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 °C and HCl-treated Fe 0 and Sn 0 at 25 and 55 °C. Surface area normalized pseudo-first-order rate constants ( k SA ) ranged from 0.44 × 10 - 3 to 4.3 × 10 - 3 h - 1 m - 2 L for Fisher Fe 0, 0.029 × 10 - 3 to 0.27 × 10 - 3 h - 1 m - 2 L for Peerless and Master Builders Fe 0, and 0.011 × 10 - 3 to 1.31 × 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 × 10 - 3 to 0.011 × 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 β-elimination reaction and hydrogenolysis reaction are likely involved in the reduction of TCE by both Fe 0 and Sn 0 .