Flocculation performance and mechanism of P (DMDAAC-AM) on clay mineral layer: Insights from DFT calculation and experiment

Abstract

In order to investigate the flocculation performance and mechanism of quaternary ammonium cationic polyacrylamide (CPAM) on clay mineral particles. Dimethyl diallyl ammonium chloride (DMDAAC) and acrylamide (AM) were used as the monomers to synthesize the polymer P (DMDAAC-AM), referred to as PDA. The flocculation and sedimentation effects of PDA on the kaolinite and montmorillonite suspensions were studied. Furthermore, the PDA structural unit was constructed, and the adsorption mechanism on the kaolinite and montmorillonite layers was explored using the density functional theory calculation method. Experimental results reveal that PDA exerts a better flocculation and sedimentation effect than the commercially polyacrylamide (PAM) on kaolinite and montmorillonite suspensions, and the effect exerted by PDA on the kaolinite suspension is stronger than that on montmorillonite. Simulation results show that the PDA structural unit can be stably adsorbed on the surface of mineral particles: kaolinite (001¯) surface (−279.46 kJ/mol) > montmorillonite (001) surface (−226.09 kJ/mol) > kaolinite (001) surface (−220.76 kJ/mol). The difference in PDA adsorption on each surface is influenced by the various quantum chemical properties of the structural unit AM and DMDAAC molecules. During flocculation, PDA is adsorbed on the surface of the mineral particles exploiting hydrogen bonds and electrostatic attraction forces. During the adsorption process, electrostatic attraction plays the leading role. The polymer chains establish a bridge between the particles, and these bridging flocs settle down under the influence of gravity.