A study to understand the role of ethylene glycol in the oxidative acid dissolution of chalcopyrite

Recent investigations suggest that ethylene glycol (EG) performs two important functions in the oxidative dissolution of chalcopyrite with hydrogen peroxide: it prevents H2O2 dismutation on the chalcopyrite surface and, secondly, it hinders H2O2 decomposition due to the presence of dissolved copper and iron in the leach liquor. Of these two, retarding the H2O2 breakdown probably contributes most to the observed improvement in copper leaching; however, the nature of the role that EG plays in the solution is unclear. For that reason, a systematic study was undertaken, at different concentrations of sulfuric acid and EG, to reveal the role of EG in the leaching process. The results of this investigation show that EG hinders H2O2 degradation by decreasing the copper and iron activities in the solution through Cu (II)-EG and Fe (II, III)-EG complex formation. Likewise, the slowing effect strongly depends on the H2SO4 concentration because the Fenton reaction, which is responsible for the decomposition, increases its efficiency with lower acid concentrations (<0.1 M). Thus, successful leaching could be attained with concentrations above 0.7 M and 0.1 M of sulfuric acid and EG, respectively; otherwise, rapid H2O2 degradation and simultaneous EG mineralization (complete oxidation, in other words, oxidation to CO2 and H2O) are favored as a consequence of the reactions between H2O2 and the leached metals and the OH* radicals produced in the leach liquor, respectively. In view of these results, a brief discussion is presented on the implications of chalcopyrite leaching with H2O2, showing alternatives to increase its performance.