Graphitic activated carbon as a catalyst for enhancing bioleaching of enargite through redox potential control

Since refractory copper (Cu) sulfides, such as enargite (Cu 3 AsS 4 ), dissolves in response to the solution redox potential ( E h ) change, the E h must be controlled for their faster kinetics, even during bioleaching. To identify a promising E h -controlling catalyst, eight activated carbons (ACs) with distinct properties were evaluated via abiotic catalysis tests and bioleaching using moderately thermophilic microorganisms. Abiotic tests showed that chemical-activated carbons (chemical-ACs) consistently maintained lower E h levels (540–550 mV vs. SHE) compared to steam-activated carbons (steam-ACs; >600 mV). Raman spectroscopy and stoichiometric analysis revealed that the E h modulation by ACs, either lowering or increasing it, depended on graphiticity, with chemical-ACs exhibiting highly developed graphitic structures. These properties enabled efficient electron mediation and redox coupling of Fe 3 + reduction with RISCs oxidation, making chemical-ACs highly effective in E h -lowering catalysis while minimizing E h -driven passivation. Stronger E h -lowering effect was indeed observed during bioleaching with 0.08 %(w/v) chemical-ACs, achieving 57 % Cu solubilization. Kinetic fitting using the shrinking core model revealed that chemical-AC contributed to the faster dissolution kinetic, indicating that the enhanced graphiticity of chemical-ACs improved the Galvanic effect by expanding reaction interfaces for anodic oxidation. This counteracted the drawbacks of E h -lowering, maintaining faster dissolution kinetics. In conclusion, chemical-ACs are identified as optimal catalysts for bioleaching of refractory Cu sulfides, offering valuable insights for sustainable metal recovery processes. • Eight ACs were evaluated via abiotic catalysis tests and bioleaching. • Chemically activated AC showed stronger E h -reducing capability. • Raman spectroscopy revealed that graphiticity of AC determines its catalysis. • Chemically activated AC successfully lowered E h during enargite bioleaching. • Higher graphiticity of chemically activated AC also facilitated Galvanic reaction.