Search

• NO 3 − inhibited TCE dechlorination by S-mZVIbm due to electron competition. • NO 3 − induced initial electron competition hardly affected dechlorination by mZVIbm. • NO 3 − facilitated formation of Fe 3 O 4 promoted dechlorination by mZVIbm after 4 d. • NO 3 − was inefficiently reduced by S-mZVIbm as S weakened its interaction with NO 3 −. Mechanistic role of NO 3 − in trichloroethylene (TCE) dechlorination by ball milled, micro-scale sulfidated and unsulfidated ZVI (e.g., S-mZVIbm and mZVIbm) was explored through experiments and density functional theory (DFT) calculations. Sulfidation inhibited NO 3 − reduction by mZVIbm as S weakened its interaction with NO 3 −. mZVIbm reduced NO 3 − within 2 h. This just resulted in a short-term electron competition during the dechlorination process by mZVIbm and hardly affected its sluggish dechlorination kinetics (complete TCE dechlorination in 11 d). On the contrary, NO 3 − suppressed TCE dechlorination by S-mZVIbm. This was attributed to that inhibited NO 3 − reduction by S-mZVIbm (40 % reduction in 6 h) induced continuous electron competition with TCE during the time span of its dechlorination by S-mZVIbm. NO 3 − reduction was also observed to facilitate formation/crystallization of Fe 3 O 4 on both ZVI particles, promoting dechlorination by mZVIbm after 4 d while not taking effect to the S-mZVIbm/TCE system, as its dechlorination time was too short for the surface of S-mZVIbm to transform. This observation has important implication on groundwater remediation by ZVI or sulfidated ZVI PRBs under a scenario of upgradient anthropogenic release of NO 3 −. [ABSTRACT FROM AUTHOR]