Effect Of Anaerobic Corrosion Of Nanoscale Zero-valent Iron On Reductive Dechlorination Of Trichloroethylene

Nanoscale zero-valent iron?NZVI?is easy to be corroded by water in practical application due to its high reactivity,thus reducing its reactive lifetime.Meanwhile,the complex groundwater chemical factors affect the corrosion mechanism of NZVI in different ways,thus affecting the removal mechanism and efficiency of contaminants.The end products of trichloroethylene?TCE?reduction by NZVI have been widely studied,but the research on toxic chlorinated byproducts?DCEs and VC?is very limited,especially the effect of anaerobic corrosion of NZVI on the reductive dechlorination of TCE and DCEs has not been reported so far.In this study,the effect of NZVI corrosion on the fate and distribution of chlorine in the process of reductive dechlorination of TCE under different anaerobic conditions was studied by batch experiments.The main conclusions are as follows:?1?Under the condition of anaerobic ultrapure water,four kinds of NZVI with different crystallinity and surface element composition have different corrosion mechanisms,which lead to significant differences in the reductive dechlorination process of TCE.The corrosion of NANOFER and NIP with high crystallinity was significantly slower than that of sNZVI and CNZVI with weakly crystalline.The Fe⁰consumption within 8 days was as follows:NANOFER<NIP<sNZVI<CNZVI.The partial dissolution of the shell on the surface of NANOFER and sNZVI with high activity allows electrons to directly contact with TCE and DCEs,and B on the surface of sNZVI has catalytic effect;however,the increase of the shell thickness of NIP limits the electron transfer,and the depletion of Fe⁰ in CNZVI system makes electrons not be utilized effectively.Therefore,the reductive dechlorination rate of TCE and DCEs:NANOFER>sNZVI>NIP>CNZVI.Except for NANOFER,the other three NZVI corrosion adsorbed highly toxic VC.?2?The difference of NANOFER corrosion mechanism caused by different groundwater solutes is the main reason for the difference in the species distribution of chlorine during the reduction of TCE and DCEs.The corrosion rate of NANOFER:Ca²⁺-HCO₃^-(3.8 wt%?d^-1)>Na⁺-NO₃^-(1.7 wt%?d^-1)>Ca²⁺-SO₄^2-(1.0 wt%?d^-1).The degradation of TCE,DCEs and sorbed chlorine:Ca²⁺-HCO₃^->Ca²⁺-SO₄^2->Na⁺-NO₃^-.The reasons are that the dissolution effect of Ca²⁺-HCO₃^-causes the shell to break,and electrons directly contact with TCE and DCEs;the pitting of Ca²⁺-SO₄^2-is conducive to the direct transfer of electrons to some extent;while NO₃^-not only competes for electrons but also passivates the surface of NANOFER,thus inhibiting the electron transfer,and the formation of passivation layer promotes the adsorption of chlorine.?3?At the same pH and ionic strength,with the increase of the initial concentration of NO₃^--N,due to the increase in the ability of electronic competition and the thickness of the passivation layer,the reductive dechlorination of TCE and DCEs was inhibited.The increase of the thickness of Fe₃O₄/?-Fe₂O₃ shell promoted the adsorption of chlorine.When NO₃^--N?20 mg/L,the reduction rate of NO₃^--N increases significantly;on the contrary,the degradation rate of TCE decreases significantly.