Interaction between PEO and Kaolinite in Flocculating: An Experimental and Molecular-Simulation Study

In this paper, the flocculation properties of polyethylene oxide (PEO) on kaolinite and the mechanism of adsorption on kaolinite anisotropic substrates were explored. As revealed by the experimental results, the settling rate and removal rate of kaolinite increased with increasing PEO concentration, but too high PEO concentration would cause the small particles to stabilize and become difficult to settle. Furthermore, to probe deep into the interactions between PEO and kaolinite anisotropic substrates, the morphology of adsorbed PEO, interfacial adsorption structure, and dynamic behavior of water molecules were determined by quartz crystal microbalance with dissipation (QCM-D) and molecular dynamics (MD) simulations. The adsorption amount of PEO on different mineral surfaces is in the order of kaolinite > alumina > silica, and the thickness of the adsorption structure formed by alumina is greater than that of silica. As illustrated by the MD simulation results, the adsorption of PEO reduces the concentration of water molecules attached to the kaolinite surface. The PEO forms a double-layer adsorption structure on the 001 surface, while forming a tight monolayer adsorption structure on the 001¯ surface, weakening the interaction between the surface and the water molecules. The above results demonstrate that the adsorption of PEO effectively weakened the hydration dispersion of kaolinite and promoted the agglomeration of kaolinite particles.