Yongyu Li, Wenqing Liu, Zhongwen Bao
Acid mine drainage (AMD) containing high Fe concentrations of 1–10 g L −1 is characterized by strong acidity, complex redox cycling, and unstable mineral precipitation, making remediation more challenging than for low-Fe AMD. Here, electrocoagulation (EC) was systematically evaluated for treating authentic Fe-rich AMD collected from two pyrite mines, focusing on pH-mediated transformation pathways by electrode combinations of Fe (anode) and stainless steel (cathode). An optimal current density of 30 mA cm −2 was identified. Experimental results indicate that an initial pH 5 serves as a practical threshold for EC applicability. Below pH 5, initial metal concentration is the dominant control on purification efficiency. Solid-phase analysis revealed interconnected transformation of Fe reduction, hydrolysis, and co-precipitation. The metal removal pathway exhibits a distinct temporal evolution under experimental conditions. Mechanistically, three pH-mediated removal stages were identified, with Fe-(oxy)hydroxide precipitation, subsequent surface complexation, and co-precipitation acting as the dominant pathways for the removal of Cu, Zn, and Mn. Under high ionic strength, pH elevation was suppressed and energy efficiency decreased, limiting the effectiveness of standalone EC-based AMD treatment. An integrated neutralization-EC configuration addressed these limitations, achieving over 97.5% removal of all target metals while reducing wet sludge production by 32%. The results demonstrate that neutralization-EC is an effective and practical strategy for treating authentic Fe-rich AMD.