Deli Wu

Dechlorination of Hexachloroethane in Water Using Iron Shavings and Amended Iron Shavings: Kinetics and Pathways

In contrast to previous studies which employed zero-valent iron powder, this paper investigated reductive dechlorination of hexachloroethane (HCA) using iron shavings and bimetallic iron shavings modified with Cu, Ag, or Pd. Results clearly show that iron shavings offer superior reductive dechlorination of HCA. In addition, surface-normalized pseudo first-order dechlorination rates of 0.0073 L·m−2·h−1, 0.0136 L·m−2·h−1, 0.0189 L·m−2·h−1, and 0.0084 L·m−2·h−1 were observed in the presence of iron shavings (Fe0) and the bimetallic iron shavings Cu/Fe, Ag/Fe, and Pd/Fe, respectively. Bimetallic iron shavings consisting of Cu/Fe and Ag/Fe could greatly enhance the reductive reaction rate; Pd/Fe was used to achieve complete dechlorination of HCA within 5 hours. The additives of Ag and Pd shifted product distributions, and the reductive dechlorination of HCA occurred via β reductive elimination and sequential hydrogenolysis in the presence of all iron shavings. This study consequently designed a reaction pathway diagram which reflected the reaction pathway and most prevalent dechlorination products. Iron shavings are a common byproduct of mechanical processing plants. While the purity of such Fe metals may be low, these shavings are readily available at low costs and could potentially be used in engineering applications such as contamination control technologies.

Reductive Dechlorination of Chlorinated Hydrocarbons in Water by Cu/Fe Bimetallic Reductant

The influence of Cu on the dechlorination rate of various chlorinated hydrocarbons including CF, CT, 1,1,2,2-TeCA, 1,1,2,2-TeCA and HCA by Fe0 and Cu/Fe was investigated in batch experiments. All organohalides can be dechlorinated rapidly by Fe or Cu/Fe in aqueous system and the contaminants were degraded via sequential reductive dechlorination to form less chlorinated homologues. The removal of CF, CT, 1,1,1-TCA, 1,1,2,2-TeCA and HCA followed pseudo-first-order kinetics both in Fe0 system and Cu/Fe system. Cu/Fe reductant could enhance the dechlorination rate of all chlorinated hydrocarbons.The degradation rate constant of a general dechlorination was increased by a factor of 3 in Cu/Fe system than that in Fe0 system. The intermediate products of dechlorination and the major pathway were summarized in this study. Hydrogenolysis and reductive elimination was the dominant reaction for various chlorinated hydrocarbons dechlorination by Cu/Fe with respect to the products.