Kinetics of trichloroethene reduction by zerovalent iron and tin: Pretreatment effect, apparent activation energy, and intermediate products

The degradation of trichloroethene (TCE) at 2 mg L-1 in headspace free aqueous solution by zerovalent iron (Fe-0) and tin (Sn-0) was studied in batch tests at 10, 25, 40, and 55 degrees C and HCl-treated Fe-0 and Sn-0 at 25 and 55 degrees C. Surface area normalized pseudo-first-order rate constants (k(SA)) ranged from 0.44 x 10(-3) to 4.3 x 10(-3) h(-1) m(-2) L for Fisher Fe-0, 0.029 x 10(-3) to 0.27 x 10(-3) h(-1) m(-2) L for Peerless and Master Builders Fe-0, and 0.011 x 10(-3) to 1.31 x 10(-3) h(-1) m(-2) L for Fisher and Aldrich Sn-0. The Aldrich Fe-0 was the least reactive with k(SA) values ranging from 0.0016 x 10(-3) to 0.011 x 10(-3) h(-1) m(-2) L. The HCl-washing increased metal surface area and observed rate constant (k) values but generally decreased k(SA) values. The calculated apparent activation energy (E-a) using the Arrhenius law for the four temperature levels ranged from 32.2 to 39.4 kJ mol(-1) for the untreated Fe-0 metals and 40.5-76.8 kJ mol(-1) for the untreated Sn-0 metals. Greater temperature effect was observed for Sn-0 than for Fe-0. Our results indicate that TCE reduction by Fe-0 and Sn-0 is likely controlled primarily by chemical reaction-limited kinetics rather than by mass transport of the TCE to the metal surface. Both reductive beta-elimination reaction and hydrogenolysis reaction are likely involved in the reduction of TCE by both Fe-0 and Sn-0.