Reconstruction of pyrrhotite fracture surfaces

The interpretation of core level Synchrotron photoemisison spectra (SPES) collected from a pristine fracture surface of monoclinic pyrrhotite (Fe7S8), as a function of photon energy, has identified the three distinct surface species. The Fe 2p photoemission spectra show the Fe in pyrrhotite is high spin Fe-II in octahedral co-ordination. Comparison of bulk and surface sensitive spectra did not identify any changes due to the broad nature of the high spin Fe 2p spectra. However, the sulfur spectrum shows an undercoordinated monosulfide at 160.8 eV, a disulfide (161.7 eV) and polysulfide species (163.2 eV) at the surface. This indicates stabilisation of the surface involves reconstruction and results in chemical transformation of sulfur species. A high binding energy tail that extends to 167 eV has been attributed to ligand to metal charge transfer satellites (LMCT) and supported by the pre-edge features observed in Fe L(2,3 )and S L-2,L-3 near edge X-ray absorption fine structure (NEXAFS). An accurate fit for the bulk pyrrhotite sulfide spectrum has been estimated by comparing spectra with different surface sensitivities, and thereby an accurate fitting method has been developed for the monoclinic pyrrhotite S 2p spectrum. This method may be used for future photoemission spectra to improve the analysis of similar samples and provide a basis for interpretation of pyrrhotite samples during mineral processing and environmental conditions.

Automated summary

The interpretation of core level Synchrotron photoemission spectra (SPES) collected from a pristine fracture surface of monoclinic pyrrhotite (Fe7S8) has identified three distinct surface species. High spin Fe-II in octahedral co-ordination was observed for Fe in pyrrhotite. Surface reconstruction and chemical transformation of sulfur species were found to stabilize the surface, resulting in the presence of undercoordinated monosulfide, disulfide, and polysulfide species. An accurate fitting method was developed for the S 2p spectrum, which can be applied to improve the analysis of similar samples and provide a basis for interpreting pyrrhotite samples in mineral processing and environmental conditions.