Removal of hexavalent uranium [U(VI)] by magnetite in the presence of metal-reducing bacteria from rice soil

Abstract

Magnetite is often associated with U(VI) in uranium (U) contaminated soils. In -situ reduction of U(VI) with magnetite has been demonstrated as a cost-effective method to remedy U pollution in the subsurface. While, the results indicate that surface passivation of magnetite may significantly affect the removal efficiency of U(VI). Hence, a mixed culture of metal-reducing bacteria, which consisted of different species in the genera of Bacillus , Clostridium XIV , Ochrobactrum , and Clostridium XI enriched from the rice soil, was employed to remove the passive film on the surface of magnetite. The results from the column experiments showed that the U(VI) removal efficiency increased from 41.8% to 93.4% after 150 days running in the presence of metal-reducing bacteria. Meanwhile, XRD and XPS analysis demonstrated that Fe(III) oxides were formed on the magnetite surface during the experiments. Furthermore, the selective bacteria also exhibited beneficiary ability in promoting the formation of UO 2 associated with Fe–U mineral, FeUO 4 in the reduction process. Nevertheless, it is noteworthy that among the four genera related to the Fe(III) and U(VI) reduction, only the genus of Ochrobactrum survived under the unsterilized condition with U(VI) and magnetite after 150 days. The existence of Ochrobactrum shows a vital contribution to the removal of U(VI), yet the underlying mechanism needs to be explored by further experiments. Along with this study, we expected that the screened metal-reducing bacteria enriched from rice soil, especially the genus of Ochrobactrum , may have potential in-situ applications in U(VI) contaminated sites. • Passive film on the magnetite can be removed with metal-reducing bacteria. • U(VI) removal efficiency of magnetite increased with metal-reducing bacteria • Ochrobactrum shows a vital contribution to the removal of U(VI) with magnetite. • Ochrobactrum promote the formation of UO 2 and FeUO 4 in the removal process.