Polyethyleneimine and carbon disulfide co-modified alkaline lignin for removal of Pb2+ ions from water

This paper reports the efficient removal of Pb2+ ions from water by modified alkaline lignin (MAL), in which alkaline lignin was used as the raw material and ornamented with amine/imine (-NH2/-NH) and dithiocarbamate (-CSS-) groups by using polyethyleneimine (PEI) and carbon disulfide (CS2) as the modifier. The pseudo-second-order model and Langmuir model expressed the adsorption kinetics and isotherm well, indicating the adsorption of Pb2+ ions on MAL was a chemisorption and monolayer. The maximum adsorption amount (q(m)) of MAL towards Pb2+ ions was 79.9 mg/g, significantly higher than that of other reported biomass-based-sorbents such as Hamimelon peels (7.9 mg/g), dairy manure-derived biochar (37.8 mg/g), and acid-treated avocado kernel seeds (21.8 mg/g). Even after six continuous adsorption-desorption cycles, the values of qm for the regenerated MAL at each cycle were still obviously higher than those aforementioned sorbents. The binding affinity of different groups of MAL towards Pb2+ ions followed the sequence: C-N > -NH2 > N-H/O-H > C-S > C=S. This work not only gave a comprehensive picture of the adsorption/desorption mechanism of Pb2+ ions on MAL but also evaluated the reusing ability of MAL. These results may provide insights for the further studies on the subsequent construction of devices to be used in bench- and pilot-scale experiments.