Experimental optimization of aurocyanide adsorption onto biomass activated carbon and re-examination of the adsorption mechanisms

• Bio-derived activated carbons were synthesized for application in CIP and CIL processes. • Successful optimization was achieved for enhanced carbon yield and aurocyanide adsorption capacity. • New mechanism elucidation in addition to the well-known [M n + ] [Au(CN) 2 − ] n ion pair mechanism. • Na[(Au(CN) 2 )] ion-pair, electrostatic and π–π interactions contributed to the overall adsorption capacity. Activated carbons (ACs) prepared from agricultural residues are ideal alternatives to the commercial coal-based ACs often applied in gold mining. Carbon activation using KOH produces high-quality carbons with good textural properties. Herein, fruit peel ACs were synthesized via KOH activation and evaluated for aurocyanide adsorption. The yield and adsorption capacity were optimized through a central composite design. The Langmuir maximum equilibrium uptake was 186.95 ± 16.44 mg/g. Re-examination of the adsorption mechanisms revealed that the presence of micro and mesopores, coupled with electrostatic binding, π–π interaction and ion-pair formations influenced the significantly high adsorption capacity. This study could be useful in the syntheses and application of agro waste-derived ACs as alternative adsorbents for gold recovery from aurocyanide leachates.