Influence of combined natural deep eutectic solvent and polyacrylamide on the flocculation and rheological behaviors of bentonite dispersion

Abstract

The influence of hybrid coagulation/ flocculation systems on the degree of flocculation and rheological behavior of highly stable bentonite suspension has been investigated throughout this study. Natural deep eutectic solvent (NADES) synthesized from choline chloride (ChCl) and lactic acid (LA) was utilized as the coagulant in the hybrid system at a fixed dosage of 1.78×10-2M. Two cationic polyacrylamides (CPAM) and two anionic polyacrylamides (APAM) with varying charge density (CD) were the studied flocculants in the hybrid system. The flocculation efficiency of the anionic and cationic hybrid systems (i.e., NADES/ FO 4350 SH, NADES/ FO 4800 SH, NADES/ AN 923 SH, and NADES/ AN 956 SH, respectively) was evaluated based on specified criteria, including the zeta potential, turbidity, floc size, and rheology of the treated suspension. Compared to a single system, the utilization of a hybrid system significantly influenced the treatment efficiency of APAMs and CPAMs. At an optimum APAM dosage of 10mgL-1 and 15mgL-1 for NADES/ AN 923 SH and NADES/ AN 923 SH, respectively, the systems showed an exceptional improvement with a turbidity removal >99%, zeta potential in the range of -10mV<ζ<0mV, and floc size >60μm. On the other hand, NADES with CPAMs (i.e., NADES/ FO 4350 SH and NADES/ FO 4800 SH) demonstrated a setback in their treatment efficiency due to the charge reversal exhibited by the hybrid systems hence, re-stabilization of the suspension. The conducted rheological analysis revealed that the studied hybrid systems could enhance the properties of produced sediment. The formation of larger, more compacted flocs resulted in nono-Newtonian shear-thinning sediment with a shear resistivity and elastic modulus more than ten times higher compared to the single systems. The tested hybrid systems with low CD CPAM and APAM (i.e., NADES/ FO 4350 SH and NADES/ AN 923 SH) achieved higher viscosity, elastic modulus, and shear resistivity than systems with high CD PAMs. Furthermore, APAM hybrid systems exhibited superior performance compared to CPAM hybrid systems. Consequently, the NADES/ AN 923 SH hybrid system was the most efficient for treating bentonite suspension resulting in viscosity of 223,340 mPa.s, an elastic modulus of 32,487 mPa, and yield stress of 694 mPa at the optimum coagulant/ flocculant dosage.