The Active-Passive Behavior of Chalcopyrite

Abstract

The oxidative behavior of chalcopyrite in H2 O- H2 S O4 - Fe2 (S O4) 3 -FeS O4 media was studied using both electrochemical techniques and leaching experiments. The results of the two methods demonstrate that chalcopyrite oxidation displays the classical active-passive behavior observed in passivating metals; values predicted electrochemically for the passivation potential Epp are in excellent agreement with leaching experiments. This result substantially improves the knowledge of the anodic behavior of chalcopyrite, which has been reported so far mostly as pseudopassive when massive chalcopyrite electrodes are used. Imposing a continuous series of potentiostatic pulses (increasing by 10 mVh), three-dimensional current density-time-potential surfaces were generated in order to establish the effects of acidity and temperature on the passivation potential, the passive current, and the critical current of chalcopyrite leaching. The concentration of sulfuric acid was systematically varied from 2 to 100 gL and temperature from 25 to 80°C. Epp increases with increasing temperature from 440 mV at 25°C up to 515 mV at 80°C; it is practically insensitive to acidity at low (25-40°C) and high (60-80°C) temperatures. At 50°C an acid-dependent transition of Epp was observed from 440 to 515 mV. The passive currents were at most one order of magnitude lower than the maximum critical current. © 2007 The Electrochemical Society.