Ternary Porosity Effects on Organic Attenuation by Clays in Clay/Organic/Electrolyte Ternary Systems Studied by Clay- Modified Electrodes and Low Angle X-ray Diffraction

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The main focus of this project in the Analytical and Surface Chemistry Program is the utilization of the electrochemical properties of clay modified electrodes to study the transport of species that should mimic the movement of organic pollutants through a clay bed. Models for the kinetic process of ion exchange (adsorption) followed by partitioning reactions in a porous medium will be developed for multisweep cyclic voltammetry. These will be fast quasi-explicit finite difference models, and will be tested experimentally at a clay-modified electrode with a variety of compounds which should fall into different kinetic regions. The model will be used to predict the effect of electrolyte speciation in maximizing retention of an organic compound diffusing through a clay bed. The role of porosity in controlling the reaction will be monitored in situ by an electroactive probe whose current will be controlled purely by diffusion, which is, in turn, controlled by the porosity of the medium. A model has been developed which relates the porosity of a well-oriented film to the interlayer spacing. The results are expected to provide an improved understanding of several important processes which occur in the clays which are used to line chemical waste disposal sites. Among these are the adsorption and absorption of chemicals by clays and the shrinking and swelling of clays as solvents and electrolytes are absorbed. It is also possible that the project will lead to the development of a rapid electrochemical method for measuring the porosity of clays.