Preparation of a novel high-performance lignin-based anionic adsorption resin for efficient removal of Cr(VI) in aqueous solutions

To remove Cr(VI) in water, a novel lignin-based anionic adsorption resin epichlorohydrin cross-linking lignin grafted by diethylenetriamine (E-DAL) was prepared by the direct cross-linking and curing of alkali lignin grafted by diethylenetriamine in aqueous solutions. Under the determined optimum synthesis conditions, E-DAL with higher nitrogen (7.46%) and lignin (32.78%) contents was obtained. Structural and physicochemical measurement results showed E-DAL was a macroporous resin, having a regular connected pore structure with porosity of 67.48% and pore size of 615.6 nm, also strong hydrophilicity, excellent acid-alkaline resistance and thermal stability. Adsorption experiment results indicated the adsorption isotherm of E-DAL to Cr(VI) was well-described by Langmuir model. E-DAL showed a higher adsorption capacity to Cr(VI), and the fitted maximum adsorption capacity reached up to 775.2 mg/g. Pseudo-second-order model could fit this adsorption process well, suggesting its chemisorption characteristics. The calculated thermodynamic parameters indicated a spontaneous and endothermic adsorption of E-DAL to Cr(VI). Dynamic column adsorption results showed E-DAL could completely remove Cr(VI) in wastewater. This whole preparation process only used a very small amount of cheaper amination agent and was relatively low-cost. This work provided efficient technical supports for the structural design of high-performance lignin-based anionic adsorption materials in water treatment field.