An Xps and Afm Coupled Study of Air and Bio-Oxidized Pyrite Surfaces

In most sulfide ore deposits, the main gangue mineral is pyrite, which is often considered a nuisance in mining enterprises and natural environments due to acid mine drainage and soil and water pollution by heavy metals. Many chemical reactions, including natural metal leaching and industrial metal recovery, involve bacteria: sulfide oxidation by Thiobacillus ferrooxidans is a typical example. Frequently, bio-oxidation of sulfides is described in terms of pure biological and chemical processes that do not take into account the variability of mineral properties. In fact, biooxidation processes are complex and strongly dependent on the crystallographic and electrochemical characteristics of the mineral, (MARION et al, 1991 ; MUSTIN et al, 1992a). These physical properties also seem to govern both development of corrosion pores and oxidized phases at the sulfide surface (MUSTIN et al, 1993a, MONROY- FERNANDEZ et al 1995). The physico-chemical modification of the mineral interface, more often neglected, could be of primary importance for the biooxidation of sulfides.