Evaluating the performance of bridging-assembly chelating flocculant for heavy metals removal: Role of branched architectures

A novel chelating flocculant with branched architectures, polyacrylamide grafted maleoyl chitosan-mercaptoacetic acid (PAM-g-M(CS-MA)), was successfully fabricated using maleic anhydride as the "bridge" between chitosan and polyacrylamide. The functional groups and structural characteristic information of copolymers were obtained via characterization analysis. Flocculation performance was systematically investigated via purifying a series of simulated wastewater containing Cu or Cd. The properties of the flocs were studied to give in-depth evidences for the role of chelation groups and branched architectures in flocculation. Results indicated that PAM-g-M(CS-MA) showed excellent flocculation capacity for heavy metals in high concentrations and was superior to other chelating flocculants. The maximum flocculation efficiency of Cu (93.90%) and Cd (92.47%) was achieved by PAM-g-M(CS-MA) at pH 7, dosage of 100 mg L^-1 and stirring speed of 90 rpm. The flocculation mechanisms of PAM-g-M(CS-MA) were deeply explored through the analyses of floc properties. The strong synergistic chelation of mercapto, carboxyl, amide and hydroxyl groups predominated for the capturing of heavy metals; and the branched architectures facilitated the formation of large and stable flocs via adsorption and bridging-furl effect. This study provided a solid foundation for the fabrication of flocculants for heavy metal wastewater treatment.