particularly consequential in heap and dump leaching environments where pH and iron speciation are difficult to control uniformly across the ore bed. 3.4 Semiconductor effects Chalcopyrite behaves as an n-type semiconductor. Selective dissolution of iron during leaching may produce a copper-rich surface layer exhibiting p-type behaviour. The resulting p–n junction introduces an electronic barrier that impedes electron transfer between the mineral surface and oxidizing species in solution (Ren et al., 2022). A key implication of this mechanism is that the oxidation potential available from the Fe³⁺/Fe²⁺ redox couple in solution, which is approximately 0.5 V vs Ag/AgCl (~0.7 V SHE) under typical percolation leaching conditions, is lower than the dielectric breakdown potential of chalcopyrite, which is approximately 0.7 V vs Ag/AgCl (0.9 V SHE) (Ren et al., 2022). Industrial heap leach conditions therefore necessarily place the system potential within the passive region of the chalcopyrite polarization curve, regardless of bulk ORP. In the framework of Figure 3, the p–n junction effect is represented by the potential-dependent junction resistance Rj(E) associated with the semiconductor interface, which is distinct from conventional film or charge-transfer resistances and cannot be reduced simply by increasing the oxidant concentration in solution. 3.5 Synthesis Taken together, these mechanisms suggest that chalcopyrite passivation is best understood as the result of multiple transport and kinetic resistances acting simultaneously and heterogeneously at the mineral surface. No single resistance dominates under all conditions: the relative contributions of Rct, Rj(E), Rfilm, and Rdiff vary spatially across the mineral surface, evolve temporally as leaching proceeds, and depend on local solution chemistry, temperature, and mineral variability. Within each surface domain these resistances act in series, as expressed by ipath = ΔV/(Rct + Rj(E) + Rfilm + Rdiff); across the surface they act in parallel through the weighted current density expression isurface = Σθkik, so that the net dissolution rate reflects both the local resistance stack and the evolving distribution of domain types. As illustrated in Figure 3, the overall dissolution rate reflects the combined and time-varying influence of all these factors. This perspective has a practical implication: improving chalcopyrite leaching kinetics requires reducing one or more of these resistances, but the most effective target will depend on which resistance dominates under the specific conditions of interest. This provides a useful framework for interpreting the emerging technologies discussed in the following section.
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