The deleterious role of gangue mineralogy in copper extraction: A case study of poor recovery in leaching low-grade Cu ores

In a series of four extended industrial column leach experiments spanning 542 days, aimed at examining Cu-recovery from low-grade sulfide ores, all instances yielded suboptimal Cu recovery rates (<27%). Through a nuanced analysis integrating time-resolved chemical data on leachate with detailed mineralogical investigations, we highlight that the dissolution of aluminosilicate gangue minerals is a pivotal factor constraining Cu recovery. The source materials, extracted from a low-grade segment of a Cu–Au porphyry deposit (∼0.32–0.36 wt% Cu), underwent diverse leaching conditions employing various lixiviants, curing phases, redox conditions, and particle size distributions. Notably, poor Cu recovery is closely tied to gangue mineralogy. The ammonia leach column experienced limited Cu leaching due to an inert gangue shielding chalcopyrite from the lixiviant. In acid columns, swift precipitation of silica-rich phases impeded effective Cu leaching at multiple scales, from large-scale-column to molecular levels. Identifying gangue mineralogy and considering their impact during acid leaching are crucial for formulating effective lixiviant strategies for Cu recovery from low-grade primary sulfide ores. The curing phase, requiring high acid concentrations (∼50 g/L H2SO4), emerges as a critical aspect for promoting effective gangue dissolution while preventing refractory silica-rich phase precipitation.