ENVR 62 |
| Jiankang Wang and James M. Farrell. Department of Chemical and Environmental Engineering, University of Arizona, Room 306, Building 72, Tucson, AZ 85721 |
| In recent years there has been increasing interest in using metallic iron filings as reducing agents for removing chlorinated solvents from contaminated groundwater. This study investigated the role of atomic hydrogen in the dechlorination of trichloroethylene (TCE) and tetrachloroethylene (PCE) at iron surfaces. Tafel analysis was used to determine the rates of iron corrosion as a function of TCE and PCE concentrations. Electrochemical impedance spectroscopy (EIS) was used to determine the number of reactions that controlled the observed rates of chlorocarbon disappearance, as well as the role of atomic hydrogen in TCE and PCE reduction. The relative reaction rates for TCE versus PCE were found to vary depending on the concentration of atomic hydrogen on the iron surfaces and the halocarbon concentration. At millimolar halocarbon concentrations and high surface concentrations of atomic hydrogen, TCE reaction rates were faster than those for PCE; while at low atomic hydrogen concentrations, PCE reaction rates were faster than those for TCE. At micromolar concentrations, TCE reaction rates were faster than those for PCE at both low and high concentrations of atomic hydrogen. These effects can be attributed to faster reaction of TCE versus PCE with atomic hydrogen and saturation of the atomic hydrogen reduction mechanism at low halocarbon concentrations. The EIS data showed that all the rate limitations for TCE and PCE dechlorination occurred during the transfer of the first two electrons. Results from this study show that reaction rates of TCE and PCE with iron are dependent on the significance of the reduction pathway involving atomic hydrogen. |
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Environmental Chemistry Awards
1:30 PM-4:05 PM, Monday, September 8, 2003 Javits Convention Center -- 1A22, Oral
Division of Environmental Chemistry |