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Application of three types of aminated lignins for efficient removal of Cd(II) and Pb(II) ions in aqueous solution

Lignin is a renewable natural aromatic polymer that is generated as a co-product during lignocellulosic biorefinery processes, and it has been applied widely as a functional biomaterial. In this study, the adsorption behavior of Cd(II) and Pb(II) metal ions was investigated via ion chelation using aminated lignins (ALs) with primary, secondary, and tertiary amine groups. ALs exhibited optimal Cd(II) and Pb(II) adsorption capacities in solution under neutral conditions due to their chelating, electrostatic, and cationic–π interactions with metal ions. The AL with the primary amine group showed the highest adsorption capacities for both Cd(II) and Pb(II), reaching 83.2 and 159.7 mg·g-1, respectively, followed by the ALs with secondary and tertiary amine groups. The adsorption kinetics and isotherm analysis demonstrated that all adsorption behaviors followed the Langmuir isotherm and pseudo-second-order kinetics. Thermodynamic studies revealed that the adsorption processes of Cd(II) and Pb(II) using the ALs were spontaneous and endothermic. These results demonstrate that ALs are promising adsorbents for the removal of Cd(II) and Pb(II) metal ions.