Experimental simulation on the electrochemical mechanism of iron pollution from “dual-source” in closed coal mine water

The closed coal mine water is mostly characterized by high iron. After mine closure and flooding, residual iron-prone devices and iron-bearing minerals form a “dual-source” iron pollution system in mine water, contributing to the release of iron in different periods after mine closure and creating environmental risks in groundwater. In order to clarify the process and reaction mechanism of “dual-source” iron release in closed coal mine water, to characterize the “dual-source” release mode of iron pollution, and compare the release rate, based on the principle of electrochemical simulation, the working electrodes were prepared by using pyrite and mining bolt as the simulated “dual-source”, and the redox reaction process and iron release mechanism in the acid mine water under the coexistence of “dual-source” at the early stage of coal mine closure were simulated using electrochemical methods such as cyclic voltammetry and polarization as well as X-ray photoelectron spectroscopy (XPS) material surface characterization techniques. The results showed that the dissolved oxygen content was an important inhibitory factor affecting the redox reaction of pyrite and bolt in acid mine drainage. The oxidation mechanism of pyrite and bolt is different, the passivation effect occurs on the surface of pyrite during oxidation, and the final oxidation products of both materials are Fe³⁺ and \rmSO_4^2-. Pyrite releases iron mainly through the oxidation reaction of Fe²⁺ on the mineral surface. Bolt released iron mainly through the reaction of iron and its oxidation products on the surface of the material with the acid substances in the solution, and the oxide reacted preferentially over the monomer. In the simulated aerobic (DO=7.0 mg/L) acid mine drainage, the annual corrosion rates of pyrite and bolt reached 8.3636 mm/a and 7.8314 mm/a, respectively, and the annual iron release rates reached 1.2240 g/a and 3.9395 g/a, respectively. In the simulated underground anoxic (DO=3.5 mg/L) acid mine drainage, the annual corrosion rates of pyrite and bolt reached 0.7324 mm/a and 0.3642 mm/a, respectively, and the estimated annual iron release rates reached 0.1072 g/a and 0.1832 g/a, respectively. The integrated electrochemical parameters and static iron release experiments showed that the total iron release rate ratios were both dual-source > bolt > pyrite under the conditions of sufficient or lack of dissolved oxygen.