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On the mechanisms of ambient chalcopyrite leaching in sulfate media

Tapera, Tendekayi (2019) On the mechanisms of ambient chalcopyrite leaching in sulfate media. PhD thesis, Murdoch University.

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Chalcopyrite accounts for about 70% of all known copper deposits. Low-grade chalcopyrite deposits may be unsuitable for exploitation by smelting. Leaching of chalcopyrite-bearing ores in sulfate solutions is a potential alternative. However chalcopyrite leaching is slow. It is believed that the low leaching rates are due to the gradual formation of a passive layer on the chalcopyrite surface. This study investigated the chalcopyrite behaviour in different mild sulfate solutions by the application of electrochemical techniques, leaching tests and surface characterisation methods. Electrochemical techniques demonstrated that the addition of silver to a leach solution enhances chalcopyrite leaching rates. The addition of silver to a leach solution also reactivated a passivated chalcopyrite surface. Leaching tests confirmed this and techniques such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that elemental Ag forms on the surface during leaching. These results have shown that this effect can be attributed to the deposition of metallic silver on the surface of the dissolving chalcopyrite which improves the surface conductivity as Ag provides an electron path. This allows electron transfer between chalcopyrite surface and the redox species in solution and in so doing enables the oxidative leaching reaction to proceed.

SEM images revealed that during leaching, the chalcopyrite does not dissolve uniformly. It was demonstrated that different surface products are present on the same surface at different stages of the leaching. The study revealed that intermediate phases forming on a chalcopyrite surface include copper-rich sulfides (or iron-deficient sulfides). It was further demonstrated through time-resolved in-situ synchrotron powder diffraction, that the intermediate Cu-rich phase is formed rapidly on the surface. The formation of elemental sulfur was identified by time-resolved in-situ synchrotron powder diffraction as well as by x-ray diffraction (XRD). Potential synergistic effects of Ag ions and other additives were also investigated experimentally using leaching tests. It was shown that the effect of Ag on Cu extraction is significantly enhanced by the presence certain secondary components and that this strategy can be used to lower the dosages of silver required for an effective copper heap leaching.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): College of Science, Health, Engineering and Education
Supervisor(s): Nikoloski, Aleksandar, Königsberger, Erich and Deditius, Artur
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