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

•A novel amphoteric lignin-based multifunctional flocculant was synthesized by “grafting to” strategy.•With the dosage of the lignin-based flocculant between 3.0 and 4.2 mg L−1, the turbidity removal rate for 0.5 g L−1 kaolin suspension reached more than 98% within 2 min.•The flocculant exhibited excellent co-sedimentation performance for the mixed solution of Cu2+ and kaolin suspension.