UBC Theses and Dissertations
Electrochemical and Raman investigation of pyrite and chalcopyrite oxidation Eghbalnia, Maziar
The electrochemical behavior of chalcopyrite and pyrite in acidic ferric solutions was investigated using leaching experiments, electrochemical techniques and micro Raman spectroscopy. The investigation of pyrite-assisted leaching of chalcopyrite concentrate in iron sulfate showed that the catalytic effect of pyrite varies depending on the source of the sample. Cyclic voltammetry using solid paraffin carbon paste electrode demonstrated that the ability of chalcopyrite to reduce ferric ions declines with time spent in the leaching reactor. Single particle microelectrode technique was employed to investigate the electrochemical and semiconducting properties of different pyrite samples by means of cyclic voltammetry, electrochemical impedance spectroscopy and Mott-Schottky methods. Cyclic voltammetry showed a difference in the magnitude of the ferric reduction reaction peaks. An equivalent analogue circuit was used to model the impedance spectra, which led to the conclusion that pyrite samples with lower charge transfer resistance are better catalysts for ferric reduction. Micro Raman investigation revealed that elemental sulfur and intermediate products of pyrite oxidation form on the surface of the effective pyrite sample, while sulfur alone forms on the surface of less effective pyrite. Gold and silver nanoparticles were deposited on pyrite at ambient temperature from colloidal solutions. The modified pyrite was investigated using Electrochemical Impedance Spectroscopy. The results revealed a decrease in charge transfer resistance for the redox couple associated with the modified pyrite. It is concluded that the inconsistencies observed in the kinetics of chalcopyrite leaching in pyrite-assisted leaching are due to erratic electrocatalytic behavior of pyrite samples from different geographical locations with various chemical compositions. The concordance between observations of sluggish charge transfer between energy levels in pyrite and electrolyte in less effective pyrite samples in the leaching experiments strengthens the hypothesis that charge transfer between pyrite and the redox couple in solution is the key step in the process.
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