Electronic structure of the non-equilibrium iron-deficient layer of hexagonal pyrrhotite

Natural hexagonal pyrrhotite before and after 1M HCl leaching has been studied, and X-ray and UV photoelectron, X-ray emission S K α, S K β, S L2,3, Fe L α and S K absorption spectra have been recorded and analyzed in conjunction with earlier reported Mössbauer spectroscopy data and available SCF-X α scattered wave MO calculations of the octahedral cluster FeS610− and the molecular ion S22−. The formation of a thick disordered non-equilibrium iron-deficient layer at the pyrrhotite surface after chemical treatment has been confirmed. Alterations of the X-ray spectra from the mineral as a result of acid etching indicated the sulphur-sulphur bonds and agreed well with the previous conclusion about the conversion of a ferrous ion from the quintet into the singlet state. The electronic structure of the metal-deficient layer has been described using a combination of structures of the SS bond containing group like S22−, of the low-spin singlet cluster FeS610−, and of a system of localized states.