Effects of non-reducible dissolved solutes on reductive dechlorination of trichloroethylene by ball milled zero valent irons.

Non-reducible solution anions have been well recognized to affect reactivity of ZVI in dechlorinating chlorinated hydrocarbons. However, their effects and corresponding functional mechanisms on electron efficiency (ε) of ZVI remain unclear. In this study, mechanochemically modified microscale sulfidated and unsulfidated ZVI particles (i.e., S-mZVI and mZVI) and trichloroethylene (TCE) were used as model particles and contaminant to explore such effects. PO as a corrosion promoter enhanced initial dechlorination rate by both particles. However, its passivating role as a surface complex agent became significant at the later stage of dechlorination by mZVI, while sulfidation alleviated this effect without inhibition of dechlorination. Compared with enhancing dechlorination, PO promoted hydrogen evolution reaction (HER) to a higher extent, decreasing ε for both particles by 17-73 %. HCO- negligibly affected dechlorination by both particles, while elevated HER. Thus, HCO- [5 mM] decreased ε for S-mZVI and mZVI by 1.9 % and 22 %. Different from PO and HCO-, Cl- and SO showed no significant effects on dechlorination, HER, and therefore ε for both particles. These results imply that even though some co-existing anions (i.e., PO and HCO-) acting as corrosion promoters could improve the dechlorination by ZVIs, they would lead to decreased ε and shortened particle reactive lifetime.