Insights to enhanced coagulation based on the control of metal forms for treating acid mine drainage: Performance and mechanisms.

This study presents an enhanced oxidation-chelation-coagulation process for efficient acid mine drainage (AMD) treatment, addressing the limitations of conventional methods in terms of efficiency, cost, and environmental risks. Through systematic optimization, it was demonstrated that combined NaClO/KMnO₄ oxidation (3:1 molar ratio) at pH 8 effectively transformed Fe/Mn ions into insoluble Fe/Mn (hydr)oxides, while 0.40 g/L carboxymethyl cellulose (CMC) enabled effective chelation and removal of Pb/Ni. The process achieved exceptional removal efficiencies, reducing Fe from 2000 to 2.85 mg/L while maintaining Mn, Pb, and Ni below or close to China's discharge limits (2.0, 0.5, and 0.5 mg/L respectively). Surface characterization (XRD, XPS, FTIR) results revealed the flocs' composition (Fe(OH)₃/MnO₂) and identified functional groups (-COOH/-OH) onto CMC as crucial for metal chelation. Notably, 36.7-57.7 % of removed metals were stabilized in environmentally inert residual forms within the sludge, minimizing leaching potential. The synergistic combination of oxidation, chelation and coagulation mechanisms provides distinct advantages over conventional approaches, including: (1) superior simultaneous removal of multiple metals (Fe, Mn, Pb, Ni); (2) reduced chemical consumption through optimized reagent combinations; and (3) effective mitigation of secondary pollution risks via metal stabilization. These results provide a robust technical foundation for sustainable AMD remediation, offering significant improvements in treatment performance, cost-effectiveness, and environmental safety. The findings highlight the potential of hybrid chemical processes for complex wastewater treatment and provide valuable insights for practical implementation in mining-affected regions.