电场对高岭石表面重金属离子吸附特征的影响

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

电动力学修复技术可有效去除煤矿区污染土壤中的重金属离子。为阐明电场对高岭石表面重金属离子吸附特征的影响规律,以矿区土壤中Pb(Ⅱ)、Cd(Ⅱ)和Cu(Ⅱ)3种常见重金属元素为研究对象,初步构建三维可视化模型,优化得到稳定的高岭石-溶液-高岭石模拟体系,运用分子动力学模拟方法,探究电场作用下重金属离子在高岭石(001)晶面的吸附方式、原子密度分布、扩散系数及径向分布函数的演化规律。结果表明:电场方向为+Z时,电场促进重金属离子和硅氧烷表面之间的络合作用,重金属离子第1水化壳的配位数随着电场强度增大而减少,外层配合物吸附百分比随着电场强度增大而增大。电场方向为-Z时,外层配合物吸附百分比随着电场强度增大而降低,高岭石表面与重金属离子相互作用减弱,更多的重金属离子游离在溶液中与氯离子配对;电场极化作用下重金属离子第1和2水化壳之间没有明显分界,水化壳之间存在水分子交换;电场作用下重金属离子在高岭石(001)面上的均方位移曲线MSD表现出各向异性,X、Y方向扩散系数大于Z方向,总扩散系数随着电场强度的增大而增大,扩散系数受电场正负方向的影响不明显;Pb(Ⅱ)离子和Cd(Ⅱ)离子在高岭石表面上仅存在外层配合物,Cu(Ⅱ)离子存在内、外层配合物共存的吸附方式;高岭石对3种重金属离子吸附优先顺序为Pb(Ⅱ)>Cu(Ⅱ)>Cd(Ⅱ)。

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).