Diversity in the species and fate of chlorine during TCE reduction by two nZVI with non-identical anaerobic corrosion mechanism

Abstract There have been many studies on TCE degradation by synthesized nanoscale zero-valent iron (nZVI B ) and commercial nanoscale zero-valent iron (nZVI H ), but the effect of anaerobic corrosion on the dechlorination pathways and speciation distribution of chlorine is still unclear. Compared with nZVI H , nZVI B has a faster degradation rate of TCE and formation rate of Cl − (aq) ( k SA, TCE  = 3.67 ± 0.85 × 10 −4 & 2.17 ± 0.13 × 10 −4  L·h −1 ·m −2 and k obs, Cl −  = 0.344 ± 0.027 & 0.166 ± 0.010 μM·h −1 for nZVI B & nZVI H , respectively). Based on the characterization of XRD, XPS and TEM during the anaerobic corrosion, the corrosion of nZVI B was dramatic under the dissolution-reprecipitation mechanism; but that of nZVI H was moderate and inward by maintaining the core-shell structure and shaping slightly rough and lumpy surface. Due to the different corrosion products (FeOOH for nZVI B and Fe 3 O 4 /γ-Fe 2 O 3 for nZVI H ) and the catalysis of boron on the nZVI B surface, the preferential dechlorination pathway of TCE was not identical by hydrogenolysis (nZVI B ) vs. reductive β-elimination (nZVI H ). Meanwhile, the dechlorination pathway of nZVI H was similar to that of ZVI and the reductive pathway to acetylene bypassed the formation of more toxic VC. This study shows that the high reactivity of nZVI B results in rapid corrosion with the side effect of enhanced adsorption of VC while nZVI H has a stable core-shell structure and less sorbed chlorine, which provides a new sight to access the ecological risk of nZVI due to the overlooked effect of non-identical corrosion.