Electrochemical study characterizations of pyrite weathering in simulated acidic soil: Iron transformation, sulfur conversion and environmental implications

Pyrite in natural environments is susceptible to weathering, which results in acid mine drainage (AMD) and heavy metal pollution-related environmental problems. The increase in mining activities has led to a large amount of pyrite entering surroundings, which may aggravate soil acidification and heavy metal pollution. In situ electrochemical techniques were used to investigate the weathering behavior of pyrite in simulated acidic soil solutions, which is conducive to understanding the weathering mechanism and environmental impact. In this study, the polarization curves and electrochemical impedance spectroscopy reveal that a higher soil solution concentration, temperature and/or acidity accelerate pyrite weathering rate, with an activation energy of 21.21 kJ·mol-1. Further investigations reveal that the pyrite is initially oxidized to initially oxidized to S0 and released Fe(II), the Fe(II) is easily transformed into Fe(III), and part of the Fe species ultimately transforms into goethite γ-FeOOH and hematite α-Fe2O3. The S0 ultimately transform into sulfate, accompanied by the release of hydrogen ions (H+), resulting in serious soil acidification. These results specifically reveal the mechanism of pyrite weathering, especially the process of iron transformation and sulfur conversion, and they also quantitatively identify the pyrite weathering rate and the quantities of heavy metal ions released, providing an experimental basis for the risk assessment of pyrite in acid soils.