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

Abstract

Conventional lime depressants used in copper sulfide flotation separation are limited by persistent challenges of scaling, corrosion, and compromised target-metal recovery, which necessitates 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 multiscale characterization techniques including mono- and mixed-mineral flotation tests and surface and solution analysis. Flotation test results showed that the combined depressant system H2O2/Fe3+ enabled efficient separation of chalcopyrite and pyrite. Under the optimal mixed-mineral separation conditions of 0.025vol% H2O2 and 2 × 10−5 mol/L Fe3+, the artificial mixed-mineral flotation test yielded a copper concentrate with a chalcopyrite grade of 30.51wt%, while chalcopyrite recovery remained stably above 88%. Investigations into the depression mechanism and surface hydrophobicity revealed that H2O2 selectively oxidized disulfide (S2−) to sulfate (SO4 2−) while facilitating Fe2+ conversion to Fe3+, generating hydrophilic Fe–SO4/Fe–OOH/Fe–OH coatings that disrupted natural surface natural hydrophobicity. Simultaneously, Fe3+ hydrolyzed to hydroxyl complexes ([Fe(OH)2]+ and Fe(OH)3), which electrostatically adsorbed onto and chemically bonded to H2O2-oxidized pyrite surfaces, forming dense hydrophilic layers. The faster oxidation of pyrite resulted from its fundamental structural properties, specifically its high surface electronic activity and relatively weak Fe–S bonds, which collectively rendered it more susceptible to H2O2 attack, unlike chalcopyrite with its stable lattice and strong covalent Cu–S bonds. Consequently, the robust covalent Cu–S bonds of chalcopyrite effectively resisted oxidation, while its limited Fe3+ adsorption capacity favored the adsorption of sodium ethyl xanthate (SEX) at copper-active sites. As a result, the H2O2/Fe3+ system exerted only minimal depression on chalcopyrite, providing a sound theoretical basis and a practical technical strategy for the selective separation of copper-sulfide ores. Furthermore, the findings of this study contribute to the development of low-alkalinity, high-selectivity sulfide-ore processing methods, demonstrating considerable potential for industrial application.

1. Introduction

Copper is a strategically indispensable metal for modern industrial infrastructure, advanced technologies, and global economic security [1–2]. It is derived primarily from chalcopyrite (CuFeS2), the dominant copper sulfide mineral governing global resource extraction [3]. It frequently cooccurs with pyrite in sulfide deposits, necessitating effective separation for efficient chalcopyrite recovery [4–5]. Flotation remains the industrial benchmark for Cu–Fe sulfide separation, where depressants enhance pyrite hydrophilicity to achieve selective chalcopyrite enrichment [6]. Although lime (CaO) can achieve effective pyrite depression [7], its application poses significant operational challenges: reaction with pulp CO2 and sulfates generates insoluble CaCO3 and CaSO4 scales, respectively, which foul pipelines, pumps, and flotation cells, impairing efficiency and increasing maintenance requirements. The resulting high alkalinity accelerates the corrosion of metallic equipment, thereby reducing service life [8–9]. Notably, excessive lime suppresses target-metal recovery, compromising the extraction of copper and precious metals [10]. Consequently, contemporary depressant research prioritizes environmental compatibility, efficiency, and selectivity to address the inherent constraints of conventional toxic or low-selectivity reagents in complex ore processing [11–13]. Although organic alternatives (polysaccharides, chelators, and plant extracts) have garnered interest owing to their eco-friendliness and abundance, they are limited by their performance instability under fluctuating conditions, high dosage demands, and marginal economics [14–15]. While inorganic depressants maintain industrial prevalence owing to their cost-effectiveness and technological maturity, their toxicity, selectivity deficits, and environmental incompatibilities demand urgent resolution. Thus, the development of high-performance, eco-compatible pyrite depressants constitutes a critical pathway towards sustainable polymetallic sulfide mineral processing [16–17].

Flotation fundamentally relies on the selective adhesion of target minerals to bubbles, governed by surface hydrophobicity modulation. In this process, the pulp system comprises a complex multi-phase suspension typically containing dissolved metal ions originating from mineral dissolution and fluid-inclusion release [18]. These metal ions critically influence flotation performance through their multifaceted effects on pulp conditions.