Oxidation of fresh surfaces of coal and mineral-pyrite has been studied using electrochemical and photoelectrochemical techniques. This work was undertaken to better understand the oxidation processes that cause self-induced flotation of pyrite. Fresh surfaces were created by fracturing pyrite in situ, i.e., in solution. Chronoamperometry was used to determine the potential at which a newly created surface does not show oxidation or reduction currents. The ''stable'' potentials for pyrite are (-)0.28 V (SHE) at pH 9.2 and 0 V at pH 4.6. Subsequent cyclic voltammograms show the incipient oxidation mechanism that involves the formation of sulfur products, which are believed to be hydrophobic. It is shown that the lower flotation edge of pyrite coincides with its incipient oxidation potential. The photocurrent generated at fractured pyrite surfaces by chopped illumination was used to determine the semiconducting characteristics of the electrodes. The results indicate that a spontaneous depletion layer is formed on the fresh surfaces of n-type pyrite. The depletion layer is attributed to an intrinsic, acceptor-like surface state. Charge storage in this surface state pins the band edges over a wide potential range, accounting for the metallic-like electrochemical behavior that has been reported for pyrite. The existence of an intrinsic surface state is consistent with XPS studies on pyrite surfaces prepared in vacuum, which reveal an FeS-like species in the surface region. During this report period, all of the data previously obtained has been analyzed in an attempt to better understand the mechanism of pyrite flotation with respect to its oxidation. The results of this analysis are included in this quarterly report. In addition, samples of pyrite from seven different sources were obtained. In situ fracture, photoelectrochemical and cyclic voltammetry studies have been conducted on electrodes made from these pyrites.
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