Effect of fulvic acid coating layer on surface oxidation of pyrite and the interfacial mechanism

Pyrite, being the most common type of tailings, readily oxidized to produce acid mine drainage when exposed to the environment. Fulvic acid (FA), as the most widespread humic substance in the environment, is effectively adsorbed onto mineral surfaces. In the study, the impact of FA on pyrite surface oxidation and the interfacial mechanism have been investigated by leaching experiments, electrochemical tests and interface characterization methods. Adsorption experiments revealed that FA adsorbs on the pyrite surface primarily through electrostatic attraction and surface complexation, with a saturated adsorption capacity of 19.20 mg/g. The adsorption of FA forms a passivation coating on the pyrite surface, effectively isolating the oxidizing medium and providing antioxidant protection to pyrite, as proved by decreased concentrations of dissolved Fe and SO42- in the leaching experiments. Cyclic voltammetry indicated that the presence of FA coating caused no alteration in the surface oxidation mechanism of pyrite, while it significantly reduced the current density of FA-pyrite electrode. Tafel polarization curve and impedance also demonstrated that the corrosion current density decreased from 14.03 µA cm−2 to 0.15 µA cm−2, while the electron transfer resistance increased significantly from 1091 Ω cm−2 to 77,380 Ω cm−2, indicating the inhibition of pyrite oxidation upon FA coating. SEM-EDS, FTIR and XPS analysis further confirmed the adsorption of FA onto the pyrite surface and its capacity to inhibit pyrite oxidation. These findings enhance our understanding of the interfacial interaction between FA and pyrite, holding profound implications for advancing our comprehension of pyrite surface oxidation processes. [Display omitted] •Pyrite surface oxidation is prone to producing acid mine drainage (AMD) to pollute the environment.•FA was readily adsorbed on the pyrite surface with a maximum saturated adsorption of 19.20 mg/g.•FA coating layer has an inhibitory effect on the surface oxidation of pyrite.•The electron transfer resistance of pyrite surface increased significantly after the adsorption of FA.