Magnesium oxide-functionalized biochar synthesis from municipal solid waste for Pb(II) removal in aqueous media and...

Pb(II) contamination from landfill leachate poses a serious environmental and public health risk. This study demonstrates the valorisation of municipal solid waste (MSW) into an efficient Pb(II) adsorbent through MgO functionalisation of MSW-derived biochar using MgCl₂·6H₂O. Pristine biochar (P-BC) and MgO-modified biochar (MgO-BC) were synthesised from the organic fraction of MSW through pyrolysis at 450 °C. SEM and FTIR analyses confirmed enhanced porosity and the introduction of Mg-O functional groups following modification. Batch adsorption experiments showed strong pH dependence, with maximum Pb(II) removal at pH 11 of 83.50% for P-BC and 99.82% for MgO-BC. Adsorption data were best described by the Freundlich isotherm and pseudo-second-order kinetic models, indicating multilayer chemisorption on heterogeneous surfaces. Langmuir maximum adsorption capacities were 24.82 mg/g for P-BC and 36.63 mg/g for MgO-BC. Intra-particle diffusion analysis revealed that boundary layer film diffusion dominated the adsorption process. Characterisations and comparative experiments confirm that MgO functionalisation significantly improves Pb(II) adsorption performance through the synergistic effects of ion exchange, electrostatic attraction, complexation, precipitation, and pore diffusion mechanisms. Overall, the results demonstrate the potential of MSW-derived biochar as a cost-effective, sustainable solution for landfill leachate treatment, supporting circularity and resource recovery in MSW management.