Reactive Transport Modeling of Coupled Processes in Nanoporous Media

Tournassat, Christophe; Steefel, Carl I.

doi:10.2138/rmg.2019.85.4

Cited by 48 publications

(51 citation statements)

References 203 publications

(214 reference statements)

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“…If the pore size in clay media is small enough, then the diffuse layers at adjacent surfaces bordering the pores overlap and the absence of bulk electroneutral solution in the center of the pore gives rise to a remarkable array of coupled macro-scale properties, such as swelling and semi-permeable membrane properties. 9 These coupled processes explain in large part why the mechanical, chemical, thermal osmosis and fluid transport processes in clay-rich media remain so challenging to understand and to model at all scales, from microsocopic to macroscopic. Numerical methods for modeling macroscopic properties of clay media with the consideration of the presence of a EDL have met a growing interest in diverse communities in the past years.…”

Section: Introductionmentioning

confidence: 99%

Influence of Polarizability on the Prediction of the Electrical Double Layer Structure in a Clay Mesopore: A Molecular Dynamics Study

et al. 2020

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The prediction of the water and ion density profiles in the electrical double layer (EDL) is a key insight for macroscopic models that intend to model transport and swelling properties in clay materials. Unfortunately, the structure of the EDL, and especially the ion distribution, cannot be probed directly by measurements, because EDL features are inherently disturbed by direct measurement techniques. In recent years, Molecular Dynamics have provided a growing set of information on the properties of the EDL, including the properties of the diffuse layer, located beyond the Stern or compact layer, and in which a diffuse cloud of ions screens the remaining uncompensated surface charge. Molecular Dynamics results are, however, dependent on the force field used to run the simulations. In this study, we investigated the influence of the choice of a force field on the structural and dynamic properties of the EDL present at montmorillonite surface/water interfaces in a 50Å wide slit-shaped mesopore. Simulations were run in the presence and in the absence of added NaCl, and the results were compared to ion distributions in the diffuse layer predicted with a Poisson-Boltzmann model. The simulations evidenced the strong influence of the consideration of polarizability of ions and water molecules on the predicted structural and dynamic properties of the EDL. While non polarizable force fields gave results in good agreement with the prediction of the Poisson-Boltzmann theory, our tested polarizable force field, PIM, showed very significant deviations, which could be mainly attributed to the enhanced formation of ion pairs.

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Section: Introductionmentioning

confidence: 99%

Influence of Polarizability on the Prediction of the Electrical Double Layer Structure in a Clay Mesopore: A Molecular Dynamics Study

et al. 2020

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“…June 04, 2020 Modeling of diffusion experiments will be carried out using CrunchClay (Steefel et al, 2015;Tournassat and Steefel, 2019a) taking full advantage of the capabilities of this reactive transport code developed at LBL. CrunchClay is currently one of only two codes that can handle diffusion processes in the diffuse layer, in which the solution is not electroneutral, and for which coupled interdiffusion processes must be taken into account to model diffusion properties with a mechanistic approach (Tournassat and Steefel, 2019b). CrunchClay has the ability to treat both electrical double layer and bulk porosity with differing anion and cation diffusivities, which makes it possible to simulate the diffusion of a range of tracers with different charges in a single run, and with the same input parameters.…”

Section: Engineered Barrier System Research Activities At Lbnl: Fy20 mentioning

confidence: 99%

Engineered Barrier System Research Activities at LBNL (FY2020 Progress Report)

Zheng

Lammers

Fox

et al. 2020

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“…Most if not all analyses of fracture-matrix interaction have assumed that molecular diffusion can be described adequately with Fick's Laws. However, the limitations of Fick's Laws have become increasingly clear as researchers have demonstrated the need to describe diffusion with the Nernst-Planck equation [24][25][26][27][28][29][30][31][32][33][34][35]. This is because charged chemical species diffuse at different rates, thus creating an electric field or diffusion potential that creates a flux that is in addition to the pure Fickian diffusion due to a concentration gradient.…”

Section: Introductionmentioning

confidence: 99%

“…In this case, the Nernst-Planck equation needs to be supplemented with the Poisson equation to provide an accurate representation of charged chemical species fluxes. Thus, the Poisson-Nernst-Planck (or PNP) equation provides the most complete continuum representation of ion fluxes in the general case of charged porous media, including clay rock and shale [28,30,36]. The Poisson-Boltzmann can be used in the case of static or equilibrium system.…”

Section: Introductionmentioning

confidence: 99%

“…Progress has been made recently in developing approaches for handling discontinuous interfaces for flow and transport problems for pore-scale and other heterogeneous problems [37,38]. In the interim, mean electrostatic potential (MEP) approaches or dual continuum approaches have been proposed that provide an upscaled if simplified approximation of the PNP equations for clay rocks [28].…”

Section: Introductionmentioning

confidence: 99%

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A model for discrete fracture-clay rock interaction incorporating electrostatic effects on transport

Steefel

Tournassat

2020

Comput Geosci

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A model based on the code CrunchClay is presented for a fracture-clay matrix system that takes electrostatic effects on transport into account. The electrostatic effects on transport include those associated with the development of a diffusion potential as captured by the Nernst-Planck equation, and the formation of a diffuse layer bordering negatively charged clay particles within which partial anion exclusion occurs. The model is based on a dual continuum formulation that accounts for diffuse layer and bulk water pore space, providing a more flexible framework than is found in the classical mean electrostatic potential models. The diffuse layer model is obtained by volume averaging ion concentrations in the Poisson-Boltzmann equation, but also includes the treatment of longitudinal transport within this continuum. The calculation of transport within the bulk and diffuse layer porosity is based on a new formulation for the Nernst-Planck equation that considers averaging of diffusion coefficients and accumulation factors at grid cell interfaces. Equations for function residuals and the associated Jacobian matrix are presented such that the system of nonlinear differential-algebraic equations can be solved with Newton’s method. As an example, we consider a 2D system with a single discrete fracture within which flow and advective transport occurs that is coupled to diffusion in the clay-rich matrix. The simulation results demonstrate the lack of retardation for anions (e.g., 36Cl−) of the contaminant plume within the fracture flow system because they are largely excluded from the charged clay rock, while the migration of cations (e.g., 90Sr++) is more strongly attenuated. The diffusive loss of divalent cations in particular from the fracture is accentuated by their accumulation in the diffuse layer within the clay-rich matrix.

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Reactive Transport Modeling of Coupled Processes in Nanoporous Media

Cited by 48 publications

References 203 publications

Influence of Polarizability on the Prediction of the Electrical Double Layer Structure in a Clay Mesopore: A Molecular Dynamics Study

Influence of Polarizability on the Prediction of the Electrical Double Layer Structure in a Clay Mesopore: A Molecular Dynamics Study

Engineered Barrier System Research Activities at LBNL (FY2020 Progress Report)

A model for discrete fracture-clay rock interaction incorporating electrostatic effects on transport

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