RECONSTRUCTION OF FRACTURE SURFACES ON BORNITE

Synchrotron-radiation X-ray Photoelectron Spectroscopy (SRXPS) and conventional X-ray Photoelectron Spectroscopy (XPS) have been used to study a pristine fracture-surface of bornite (Cu5FeS4). Comparisons of these high-resolution spectra reveal, for the fi rst time, four distinct contributions to the S 2p spectra. The main symmetric peak of the S 2p spectra for bornite is located at about 163.51 eV and is derived from bulk S atoms. The broad nature of the bulk contribution, in comparison to other 3d transition-metal sulfi des such as chalcopyrite, is consistent with the presence of eight crystallographically distinct S sites within the structure, these sites being energetically as well as structurally distinct. A second peak located at 160.1 eV is attributed to a surface monomeric species (S2–) of lower coordination. The presence of a second broad surface-contribution at 162.1 eV likely represents surface polymeric species (Sn2–). The presence of surface sulfur polymers indicates the stabilization of the bornite surface upon fracture through formation of S–S bonds. These data suggest that surface polymers form where polar surfaces are exposed during conchoidal fracture. A high binding-energy tail was observed at about 163 eV and extends to about 166 eV, the origin of which is uncertain. Conventional XPS Cu 2p and Fe 2p spectra collected from a pristine fracture-surface of bornite reveal a Cu1+ peak centered at about 932.2 eV and a high-spin Fe3+ peak centered at 708 eV