REACTIVITY OF SURFACE CHEMICAL-STATES ON FRACTURED PYRITE

Synchrotron-radiation-excited photoelectron spectroscopy was used to m onitor sulfur chemical states on fractured pyrite surfaces reacted wit h atmospheric gases. The results demonstrate that there are at least t hree distinct states at the pyrite surface and each is oxidised at a v ery different rate in air. The two surface chemical states are more re active than bulk sulfur, the most reactive surface sulfur component be ing S2-. The second chemical state is identified as the surface atom o f the first disulfide layer (S-2(2-)): and the least reactive species are sulfur atoms of disulfide groups beneath the surface layer (i.e., all sulfur atoms having bulk coordination). A model combining the inte rpretation of sulfur surface species after Nesbitt et al. (Am. mineral . in press) and the proposed oxidation mechanism of Eggleston et al. ( Am. Mineral. 81 (1996) 1036) was developed to explain the initial oxid ation processes on pyrite surfaces, where air oxidation of pyrite comm ences with the oxidation of S2- sites at the surface. (C) 1998 Elsevie r Science B.V. All rights reserved.