Effect of electric field on the adsorption characteristics of heavy metal ions on kaolinite surface

Abstract

Electrokinetic remediation technology can effectively remove heavy metal ions from contaminated soil in coal mine area. In order to clarify the effect of electric field on the adsorption characteristics of heavy metal ions on the surface of kaolinite, three common heavy metal elements Pb(II), Cd(II) and Cu(II) in mine soil were studied, a three-dimensional visualization model was established, and a stable kaolinite-solution-kaolinite simulation system was optimized. Molecular dynamics simulation method was used. The adsorption mode, atomic density distribution, diffusion coefficient and radial distribution function of heavy metal ions on kaolinite (001) crystal plane under electric field were investigated. The results show that when the electric field direction is +Z, the electric field promotes the complexation between heavy metal ions and siloxane surface, and the coordination number of the first hydration shell of heavy metal ions decreases with the increase of electric field intensity. The adsorption percentage of outer complexes increases with the increase of electric field intensity. When the electric field direction is −Z, the adsorption percentage of the outer complex decreases with the increase of the electric field intensity, the interaction between the kaolinite surface and heavy metal ions weakens, and more heavy metal ions dissociate in the solution and pair with chloride ions; under the action of electric field polarization, there is no obvious boundary between the first and second hydration shells of heavy metal ions, and there is water molecular exchange between the hydration shells; under the action of electric field, the MSD curve of heavy metal ions on kaolinite shows anisotropy. The diffusion coefficient in X and Y direction is larger than that in Z direction, the total diffusion coefficient increases with the increase of electric field intensity, and the diffusion coefficient is not obviously affected by the positive and negative direction of electric field. Pb(II) ion and Cd(II) ion only have outer complexes on the surface of kaolinite, while Cu(II) ions have the adsorption mode of coexistence of inner and outer complexes. The adsorption priority of kaolinite to three heavy metal ions is Pb(II) > Cu(II) > Cd(II).

Keywords

• electric field
• heavy metals
• kaolinite
• adsorption
• molecular dynamics