The effects of X-ray irradiation and temperature on the formation and stability of chemical species on enargite surfaces during XPS

An investigation of the species present on the surface of natural enargite and the effects of X-ray radiation on the surface after electrochemical oxidation at pH 10 has been carried out using X-ray photoelectron spectroscopy. Surface species present on fractured and polished unoxidized enargite have been compared with those present on the polished surface after oxidation at pH 10. The effect of X-ray irradiation time as a function of temperature on the forms and intensities of the photoelectron signals from the enargite surface was studied. High binding energy (BE) components and shake-ups of the Cu 2p signals, characteristic of a copper (II) hydroxide surface layer, reduced in intensity with increasing X-ray exposure time. Associated changes in the relative concentrations of surface oxygen species were also observed. Comparing a surface exposed to X-rays at 35 °C with that maintained at −135 °C, temperature was shown to significantly influence the rate of change. The observed changes were evaluated in terms of a proposed two-stage mechanism involving the dehydration of Cu(OH) to CuO, followed by photoreduction of CuO to Cu2O. The photoreduction effects of X-ray irradiation should be significantly reduced by sample cooling for consistent analysis of the enargite surface using XPS.