A high solution potential has been shown to adversely affect the chalcopyrite leaching rate (Koleini et al., 2010). In contrast, the dissolution rate of pyrite is significant at redox potential above 500 mV (Tshilombo, 2004). Therefore, the low chalcopyrite leaching selectivity in biotic leaching compared to abiotic leaching is likely linked to the high solution Eh in the former whereby pyrite leaching kinetic is enhanced. When chalcopyrite was leached abiotically, the solution Eh is maintained at