Investigating the Release of Co-precipitated Uranium from Iron Oxides

The removal of uranium (VI) in zerovalent iron permeable reactive barriers and wetlands can be explained by its association with iron oxides. The long term stability of this immobilized U is yet to be addressed. The presented study investigates the remobilization of U(VI) from iron oxides via diverse reaction pathways (acidification, reduction, complex formation) in the laboratory. Prior uranium co-precipitation experiments were conducted under various conditions. The addition of various amounts of a pH-shifting agent (pyrite), an iron complexing agent (EDTA) or an iron (III) reduction agent (TiCl3) yielded in uranium remobilisation to concentrations above the US EPA maximum allowed contaminant level (MCL = 30 mg/L). This study demonstrates that U(VI) release in nature will strongly depend on the conditions and the mechanism of its fixation by geological materials.