Explicit and implicit coupling during solute transport through clay membrane barriers

• Published in: Journal of contaminant hydrology Vol. 72; no. 1; pp. 259 - 285
• Main Authors: Malusis, Michael A., Shackelford, Charles D.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.08.2004; Elsevier Science
• Subjects: Adsorption; Advective–dispersive transport; Aluminum Silicates; Biological Transport; Chemico-osmosis; Clay membranes; Containment; Coupled solute transport; Diffusion; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Hydrogeology; Hydrology. Hydrogeology; Hyperfiltration; Models, Theoretical; Osmosis; Pollution, environment geology; Soil Pollutants; Time Factors; Ultrafiltration; Water Movements; Advective–dispersive transport; Chemico-osmosis; Clay membranes; Coupled solute transport; Diffusion; Hyperfiltration; Containment; experimental studies; diffusion; potassium; ground water; bentonite; digital simulation; pollution; Advective-dispersive transport; clay; coupling; hydraulic conductivity; osmosis; solution; clastic rocks; advection; chlorides; geochemical barriers; efficiency; solutes; salt; transport; halides; chemically precipitated rocks; evaporites; sedimentary rocks; filtration; tortuosity; dispersion; theory
• ISSN: 0169-7722; 1873-6009
• DOI: 10.1016/j.jconhyd.2003.12.002

Simulations of salt (KCl) flux through a 1-m-thick clay membrane barrier (CMB) based on coupled solute transport theory are compared to simulated fluxes based on traditional advective–dispersive transport theory. The simulations are based on measured values for the effective salt-diffusion coefficient ( D s*) and chemico-osmotic efficiency coefficient ( ω) for a bentonite-based barrier material subjected to KCl solutions. The results indicate that the exit salt flux is reduced due to both explicit coupling (hyperfiltration and chemico-osmotic counter-advection) and an implicit coupling effect resulting from the decrease in D s* due to a decrease in the apparent tortuosity factor, τ a, with an increase in ω. Implicit coupling is shown to be more significant than explicit coupling for reducing and retarding salt flux through a CMB under diffusion-dominated conditions. Failure to account for the implicit coupling effect may result in unrealistic results, such as the existence of salt flux through a perfect (ideal) clay membrane (i.e., ω=1).