Cu and Fe chalcopyrite leach activation energies and the effect of added Fe |
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| Authors: | K Kaplun |
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| Institution: | Minerals and Materials Science and Technology, Mawson Institute, University of South Australia, Mawson Lakes, SA 5095, Australia |
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| Abstract: | The leaching kinetics of chalcopyrite (CuFeS2) concentrate in sulfuric acid leach media with and without the initial addition of Fe3+ under carefully controlled solution conditions (Eh 750 mV SHE, pH 1) at various temperatures from 55 to 85 °C were measured. Kinetic analyses by (i) apparent rate (not surface area normalised), and rate dependence using (ii) a shrinking core model and (iii) a shrinking core model in conjunction with Fe3+ activity, were performed to estimate the activation energies (Ea) for Cu and Fe dissolution.The Ea values determined for Cu and Fe leaching in the absence of added Fe3+ are within experimental error, 80 ± 10 kJ mol−1 and 84 ± 10 kJ mol−1, respectively (type iii analyses Ea are quoted unless stated otherwise), and are indicative of a chemical reaction controlled process. On addition of Fe3+ the initial Cu leach rate (up to 10 h) was increased and Cu was released to solution preferentially over Fe, with the Ea value of 21 ± 5 kJ mol−1 (type ii analysis) suggestive of a transport controlled rate determining process. However, the rate of leaching rapidly decreased until it was consistently slower than for the equivalent leaches where Fe3+ was not added. The resulting Ea value for this leach regime of 83 ± 10 kJ mol−1 is within experimental error of that determined in the absence of added Fe3+. In contrast to Cu release, Fe release to solution was consistent with a chemical reaction controlled leach rate throughout. The Fe release Ea of 76 ± 10 kJ mol−1 is also within experimental error of that determined in the absence of added Fe3+. Where type (ii) and (iii) analyses were both successfully carried out (in all cases except for Cu leaching with added Fe3+, <10 h) the Ea derived are within experimental error. However, the type (iii) analyses of the leaches in the presence of added Fe3+ (>10 h), as compared to in the absence of added Fe3+, returned a considerably smaller pre-exponential factors for both Cu and Fe leach analyses commensurate with the considerably slower leach rate, suggestive of a more applicable kinetic analysis.XPS examination of leached chalcopyrite showed that the surface concentration of polysulfide and sulfate was significantly increased when Fe3+ was added to the leach liquor. Complementary SEM analysis revealed the surface features of chalcopyrite, most likely due to the nature of the polysulfide formed, are subtly different with greater surface roughness upon leaching in the absence of added Fe3+ as compared to a continuous smooth surface layer formed in the presence of added Fe3+. These observations suggest that the effect of Fe3+ addition on the rate of leaching is not due to the change in the chemical reaction controlled mechanism but due to a change in the available surface area for reaction. |
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