Surface oxidation of chalcopyrite (CuFeS 2) under ambient atmospheric and aqueous (pH 2-10) conditions: Cu, Fe L- and O K-edge X-ray spectroscopy

Abstract

X-ray absorption and emission spectra were used to characterize the surface of chalcopyrite after oxidation both in air and in air-saturated aqueous solution (pH = 2–10). For chalcopyrite oxidized in aqueous solution, the Cu and Fe L-edge spectra show that the surface oxidation layer is copper deficient. As the pH increases, O K-edge spectra reveal a change in the nature of the oxidation layer. An iron (hydroxy)sulfate is dominant at low pH, whereas FeOOH is the major surface phase under alkaline conditions. Fe 2O 3 may be present at intermediate pH. The surfaces of chalcopyrite samples oxidized in air consist of a mixture of copper oxides, FeOOH, and sulfate phases. Sulfate is much more abundant on the surface of air-oxidized chalcopyrite because of its high solubility in aqueous solution. Likewise, copper oxidation products can be observed in the O K-edge spectra of air-oxidized chalcopyrite in contrast to the aqueous samples.