Highly efficient renewable aminating lignin adsorbent for co-adsorption of Arsenic(III) and Chromium(VI)

Heavy metal ions represent common toxic pollutants in industrial wastewater, posing significant risks to human health and ecosystems. Biomass-based materials have been proposed to improve the efficiency and selectivity of heavy metal adsorption. In this study, a novel magnetic polyethyleneimine-functionalized lignin adsorbent (Fe-PEI/SLS) was synthesized, and its structure and surface properties were characterized via SEM, FTIR, and XPS. The results indicated that polyethyleneimine (PEI) modification significantly enhanced both the magnetic responsiveness and affinity toward heavy metal ions of SLS. The Fe-PEI/SLS featured fast adsorption kinetics and exceptional adsorption capability for As(III) and Cr(VI). The adsorption results showed that the adsorption capacities of Fe-PEI/SLS for As(III) and Cr(VI) were 54.98 and 71.68 mg/g, representing a 20- and 14-fold enhancement over pristine SLS, respectively. This demonstrates outstanding single-component adsorption performance. In the combined system of As(III)-Cr(VI), the adsorption of As(III) and Cr(VI) was competitive on Fe-PEI/SLS. Specifically, the adsorption mechanism of Fe-PEI/SLS was electrostatic adsorption and ternary surface complexation. The Fe-PEI/SLS also exhibited excellent regeneration and recovery abilities. Significantly, this study confirmed that Fe-PEI/SLS achieved 70% of As(III) and Cr(VI) removal in actual muddy water, with excellent application potential. This study provides an experimental foundation for treating As(III) and Cr(VI) wastewater using lignin-based adsorbents and offers mechanistic insights into the co-removal of complex pollutants.