Specific polarizability of sand-clay mixtures with varying ethanol concentration
2016
We utilise a concept of specific polarizability (cs), represented as the ratio of mineral–fluid interface
polarization per pore-normalised surface area Sp, to demonstrate the influence of clay-organic interaction
on complex conductivity measurements. Complex conductivity measurements were performed
on kaolinite– and illite–sand mixtures as a function of varying ethanol (EtOH) concentration
(10% and 20% v/v). The specific surface area of each clay type and Ottawa sand was determined
by nitrogen-gas-adsorption Brunauer–Emmett–Teller method. We also calculated the porosity and
saturation of each mixture based on weight loss of dried samples. Debye decomposition, a phenomenological
model, was applied to the complex conductivity data to determine normalised chargeability
(mn). Specific polarizability estimates from previous complex conductivity 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 with a level of
significance α = 0.05 suggests that the suppression in cs responses with increasing EtOH concentration
was 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 complex conductivity measurements to alteration in surface chemistry at available
surface adsorption sites for different clay types, likely 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 changes in clay mineralogy.
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