GAS PHASE REDUCTION OF TRICHLOROETHYLENE BY ZERO VALENT IRON

摘要

The removal of TCE by Fe~(?s - )was investigated in gaseous reactors simulating conditionsrnin the vadose zone. TCE was removed by Fe~(?s - ) via two mechanisms; adsorption andrndechlorination. The water content (reported as relative humidity, RH) was critical forrnTCE dechlorination. TCE was removed by adsorption at low RH and the critical RHrnwas determined by the formation of by-products, such as, DCE, VC, and ethylene, inrnthe reactors containing RH of 6-97% at 24~(?s - )C. The critical RH was 72% for acidwashedrnFe~(?s - )(clean) and 92% for the unamended (partially oxidized) Fe~(?s - )particles. Arnfirst-order reaction rate law was developed based on the chemical reaction being raternlimiting for the reactors containing excess water, in which Fe?s~(?s - )particles were coveredrnby water and RH of the gas phase was 100%. The chemical reaction control on overallrnreaction rate was verified by the apparent activation energy, E_(app) ≌ 54 kJ/mol, whichrnexceeded the values reported for mass transfer controlling reactions. The formation ofrniron oxides as TCE dechlorination proceeds was shown as a factor affecting the raternof TCE dechlorination by testing the reaction rate on acid-washed and unamended Fe~(?s - )rnsurface in anaerobic conditions at 24~(?s - )C. The dechlorination rate of TCE was 2.2 timesrnless for unamended Fe~(?s - )than for acid-washed Fe~(?s - ). The presence of oxygen also decreased the reaction rate 3.1 times compared to anaerobic conditions due to the