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COUNTER-DIFFUSION OF ISOTOPICALLY LABELED TRICHLOROETHYLENE IN SILICA GEL AND GEOSORBENT MICROPORES: COLUMN RESULTS. (R822626)
Citation:
Werth, C. J. AND M. Reinhard. COUNTER-DIFFUSION OF ISOTOPICALLY LABELED TRICHLOROETHYLENE IN SILICA GEL AND GEOSORBENT MICROPORES: COLUMN RESULTS. (R822626). ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 33(5):730-736, (1999).
Description:
To investigate counter-diffusion in microporous sorbents, the rate of
exchange between deuterated trichloroethylene (DTCE) in fast desorbing sites and
nondeuterated TCE (1HTCE) in slow desorbing sites was measured.
Exchange rates were measured for a silica gel, a Santa Clara sediment, and a
Livermore clay/silt fraction, all at 100% relative humidity and 30 src="/ncer/pubs/images/deg.gif">C. Initially, solids were packed into stainless
steel columns and incubated with 1HTCE for 1-3 weeks. After
incubation, 1HTCE was replaced with DTCE in fast desorbing sites.
Next, columns were capped (i.e., sealed), and DTCE was allowed to exchange with
1HTCE in slow desorbing sites for 1, 3, or 30 days. Elution profiles
were then measured to determine the extent of exchange that occurred while the
columns were capped. Results from experiments conducted with different exchange
times support the hypothesis that slow sorption kinetics is controlled by
diffusion in micropores. For the silica gel and the Santa Clara sediment,
1HTCE was incompletely exchanged with DTCE after 30 days (a time
period that was sufficient for apparent equilibrium of a single sorbate). This
indicates that the counter-diffusion rate of DTCE into 1HTCE-filled
micropores is less than the diffusion rate of 1HTCE into micropores
not filled with TCE.