INVESTIGATIONS ON THE MECHANISMS OF SULFURIC ACID LEACHING OF CHALCOPYRITE IN THE PRESENCE OF HYDROGEN PEROXIDE

The sulfuric acid leaching behavior of chalcopyrite in the presence of hydrogen peroxide was studied at 25°C using electrochemical techniques. The effects of increasing the concentrations of hydrogen peroxide up to 3 M on chalcopyrite dissolution were carried out in shake flasks prior to electrochemical studies. Electrochemical investigations were carried out on particulates electrode made from powdered chalcopyrite samples using potentiodynamic and chronoamperometric techniques. Increasing the concentrations of hydrogen peroxide considerably accelerated the leaching of both copper and iron. Morphologies of the leached residues examined by scanning electron microscope revealed similar products on the surfaces of chalcopyrite for all the conditions of leaching. A reduction in sizes of the particles, which increase the porosity of the residues, was observed at increasing concentrations of hydrogen peroxide. X-ray analysis revealed the presence of elemental sulfur in the solid residues with increasing crystallinity as the concentration of hydrogen peroxide increased. Polarization curves showed that hydrogen peroxide raised the dissolution potentials of chalcopyrite toward more noble values. The addition of hydrogen peroxide also drastically increased the dissolution currents, current densities, and dissolution rates, and reduced the passivity of chalcopyrite. Increasing the concentration of hydrogen peroxide and dissolution potential resulted in a characteristic current increase/decrease behavior of the ore. Higher dissolutions obtained at increased concentrations of hydrogen peroxide were attributed to the porous agglomerate nature of the leached residues that did not passivate the chalcopyrite surface, but aided further dissolution through electron transfer.