Analysis of iron and copper speciation and activities in chloride leaching solutions of high ionic strength

Abstract

In light of the recent increased use of seawater for copper heap leaching, we analyzed the speciation and activities of iron and copper in chloride media, with a focus on chalcocite leaching. Compared with other published work, the present study carried out such analysis at high solution ionic strength up to 3 M. For this purpose, the SIT (Specific ion Interaction Theory) activity model was used in the thermodynamic calculations performed by the STABCAL software. The speciation results obtained from the software were validated by the experimental measurements of solution potential, which were performed in a sealed jacketed reactor under an ultra-high purity nitrogen environment. The speciation results showed that FeCl2+ and hydrated Fe2+ were the dominant Fe(III) and Fe(II) species in the chloride concentration range 0.5 M – 3 M. In the case of copper speciation, hydrated Cu2+ and CuCl2− dominated at chloride concentrations <0.5 M. In the chloride concentration range 0.5 M – 3 M, CuCl+ and CuCl32− were the dominant copper species. Based on the speciation and activities results, we determined the actual cathodic and anodic half reactions responsible for copper leaching from chalcocite in chloride media. The proposed cathodic half reactions pinpoint ways of manipulating solution potentials, which is vital for determining the kinetics of the second stage of chalcocite leaching.