Reductive dechlorination of chlorinated ethenes by ball milled and mechanochemically sulfidated microscale zero valent iron: A comparative study

Ball milling is an effective technique to not only activate and reduce the size of commercial microscale zero valent iron (mZVI) but also to mechanochemically sulfidate mZVI. Yet, little is known about the difference between how chlorinated ethenes (CEs) interact with ball milled mZVI (mZVIbm) and mechanochemically sulfidated mZVI (S-mZVIbm). We show that simple ball milling exposed the active Fe0 sites, while mechanochemical sulfidation diminished Fe0 sites and meanwhile increased S2- sites. Mechanochemical sulfidation with [S/Fe]dosed increased from 0 to 0.20 promoted the particle reactivity most for TCE dechlorination (∼14-fold), followed by PCE and 1,1-DCE while it diminished the reactivity for trans-DCE (∼0.4-fold), cis-DCE (∼0.02-fold) and VC (∼0.002-fold) compared to simple ball milling. Sulfidation also improved the electron efficiency of CE dechlorination, except for cis-DCE and VC. The kSA of cis-DCE, VC and trans-DCE dechlorination positively correlated with surface Fe0 content, suggesting their dechlorination was mainly mediated by Fe0 site or reactive atomic hydrogen. The kSA of TCE dechlorination positively correlated with surface S2- content and the dechlorination mainly occurred on S2- sites via direct electron transfer. Increased sulfidation favored direct electron transfer mechanism. The kSA of PCE and 1,1-DCE was not dependent on either parameter and their dechlorination was equally achieved through either mechanism.