Influence mechanism of Fe3+ doping on the hydrophobic regulation of kaolinite/water interface: Experiments and MD simulations

Abstract

The surface/interfacial reactivity of clay is a critical factor influencing the sedimentation of coal slurry water. To achieve efficient sedimentation of coal slurry water, this paper introduces a novel approach that regulates the hydrophobicity of defective active sites in clay minerals. Fe³⁺-doped kaolinite (Fe³⁺-Kao) was synthesized by hydrothermal methods. Subsequently, tests were conducted on the adsorption capacity, surface wettability, and agglomeration sedimentation of alkyl amine/ammonium salts (AAS) on Fe³⁺-Kao surfaces. Fe³⁺ doping significantly enhances AAS adsorption and alters surface properties from hydrophilic to hydrophobic, promoting kaolinite particle aggregation and sedimentation, thereby improving coal slurry water treatment efficiency. Molecular dynamics (MD) simulations were performed to analyze the statistical adsorption behavior of AAS on Fe³⁺-Kao surfaces. The simulation results indicate that the mechanism by which Fe³⁺ doping influences the hydrophobic regulation of kaolinite surfaces is due to the enhanced interfacial interactions between the kaolinite surface and AAS, where the interfacial effects are more pronounced on surfaces closer to the dopant sites. The findings of this research offer valuable insights for future studies on other types of lattice defects in clay minerals, as well as for the development of more efficient treatment chemicals for coal slurry water.