Highly efficient adsorption of Hg²⁺ from aqueous solutions by amino-functionalization alkali lignin

Lignin, as a biodegradable byproduct of industry, has become popular in developing low-cost and high-performance heavy metal adsorbents. Herein, a high-efficiency novel adsorbent for mercury ion, amino-functionalization alkali lignin (AAL) was facile synthesized by one-step approach under very mild conditions. The as-prepared AAL was characterized by FT-IR, BET, XPS and SEM. The adsorption properties of AAL for Hg²⁺ were elucidated in batch system. The results showed that AAL exhibited exceptionally high adsorption capacity for Hg²⁺ at pH of 4- 6, the maximum adsorption capacity can reach 553.9 mg g^-1. The remove efficiency could above 99% when dealing with 300 mg L^-1 of Hg²⁺ solution at 30 °C using 1 g L^-1 adsorbent. The adsorption was a spontaneous endothermic process. Pseudo-second-order kinetic and Langmuir isotherm model fitted well with the sorption data, which proposed the adsorption was a monolayer chemical adsorption process. The mechanism analysis demonstrated that nitrogen-containing functional groups of AAL were mainly contributed to the adsorption of Hg²⁺. Moreover, the adsorption capacity of the regenerated AAL could still be maintained at 91% by the fifth cycle. These findings demonstrated that AAL can provide an effective way to enhancing removal of Hg²⁺ from aqueous solutions.