A comparative X-ray absorption near-edge structure study of bornite, Cu5FeS4, and chalcopyrite, CuFeS2

High resolution Fe L-, Cu L-, S L-edge and O K-edge X-ray absorption near-edge structure (XANES) spectra of synthetic bornite and the samples oxidized in air and leached in a ferric chloride solution have been recorded and compared with the spectra of chalcopyrite. The pre-edge shoulder in the Cu L-edge spectrum of bornite and the strong leading peak in the spectrum of chalcopyrite were attributed to the electron transitions to the minor density of unoccupied Cu 3d states, and the post-edge features were related to the states of s- and p-type. The Fe L-edge XANES showed the presence of predominant Fe2+ for chalcopyrite, and some quantity of Fe2+ for bornite cannot be excluded despite XPS and Mössbauer spectroscopy had previously detected only Cu+ and Fe3+ species in both minerals. The Cu L- and S L-edge spectra of bornite considerably modify and become similar to those of chalcopyrite after the oxidative leaching that produces the heavily metal-depleted surface layers, and the Fe L-edge XANES shows only a slightly increased contribution of Fe2+. The multiparticle configurations involving Fe2+ and Cu2+ or holes at S atoms may play a role in the L-spectra.