An experimental study of the ferric oxidation kinetics of pyrite was conducted under controlled redox potentials of 700, 800 and 900 mV (vs. SHE). The rate of pyrite oxidation strongly depends on redox potential, increasing fivefold when redox potential is increased by 100 mV. Pyrite dissolution is significantly affected by temperature. Activation energies of 56.6, 55.9 and 51.9 kJ/mol calculated from pyrite dissolution at redox potentials of 700, 800 and 900 mV (vs. SHE) respectively confirmed a chemical or an electrochemical rate-determining reaction on the pyrite surface. A mineralogical study of the residue after dissolution of pyrite confirmed that elemental sulfur formed during pyrite dissolution. Iron hydroxide/oxide precipitation and jarosite were not observed in residual pyrite by X-ray diffraction spectroscopy analysis. Results of scanning electron microscope analysis of residual pyrite indicated that oxidation readily occurred at specific sites with high surface energy, such as particle edges, corners, defects, and fractures. The products of pyrite dissolution were heterogeneously distributed on the pyrite surface. These results provide useful information for optimizing the conditions that could be used for heap bioleaching of refractory gold ores containing pyrite.
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