EDTA functionalized Mg/Al hydroxides modified biochar for Pb(II) and Cd(II) removal: Adsorption performance and mechanism

This study has successfully synthesized layered double hydroxide (LDH) biochar (E-Mg/Al-LDH BC) with ethylenediaminetetraacetic acid (EDTA) and examined its adsorption capabilities towards Pb(II) and Cd(II). The results demonstrate that the kinetics of heavy metal removal can be well described by the pseudo-second-order model. The intraparticle diffusion model indicates that the controlling steps for Pb(II) and Cd(II) are not uniform. The adsorption isotherm for Cd(II) conforms to the Langmuir model, while for Pb(II), it adheres to the Freundlich model. The distribution coefficient (Kd) shows that Pb has a significantly higher competitive adsorption capacity than Cd(II). Therefore, in comparison to single adsorption, the maximum adsorption capacity of Cd(II) in competitive adsorption decreased by 58.86%, while Pb(II) only decreased by 13.54%. Surface complexation, cation exchange, chemical precipitation, electrostatic interaction, and cation-π bonding are the inherent mechanisms by which E-Mg/Al-LDH BC removes heavy metal ions. E-Mg/Al-LDH BC has the potential to remediate heavy metal-contaminated water, and it also provides insights for the application of modified biochar in the treatment of multi-metal water pollution.