Adsorption of Pb2+ and Cu2+ ions on the CS2-modified alkaline lignin

[Display omitted] •FLAL exhibited higher adsorption ability for Cu2+ ions than Pb2+ ions.•The -CSS functional group carried by FLAL was confirmed as the main binding site.•The binding energy of SCuS was lower than that of SPbS.•FLAL had higher adsorption capacity for Cu2+/Pb2+ ions as compared with other materials. A kind of alkaline lignin (AL)-based modified material (FLAL) was fabricated, in which CS2 was selected as the modifier. FLAL can be used to treat Pb2+ and Cu2+ ions loaded water. When the initial concentrations of Pb2+ and Cu2+ ions were 30 mg/L, the removal efficiencies were 97% for Pb2+ at 100 min while 98% for Cu2+ at 5 min, respectively. The maximum adsorption capacities (qm) of Pb2+ and Cu2+ ions were 0.322 and 1.010 mmol/g, indicating that the adsorption capacity of FLAL for Cu2+ ions was better than for Pb2+ ions. The groups of hydroxyl, methoxyl and dithiocarbamate carried by FLAL contributed to binding with Pb2+/Cu2+ ions. Dithiocarbamate (CSS) was proved to be the primary active site, in which the binding energy (Ead) of SCuS and SPbS were −1.1739 and −0.8709 Ha. These results suggest the interaction between FLAL and Cu2+ ions was stronger and FLAL-Cu2+ complexes were more stable, revealing the reason why the uptake of Cu2+ ions by FLAL was quicker in speed and larger in amount. The reusing ability of FLAL was evaluated through a four-adsorption–desorption cycle. The values of qm for Pb2+ and Cu2+ ions were 0.258 and 0.878 mmol/g corresponding to the fourth regeneration, decreased by 19.87% and 13.06% compared to fresh FLAL. The adsorption performance of both fresh and regenerated FLAL is better than many other biomass-based adsorbents. FLAL can be regarded as a promising material with high application potential, which warrants future studies on optimizing FLAL for real-world applications.