Effect of surfactants on the removal of nitrobenzene by Fe-bearing montmorillonite/Fe(II).

Nonionic and anionic surfactants often occur in anaerobic environments, but their roles in the removal of organic contaminants by Fe-bearing mineral/Fe(II) have not been determined. In this study, batch experiments were performed to investigate the effects of a nonionic surfactant (TX-100) and an anionic surfactant (SDBS) on the removal of nitrobenzene (NB) by Fe-bearing montmorillonite (FM)/Fe(II). Mössbauer spectrum and XPS were applied to analyze the edge surface bound Fe(II) and secondary minerals formed on FM. The contribution of surfactant to the enrichment of NB on FM was studied. The results showed that TX-100 and SDBS had opposite effects on the removal of NB by FM/Fe(II) at neutral pH. The presence of TX-100 improved the removal efficiency of NB from 36.4% to 70.0%, and increased the initial removal rate by 1.7 times. This enhancement effect was mainly attributed to the formation of more active edge surface bound Fe(II) that can reduce more NB to aniline. Formation of more magnetite on FM and selective enrichment of NB on the reactive surface also contributed to the removal of NB. In contrast, the presence of SDBS reduced the amount of edge surface bound Fe(II) via formation of SDBS-Fe(II) complex, which decreased the removal efficiency of NB.