Ralf R. Haese

Many metals of economic value are commonly recovered from low grade ores through heap leaching at mine sites. The recovery of metals in heaps is often limited for multiple reasons including mineral overgrowth of targeted minerals resulting in suboptimal mineral dissolution rates. Chalcopyrite is a major copper iron sulfide mineral found in copper sulfide ores and its dissolution is controlled by multiple dissolution reaction mechanisms and potential mineral overgrowth. Traditional continuum scale reactive-transport models, including those applied to simulate heap leaching, do not account for local, mineral surface-controlled processes which may have implications for large-systems such as copper recovery in heaps. A new finite element, multicomponent reactive-transport model was developed and enabled the simulation of concurrent reactions at the discrete chalcopyrite surface and its surrounding gangue mineral and the fluid phase. The model predicts the rate of chalcopyrite dissolution controlled by different reaction mechanisms (proton- and ferric-iron promoted) as well as the rate of secondary mineral formation (jarosite) at the mineral surface. The latter may increasingly inhibit copper mobilization over time through surface passivation. The onset and growth of the surface passivation layer is largely controlled by the surrounding fluid composition and ion transport through the gangue mineral. The reduction in porosity of the surface passivation layer leads to the breakdown of ionic transport to the chalcopyrite surface and associated copper mobilization. Maximum copper recovery is achieved by high ferric iron concentrations and low pH and by preventing the formation of a passivation layer by keeping the sulfate concentration low.

Copper is a critical metal required for green energy technologies such as wind turbines and solar cells. However, copper supply is limited by copper recovery from primary copper sulphides (e.g., chalcopyrite-CuFeS₂) due to passivating reaction products. Therefore, this study examined surface ‘passivation’ of primary copper sulphide minerals undergoing coupled dissolution with reprecipitation (CDR) reactions and the associated mineral surface changes in acidic and chloride-rich lixiviants (FeCl₃-only, AlCl₃-rich, NaCl-rich, and CaCl₂-rich lixiviants). Acidic FeCl₃-only, NaCl-rich, and CaCl₂-rich lixiviants resulted in only bornite dissolution and the formation of a residual Cu-S phase and Fe-SO₄ phase on the chalcopyrite surface. In contrast, leaching with the AlCl₃-rich lixiviant resulted in both chalcopyrite and bornite dissolution with limited hydrolysis of Fe³⁺ to Fe-hydroxy sulphates and minimal Fe³⁺ flux inhibition to the copper sulphide minerals surface due to the ion exchange mechanism between Al³⁺ and Fe³⁺. Further, there was preferential formation of an Al-SO₄ phase at consistently high Eh and acidity, thereby a high availability of Fe³⁺ in solution for enhanced copper dissolution from both bornite and chalcopyrite. These findings could serve as a reference for coupled dissolution with reprecipitation reactions during copper sulphide leaching, offering a pathway to more efficient and sustainable copper extraction from low-grade ores.

Dr Achyut Mishra and Professor Ralf Haese at the University of Melbourne developed a new approach for high-resolution geological modelling.