Effect of Inorganic Anions on Reduction of Nitrobenzene in Water by Structural Ferrous Iron

Abstract

Nitrobenzene is an important contaminant existed in water and wastewater widely. Because of its toxicity to organisms, it is hardly biodegradable. A new structural Fe(II): Ferrous Hydroxy Complex (FHC) was prepared with ferrous sulfate to investigate the reduction of nitrobenzene by structural ferrous iron. This study focused on the effects of inorganic anions on the reactivity of FHC towards nitrobenzene. It was found that soluble Fe(II) could hardly reduce any nitrobenzene within 2h while FHC could reduce nitrobenzene to aniline rapidly within 0.5h. Various anions such as CO32-, PO43-, SiO32-, S2- might have significant impact on the reactivity of structural Fe(II) in nitrobenzene reduction. These anions would slow down the rate of the reaction. Among these anions, SiO32- and PO43- had a greater effect on the reduction of nitrobenzene than CO32- and S2-. Structural ferrous iron (SFI) was prepared by two ways: (i) Aqueous Fe2+ was directly added to wastewater, then adjusted the pH value of water to 8-9; (ii) FHC prepared in advance was added to wastewater, SFI(II). Results indicated that the effect of anions on reactivity of SFI(I) was greater than that of SFI(II). When the initial concentration of nitrobenzene was 60mg/L and ferrous iron dosage was 240mg/L, NO3- with the concentration of 4mM had little effect on the reduction of nitrobenzene by both forms of Fe(II); NO2- had greater effect on reactivity of SFI(I) than that of SFI(II).