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Specific polarizability of sand–clay mixtures with varying ethanol concentration
Citation:
Sharma, S., L. Slater, D. Ntarlagiannis, D Werkema, AND Z. Szabo. Specific polarizability of sand–clay mixtures with varying ethanol concentration. Near Surface Geophysics. John Wiley & Sons, Inc., Hoboken, NJ, 15(6):615-624, (2017). https://doi.org/10.3997/1873-0604.2017049
Impact/Purpose:
Ethanol is now widely used as an additive to conventional fuel to provide cleaner emissions during internal combustion in various automotive engines. Ethanol enters groundwater reserves in the subsurface through accidental spills and it has emerged as a leading contaminant in groundwater (Gomez and Alvarez, 2010). Powers et al. (2001a) described the potential risks to groundwater due to accidental spills of large volumes of gasoline containing ethanol during transportation. Increased concentrations of ethanol in ground water can result in slower degradation of the BTEX (benzene, toluene, ethyl-benzene and xylene) compounds present in gasoline. In groundwater containing ethanol and BTEX compounds, ethanol is preferentially biodegraded by microbes over BTEX compounds (Corseuil et al., 1998; Powers et al., 2001b; Lovanh et al., 2002; Ruiz-Aguilar et al., 2002; Österreicher-Cunha et al., 2007; Schaefer et al., 2010), resulting in rapid depletion of dissolved oxygen and other essential electron acceptors required for BTEX biodegradation.
Description:
We utilize a concept of specific polarizability (cs), represented as the ratio of mineral-fluid interface polarization per pore-normalized surface area (Sp), to demonstrate the influence of clay-organic interaction on complex conductivity (CC) measurements. CC measurements were performed on kaolinite- and illite-sand mixtures as a function of varying ethanol (EtOH) concentration (10% and 20% v/v). Specific surface area of each clay type and Ottawa sand was determined by nitrogen gas adsorption-BET method. We also calculated porosity and saturation of each mixture based on weight loss of dried samples. Debye decomposition, a phenomenological model, was applied to the CC data to determine a normalized chargeability (mn). Specific polarizability estimates from previous CC measurements for bentonite-sand mixtures were compared with our dataset. The cs for all sand-clay mixtures decreased as the EtOH concentration increased from 0% to 10% to 20% v/v. We observe similar cs responses to EtOH concentration for all sand-clay mixtures. Analysis of variance (ANOVA) with a level of significance α=0.05 suggests that the suppression in cs responses with increasing EtOH concentration were statistically significant for all sand-clay mixtures. On the other hand, real conductivity showed only 10% to 20% v/v changes with increasing EtOH concentration. The cs estimates reflect the sensitivity of CC measurements to alteration in surface chemistry at available surface adsorption sites (internal and external) for different clay types, assumingly resulting from ion exchange at the clay surface and associated with kinetic reactions in the electrical double layer of the clay-water-EtOH media. Our results indicate a much larger influence of specific surface area and ethanol concentration on clay-driven polarization relative to just changes in clay mineralogy.
URLs/Downloads:
DOI: Specific polarizability of sand–clay mixtures with varying ethanol concentration