Two approaches to prepare cationic lignin‐based adsorbents for efficient removal of phosphate ion from wastewater

Abstract In this work, two types of cationic lignin‐based adsorbents (AL‐METAC and AL‐GTA) were prepared through free radical polymerization or etherification reaction of alkali lignin with 2,3‐epoxypropyl‐3‐trimethylammonium chloride or methylacrylloxyethyl trimethyl ammonium chloride (METAC). The contents of quaternary ammonium groups in the adsorbents were adjusted by changing the dosages of 2,3‐epoxypropyl‐3‐trimethylammonium chloride and METAC to fabricate the adsorbents with excellent adsorption capacity. The structures, aqueous solubility, and physical properties of adsorbents were analyzed. Meanwhile, the effects of adsorbents dosage, pH value of solution, temperature, and ionic strength on the adsorption capacity of adsorbents were also analyzed. These two types of adsorbents exhibited outstanding affinity for phosphate, with a maximum removal efficiency of 51.8 and 73.2 mg/g, respectively. The adsorption processes followed pseudo‐second‐order and Langmuir models well. In addition, the AL‐GTA exhibited higher removal efficiency than AL‐METAC. Moreover, the AL‐METAC and AL‐GTA still retained 69.7% and 69.0% adsorption capacity after four times regeneration. The fabricated lignin‐based adsorbents have potential applications in the removal of phosphate from wastewater, which would promote the high‐value application of lignin.