THE INFLUENCE OF THE Fe~(3+)/Fe~(2+) REDOX COUPLE ON THE CHALCOPYRITE LEACHING

摘要

The effect of the Fe~(3+)/Fe~(2+) redox couple on the chemical and biological dissolution of chalcopyrite was studied. All the tests were carried out in stirred flasks with 100 mL of a ferric/ferrous sulphate solution, in the absence or in the presence of bacteria (iron- or sulphur-oxidizing) and at low (35 deg C) and high (68 deg C) temperature. The initial redox potential was controlled between 300 and 600 mV Ag/AgCl and silver was used as chemical catalyst. The results showed that the oxidizing action of ferric ion on the chalcopyrite was controlled, in all cases, by nucleation and precipitation of jarosites on unreacted particles. The tendency of Fe~(3+)/Fe~(2+) solutions towards equilibrium favours the activities of both ions to be equal. Consequently, the dissolution rate was faster at relatively low redox potentials (between 400 and 500 mV) than at high values (600 mV). In this sense, the presence of ferrous ion in the system is a key factor to control hydrolysis and precipitation of ferric ion. Unlike jarosite, the elemental sulphur produced during dissolution of chalcopyrite was porous and did not act as a diffusion barrier.