Cationic etherified starch-acrylamide-DMDAAC graft flocculant: Synthesis, flocculation performance, metal ion synergistic effect and cost-effectiveness

The flocculants based on naturally derived polymers are promising due to their wide availability and biodegradability. However, the flocculation performance and cost-effectiveness are less than satisfactory. This study developed novel flocculants with cationic etherified starch-acrylamide-dimethyl diallyl ammonium chloride (CAD), specifically designed for the efficient removal of anionic dyes. The synthesis conditions were optimized through the flocculation efficiency of anionic acid black-172 (AB) dye. Experimental results showed that CAD achieved a removal ratio of 91.6±1.8% with a flocculant dosage of 150 mg/L and maintained excellent decolorization efficiency across different pH, environmental temperatures, and ionic strengths. Most importantly, the synergistic effect with the presence of metal ions, particularly Fe3+, on the decolorization efficacy of CAD was observed. In the presence of Fe3+ (0.02 mol/L), the required flocculant dosage was reduced by two-thirds, while the maximum dye removal ratio reached 94.2±1.9%. The study indicates that the high efficiency of CAD primarily originates from dual mechanisms of charge neutralization and bridging. Furthermore, the operation cost of removing an equivalent amount of AB dye with CAD is about 40% of that incurred using commercial cationic polyacrylamide, highlighting its economic advantage in industrial applications. In summary, the CAD flocculant shows great promise for complex wastewater treatment.