Preparation of carboxymethylated lignin-based multifunctional flocculant and its application for copper-containing wastewater

High efficiency lignin-grafted cationic polyacrylamide multifunctional flocculant (CL-CPAs) was synthesized via "grafting to" strategy using carboxymethylated lignin (CL), acrylamide (AM) and methylacryloyloxyethyl-trimethyl ammonium chloride (DMC) as raw materials. The synthesized CL-CPAs showed high flocculation efficiency. Only a small dosage between 3.6 and 4.2 mg.L-1 of CL-CPAs and a short flocculation time of 1-2 min were needed for sedimentation of kaolin suspension. Meanwhile, the carboxyl groups on the modified lignin endowed CL-CPAs with good copper ion capture function through complexation and electrostatic interaction. In addition, simultaneous flocculation of kaolin suspension and removal of copper ion was achieved for CL-CPAs attributing to the charge neutralization, bridging, and electrostatic complexation. The synthesized carboxymethylated lignin-based flocculants are cheap, environmentally friendly and technically feasible, showing broad prospects in wastewater treatment.