UV-Initiated Graft Copolymerization of Cationic Chitosan-Based Flocculants for Treatment of Zinc Phosphate-Contaminated Wastewater

In this study, acrylamide and [2-(acryloyloxy)ethyl] trimethylammonium chloride were grafted onto CS by UV initiation to obtain an environmentally friendly graft copolymer, CS-g-poly(acrylamide-acryloyloxyethyl) trimethylammonium chloride (CS-g-PAD). Poly(acrylamide-acryloyloxyethyl) trimethylammonium chloride was named as PAD. Nuclear magnetic resonance hydrogen spectroscopy (¹H NMR), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and thermal gravimetric analysis (TG-DSC) were used to characterize CS-g-PAD. Results confirmed the synthesis of CS-g-PAD. SEM results showed that CS-g-PAD exhibited a porous structure with numerous 2-6 μm micropores. The enhanced CaCl₂-aided flocculation tests of wastewater contaminated by zinc phosphate coating indicated that CS-g-PAD had better flocculation performance than PAD and the commercially available cationic polyacrylamide (CPAM). The removal rates of zinc concentration, total phosphorus concentration, and chemical oxygen demand were 99.3, 98.8, and 72.5%, respectively, at 6 mg·L^-1 CS-g-PAD and pH 10. The precipitated flocs were mainly in crystalline form.