Efficient removal of Cu2+, Pb2+, and Cd2+ by two magnetic biochar-montmorillonite composites and the application in synthetic wastewater

Acid mine drainage (AMD) originates from mineral extraction and processing operations, exhibiting high acidity and containing elevated concentrations of metals and sulphates, which frequently pose significant environmental challenges. This study combined biochar with clay minerals to prepare two magnetic biochar-montmorillonite composites (FMBC1 and FMBC2) via coprecipitation-pyrolysis and impregnation-pyrolysis methods for investigating their removal efficiency and mechanisms for Cu, Pb, and Cd from metal solutions. Adsorption results indicate that at a dosage of 1.5 g/L, both FMBC1 and FMBC2 achieve removal efficiencies exceeding 99% for Cu (100 ppm), Pb, and Cd (50 ppm). Material characterization revealed that functional group complexation, crystallization-precipitation, possible ion exchange and reduction precipitation were the mechanisms by which FMBC1 and FMBC2 interact with Cu, Pb, and Cd in solution. Furthermore, FMBC1 and FMBC2 effectively removed Cu, Pb, and Cd from synthetic wastewater and could be recovered rapidly via magnetic attraction. Following desorption with EDTA-HCl, adsorbed FMBC1 and FMBC2 can be reused. The findings of this study provide potential theoretical foundation for treating heavy metals in AMD.