and have been used to estimate the rate of oxidative dissolution of the mineral which value
agrees reasonably well with previously reported leaching rates under similar conditions. Reduction of dissolved oxygen has
been found to be very much slower that that of copper(II) ions under ambient conditions. |
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Keywords: | Chloride Covellite Cupric Dissolution Reduction Oxygen |
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