A new insight into the adsorption behavior of NPAM on kaolinite/water interface: Experimental and theoretical approach

The adsorption behavior and bridging mechanism of NPAM and kaolinite in aqueous solution were investigated using MD simulation and experiment. Turbidity, Zeta potential, and floc size were involved in the analysis of the settlement test; microscopic interaction mechanisms were further discovered via interaction energy, number and water density distribution, and self-diffusion coefficient. It emerged that too little NPAM has a high diffusivity in bulk water, NPAM cannot be directly adsorbed to kaolinite surfaces and the bridging mechanism is difficult to appear; experiment results in the high turbidity of the supernatant and inability to form flocs. As the number of chains increases, the adsorption probability and the adsorption capacity of NPAM on kaolinite surfaces are improved, the range of NPAM diffusion in bulk water expands and the bridging performance is enhanced; the turbidity decreases and the floc formation. When the number of NPAM chains is excessive, the interaction energy of NPAM in surface water with kaolinite surfaces is slightly weakened, NPAM in bulk water may weaken the combined affinity, but the bridging effect is further enhanced; which increases the turbidity and floc size. The adsorption of NPAM in surface water and kaolinite surfaces is the prerequisite for the formation of bridging mechanism, NPAM in bulk water is the crux to enhancing bridging performance. A large number of water molecules and NPAM have strong competitive adsorption on kaolinite surfaces. The interaction energy between NPAM and kaolinite surfaces in aqueous solution is mainly contributed by van der Waals interaction.