Heavy metal ions, commonly found in wastewater, pose significant environmental and health hazards due to their toxicity and persistence. The development of efficient adsorbents for the removal of these pollutants is essential for effective wastewater treatment. Biomass-based adsorbents have emerged as promising materials for enhancing the efficacy and selectivity of heavy metal ion removal due to their green and renewable nature. In this study, we introduce a novel magnetic lignin-based adsorbent, Fe-PEI/SLS, which was synthesized by modifying sodium ligninsulfonate (SLS) with polyethyleneimine (PEI) to enhance its magnetic properties. The modification improves the adsorbent's performance in the removal of heavy metal ions from aqueous solutions. The adsorption capacity of Fe-PEI/SLS for As(Ⅲ) and Cr(VI) was found to be significantly higher compared to unmodified SLS. Specifically, Fe-PEI/SLS exhibited adsorption capacities of 54.98 mg/g for As(Ⅲ) and 71.68 mg/g for Cr(VI), which were 20 and 14 times greater than those of SLS, respectively. In a combined As(Ⅲ)-Cr(VI) system, the adsorption of these ions was competitive, indicating that the two contaminants interact differently with the adsorbent. The primary adsorption mechanisms were electrostatic interactions and ternary surface complexation, which were identified through detailed analysis. Furthermore, Fe-PEI/SLS demonstrated excellent regeneration and recovery capabilities, suggesting its potential for repeated use in wastewater treatment applications. Notably, the adsorbent showed superior performance in treating actual muddy water, indicating its practical applicability in real-world scenarios. This study highlights the potential of Fe-PEI/SLS as an effective adsorbent for the simultaneous removal of As(Ⅲ) and Cr(VI), providing valuable insights into the co-removal of complex pollutants and offering a promising solution for wastewater treatment.

Sodium Ligninsulfonateco-adsorption, Co-adsorption, As (III) and Cr (VI)