Mechanistic Insight of Biochar-layered Double Hydroxide Composite for Efficient Removal of Aqueous Pb(II) and Cu(II)

Abstract To explore the heavy metal adsorption mechanisms by biochar-based materials, MgAl-layered double hydroxide (MgAl-LDH) was loaded on a commercial coconut shell biochar (BC) to obtain the composite (BC-LDH) for adsorptive decontamination of Pb(II) and Cu(II) in water. The removal capacities of BC-LDH (294 and 38.6 mg/g) was higher than BC (13.3 and 11.4 mg/g) and LDH (126 and 22.7 mg/g) for aqueous Pb(II) and Cu(II). The pseudo-second-order equation and the Langmuir model could better illustrate the adsorption process, respectively. The interaction mechanisms between BC-LDH and heavy metals were classified as mineral precipitation (Qpre), cation exchange and isomorphic replacement (Qexc), electrostatic attraction (Qele), and surface complexation (Qcom) according to the characterization results. The quantitative analysis indicated that the contributions of the above mechanisms of BC-LDH for Pb(II) and Cu(II) followed the order of Qpre > Qele > Qexc and Qpre > Qexc > Qele, respectively. Compared with BC, the Qpre increased and Qele decreased significantly, certified the combination of BC and LDH provided a kind of viable composite in heavy metal wastewater treatment.