Near-surface Regions of Electrochemically Polarized Chalcopyrite (CuFeS2) as Studied Using XPS and XANES

Characteristics of the non-stoichiometric near-surface layers formed at reacted chalcopyrite are important for understanding its behavior as the main mineral of copper and for various materials applications. Here, we measured Cu L-, Fe L-, and S L-edge TEY XANES, and conventional XPS from chalcopyrite electrochemically polarized in 1 M HCl solution. The spectra of copper, in contrast to those of Fe and S, remain almost unchanged on the first potential cycle despite strongly varying composition of the Fe-depleted near-surface regions. The Cu L-XANES spectra of chalcopyrite electrochemically pre-reduced and then anodized, and of that first anodized and then cathodically reduced, show the same leading peak but post-edge features indicative of covellite CuS and bornite Cu5FeS4, respectively. We suggest that the invariability of the Cu L-edge XANES and Cu 2p spectra is due to tetrahedral coordination CuS4 units stable even in the highly distorted non-stoichiometric structures.