Spectroscopic and electrochemical characterization of the surface layers of chalcopyrite (CuFeS2) reacted in acidic solutions

XPS, Fe La,b and Cu La,b X-ray emission and Fe L-, Cu L-, S L-edge and O K-edge absorption spectroscopies, Mo¨ssbauer spectroscopy and cyclic voltammetry were applied to study reacted surface layers of natural chalcopyrite, CuFeS2. The surfaces became metal-depleted after the anodic oxidation in 1 M HCl and the leaching in 1 M H2SO4 þ 0:2 M Fe2(SO4)3 or 1 M HCl þ 0:4 M FeCl3 solutions, with the sulfur excess and iron/copper ratio been higher in the last instance, and were enriched in copper after the electrochemical reduction. The electronic structures of the metal-deficient layers up to several tenths of micrometer thick were similar to that of chalcopyrite, except that the density of the highest occupied states depended on sulfur anions formed (predominant S3-anions after the ferric sulfate treatment, S4-anions after the ferric chloride leaching or the potential sweep to 0.9 V, etc.). The layers created by the preliminary oxidation had only a small effect on the chalcopyrite voltammetry. We suggest a new reaction mechanism considering a role of the surface changes, including disordering and Anderson localization of the electronic states. # 2003 Elsevier B.V. All rights reserved