Atmospheric Leaching of Enargite in the Presence of Carbon Based Catalyst
Pyrometallurgy is not the most sustainable option for enargite concentrate treatment due to the environmental limitations on arsenic release. Therefore, developing an effective hydrometallurgical process is a promising solution for enargite treatment. Most hydrometallurgical processes proposed in literature have not reached commercial utilization because of common issues such as slow dissolution rate of the mineral, incomplete copper or precious metals recovery, sulfate generation, arsenic fixation problems, and high capital and operating costs. In this thesis, the atmospheric leaching of enargite in chloride media was investigated in the presence of activated carbon (AC) and AF 5, a novel carbon based catalyst. Both catalysts were found to be very effective in facilitating the enargite leaching process and improved the oxidation and copper recovery from 65% to 92% (AC) or 96% (AF 5) after 96 hours. The best leaching condition was found to be: ferric and cupric concentrations greater than 5 g/L, concentrate to catalyst mass ratio of 1:2, and a 90 °C working temperature or higher. The elemental sulfur product of the leach reaction did not coat the surface of the partially leached mineral particles. When AF 5 was used as the catalyst in the leaching process, it collected the generated elemental sulfur. The arsenic also precipitated in the form of scorodite, one of the most stable forms of arsenic, during the leaching in chloride media at temperatures higher than 80 °C. The catalytic properties of the carbon-base catalysts (CBC) was due to the oxidation via oxygen functional groups on their surfaces, which were detected by XPS analysis. The results showed that the chemical pre-treatment of CBC can be effective in increasing its catalytic effect on enargite leaching. The comparison between the chloride and sulfate media showed that the sulfate media has better copper and iron dissolution kinetics and promotes sulfur collection, whereas the remediation of arsenic in the form of scorodite can be superior in chloride media.