Sorption of VX to Clay Minerals and Soils: Thermodynamic and Kinetic Studies
Final rept. Oct 2009-Sep 2010
SCIENCE APPLICATIONS INTERNATIONAL CORP GUNPOWDER MD
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Organophosphorus-based chemical warfare agents are unique military chemicals that are extremely toxic and could be found in the soils of military installations and former production facilities. Little data exists on the fate and transport of these chemicals in soil environments, particularly when the agent is present in low concentrations. This report summarizes data from a study in which isothermal titration calorimetry was used to examine the sorption of VX to clay minerals and soils. Thermodynamic characteristics such as observed enthalpy of binding, entropy, free energy, binding and dissociation constants, and saturation capacity were obtained. Complementary sorptiondesorption profiles and batch equilibrium sorption isotherms were also generated during the study. Kinetic time-point samples were analyzed using a variety of analytical techniques to provide insights into the sorption pathways, and to distinguish sorption from degradation occurring in the bulk solutions. In a montmorillonite clay, there was a sharp break in the thermodynamic profile that corresponded to the lower critical temperature LCT of VX. The predominant mechanism above the LCT was an exothermic physisorption process, consistent with an ion exchange mechanism. Below the LCT, bimodal behavior was observed, with a second type of endothermic interaction occurring after the initial ion exchange.
- Geology, Geochemistry and Mineralogy
- Chemical, Biological and Radiological Warfare