Abstract
The dechlorination of carbon tetrachloride (CT) and tetrachloroethylene (PCE) by zerovalent silicon (Si0) as an electron donor was investigated to evaluate the feasibility of using silicon as a novel material to remedy the contaminated sites with chlorinated hydrocarbons. CT and PCE can be completely degraded via sequential reductive dechlorination to form less chlorinated homologs by Si0. The productions of chloroform (CF) and trichloroethene (TCE) accounted for 56-88 % and 63 % of CT and PCE dechlorination, respectively. The pseudo first-order rate constant(kobs) for CT dechlorination increased upon increasing CT concentration. Also, the increase in pH and Si0 amount enhanced the dechlorination efficiency and rate of CT. The normalized surface reaction rate constants (kSA) were in the range of 0.024-0.104 L h-1 m-2. The combination of Si0 and Fe0 also can enhance the dechlorination efficiency and rate of PCE. Zerovalent silicon dominates the dechlorination processes at the first stage, while Fe0 plays an important role in controlling the distribution of end products in Si0/Fe0-H2O system. From the results obtained in this study, it is clear that transformation of chlorinated compounds with silicon is practicable. Reductive dechlorination is the major degradation pathway, while the distribution of products will change to nontoxic alkane when Si0 was mixed with Fe0.