Abstract
Abstract The dechlorination of carbon tetrachloride (CT) and tetrachloroethylene (PCE) using silicon as an electron donor was investigated. It was to evaluate the feasibility of using silicon as a novel material to remedy sites contaminated by chlorinated hydrocarbons. CT and PCE can be completely degraded via sequential reductive dechlorination to less chlorinated homologs by Si0. The productions of CF and TCE accounted for 85 % of CT and 63 % of PCE dechlorination, respectively. Increasing pH and Si amount also increased the dechlorination efficiency of CT. The degradation of CT and PCE by Si0 followed a pseudo first order kinetics and the rate constants were 0.17 L h-1 m-2 and 0.0015 L h-1 m-2, respectively. The combination of Si and Fe can also enhance the dechlorination rate of CT and PCE. Reductive dechlorination was the main reaction mechanism for CT dechlorination, while b-elimination and reductive dechlorination are the predominant reaction pathways for PCE dechlorination in the Si0/Fe0-H2O system. Reductive dechlorination was dominant at the on-set of the reaction and high pH and b-elimination was the main reaction pathway for PCE dechlorination as pH decreased. Fe0 plays an important role in the reduction of chlorinated hydrocarbons in the Si0/Fe0-H2O system and Si0 would act as pH buffer to maintain the pH in the range of 7.3 – 8.1. This corresponds to a change of 0.8 pH unit as the Fe0 dose increased by 2 orders of magnitude. Addition of catalyst or nickel ion can also enhance the dechlorination of PCE. Results clearly indicated the transformation of chlorinated compounds by silicon is practicable. Reductive dechlorination is the major degradation pathway, while the distribution of products will change to nontoxic alkane when Si0 was applied simultaneously with Fe0.