Mitigating amine-induced gold depression: mechanistic insights into stepwise xanthate addition in copper–gold flotation with pyrrhotite rejection

• TETA competes with xanthate on gold, lowering recovery via surface disruption. • Higher SIBX dosage boosts gold and pyrrhotite recovery, reducing selectivity. • Split SIBX dosing enhances gold recovery while maintaining pyrrhotite depression. • Stepwise SIBX addition forms stable films that resist TETA interference. • DFT shows xanthate films block TETA via steric and electrostatic effects. The sodium metabisulfite (SMBS)–triethylenetetramine (TETA) system is widely used in copper–gold flotation to depress pyrrhotite, but often reduces gold recovery due to competitive TETA adsorption on gold surfaces. This study presents a practical, flowsheet-compatible strategy to counter this effect by optimising the dosage and addition sequence of sodium isobutyl xanthate (SIBX), the primary gold collector. Increasing the SIBX dosage from 2.5 to 5 g/t (added entirely in the flotation cell) improved gold recovery from 53% to 59%, but also raised pyrrhotite recovery. In contrast, splitting the same total SIBX dose between milling and flotation significantly improved gold recovery to 73% while maintaining pyrrhotite depression, highlighting the importance of extended interaction time and surface pre-conditioning. Electrochemical measurements showed that stepwise addition promotes a more stable and coherent xanthate/dixanthogen layer with enhanced surface passivation, interfacial resistance, and resistance to TETA disruption. Density functional theory calculations further revealed that TETA adsorbs preferentially at unprotected gold sites via electrostatic stabilisation and Au–N dative bonding. However, a well-organised xanthate layer sterically and electrostatically blocks TETA adsorption. These findings offer mechanistic insights into collector–depressant competition and demonstrate a simple, effective strategy to enhance gold recovery without compromising pyrrhotite selectivity.