Thesis (Ph. D., Chemistry)--University of Idaho, December 2008. / Major professor: Thomas Bitterwolf and Ray von Wandruszka. Includes bibliographical references (leaves 179-189). Also available online (PDF file) by subscription or by purchasing the individual file.

Thesis (M.App.Sc.)--University of South Australia, 1996.

The potential region in which chalcopyrite dissolves during the oxidative leaching of the mineral in ferric sulphate solutions has been established. These results have been modelled using an extended mixed-potential description of the system. The initial stages of the dissolution process have been studied using a chalcopyrite disk and a platinum ring electrode held at appropriate potentials for the detection of ferrous and cupric ions. These experiments have shown that the initial stages of oxidation of the mineral involve the formation of soluble sulphur species in addition to elemental sulphur. The ring-disk experiments are generally consistent with thiosulphate as this species. The effectof potential and various ratios of ferric to ferrous ions on the rate has been investigated by both electrochemical and chemical analysis techniques. The role of non-oxidative dissolution in the leaching of chalcopyrite has been explored and it has been shown that the initial rate of non-oxidative dissolution is significant and could exceed the oxidative rate at long leach times.

Thesis (Ph.D.)--Murdoch University, 2001. / Thesis submitted to the Division of Science and Engineering. Bibliography: leaves 279-300.

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One of the most important outstanding problems with the hydrometallurgy of copper is the low temperature leaching of chalcopyrite. In this thesis, a fundamental study at low temperature was undertaken in order to establish a mechanism, which is consistent with the data obtained in an extensive study of the kinetics of dissolution of several chalcopyrite concentrates. It will be demonstrated that enhanced rates of dissolution can be achieved at ambient temperatures by the application of controlled potentials in the range 560-650 mV, depending on the concentration of chloride ions. However, control of the potential by the use of electrochemical or chemical oxidation of iron(II) or copper(I) ions is ineffective unless carried out in the presence of dissolved oxygen. The rates of dissolution are approximately constant for up to 80% dissolution for sized fractions of the concentrates with an activation of energy of about 75 kJ mole-1. Chalcopyrite from different sources appears to dissolve at approximately the same rate which is largely independent of the iron and copper ion concentrations, the acidity and chloride ion concentration but depends in some cases on the presence of additives such as fine pyrite or silver ions. Based on the results of these leaching experiments and detailed mineralogical analyses of the residues, a mechanism involving non-oxidative dissolution of the mineral coupled to oxidation of the product hydrogen sulfide will be proposed. The latter reaction is shown to occur predominantly by a copper ion – catalyzed reaction with dissolved oxygen. The results of an independent study of the kinetics of this reaction will be presented which will demonstrate that the rates are consistent with those obtained for the dissolution of the mineral. The possible involvement of a covellite-like surface layer on the chalcopyrite under some conditions will also be discussed as it relates to the mechanism. It will also be shown that fine pyrite particles can also act as a catalyst surface for the oxidation of hydrogen sulfide. This mechanism is consistent with the mineralogy which confirmed the formation of secondary sulfur which is not associated with chalcopyrite but is associated with fine pyrite if present. A comparison of this mechanism with that proposed in other more limited studies of the dissolution of chalcopyrite under similar conditions in sulfate solutions has been made.

Chalcopyrite (CuFeS2) is the most abundant of the copper sulfides and also one of the most refractory for leaching. Several processing routes have been proposed to overcome drawbacks associated with environmental problems related to copper extraction from this mineral. Atmospheric leaching in acidic ferric sulfate is regarded as being particularly attractive over other hydrometallurgical systems. However, the challenge has been to overcome the problem of slow extraction rates due to passivity encountered at high solution potentials in this system. This highlights the need to investigate better operating conditions to optimize copper extraction and prevent the problem of passivation, and to develop suitable modeling tools to assess and diagnose leaching performance. In this work, a dissolution rate expression for chalcopyrite leaching in acidic ferric sulfate media is proposed accounting for effects in the active and passive regions under potentials from 415 to 550 mV (Ag/AgCl). A model of chemical speciation in the bulk solution elucidates the idea of passivation caused by precipitation of ferric species and their consequent adsorption onto the chalcopyrite surface. Electrochemical studies on massive samples of chalcopyrite involving characterization and modeling of the anodic and cathodic half-cell reactions of chalcopyrite leaching together with mixed potential considerations lead to the development of the mathematical expression for dissolution rate. The mathematical model was calibrated with electrochemical parameters and results are in good agreement with real leaching data from batch tests for solution potential regions where passivity is not observed. On the other hand, the passive region was modeled by means of adjusting parameters related to adsorption energies of the passivating species. Results of the model for this region deviate from real data as potential becomes higher probably due to diffusion resistance through a layer composed of ferric complexes.

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