Quantitatively ion-exchange between Mg(II) and Pb(II)/Cd(II) during the highly efficient adsorption by MgO-loaded lotus stem biochar

Background Toxic metals such as Pb(II) and Cd(II) have thrown great threat to human health. Adsorption has been drawn more attention due to its low-cost, easy process and extensive raw materials. However, high efficient and environmental-friendly adsorbents are still in great need. Furthermore, the quantitatively adsorption mechanisms of Pb(II) and Cd(II) remain unclear. MgO-loaded lotus stem biochar was proposed as a highly efficient adsorbent to removal aqueous Pb(II) and Cd(II). Methods MgO-loaded biochar was prepared by using lotus stalk as a precursor to be pyrolyzed with MgCl 2 impregnation. Adsorption isotherms , kinetics, thermodynamics experiments were carried out. SEM, XRD, FTIR, XPS, etc. were employed to characterize the adsorbent before and after adsorption. Significant findings The adsorption capacities of MgO-loaded biochar for Pb(II) and Cd(II) reached 1379.54 mg/g and 404.04 mg/g, respectively, which were 5 and 20 times higher than that of the original biochar. The adsorption kinetics and thermodynamics indicated that the adsorption process was a chemisorption-based heat absorption reaction, and the characterization results showed the main adsorption mechanisms were ascribed to ion-exchange, precipitation, surface complexation between biochar and Pb(II)/Cd(II) ions, in which the ion exchange mechanism was quantitatively confirmed. Finally, MgO-loaded biochar has been proved to be an efficient adsorbent.