Second ISSMGE R. Kerry Rowe Lecture: On the intrinsic, state, and fabric parameters of active clays for contaminant control

Abstract

The osmotic, hydraulic and self-healing efficiency of bentonite-based barriers for the containment of subsoil pollutants is governed not only by the intrinsic chemicophysical parameters of the bentonite, i.e., the solid phase density, ρsk; the total specific surface, S; the surface density of the electric charge, σ; and the Stern layer thickness, dStern, and fraction, fStern, but also by the chemicomechanical fabric parameters that quantify the structure or texture of the solid skeleton, such as the micro, em, and nano, en, void ratios; the average number of platelets or lamellae per tactoid, Nl,AV; and the solid skeleton effective electric charge concentration, [Formula: see text]. In turn, the fabric parameters are controlled by state parameters, such as the total void ratio, e; and the salt concentration of the equilibrium solution, cs. A theoretical framework has been developed to describe the relationships between the aforementioned intrinsic, state, and fabric parameters for a bentonite barrier and its performance parameters: the hydraulic conductivity, k; the effective diffusion coefficient, [Formula: see text]; the chemico-osmotic efficiency coefficient, ω; and the osmotic swelling pressure, usw. The proposed theoretical hydrochemicomechanical model has been validated through comparison with a large amount of experimental results.

Assessing the influence of chemico-osmosis on solute transport in bentonite membranes based on combined phenomenological and physical modeling

“…Thus, prediction of kh and  (which is necessary to predict N via Eq. 3) requires knowledge of the total void ratio and the fabric boundary surface of the bentonite, which is the combination of em, Nl,AV, and Cs (Manassero, 2020). Manassero (2020) proposed the following equations for characterizing the fabric boundary surface of bentonite exposed to monovalent salt solutions (e.g., NaCl, KCl) based on analysis of experimental data for different sodium bentonites:…”

“…where Nl,AV0 = ideal average minimum number of lamellae per tactoid when Cs = 0 and em → ∞,  = emꞏ(Nl,AV -Nl,AV0) for Cs = 0, and  is a constriction coefficient accounting for mechanical constraints hindering the movement of lamellae at medium to high void ratio. These three parameters (Nl,AV0, , ) are unique for a given bentonite, but can be estimated from laboratory tests (see Manassero, 2020). Substitution of Eq.…”

“…In this paper, global osmotic numbers, Ng, are predicted for a GCL containing sodium bentonite. The total specific surface, S, surface charge density, , and solids density, s, are assumed to be 750 m 2 /g, 0.114 C/m 2 , and 2.61 Mg/m 3 , respectively Manassero, 2020). The Stern layer thickness, dst, the half-distance between lamellae in a tactoid, bn, and the Stern fraction, fst, are expected to lie within the relatively narrow ranges of 1.2-2.0 nm, 0.2-0.5 nm, and 0.70-0.95, respectively (Laird, 2006;Dominijanni et al, 2017;Manassero, 2020).…”

“…significance of chemico-osmosis on solute migration in bentonite membranes using a phenomenological transport framework combined with a physical model relating the macroscale properties of the bentonite, namely  and kh, to the microscale physicochemical and fabric properties Manassero, 2005, 2012a,b;Dominijanni et al, 2017;Manassero, 2020). The model is used to simulate the coupled transport of a monovalent salt (KCl) through a sodium bentonite GCL for different source concentrations and void ratios based on predicted values of N.…”

Diffusion through sodium and polymer enhanced bentonites exposed to dilute and aggressive solutions

“…Properties of NaB that are desirable for environmental containment include high osmotic swell and low hydraulic conductivity (k) to water (e.g., 5 Â 10 À11 m/s; Rowe 2012), limiting advective flux of contaminants into the environment (e.g., Norrish and Quirk 1954;van Olphen 1977;McBride 1994;Petrov and Rowe 1997;Shackelford et al 2000;Jo et al 2001Jo et al , 2005. However, exposure to aggressive liquids, such as leachates with multi-valent cationic species, high ionic strength, and (or) extreme pH (2 > pH > 12), can negatively alter the osmotic swell and hydraulic properties of NaB (e.g., Egloffstein 1997;Vasko et al 2001;Kolstad et al 2004aKolstad et al , 2004bBenson and Meer 2009;Benson et al 2010b;Gates et al 2009;Gates and Bouazza 2010;Hornsey et al 2010;Bouazza and Gates 2014;Tian et al 2016a;Chen et al 2018Chen et al , 2019Manassero 2020). Thus, chemical incompatibility between NaB and the contained waste-chemical solutions is detrimental to the long-term performance of the barrier.…”