XPS study of sulfide minerals surface oxidation under high-voltage nanosecond pulses

Surface modification of natural metal sulfides (pyrite, arsenopyrite, chalcopyrite, sphalerite, galena, and molybdenite) treated by high-power electromagnetic pulses (HPEMP treatment) has been studied by X-ray photoelectron spectroscopy as a function of HPEMP treatment duration. Two principal common steps and some differences in the surface evolution process were identified. The initial surface modification step was observed at low treatment doses (up to N similar to 10(3) pulses). Formation or accumulation in the surface layer of metal-deficient sulfide phase, oxides and hydroxides, elemental/polysulfide sulfur and/or metastable sulfur (thiosulfate, sulfite) was observed at this step. The second step (N >= 3.10(3) pulses) is characterized by thermal loss of elemental sulfur. Differences in the modification process, it was found that the chemical transformations of sulfur in the surface layer of pyrite, arsenopyrite, chalcopyrite include accumulation/formation of S-0 (S-n(2-)) at the first transformation stage (up to N similar to 10(3) pulses) followed by its removal. In the case of sphalerite and galena, the surface sulfur transformation had a different pattern. It included formation/accumulation at the first stage of metastable sulfur species (thiosulfate, sulfite) converted at an increase treatment duration to the initial state (sulfide or disulfide).