Atmospheric and electrochemical oxidation of the surface of chalcopyrite (CuFeS₂)

Atmospheric and electrochemical oxidation of the surface of chalcopyrite has been investigated using electrochemical techniques with subsequent surface analysis by X-ray photoelectron spectroscopy (XPS) and aqueous phase analysis by inductively coupled plasma-atomic emission spectrometry (ICPAES). The extent of atmospheric oxidation of chalcopyrite was assessed qualitatively by measuring the increase in the open circuit potential; quantitative estimation was made either by comparing the reduction charges of an atmospherically oxidised electrode with an unoxidised electrode and/or by comparing their oxidation charges at potentials less positive than those at which the main decomposition occurred. The oxidation current wave at potentials 0.1 V to 0.6 V vs. S.C.E. consists of two peaks, the charges of which vary with the surface roughness and the peak potentials of which vary with the electrolyte pH in the alkaline region. As the pH of the electrolyte was increased from 0 to 13, the mole ratio of sulfur to sulfate formed during the anodic oxidation decreased from 6:1 to 3.2:1 but remained around 6:1 as the potential was increased from 1.0 V to 1.8 V vs. S.C.E. in acidic electrolytes. A mechanism for the oxidation and passivation of chalcopyrite is proposed.