Preparation of grafted starch‐based cationic flocculants and its removal of reactive and disperse dyes

Abstract In this paper, a starch‐based flocculant (ADSt) with medium and low temperature solubility and enhanced flocculation effect was synthesized using corn starch, acrylamide, and dimethyldiallyl ammonium chloride as main materials by the ethanol‐alkali method and grafting method. The main mechanism of ADSt's flocculation was electrical neutralization and bridging. The flocculation performance of ADSt was verified by using it along with polymeric aluminum chloride (PAC) as coagulant/flocculant, dispersible dye (dispersible yellow RGFL), and reactive dye (active trimeric blue KN‐G) to simulate dye wastewater. For the dispersed yellow water sample and active emerald blue water sample, the dosage of PAC was 40 and 35 mg/L respectively. When the dosage of ADSt was 10 mg/L with a dye content of 100 mg/L, the decolorization rates for both dyes reached up to 96.2% and 94.4% respectively. The properties of the flocs such as size and two‐dimensional fractal structure were described. The prepared ADSt maintained a good flocculation effect in the pH range of 5–9 due to its excellent water solubility achieved through the ethanol‐alkali preparation process, where its solubility reached 86.7% at 30°C. Overall, the preparation process for ADSt is simple, cost‐effective, while providing an effective solution for treating printing and dyeing wastewater.