Analysis of Halogenated Organic Particle-Scale Desorption via Column Studies and 13C Solid State NMR SpectroscopyEPA Grant Number: R822626
Title: Analysis of Halogenated Organic Particle-Scale Desorption via Column Studies and 13C Solid State NMR Spectroscopy
Investigators: Reinhard, Martin
Institution: Stanford University
EPA Project Officer: Hiscock, Michael
Project Period: September 1, 1995 through August 1, 1998 (Extended to August 31, 2000)
Project Amount: $177,916
RFA: Exploratory Research - Chemistry and Physics of Water (1995) RFA Text | Recipients Lists
Research Category: Water , Land and Waste Management , Engineering and Environmental Chemistry
Description:The objective of this project is to elucidate the mechanisms controlling the slow desorption of volatile organic chemicals from soils and sediments using column studies and 13C solid state nuclear magnetic resonance (NMR) spectroscopy.
Column studies involve measuring desorption isotherm and kinetic profiles for trichloroethylene on model and natural solids over a 45oC temperature range. NMR spectroscopy will be used to compare the resonance frequency of trichloroethylene, sorbed to model and natural solids, to the resonance frequency of pure phase and aqueous phase trichloroethylene. Model solids include a silica gel and zeolites of known composition and structure, and natural solids include soils and sediments. Results for the natural solids will be compared to results for the model solids to infer equilibrium and kinetic mechanisms. Isosteric heats of adsorption will be calculated from isotherms and activation energies will be calculated from slow kinetic profiles. In zeolites, adsorption in micropores controls equilibrium partitioning. In natural solids, isosteric heats of adsorption are expected to increase with decreasing concentration. At low concentrations, these values are expected to be on the order of those measured in zeolites, and adsorption in micropores is expected to control uptake. NMR spectroscopy is expected to show that sorbed trichloroethylene is in the pure phase at low concentrations. With respect to kinetics, mass transfer in zeolites is controlled by activated diffusion in micropores. Activation energies in natural solids are expected to be on the order of those in zeolites and activated diffusion in micropores is expected to control slow desorption.
These studies will allow contaminant transport models to be developed which mechanistically describe slow desorption and the effects of temperature on this process. These studies will also allow decision makers to gauge the viability of enhanced thermal recovery methods with respect to slow desorption.