A novel composite flocculant of cationic etherified starch and microbially induced calcium carbonate precipitation for kaolin suspension: Optimization, performance, and mechanism

This study aims to develop an efficient and environmentally friendly flocculation system. The approach involved coupling biodegradable cationic etherified starch (CES) with microbially induced calcium carbonate precipitation (MICP), thereby establishing a novel CES-MICP composite system. The flocculation performance of CES and MICP was investigated in single and composite systems. Response surface methodology (RSM) was employed to optimize the composite system by varying CES dosage, MICP dosage, and initial pH. The optimal conditions were identified at the CES dosage of 2.4 mg/g, the MICP dosage of 16.2 mg/g, and an initial pH of 5.1. Under these conditions, the composite system achieved the 30 min settling ratio of 40.3% and the turbidity percentage removal of 98.13%. Compared to individual CES and MICP systems, the MICP dosage was reduced by 35.2%, while the settling ratio and turbidity percentage removal showed significant improvement. Mechanistic analysis indicates that the composite system achieves efficient flocculation and rapid sedimentation through a synergistic mechanism involving charge neutralization, adsorption bridging, sweep flocculation, and crystal-nuclei ballasting.