An Electrochemical Study of the Effect of Sulfate on the Surface Oxidation of Pyrite

Pyrite is one of the most abundant metal sulfide tailings and is susceptible to oxidation, yielding acidic mine drainage (AMD) that poses significant environmental risks. Consequently, the exploration of pyrite surface oxidation and the kinetic influencing factors remains a pivotal research area. Despite the oxidation of pyrite producing a significant amount of sulfate (SO₄^2-), a comprehensive investigation into its influence on the oxidation process is lacking. Leveraging pyrite's semiconducting nature and the electrochemical intricacies of its surface oxidation, this study employs electrochemical techniques-cyclic voltammetry (CV), Tafel polarization, and electrochemical impedance spectroscopy (EIS)-to assess the effect of SO₄²⁻ on pyrite surface oxidation. The CV curve shows that SO₄^2- does not change the fundamental surface oxidation mechanism of pyrite, but its redox peak current density decreases with the increase in SO₄^2-, and the surface oxidation rate of pyrite decreases. The possible reason is attributed to SO₄^2- adsorption onto pyrite surfaces, blocking active sites and impeding the oxidation process. Furthermore, Tafel polarization curves indicate an augmentation in polarization resistance with elevated SO₄^2- concentrations, signifying heightened difficulty in pyrite surface reactions. EIS analysis underscores an increase in Weber diffusion resistance with increasing SO₄²⁻, indicating that the diffusion of Fe³⁺ to the pyrite surface and the diffusion of oxidized products to the solution becomes more difficult. These findings will improve our understanding of the influence of SO₄^2- on pyrite oxidation and have important implications for deepening the understanding of surface oxidation of pyrite in the natural environment.