Application of Lignin and Its Derivatives in Adsorption of Heavy Metal Ions in Water: A Review

Water pollution by heavy metal ions is currently of great concern due to their high toxicity and carcinogenicity. In recent years, great efforts have been devoted to the search for new cost-effective adsorbents derived from biomass. Lignin is a natural amorphous polymer that has great potential for use as a building block in the production of biorenewable materials. Due to its unique polyphenol structure, physicochemical properties, and abundance, a wide variety of sorbents, particularly heavy metal ion sorbents, can be potentially obtained from lignin. This paper provides a comprehensive review of the literature about different feedstock lignin and versatile lignin derivatives used as heavy metal ion adsorbents. The adsorption capability improvement mechanism of the lignin derivatives and the comparison with commercial resins are also discussed. Therefore, this review aims to discuss the different modification categories that have been reported for the conversion of lignins into advanced heavy metal ion adsorbents. Most importantly, adsorbents derived from lignin can confer high environmental benefits due to its stability, biocompatibility and abundance in the plant kingdom. This review may pave the way for the design and fabrication of new lignin-based adsorbents with enhanced adsorbent performance for heavy metal ions in water.