644 dissolution rate reflects the combined influence of charge-transfer resistance (Rct), semiconductor junction resistance (Rj(E)), surface film resistance (Rfilm), and diffusion resistance (Rdiff). Each technology targets a different subset of these resistances, and their relative maturity and commercial viability differ substantially. Table 1 summarizes the key distinguishing features of each approach within this framework. The most commercially advanced approaches for CuFeS2 leaching, the Jetti thiocarbonyl system and Nuton elevated-temperature bioleaching, achieve their results through fundamentally different mechanistic strategies. The Jetti approach chemically dismantles the p–n junction at the chalcopyrite surface, restoring the mineral to its native resistor state and allowing dissolution to proceed at lower mixed potential. The Nuton approach circumvents the passive regime through sustained elevated temperature and active microbial oxidation, maintaining conditions in which passivation is continuously destabilized rather than chemically removed. The BHP chloride systems occupy an intermediate position, engineering the solution potential to remain within an active dissolution window and exploiting the beneficial morphology of sulfur formed under chloride conditions. The nitrate-based approaches are mechanistically distinct in operating at what are likely transpassive potentials, where the passive regime is bypassed entirely by oxidative force, at the cost of significant NOx management requirements that present a practical barrier to deployment. Viewed collectively, these technologies confirm the conclusion from Section 3 that the apparent phenomenon of “chalcopyrite passivation”, at industrial percolation leach scale, cannot be attributed to a single mechanism or overcome by a single lever. The most effective strategies may be those that address multiple resistances simultaneously, whether through chemistry, temperature, microbiology, or heap engineering design. An additional consideration for all four approaches is compatibility with existing SX– EW infrastructure. Any of the technologies reviewed here would need to produce a PLS processable through conventional SX-EW without major circuit modifications. From a deployment perspective, the ability to retrofit existing operations without major downstream capital expenditure is likely as important a selection criterion as leach kinetics or ultimate recovery.
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