Redox potential Eh and anion effects of

Pyrite plays the central role in the environmental issue of acid rock drainage. Natural weathering of pyrite results in the release of sulphuric acid which can lead to further leaching of heavy and toxic metals from other associated minerals. Understanding how pyrite reacts in aqueous solution is critical to understanding the natural weathering processes undergone by this mineral. To this end an investigation of the effect of solution redox potential (Eh) and various anions on the rate of pyrite leaching under carefully controlled conditions has been undertaken. Leaching of pyrite has been shown to proceed significantly faster at solution Eh of 900 mV (SHE) than at 700 mV, at pH 1, for the leach media of HCl, H2SO4 and HClO4. The predominant effect of Eh suggests electrochemical control of pyrite leaching with similar mechanisms at Eh of 700 and 900 mV albeit with different kinetics. Leach rates at 700 mV were found to decrease according to HCl > H2SO4 > HClO4, and were matched by H2SO4 > HClO4 > HCl for pyrite leaching activity is found to continually increase during all leaches; however, this is not accompanied by an increase in leach rate. Synchrotron based photoelectron spectroscopy (PEEM) measurements showed a localised distribution of adsorbed and oxidised surface species highlighting that pyrite oxidation and leaching is a highly site specific process mediated by adsorption of oxidants onto surface sites.