Lignin-based adsorbents for heavy metals

The pollution of heavy metal ions in wastewater has caused a certain degree of threat to the environment and the human body, so the removal of heavy metals in wastewater has become urgent. As the content of lignin is second only to cellulose in nature, it has a three-dimensional amorphous network structure, phenolic hydroxyl, methoxy and other functional groups, and has biocompatibility, which lays the foundation for lignin as an adsorption material. In this review, we introduced the performance and differences of adsorbents prepared from different types of lignin (alkali lignin, enzymatic lignin, lignosulfonate, etc.). And it also introduces the adsorption effect of adsorbents on different heavy metals, adsorbents prepared by introducing active functional groups such as amino, carboxyl, ester, and sulfonic acid groups with lignin as raw materials, and various composite adsorption materials have electrostatic attraction, ion exchange, complexation, redox reaction for heavy metal ions and physical adsorption, Due to the existence of multiple active functional groups, the affinity of the adsorbent to heavy metal ions is also different, which results in the adsorbent having both selectivity and simultaneous adsorption to heavy metal ions. Finally, this review summarizes and looks forward to the challenges and opportunities of lignin in the preparation of adsorbents.