Coupled dissolution with reprecipitation reactions constraining copper mobilization in heap leach systems

Copper is a key metal in the transition to a low-carbon economy. Currently, low grade copper sulphide (e.g., chalcopyrite, CuFeS2) ores make up more than 70% of the global reserves. However, the extraction of copper from low-grade copper sulphides faces several challenges including the use of large volumes of water and the precipitation of secondary minerals that passivate the surface of these low-grade copper minerals and/or clog lixiviant flow pathways in heap systems. While the dissolution of chalcopyrite, one of the main low-grade copper sulphide minerals, has been extensively studied, it is still unclear what mechanisms and secondary minerals lead to surface passivation and how passivation can be inhibited. Hence, this study examined the passivation of primary copper sulphide minerals undergoing coupled dissolution with reprecipitation reactions and the role of reaction-induced porosity. In Chapter 2, the saturation state of potential secondary minerals is modelled using a newly formulated surface-passivate model (SPM). The SPM showed that the precipitation of jarosite at the chalcopyrite surface lowered the reactive surface area and the dissolution rate of chalcopyrite. However, the SPM was limited in modelling the incongruent dissolution of chalcopyrite leading to precipitation of Fe-deficient copper phases because the Fe-deficient copper phase remained consistently undersaturated in trial models. This chapter provides insight for the design of experiments in the subsequent chapters of this thesis. Chapter 3 investigates the nature of secondary minerals and their effects on Cu-mineral surface area and Cu release rates using batch experiments conducted with acid-only and highly concentrated chloride (AlCl3, NaCl, CaCl2) lixiviant. This study showed that Fe leaches ahead of Cu during proton-promoted dissolution of a low-grade porphyry. Also, there was the mobilization of Cu ahead of Fe-S during combined ferric-iron and proton-promoted dissolution of copper sulp