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

Abstract

Metaschoepite (UO3·2H2O) 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.

Earthworm Enhanced Phytoremediation of U in Army Test Range Soil with Indian Mustard and Sunflower

“…Currently, soils contaminated by DU were usually treated and disposed as hazardous waste or removed to low level radioactive waste repository, while the costs of contaminated soil disposal are high and only suitable for small areas . A number of techniques have also been proposed to remediate DU-contaminated soils, such as chemical leaching, chemical immobilization, electrokinetic remediation, and bio/phytoremediation. , Phytoremediation, the use of plants to remove heavy metals from soil, appeared to be a promising technique for remediating U-contaminated soils due to its simplicity and cost-effectiveness with high public acceptance. , Sunflower was used to remediate Jordanian U-rich carbonate soils, and its resistance to U at the level of <318 mg kg –1 in these soils was found . Also, sunflower and Indian mustard were used to clean up soils contaminated with different U forms (UO 2 , UO 3 , and UO 2 (NO 3 ) 2 ), and both plants were proved to be candidate plants for the phytoremediation of U-contaminated soils …”

“…12 Currently, soils contaminated by DU were usually treated and disposed as hazardous waste or removed to low level radioactive waste repository, while the costs of contaminated soil disposal are high and only suitable for small areas. 13 A number of techniques have also been proposed to remediate DU-contaminated soils, such as chemical leaching, 13 chemical immobilization, 14 electrokinetic remediation, 15 and bio/ phytoremediation. 16,17 Phytoremediation, the use of plants to remove heavy metals from soil, 18 appeared to be a promising technique for remediating U-contaminated soils due to its simplicity and cost-effectiveness with high public acceptance.…”