Electrochemical oxidation of tennantite was investigated in this study. Cyclic voltammetry, potential sweep, and potential step techniques were employed for the study. Based on the experimental results, a reaction mechanism of internal diffusion of H2O through a sulfur film was proposed to describe the effect of H+, Cu2+, Cl-, and temperature. The relatively small value of charge-transfer coefficient of the reaction, which was obtained from the Tafel slope, and the irreversibility of the reaction could also be explained by this mechanism. Different sulfur allotropes with various porosities and thicknesses contribute to an unusual temperature effect on tennantite oxidation in conditions of below 60 degrees C and a potential range of 0.8-1.2 V. (c) 2006 The Electrochemical Society.