Stabilization Effects of Mn(II)-Salts on Metaschoepite in Soil under Different Water Regimes

Metaschoepite (UO3 center dot 2H(2)O) is a product of the corrosion of depleted uranium munition and is commonly found in former war zones and at military test sites. Understanding metaschoepite transformation and uranium (U) mobility is important for the sustainable operation of U-containing test-firing and nuclear waste disposal sites. In the present study, the stabilization effects of Mn(II)-salts on metaschoepite in soil under different water regimes (saturation and flooding) were investigated. Results indicated that the dissolution and transformation of metaschoepite were controlled by water regimes and redox processes in the soil system. The concentrations of water-extractable U in the metaschoepite-amended soils after 270 days of incubation for the saturation and flooding groups were 299 and 173 mg kg(-1), respectively. The addition of Mn(II)-salts significantly retarded the release of U(VI) in the metaschoepite-amended soils. The U stabilization efficiency of Mn(II) was persistently > 90% during the 270 days of incubation, irrespective of water regimes. The X-ray photoelectron spectroscopy results showed no detectable reduction of liberated U(VI) in the "open waterlogged" soil system, while the X-ray diffraction analyses confirmed the transformation of metaschoepite with signals of schoepites disappearing over the course of the experiment. The study highlights the potential for the use of Mn(II)-salts in practical applications for in situ stabilization of U-contaminated sites and nuclear waste disposal.