Effect of externally adding pyrite and electrical current on galvanic leaching of chalcopyrite concentrate

Although the operating properties of GalvanoxTM leaching have been widely studied in the literature, several factors concerning chalcopyrite passivation during the process remain unknown so far. The present work hence aims at investigating the significant effect of externally added pyrite features with a particular focus on its particle size (d(80) of 0.52, 20, 45 and 2000 mu m) through a series of experiments performed in a 2-L stirred-tank electro-reactor. To this end, the role of pyrite: chalcopyrite ratio (0.49:1, 2:1 and 4:1) and presence of electrical current were examined while the rest of the parameters kept constant (80 degrees C temperature, 400-500 mV (Ag/AgCl) redox potential, pulp density of 10% (w/v), and stirring rate of 1200 rpm). Plus, kinetic models of the leaching tests were studied based on the diffusion and chemical controlling concepts. It was found that the coarser the pyrite particles, the more favorable the copper extraction from the concentrate due to acceleration of reactions in the cathodic electrode and high mass transfers. However, this was in contradiction with the existing reports in the literature. Moreover, galvanic interactions became intensive in the presence of pyrite meaning extensive chalcopyrite dissolution with significantly reduced passivation. Ultimate copper extraction values of 24.17 +/- 1.25%, 55.79 +/- 0.91% and 57.26 +/- 1.59% were resulted at Py:Cp ratios of 0.49:1 (natural), 2: 1 and 4:1, respectively. The results showed that maximum copper recovery of 67.32 +/- 2.34% was obtained at an optimum condition of pyrite grain size=2000 mu m, Py:Cp=4:1, current application=500 mA, 8 h and 80 degrees C. Finally, detailed kinetic modeling indicated that the chemical control mechanism was dominant in the early reaction stages (t<3.5 h) concerning the availability of fresh surface for chemical agents; however, the second half of the process (8.0 h>t>3.5 h) was controlled by the diffusion control.