Hierarchical oxidation and asymmetric corrosion mechanism of pyrrhotite

Pyrrhotite, a gangue mineral involved in the separation of polymetallic sulfide ore, is prone to oxidation, which deteriorates the pulp environment and reduces flotation efficiency. In this study, the oxidation-corrosion characteristics of pyrrhotite were systematically investigated, revealing the influence of pulp oxygenation and pH on surface oxidation-corrosion, as well as the mechanism. Dissolved oxygen measurements and inductively coupled plasma emission spectroscopy demonstrated that elevated pulp pH enhances the oxidation kinetics and extent. Under acidic conditions, pulp aeration intensifies Fe-dominated asymmetric corrosion, generating Fe-deficient/S-abundant surfaces. Conversely, pulp aeration is conducive to the selective corrosion of S under alkaline conditions, yielding Fe-abundant/S-deficient surfaces. X-ray photoelectron spectroscopy revealed that enhancing the aeration intensity or raising the pH promotes the oxidation of Fe and S sites and accelerates the hydroxylation of Fe site. Supported by the surface etching analysis, the hierarchical oxidation pathways were clarified: Fe(II)-S → Fe(III)-S → Fe(III)-O, S 2 - → S 2 2 - → S n 2 - → SO 4 2 - , and Me-O → Me-OH → H 2 O. Scanning electron microscopy combined with energy dispersive spectroscopy further confirmed the hierarchical oxidation and asymmetric corrosion characteristics, with corrosion becoming more pronounced as oxidation progresses. These findings elucidate the transformation of surface states and provide a theoretical foundation for understanding the reactivity of pyrrhotite during pretreatment and flotation.