• Gum Arabic (GA) is introduced as a novel, eco-friendly depressant for selective flotation separation of chalcopyrite from molybdenite.
• At pH 8.0 with 20 mg/L GA, chalcopyrite recovery in mixed mineral flotation was 67.49% higher than molybdenite, demonstrating strong selectivity.
• GA adsorbs onto molybdenite via chemical chelation, hydrogen bonding, and hydrophobic interactions, while showing weak interaction with chalcopyrite, preserving its floatability.
• Pre-adsorbed GA prevents butyl xanthate adsorption on molybdenite, and GA primarily adsorbs on the 'face' rather than 'edge' of molybdenite, offering a promising Cu–Mo separation strategy.