Novel insights into the synergistic depression mechanism of H2O2 and Fe3+ on pyrite in low-alkalinity Cu–S flotation separation

Conventional lime depressants used in copper sulphide flotation separation are constrained by the persistent challenges of scaling, corrosion and compromised target metal recovery, necessitating the development of efficient and green alternatives. This study demonstrates the synergistic depression of pyrite by H2O2/Fe3+ under low-alkalinity conditions. The complementary action pathways were systematically elucidated by multi-scale characterisation techniques including mono- and mixed-mineral flotation tests, surface and solution analysis. Flotation tests demonstrate that the combined depressant H2O2/Fe3+ achieves efficient separation of chalcopyrite and pyrite, reducing the pyrite recovery to 5.11% while maintaining the chalcopyrite recovery above 91%. Investigations into the depression mechanism and surface hydrophobicity reveal that H2O2 selectively oxidises disulphide (S₂2−) to sulphate (SO42−) while facilitating Fe2+ conversion to Fe3+, generating hydrophilic FeOOH/ Fe(OH)3 coatings that disrupt the surface hydrophobicity. Simultaneously, Fe³⁺ hydrolytic to the hydroxyl complexes (Fe(OH)₂⁺ and Fe(OH)₃), its electrostatically adsorb and chemically bond to H2O2-oxidised pyrite surfaces and forming dense hydrophilic layers. This dual role of which oxidation destroys the hydrophobic structure and the adsorption-reinforced hydrophilic layer, constitutes the synergistic depression mechanism. The robust covalent Cu–S bonds of chalcopyrite resist oxidation, while its limited Fe3+ adsorption capacity maintains the adsorption of sodium ethyl xanthate at the Cu sites. Consequently, H2O2/Fe3+ minimally depresses chalcopyrite, providing a theoretical foundation and technical framework for selective Cu–S separation. Furthermore, the results of the present study support the advances in low-alkalinity, high-selectivity sulphide ore processing with significant industrial application potential.