Preparation of cationic modified starch flocculant starch-grafted-poly (methacryloyloxyethyl trimethylammonium chloride) (St-g-PDMC) and its application in oily sludge treatment

Oily sludge is a typical hazardous pollutant with complex components and multiple emission sources, posing severe threats to the ecological environment and human health. Physicochemical conditioning with high-efficiency flocculants is a promising method for oily sludge treatment. In this study, a cationic modified starch flocculant with a backbone-branch dual cationic site structure (St-g-PDMC) was prepared via two-step etherification and graft polymerization using soluble starch (St) as the raw material, 3-chloro-2-hydroxypropyltrimonium chloride (CTA) as the etherifying agent, and methacryloyloxyethyl trimonammonium chloride (DMC) as the grafting monomer, with potassium persulfate (KPS) as the initiator. The optimal preparation conditions were optimized by single-factor experiments and orthogonal tests: initiator dosage 0.35%, mass ratio of DMC to starch 3:1, mass ratio of CTA to starch 2:1, and reaction temperature 85 °C. When applied to oily sludge treatment, the flocculant achieved a maximum oil removal rate of 87 ± 1% under the conditions of 80 mg/L dosage, 60 °C temperature and pH 8, which was significantly superior to the commercial flocculants polyacrylamide (PAM) and polyaluminum chloride (PAC). Zeta potential, XRD, FT-IR and other characterization results confirmed the successful synthesis of St-g-PDMC, and its oil removal mechanism for oily sludge was clarified as the synergistic effect of electric double layer compression, electric neutralization, adsorption bridging and sweep flocculation.