Gangue-driven surface processes during oxidative acid column leaching of chalcopyrite

Understanding the role of surface phenomena during chalcopyrite leaching offers insights relevant for the development of heap leaching operations. This study evaluated the surface processes at play during oxidative acid column leaching of low-grade chalcopyrite ore, with and without the presence of chloride ions. Column leaching experiments typically rely on solution assays of the final leachate. In this paper, this was extended by connecting columns in series so that intermediate solution samples could be collected. This also facilitates the periodic removal and replacement of particles so that surface characterisation can be carried out and the evolution of surface processes assessed. The results from this study demonstrate that the occurrence of different surface processes depends on both time and location: surface changes are more intense as the solutions become progressively enriched in dissolved species. The use of low-grade ore enabled the identification of surface processes that are driven by the presence of gangue, information that would not have been captured if the study had focused on pure minerals or high-grade ore. Silicon rich layers were shown to form on the mineral surfaces in the chloride-free system, indicating that silicon gangue minerals dissolved to a certain extent, before being transported and reprecipitating. In the chloride-containing system, the formation of an iron-, titanium-, and phosphorus-containing layer was apparent. The results from this study highlight the importance of performing a surface-level assessment on a case-by-case basis, as the dominant processes are dependent on ore and process conditions. This clearer understanding of surface phenomena has important implications for the fine tuning or selection of mitigation strategies for process optimisation.