SURFACE OXIDATION OF CHALCOPYRITE (CUFES2) 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. Fe2O3 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.