Anti-passivation ability of sulfidated microscale zero valent iron and its application for 1,1,2,2-tetrachloroethane degradation

The performance of sulfidated zero valent iron (ZVI) for the degradation of chlorinated hydrocarbons under aerobic conditions remains unclear. In this study, sulfidated microscale ZVI (S-mZVI) was prepared for 1,1,2,2-tetrachloroethane (TeCA) degradation under aerobic conditions. Compared with mZVI, S-mZVI showed excellent passivation resistance during the degradation of TeCA and its hydrolysis/reduction products. This was probably because the existence of FeSx shell (FeS/FeS2/FeSn) protected the internal ZVI core from passivation. Though the outer layer of FeSx shell could be oxidized to FeSn and Fe2(SO4)3 as the reaction proceeded, the inner layer remained stable, which maintained the fast electron transfer capability of S-mZVI. The high temperature could enhance the degradation of TeCA, without compromising the anti-passivation and reusability of S-mZVI. Even after the fifth cycle, S-mZVI could still efficiently degrade 90% of TeCA within 24 h. Furthermore, it was found that the degradation of TeCA and its reduction products (e.g., dichloroethylene (DCE)) by S-mZVI relied on direct electron transfer and hydrogen radical (H•), respectively, which might explain the lower levels of toxic DCE in the S-mZVI system. This study provides valuable information for the practical application of S-mZVI in the treatment of wastewater containing halogenated hydrocarbons under ambient conditions.