黏土中多离子体系的扩散机理研究

Microcosmic mechanism of ion transport in charged clay soils

黏土微观结构、颗粒表面电场以及黏土孔隙液中离子之间相互作用对离子运移有着重要的影响,但如何考虑上述因素对离子运移的影响一直是个没有解决的难题。针对黏土颗粒表面电场对离子运移影响这一核心问题,从微观角度(纳米级)采用Nernst-Planck方程和Poisson方程描述离子在带电黏土多孔介质中的运移。在参考已有实验成果的基础上,建立了黏土中微观多离子运移数值分析模型,采用多场耦合分析有限元软件Comsol Multiphysics求解。数值分析表明:由于黏土颗粒表面负电荷的作用,阳离子浓度明显升高,阴离子浓度则明显降低;不考虑颗粒带电,阳离子和阴离子浓度分布相同。在颗粒表面形成明显的双电层,浓度越高,双电层厚度越小;浓度越低,双电层厚度越大。研究成果将有助于深入理解离子在黏土垫层中的扩散运移机理,为进一步宏观分析提供详尽的基础数据。

The microstructure of clay,the surface electric field of clay particles and the interaction of ions have great effect on the ion transport.However,the problem of how to consider the effect on ion the transport by the electric field hasn＇t been solved.The Nernst-Planck equation is combined with the Poisson equation to describe the ion transport in charged clay soils at the microscale.The combined equation simultaneously considers the coupling influence of the concentration field and static-electric field on the ion transport.A finite element model is set up based on experimental results.The numerical analysis indicates that cation concentration visibly increases due to a particle negative charged attraction,on the other hand,anion concentration reduces due to charged repel.But the traditional method does not take into account the influence of a particle charged,because the distribution of the cation is the same as that of the anion concentration.Double-layer is obviously formed on the particle surface,the higher the concentration,the thinner the thickness of double-layer;the lower the concentration,the thicker the thickness of double-layer.The analytic results will be important to in-depth understanding of the coupling influence between the concentration field and static electric field during the ion transport.The research macroscopically provides the exhaustive foundation data for further analysis.