title: Complex resistivity signatures of ethanol in sand-clay mixtures.
abstract: We performed complex resistivity (CR) measurements on laboratory columns to investigate changes in electrical properties as a result of varying ethanol (EtOH) concentration (0% to 30% v/v) in a sand-clay (bentonite) matrix. We applied Debye decomposition, a phenomenological model commonly used to fit CR data, to determine model parameters (time constant: τ, chargeability: m, and normalized chargeability: mn). The CR data showed a significant (P≤0.001) time-dependent variation in the clay driven polarization response (~12 mrad) for 0% EtOH concentration. This temporal variation probably results from the clay-water reaction kinetics trending towards equilibrium in the sand-clay-water system. The clay polarization is significantly suppressed (P≤0.001) for both measured phase (ϕ) and imaginary conductivity (σ″) with increasing EtOH concentration. Normalized chargeability consistently decreases (by up to a factor of ~2) as EtOH concentration increases from 0% to 10% and 10 to 20%, respectively. We propose that such suppression effects are associated with alterations in the electrical double layer (EDL) at the clay-fluid interface due to (a) strong EtOH adsorption on clay, and (b) complex intermolecular EtOH-water interactions and subsequent changes in ionic mobility on the surface in the EDL. Changes in the CR data following a change of the saturating fluid from EtOH 20% to plain water indicate strong hysteresis effects in the electrical response, which we attribute to persistent EtOH adsorption on clay. Our results demonstrate high sensitivity of CR measurements to clay-EtOH interactions in porous media, indicating the potential application of this technique for characterization and monitoring of ethanol contamination in sediments containing clays.
authors.affiliation: Department of Earth and Environmental Sciences, Rutgers University, 101 Warren Street, Newark, NJ 07102, USA. personna@andromeda.rutgers.edu
authors.forename: Yves Robert
authors.initials: YR
authors.lastname: Personna
authors.forename: Lee
authors.initials: L
authors.lastname: Slater
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Ntarlagiannis
authors.forename: Dale
authors.initials: D
authors.lastname: Werkema
authors.forename: Zoltan
authors.initials: Z
authors.lastname: Szabo
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry*; D000077215:Clay; D000431:Ethanol / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*
chemical_list: D000538:Aluminum Silicates; D000431:Ethanol; D012822:Silicon Dioxide; D000077215:Clay