Reductant-Free Cobalt Recovery from Similar Copper–Cobalt Oxide Ores via Synergistic Reductive-Acid Leaching

Enhancing cobalt recovery from complex low-grade copper–cobalt oxide ores represents a pressing industrial challenge in the Democratic Republic of the Congo (DRC). This study comparatively examined the sulfuric acid leaching behaviors of two copper–cobalt oxide ores with similar mineralogical characteristics and developed a synergistic blending strategy to enhance cobalt recovery. At an endpoint pH of 1.5, both ores achieved high copper extraction (>90%). However, the reductive Re-ore attained >75% Co leaching efficiency, contrasting sharply with the oxidative Ox-ore’s limited 22% recovery. This disparity was attributed to refractory high-valent cobalt phases in Ox-ore requiring a reductive environment. Blending Re-ore with Ox-ore generated a pronounced synergistic effect, progressively lowering the slurry potential with increasing Re-ore mass ratio. At 50% Re-ore incorporation, the leaching efficiency of cobalt from Ox-ore surged from 22.5% to 76% owing to the decrease in slurry potential to 557 mV, substantially exceeding proportional predictions. Residue characterizations confirmed that cobalt phases in Ox-ore were solubilized in the reductive environment facilitated by the residual sulfide phase in Re-ore. Enhanced dissolution of Fe2+ and Mn2+ further correlated with potential-dependent cobalt recovery. This ore-blending strategy provides a cost-efficient alternative to chemical reductants by leveraging intrinsic ore properties to optimize cobalt extraction from challenging oxidized ores.