Electrochemical hysteresis and bistability in chalcopyrite passivation

Abstract

A literature review of studies where the kinetic response of chalcopyrite leaching has been investigated as a function of controlled slurry potential, and the results of potentiostatic anodic polarizations, show that this mineral passivates at potentials higher than either ~ 440 mV or ~ 510 mV(SCE). These two values have been consistently observed in leaching practice regardless of the geological source of the mineral, which indicates that its passivation potential is little affected by impurity content. The factors or variables determining which one of these two passivation potentials will actually be observed remain unexplained. This paper uses steady-state sampled-current voltammetry to demonstrate that chalcopyrite active–passive behavior at high temperatures displays considerable hysteresis in response to an externally applied potential. When it is polarized in the positive (anodic) direction from the open circuit potential, the active–passive transition is observed at ~ 510 mV. When polarized in the negative (cathodic) direction, from high passive potentials to the open circuit potential, the passive–active transition (depassivation) is observed at ~ 440 mV. Hence, a potential range exists, approximately between 440 and 510 mV, where chalcopyrite presents thermodynamic bistability, and can be either passive or active depending on how it was brought to that particular potential.