Kinetic modelling of chalcopyrite leaching assisted by iodine in ferric sulfate media

Chalcopyrite leaching at moderate temperature exhibits slow kinetics due to surface passivation. The presence of iodine has been reported to significantly enhance copper dissolution from chalcopyrite in ferric sulfate media at ambient temperature. However, the key factors controlling the reaction rate and the mechanisms have not been well understood. This study quantified the effect of different parameters on the kinetics of copper extraction in the presence of iodine and elucidated the possible rate-limiting steps. A series of leaching tests was carried out in PTFE (polytetrafluoroethylene) bottles with high chemical resistance to investigate the effect of solution potential (673–769 mV vs SHE), total iodide concentration (50–200 mg/L), particle size (53–90 μm), and temperature (25–45 °C) on chalcopyrite concentrate leaching. PTFE bottles were used to prevent iodine loss via evaporation and iodine corrosion of the experimental apparatus. The experimental results show that redox potential was the principal factor determining the leaching performance via controlling the aqueous iodine speciation. In the potential range where triiodide or diiodine dominates, the copper extraction increased with increasing potential, increasing total iodide concentration, and increasing temperature. Particle size did not affect the kinetics, possibly resulting from the narrow size ranged used. A preliminary kinetic model shows that the reaction orders with respect to Fe(III)/Fe(II) concentration ratio and the total iodide concentration were 0.36 and 0.91, respectively. The activation energy (47 kJ/mol) was significantly lower than those reported for the conventional chalcopyrite leaching in ferric sulfate media, suggesting that the presence of iodine changed the reaction mechanism. Further investigation is required to uncover the exact role of different iodine species in the leaching process.