Coupled reduction of chlorinated hydrocarbons and heavy metals by zerovalent silicon
Doong, R.A.; Lee, C.C.; Chen, K.T.; Wu, S.F.
Water Science and Technology a Journal of the International Association on Water Pollution Research 50(8): 89-96
2004
ISSN/ISBN: 0273-1223 PMID: 15566191 Document Number: 571531
The feasibility of using zerovalent silicon (Si (super 0) ) as a novel reductant to remove chlorinated compounds and heavy metals in contaminated sites was investigated. The kinetics and degradation mechanism of carbon tetrachloride (CT) by Si (super 0) were also examined. Results showed that zerovalent silicon could effectively dechlorinate the chlorinated compounds. A nearly complete dechlorination of CT by Si (super 0) was obtained within 14 h. The produced concentrations of chloroform (CF) accounted for 71-88% loss of CT, showing that reductive dechlorination is the major degradation pathway for the degradation of chlorinated hydrocarbons by Si (super 0) . The degradation followed pseudo first-order kinetics and the normalized surface reaction rate constant (k (sub sa) ) for CT dechlorination ranged between 0.0342 and 0.0454 L m (super -2) h (super -1) when CT concentrations were in the range of 3-20 mu M. A linear relationship between the k (sub sa) and pH value was also established. In addition, zerovalent silicon has a high capability in the removal of heavy metals. 83% of Cr(VI) was removed by 0.5g Si (super 0) within 5 h, which is higher than that by Fe (super 0) . The removal efficiency of divalent metal ions by Si (super 0) followed the order of Cu(II)>Pb(II)>Ni(II). This indicates that zerovalent silicon is an alternative reductant and can undergo coupled reduction of heavy metals and chlorinated hydrocarbons in contaminated groundwater.