Vanadium mobilization and redistribution during mineral transformation of vanadium-titanium magnetite tailings with different weathering degrees.

Due to the long-term open stockpile, the release of vanadium (V) from V-containing tailings will cause continuous V pollution in the mining area. Previous studies on the concentration and speciation of V primarily focused on surface tailings at a regional scale. However, the mobilization and redistribution of V within the tailing profile during the mineral transformation of tailings remain unclear. Herein, a series of concentrations of V(V) (0-200 mg L-1) solutions were added to the vanadium­titanium magnetite tailings at different depths separately to simulate the redistribution of dissolved V released from tailings in the solid phase of tailings. During the 56-day incubation, the concentrations of aqueous V in the surface tailings were significantly lower than those in the deep tailings under the same level of V(V) treatment, indicating that the shallow tailings had a stronger immobilization capacity for V than the deep tailings. Morphological analysis and color overlays of the elements demonstrated that most of V was immobilized into the tailings and adsorbed or precipitated by the Fe (hydr)oxides in the tailings in 200 mg L-1 V(V) treatment. This portion of V mainly occurred in acid-soluble and reducible fractions in the tailings after a 7-day incubation, accounting for >71.7 % of the total V. However, these two factions of V with high bioavailability were gradually mineralized over time and transferred to residual V, which is difficult to move and has low bioavailability. Mineral phase analysis revealed that additional V(V) favored the formation of melanovanadite (Ca2V8O20·10H2O) and chromium vanadium oxide (Cr2V4O13) in the tailings. This study reveals that the dissolved V influenced the fractionation and redistribution of solid-phase V during tailing weathering, improving the understanding of the geochemical processes of V in tailing profiles and providing important guidance for the management of V-containing tailings.

Shewanella oneidensis MR-1 and oxalic acid mediated vanadium reduction and redistribution in vanadium-containing tailings.

The microbially- and chemically-mediated redox process is critical in controlling the fate of vanadium (V) in tailing environment. Although the microbial reduction of V has been widely studied, the coupled biotic reduction mediated by beneficiation reagents and the underlying mechanism remain unclear. Herein, the reduction and redistribution of V in V-containing tailings and Fe/Mn oxide aggregates mediated by Shewanella oneidensis MR-1 and oxalic acid were explored. The dissolution of Fe-(hydr)oxides by oxalic acid promoted the microbe-mediated V release from solid-phase. After 48-day of reaction, the dissolved V concentrations in the bio-oxalic acid treatment reached maximum values of 1.72 ± 0.36 mg L-1 and 0.42 ± 0.15 mg L-1 in the tailing system and the aggregate system, respectively, significantly higher than those in control (0.63 ± 0.14 mg L-1 and 0.08 ± 0.02 mg L-1). As the electron donor, oxalic acid enhanced the electron transfer process of S. oneidensis MR-1 for V(V) reduction. The mineralogical characterization of final products indicates that S. oneidensis MR-1 and oxalic acid promoted solid-state conversion from V2O5 to NaV6O15. Collectively, this study demonstrates that microbe-mediated V release and redistribution in solid-phase were promoted by oxalic acid, suggesting that the role of organic agents for the V biogeochemical cycle in natural systems deserves greater attention.

Impact of soil moisture on cesium uptake by plants: Model assessment.

Computational models of radioisotopes soil-to-plant transfer are an essential component of decision support systems for nuclear emergency and assessment impact of nuclear accidents on human beings and the environment. The soil water regime impact on cations behavior in the «soil-plant ¼ system. Therefore, relationships between radioisotopes accumulation by plants and soil moisture should be included in the computational models. A kinetic model for simulation of Cs+ root uptake under alteration of soil moisture content in soil is presented in this paper. The model simulates Cs+ and K+ diffusion from bulk soil into rhizosphere under alteration of water content. The model results show a drop of Cs+ and K+ concentration in the rhizosphere with decreasing soil moisture. The magnitude of enhanced root uptake of Cs+ with soil moisture alteration depends on the exchangeable potassium content and soil texture. The Cs+ root uptake rate has a maximum at 60%-80% of field capacity under sufficient and high exchange potassium content. A similar dependence should also be seen for the RCs soil-to-plant transfer factor. The results indicate the importance of soil water content for modification of the RCs accumulation by plants and the necessity to include this factor into an appropriate semi-mechanistic model.

Impact of effective microorganisms on the transfer of radioactive cesium into lettuce and barley biomass.

Soil microorganisms play an important role in determining the physical and chemical properties of soils. Soil microorganisms have both direct and indirect effects on the physical and chemical states of radionuclides and their availability for uptake by plant roots. Controlling the soil microorganisms to immobilize radionuclides is a promising strategy to reduce the content of radionuclides in the food chain. In this study, we evaluated the impact of effective microorganisms (EM) comprising lactic-acid bacteria, photosynthetic bacteria, and yeast on the transfer of 137Cs into the aboveground biomass of barley and lettuce. The application of EM or fermented organic fertilizer (bokashi) alone to sod-podzolic sandy-loam soil significantly reduced the aggregated transfer factor of 137Cs in barley by 37% and 44%, respectively. The combination of EM with bokashi or potassium fertilizer produced the largest reductions in 137Cs transfer into barley biomass (50% and 63%, respectively). EM had a stronger effect on 137Cs transfer into barley compared to lettuce. Laboratory experiments suggested that the effect of microorganisms on 137Cs uptake can be attributed to a reduction in the proportion of bioavailable physicochemical forms of 137Cs in the soils treated with EM and bokashi. This study, to the best of our knowledge, is the first to report the mechanism by which microbial fertilizers reduce the transfer of 137Cs into plants.

Main results of the 2012 joint Norwegian-Russian expedition to the dumping sites of the nuclear submarine K-27 and solid radioactive waste in Stepovogo Fjord, Novaya Zemlya.

This paper reports the main results of the 2012 joint Norwegian-Russian expedition to investigate the radioecological situation of the Stepovogo Fjord on the eastern coast of Novaya Zemlya, where the nuclear submarine K-27 and solid radioactive waste was dumped. Based on in situ gamma measurements and the analysis of seawater and sediment samples taken around the submarine, there was no indication of any leakage from the reactor units of K-27. With regard to the radioecological status of Stepovogo Fjord, activity concentrations of all radionuclides in seawater, sediment and biota in 2012 were in general lower than reported from the previous investigations in the 1990s. However in 2012, the activity concentrations of (137)Cs and, to a lesser extent, those of (90)Sr remained elevated in bottom water from the inner part of Stepovogo Fjord compared with surface water and the outer part of Stepovogo Fjord. Deviations from expected (238)Pu/(239,240)Pu activity ratios and (240)Pu/(239)Pu atom ratios in some sediment samples from the inner part of Stepovogo Fjord observed in this study and earlier studies may indicate the possibility of leakages from dumped waste from different nuclear sources. Although the current environmental levels of radionuclides in Stepovogo Fjord are not of immediate cause for concern, further monitoring of the situation is warranted.