Sustaining reactivity of Fe-0 for nitrate reduction via electron transfer between dissolved Fe2+ and surface iron oxides

摘要

The mechanism of the effects of Fe-aq(2+) on the reduction of NO3- by Fe-0 was investigated. The effects of initial pH on the rate of NO3- reduction and the Fe-0 surface characteristics revealed Fe-aq(2+) and the characteristics of minerals on the surface of Fe-0 played an important role in NO3- reduction. Both NO3- reduction and the decrease of Fe-aq(2+) exhibited similar kinetics and were promoted by each other. This promotion was associated with the types of the surface iron oxides of Fe-0. Additionally, further reduction of NO3- produced more surface iron oxides, supplying more active sites for Fe-aq(2+), resulting in more electron transfer between Fe2+ and surface iron oxides and a higher reaction rate. Using the isotope specificity of Fe-57 Mossbauer spectroscopy, it was verified that the Fe-aq(2+) was continuously converted into Fe3+ oxides on the surface of Fe-0 and then converted into Fe3O4 via electron transfer between Fe2+ and the pre-existing surface Fe3+ oxides. Electrochemistry measurements confirmed that the spontaneous electron transfer between the Fe2+ and structural Fe3+ species accelerated the interfacial electron transfer between the Fe species and NO3-. This study provides a new insight into the interaction between Fe species and contaminants and interface electron transfer. (C) 2016 Elsevier B.V. All rights reserved.