Preparation of Starch-Based Cationic Flocculants and Its Study on the Removal of Textile Dyes

To effectively solve the problem of wastewater pollution, in this paper, corn starch, 3-chloro-2-hydroxypropyl trimethylammonium chloride (CTA), vinyl acetate (VAC), and methylacryloxyethyltrimethylammonium chloride (DMC) were used as raw material, etherifying agent, esterifying agent, and grafting monomer, respectively. A starch (St)-based natural polymer cationic flocculant (DMSt-g-DMC) was prepared via etherification, esterification, and grafting copolymerization triple modification. This study is of great significance for the removal of dyes from wastewater. There are two keys to success. First, DMSt-g-DMC not only enhances flocculation but also improves water solubility through triple modification. Second is grafting reaction, in which the number of positive charges in the main chain of the DMSt-g-DMC macromolecule is further increased and its molecular structure adjusted to give full play to its electrical neutralization, bridging, and net trapping effects on anionic dyes in the water, so as to achieve the purpose of improving the flocculation effect. The removal rates of DMSt-g-DMC were 94.1% for Acid Light Yellow G, 83.7% for Reactive Brilliant Blue X-BR, and 97.1% for Direct Lake Blue 5B. DMSt-g-DMC not only has a wide flocculation window but also maintains good flocculation performance in a wide pH range, which is conducive to the treatment of wastewater with high alkalinity and complex composition. Finally, the removal rate of dye was tested when DMSt-g-DMC and PAC were flocculated together; the dosages of DMSt-g-DMC and PAC were 70 and 100 mg/L, respectively. The removal rates of Disperse Red GS, Disperse Yellow 2G-FL, and Direct Lake Blue 5B reached 87.5, 89.8, and 95.6%, respectively. In addition, DMSt-g-DMC and PAC remained stable after a long flocculation time, which may bring far-reaching changes if applied in industrial wastewater treatment.