Cation Diffusion in Compacted Clay: A Pore-Scale View

Yang, Yuankai; Wang, Moran

doi:10.1021/acs.est.8b05755

Cited by 19 publications

(33 citation statements)

References 43 publications

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“…This study simplifies Na‐bentonite to montmorillonite because they have the similar characteristics of microstructures. The reproduced microstructure contains the major statistical information of porous media and the predictions of ion diffusivity using these microstructures have validated this strategy (González Sánchez et al, 2008; Wang & Pan, 2008; Yang & Wang, 2018b, 2019). Figures 2a and 2b show the photograph and the SEM image of compacted I/S.…”

Section: Modelingmentioning

confidence: 86%

“…The constant surface charge density at the clay surface is adopted as the boundary condition for the Poisson equation,

\frac{normald ψ^{P}}{normald \overset{n}{true}} = - \frac{σ_{0}}{ε_{r} ε_{0}},

with the vector

\overset{n}{true}

normal to the surface and the surface charge density σ 0 . σ 0 is the charge site density on the solid clay surface, which corresponds to the cation exchange capacity (CEC in equiv/kg) and to the total specific surface area (SSA in m 2 /kg) (Yang & Wang, 2019):

σ_{0} = - \frac{{eN}_{A} CEC}{SSA} .

…”

Section: Modelingmentioning

confidence: 99%

“…It ranges from −0.1 to −0.2 C/m 2 in illite or montmorillonite (Tachi & Yotsuji, 2014). In this study, the surface charge density is set as −0.12 C/m 2 based on the previous studies (Tachi & Yotsuji, 2014; Yang & Wang, 2019).…”

Section: Modelingmentioning

confidence: 99%

“…Therefore, it is necessary to improve the understanding the influence of the overlapping EDL on anionic concentration and electrical potential distributions. Recently, a 3‐D pore‐scale model has been used to predict the diffusion of ions in clays (Yang et al, 2019; Yang & Wang, 2018b, 2019). Compared with other models, the pore‐scale model can capture the local ionic concentration and electrical potential distributions automatically at the pore scale.…”

Section: Introductionmentioning

confidence: 99%

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Anion Diffusion in Compacted Clays by Pore‐Scale Simulation and Experiments

Yang

Wang

et al. 2020

Water Resources Research

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Accurate understanding of diffusion of anionic radionuclides in different clays is significant to predict long-term performance of high-level radioactive waste (HLW) repositories. The importance of electrical double layer (EDL) on anionic tracer diffusion in different clays has been studied by both through-diffusion experiments and pore-scale simulations in this work. The through-diffusion experiments measured the effective diffusion coefficient and the accessible porosity of Re (VII) in compacted montmorillonite, Na-bentonite, and illite/smectite mixed layer (I/S) at different salinities. The results showed that the accessible porosity and the effective diffusion coefficient of Re (VII) in montmorillonite and Na-bentonite were similar but lower than those in I/S under the same conditions. For mechanism analysis and predictions, a pore-scale modeling was implemented to simulate the diffusion of anions in compacted clays. In the simulations, the characteristics (porosity, density, and total surface area) of microstructures of montmorillonite and I/S were used to regenerate three-dimensional pore structures numerically by a Quartet Structure Generation Set method. The Re (VII) diffusion was then simulated by directly solving coupled Poisson-Nernst-Planck equations via the lattice Boltzmann method. The diminished effect of EDL was therefore calculated and compared with Donnan and multiporosity models. As EDLs overlap in compacted clays, the Donnan model overestimates the influence of EDL on Re (VII) diffusion, while the multiporosity model underestimates it. The pore-scale modeling, which captures the structure of overlapping EDLs automatically, can simulate the diffusion of anionic radionuclides in compacted clays without any fitting parameters.

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Section: Modelingmentioning

confidence: 86%

“…The constant surface charge density at the clay surface is adopted as the boundary condition for the Poisson equation,

\frac{normald ψ^{P}}{normald \overset{n}{true}} = - \frac{σ_{0}}{ε_{r} ε_{0}},

with the vector

\overset{n}{true}

σ_{0} = - \frac{{eN}_{A} CEC}{SSA} .

…”

Section: Modelingmentioning

confidence: 99%

Section: Modelingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Anion Diffusion in Compacted Clays by Pore‐Scale Simulation and Experiments

Yang

Wang

et al. 2020

Water Resources Research

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“…Here, we consider the system is under elevated isothermal situation only in this work. Otherwise, the thermodiffusion effect or the Soret effect may play an important role on ion transport [40‐44]. Figure 2B demonstrates that the acquired surface charge (σ 0 ) enhances by increasing the solution temperature.…”

Section: Resultsmentioning

confidence: 99%

Temperature effects on electrical double layer at solid‐aqueous solution interface

Alizadeh

Wang

2020

Electrophoresis

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Despite the significant influence of solution temperature on the structure of electrical double layer, the lack of theoretical model intercepts us to explain and predict the interesting experimental observations. In this work, we study the structure of electrical double layer as a function of thermochemical properties of the solution by proposing a phenomenological temperature dependent surface complexation model. We found that by introducing a buffer layer between the diffuse layer and stern layer, one can explain the sensitivity of zeta potential to temperature for different bulk ion concentrations. Calculation of the electrical conductance as function of thermochemical properties of solution reveals the electrical conductance not only is a function of bulk ion concentration and channel height but also the solution temperature. The present work model can provide deep understanding of micro‐ and nanofluidic devices functionality at different temperatures.

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Elucidating the role of water films on solute diffusion in unsaturated porous media by improved pore‐scale modeling

Yang,

Patel,

Prasianakis

et al. 2024

Vadose Zone Journal

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Solute diffusion in partially saturated porous media is an important fundamental process in many natural and environmental systems. At low water saturation, the solute transport is governed by the diffusion in thin water films on the surfaces of solids. In this study, we established an improved pore‐scale simulation framework successfully describing the solute diffusion in variably saturated porous media (e.g., soils), which considers the contribution of the diffusion within the thin water film on the surface of the solid matrix. The model takes into account the liquid–gas distribution in the underlying porous media by the Shan‐Chen lattice Boltzmann Method (LBM) and simulates the solute diffusion in the bulk liquid phase and the water film. Based on the numerical results, an easy‐to‐use theoretical formula was also developed to predict the effective diffusivity in microporous materials at low saturation levels. The average relative error of its prediction with respect to the experimental data from the literature is about 30%, while that of the classical power law exceeds 70%. A simple phase diagram was defined, which allows us to identify the situations under which it is necessary to take the influence of surface water films on the effective diffusivity in unsaturated microporous media into account. The present study improves the pore‐scale model to address solute diffusion in the water films at low water saturation and elucidates the contribution of thin water films on solute transport.

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Cation Diffusion in Compacted Clay: A Pore-Scale View

Cited by 19 publications

References 43 publications

Anion Diffusion in Compacted Clays by Pore‐Scale Simulation and Experiments

Anion Diffusion in Compacted Clays by Pore‐Scale Simulation and Experiments

Temperature effects on electrical double layer at solid‐aqueous solution interface

Elucidating the role of water films on solute diffusion in unsaturated porous media by improved pore‐scale modeling

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