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. Table 1 – Comparison of approaches to overcoming chalcopyrite passivation, interpreted within the resistance framework of Figure 3. Technology Resistances targeted Mixed potential effect Key operating conditions Representative metrics Status Thiocarbonyl catalysis (Jetti; Tu, ETu, TA, SDDC, ETC, TSCA) ↓Rj(E), ↓Rfilm, ↓Rct Raises id; lowers EM while increasing rate pH ~1.8–2; 25 °C; ~0.2–30 mM reagent; Fe(III) oxidant Columns: >70% Cu extraction; electrochem: ~6× rate with 10 mM Tu; Tu+Fe(III) ~30× vs Fe(III) alone Commercial deployments reported Thiocarbonyl + surfactants (Jetti extended family) ↓Rdiff (wetting, O₂ transfer, S⁰ hydrophobicity) plus catalytic depassivation As above; transport bottlenecks reduced to realize catalytic benefit pH ~1.5–2.5; ambient T Synergistic extraction improvements reported in patent Field status not publicly confirmed Chloride Eh-window control (BHP SaL/Full SaL family) Avoids growth of Rfilm and Rj(E) by operating in active potential window; ↓Rdiff via O₂ management Keeps EM below passive onset (~600 mV SHE) pH ~1–2; Cl⁻ ~5– 100 g/L; O₂ >1 ppm; Eh ~550– 600 mV SHE ~70% Cu at low potential vs ~7% at high potential (912 h); 73–79% at 550–600 mV vs 22.5% at 620 mV (1000 h); 88% at 550 mV (1240 h) Full SaL commercially deployed at Escondida (June 2025), primarily targeting secondary sulfides; primary sulfide application under study Nitrate/transpassive oxidation (BHP WO2024057216A1; Ceibo DOP) Bypasses passive regime entirely via transpassive potential; S⁰ oxidized to sulfate so ↓Rfilm; ↓Rct Sets EM above transpassive threshold via NO⁺ high oxidation potential High NO₃⁻ (~25– 80 g/L BHP; ~0.02–0.4 M Ceibo); ORP >770 mV SHE; covers/scrubbing required for NOx Metathesis to covellite and chalcocite possible under these conditions; full kinetic data not public Pre-commercial; NOx management is key barrier Elevatedtemperature bioheap leaching (Nuton, Rio Tinto) ↓Rct (temperature); ↓Rdiff (aeration, moisture Sustained oxidant supply strengthens cathodic Ambient to elevated T (selfheating via microbial Up to ~84% Cu recovery from primary sulfides reported; column First commercial production achieved (Johnson Camp, 2025)
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