[Reductive dechlorination of chlorinated hydrocarbons in water by Ag/Fe catalytic reduction system].

Dechlorination of many kinds of chlorinated hydrocarbons including trichloromethane (CF), tetrachloromethane (CT), 1, 1,1-trichloroethane (1, 1, 1-TCA), 1, 1, 2, 2-tetrachloroethane (1, 1, 2, 2-TeCA), hexachloroethane (HCA), trichloroethylene (TCE), perchloroethylene (PCE) in water by Fe and Ag/Fe were investigated. Results show that the existence of Ag on Fe can enhance the dechlorination rate of chlorinated hydrocarbons. When the surface area concentration of iron is 150 m2 x L(-1), the dechlorination rate constant of CF, CT, 1, 1, 1-TCA, 1, 1, 2, 2-TeCA, HCA are 0.084 h(-1), 2.358 h(-1), 0.417 h(-1), 0.215 h(-1), 1.098 h(-1) by single Fe0, in this condition, no dechlorination of TCE and PCE during 10h, while the dechlorination rate constant of CF, CT, 1, 1, 1-TCA, 1, 1, 2, 2-TeCA, HCA, TCE, PCE are up to 1.850 h(-1), 9.504 h(-1), 1.624 h(-1), 1.778 h(-1), 2.842 h(-1), 0.463 h(-1), 1.251 h(-1) by Ag/Fe. The dechlorination rate constant of CF can increase by the factor of 20. The reaction pathways of chlorinated hydrocarbons with Fe and Ag/Fe were mainly including hydrogenolysis, reductive elimination and dehydrochlorination. The hydrogenolysis is the main reaction pathway for CF, TCE and PCE. The dechlorination pathway of 1, 1, 1-TCA are both hydrogenolysis and dehydrochlorination. Reductive beta elimination to form DCE is the dominant reaction pathway of 1, 1, 2, 2-TeCA, and HCA is via reductive beta elimination to form PCE firstly, then via hydrogenolysis to DCE.