Kinetics of Trichloroethene Reduction by Zerovalent Iron and Tin:  Pretreatment Effect, Apparent Activation Energy, and Intermediate Products

Abstract

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 .

Understanding Trichloroethylene Chemisorption to Iron Surfaces Using Density Functional Theory

“…The activation energy between physically adsorbed TCE and the transition state is 49 kJ/mol. This value is close to range of 32 to 39 kJ/mol that has been experimentally observed for TCE reduction by iron filings (35). The transition state is an early one in that it more closely resembles the initial structure than the final structure.…”

The effect of silica on the degradation of organohalides in granular iron columns

“…Different types of iron exhibit different reactivities toward TCE (Su and Puls, 1999). Connelly iron was selected for the present study because this material is currently used for the majority of iron-based PRBs within the US (Connelly-GPN, 2004).…”

Integrating Fluidized Copper/Iron Bimetal Nanoparticles and Microwave Irradiation for Treating Chlorobenzene in Aqueous Solution

“…The activation energies for diffusion-controlled reactions in solution are generally between 10-20 kJ/mol (Liou et al, 2005). Rates of CB degradation with Cu/Fe, Fe 0 and Cu 0 particles at various temperatures are well fitted with linear plot of the Arrhenius equation expressed as (Su & Puls, 1999):…”

“…A metal with lower hydrogen over-voltage (Fe 0 ) will be more easily oxidized than the metal with higher hydrogen over-voltage (Cu 0 ) that stays mostly in element form. The metal oxidation releases hydrogen in atomic form, which favors the reduction of organic matter (Su & Puls, 1999 For heterogeneous reactions, the effect of temperature on reaction rates reveals whether the rate-limiting step is to due chemical reactions at the surface, or the diffusion of the reactant in question (Lien & Zhang, 2001) because a slower reaction step requires more activation energy (Ea). Lower Ea values are usually associated with the rate-limiting step that is a reactant diffusion, or diffusion-controlled process.…”

“…Lower Ea values are usually associated with the rate-limiting step that is a reactant diffusion, or diffusion-controlled process. Higher Ea values show that the process is chemical-controlled (Su and Puls, 1999). The activation energies for diffusion-controlled reactions in solution are generally between 10-20 kJ/mol (Liou et al, 2005).…”