An amphiphilic flocculant with a lignin core for efficient separation of suspended solids

The synthesis and application of conventional polymeric flocculants suffer from low flocculation efficiency and toxic residues; therefore, there is an urgent need to develop green and efficient flocculants and corresponding technologies. An amphiphilic copolymer (NPL) was synthesized by a "grafting to" strategy, using acrylamide, 3-chloro-2-hydroxypropyltrimethylammonium chloride, and kraft lignin. NPL consists of a lignin core that is attached to a polyacrylamide branched chain and a cationic group, and has the properties of an amphoteric polyelectrolyte. This structure demonstrates superior flocculation performance on suspended solids. Two typical clay suspensions, kaolin and bentonite, were selected to evaluate the flocculation performance of NPL. The results showed that the turbidity of kaolin and bentonite could be reduced to 2.08 NTU and 0.31 NTU, respectively, by using NPL in combination with polymeric aluminum chloride. The synergistic effect of charge neutralization and bridging was confirmed as the main mechanism of flocculation on the two clay suspensions by a series of characterization techniques, such as zeta potential determination, particle size analysis, and focused beam reflectance measurement. The treatment of high-turbidity wastewater/feedwater with NPL was investigated, and was found to significantly improve the effluent quality. The use of NPL is efficient, environmentally friendly, and technically feasible, and shows excellent potential for the treatment of wastewater.