Diffusion of Water through the Dual-Porosity Swelling Clay Mineral Vermiculite

Abstract

Prediction of water and solute migration in natural clay-based materials requires a detailed understanding of the roles played by different porosity types (around or inside clay particles) on the overall transfer process. For smectite, a reference material for the design of migration models, this discrimination is complex because of osmotic swelling of the structure under water-saturated conditions. Diffusion experiments with a water tracer (HDO) were conducted on 0.1-0.2, 1-2, and 10-20 μm size fractions of Na-vermiculite, a swelling clay mineral with no osmotic swelling. Results obtained for the two finest fractions suggest that osmotic swelling and the associated impact on pore structure are responsible for the low D values reported in the literature for smectite compared to those of vermiculite. When considering only interparticle porosity, D values for vermiculite are similar to those reported for nonporous grains (Na-kaolinite and Na-illite). This indicates that interparticle porosity has a primary effect on the overall water diffusion process, whereas interlayer porosity is shown to imply a small proportion of HDO adsorption. This study provides evidence that vermiculite is a promising reference mineral for the understanding of the roles played by pore structure and mineral-water interaction in the transport properties of water in claystones and for associated refinement of dual-porosity diffusion models.

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

“…Since the pore size is very small, many studies have shown that the diffusion process dominates the transportation of radionuclides in bentonite buffer (Idiart & Pękala, 2016; Tournassat & Appelo, 2011; Van Loon et al, 2007). Radionuclides diffusion is influenced by many factors, such as dry densities of bentonite (Sato et al, 1992; Wu et al, 2018), salinities and compositions of pore solution (Glaus et al, 2020; Tachi & Yotsuji, 2014; Wigger & Van Loon, 2018), and sizes and shapes of clay particles (Tertre et al, 2018).…”

Water Mobility within Compacted Clay Samples: Multi-Scale Analysis Exploiting1H NMR Pulsed Gradient Spin Echo and Magnetic Resonance Imaging of Water Density Profiles

“…Although this study concerns only experimental NMR measurements performed for a single clay sample, we feel justified to compare the water mobility measured by 1 H PGSE-NMR within kaolinite clay and that evaluated by HDO through diffusion 17,21,31 and PGSE-NMR 37 within porous networks of various granular materials. While PGSE-NMR experiments directly quantify the intrinsic self-diffusion coefficient 33 D of the fluid confined within various porous networks, 12,16,24,37,39,40,54,55 through-diffusion measurements are sensitive to the fluid permeability of the macroscopic porous media, leading to an effective diffusion coefficient 17,21,31 D e . The corresponding intrinsic mobility of the fluid inside the porous network may be evaluated by the simple relationshipwhere, ϕ is the porosity of the porous network.…”

Water and Ion Dynamics in Confined Media: A Multi-Scale Study of the Clay/Water Interface

“…Such effective diffusion coefficient is directly linked to the pore diffusion parameter commonly derived from NMR measurements probing only the porosity accessible for the investigated probe. A large number of experiments were performed in literature to investigate the influence of porosity on the diffusion of water and ions in porous media made of clayey particles [69,[92][93][94]. Water diffusion coefficients obtained using Through-Diffusion experiments and PGSE-NMR analyses performed with compacted kaolinite samples, characterized by the same porosity and preferential particle orientation, revealed similar results (see Figure 23), despite the different time scale probed by the two methods (i.e., ms for PGSE-NMR versus several days for Through-Diffusion [52]).…”