Biochar MMT ZnAl LDH composite materials derived from solid waste for heavy metal removal in artificial acid mine drainage

This study investigates the synthesis and performance of a biochar-based composite, integrating montmorillonite (MMT) and ZnAl layered double hydroxide (LDH), for the removal of Fe and Mn from acid mine drainage. The biochar_MMT_ZnAl LDH composite, synthesized from solid waste materials, was characterized using BET, XRD, FTIR, TGA, and SEM-EDS analyses. The material demonstrated a surface area of 117.54 m²/g and a pore volume of 0.21 cm³/g, significantly surpassing non-composite biochar with a surface area of 14.81 m²/g. The batch sorption experiment showed rapid adsorption kinetics, achieving 99% Mn removal within 7 min at 0.5 g adsorbent dosage, reducing Mn concentration from 100 mg/L to 0.07 mg/L. For Fe, an 87% reduction was achieved after 400 min using 0.5 g of plain biochar, while biochar_MMT_ZnAl LDH showed superior adsorption performance with a final Fe concentration below 0.07 mg/L. Adsorption isotherm analysis indicated that biochar followed the Dubinin–Radushkevich model, while the composites adhered to the Redlich–Peterson model. Kinetic studies revealed a strong fit with the Pseudo-Second-Order model (R² = 1 for biochar_MMT), suggesting chemisorption as the dominant mechanism. Thermodynamic analysis confirmed the spontaneity and endothermic nature of the adsorption process, with ΔG values ranging from − 18,758 to − 92,932 J/mol for Fe and Mn removal. The findings highlight the potential of biochar-based composites in developing cost-effective and environmentally sustainable solutions for acid mine drainage treatment.