Incipient oxidation of fractured pyrite surfaces in air

Synchrotron excited and conventional X-ray photoelectron spectroscopy has b een used to study the initial oxidation of fractured pyrite surfaces in air , The dramatically enhanced surface sensitivity obtained with synchrotron r adiation allowed us to follow the reactivity of each of the different sulph ur surface sites and to detect intermediate sulphur oxidation species. It h as been shown that the surface sulphur components that are directly exposed to atmospheric gases undergo oxidation to sulphate, whereas bulk sulphur m ainly forms 'electron deficient' disulphides. Fe 2p spectra were used to in vestigate the oxidation of Fe(II) and Fe(III) surface sites. The intensity of Fe(III)-S sites does not change significantly within a 14 h oxidation ti me. The number of Fe(II) surface sites diminishes and FeOOH is formed. The results have been used to propose an oxidation mechanism including the oxid ation of different iron as well as sulphur sites. (C) 1998 Elsevier Science B.V. All rights reserved.