Magnetic flocculation of Cu(II) wastewater by chitosan-based magnetic composite flocculants with recyclable properties

In this study, three magnetic flocculants, namely, MC, MC-g-PAM, and MC-g-PAA, were prepared. The structure characteristics, flocculation performance, and floc characteristics of the three magnetic flocculants were systematically studied and compared. SEM, FT-IR, XPS, XRD, TG–DSC, and VSM characterization results show that MC, MC-g-PAM, and MC-g-PAA are successfully prepared and exhibit good magnetic induction. The removal rates of copper ions by MC, MC-g-PAM, and MC-g-PAA under the optimal coagulation conditions are 93.39 %, 88.64 %, and 61.41 %, respectively. Kinetic fitting shows that the flocculation reaction process of MC and MC-g-PAM conforms to pseudo first-order kinetics, while the flocculation reaction process of MC-g-PAA conforms to pseudo second-order kinetics. The flocs produced by MC-g-PAA have larger particle size and fractal dimension than those by MC and MC-g-PAM. At 80 mg/L dosage and pH 6, the floc size and floc fractal dimension obtained by MC-g-PAA reach the maximum values of 48.28 um and 1.468, respectively. Zeta potential studies show that the flocculation functions of the three flocculants are mainly adsorption bridging, adsorption electric neutralization, and chelating precipitation. Recycling experiments show that MC-g-PAA has good recyclability, and the recovery rate after the fifth use is 77.24 % with the Cu(II) removal rate of 67.53 %.