Enhanced flocculation performance and coal slurry water by using starch-based flocculant with rich charges and its flocculation mechanism

Abstract

A cationic starch-based flocculant as an efficient and environmentally friendly flocculant is designed for the improvement of flocculation performance of coal slurry water by the method of combining grafting and etherification. Structure and properties of the obtained samples are characterized by XRD, FTIR, NMR, and TG. Effects of grafting conditions and etherification conditions on intrinsic viscosity and cationic degree are investigated. The flocculation performance of grafted etherified starch (GE-St) is studied, and compared to cationic polyacrylamide (CPAM) and anionic polyacrylamide (APAM) flocculants, the final turbidities are 417 NTU for APAM, 20.6 NTU for CPAM and 59.1 NTU for GE-St demonstrating that the flocculation performance of grafted and etherified starch (GE-St) is slightly weaker than that of CPAM and significantly better than APAM. It can be supposed that GE-St is an effective flocculant for coal slurry water. The flocculation process of coal slurry water was analyzed by zeta potential analysis, extended DLVO theory calculation and microscopic images of flocs indicating that designing the molecular structure with rich charges and moderate molecular weight through grafting and etherification is beneficial for flocculation. The possible flocculation mechanism can be proposed that fine particles are agglomerated and settled by the flocculant GE-St through charge neutralization, adsorption bridging and sweeping, which is attributed to the matching of flocculant structure and mineral surface.