Fate of tetravalent uranium under reducing conditions
Final Report Abstract
In this project, successful team work between the three groups Hannover, Lausanne and Vienna was conducted and significant knowledge transfer was gained, e.g. during several visits between members of the working groups or in an organized conference on U biogeochemistry in Ascona. The main focus of this project was the investigation of non-crystalline U(IV), which was discovered relatively recently in nature and is apparently easier to re-oxidize or mobilize than e.g. crystalline uraninite. The investigation of U isotope fractionation during mobilisation of non-crystalline U(IV) was the main focus of the DFG founded group in Hannover. Uranium isotopes are suggested to monitor the success of (bio)remediation relying on the reduction of soluble and mobile U(VI) to less soluble U(IV). However, the subsurface stability of U(IV), typically present as solid-phase non-crystalline U, may be affected by complexation or oxidation. Understanding these processes and their impact on U isotope fractionation is important to correctly interpret field U isotope signatures. The focus of the Hannover group in particular, was the investigation of the mobilization by complexation and oxidation and the associated U isotope fractionation was conducted in laboratory batch experiments. Non-crystalline U(IV) was produced as the starting material by reducing a U(VI) isotope standard with Shewanella oneidensis MR-1. Subsequently, U(IV) was mobilized anoxically, with ligands (EDTA, citrate, or bicarbonate) or with molecular oxygen at low pH in the presence of the bacterium Acidithiobacillus ferrooxidans. All ligands mobilized U(IV) and enriched 238U in the complexed fraction (δ238U: 0.2 to 0.6 ‰). Oxidative U mobilization both, with Fe(III) or with At. ferrooxidans biomass, resulted in insignificant U isotope fractionation. Either isotope fractionation during all involved reaction steps was very small or cancelled each other out. The latter may be indicated by the observation of high aqueous δ238U values (~0.8 ‰) in corresponding abiotic control experiments (without biomass), which may be the result of adsorption effects after oxidative U mobilization. During the project time, it was shown that U isotope fractionation is a powerful tool to distinguish between U reduction, U complexation or (a)biotic U oxidation, and it helps to further characterize and enhance remediation efforts. Important investigations and findings of the other groups which were involved in the project are the effect of aging on the stability of microbially reduced uranium in natural sediment, the role and isotopic signature of U(V) in magnetite generated during U reduction and the discovery of non-crystalline U(IV) as the major component in an undisturbed U roll-front ore deposit in Wyoming, USA.
Publications
- (2017) Biogenic non-crystalline U(IV) revealed as major component in uranium ore. Nature Communications
Bhattacharyya, A., Campbell, K-M., Kelly, S., Roebbert, Y., Weyer, S., Bernier- Latmani, Rizlan and Borch, T.
(See online at https://doi.org/10.1038/ncomms15538) - (2019). Effect of aging on the stability of microbially reduced uranium in natural sediment. Environmental science & technology, 54(1), 613-620
Loreggian, L., Novotny, A., Bretagne, S. L., Bartova, B., Wang, Y., & Bernier-Latmani, R.
(See online at https://doi.org/10.1021/acs.est.8b07023) - Uranium isotope fractionation during mobilization of non-crystalline U(IV) by complexation with organic ligands. ES&T
Roebbert, Yvonne; Rosendahl, Chris Daniel; Brown, Ashley; Schippers, Axel; Bernier- Latmani, Rizlan; Weyer, Stefan
(See online at https://doi.org/10.1021/acs.est.0c08623) - (2022). Ligand-Induced U Mobilization from Chemogenic Uraninite and Biogenic Noncrystalline U (IV) under Anoxic Conditions. Environmental Science & Technology 56, 6369-6379
Chardi, K. J., Satpathy, A., Schenkeveld, W. D., Kumar, N., Noël, V., Kraemer, S. M., & Giammar, D. E.
(See online at https://doi.org/10.1021/acs.est.1c07919) - (2022). Persistence of the Isotopic Signature of Pentavalent Uranium in Magnetite. Environmental science & technology, 56(3), 1753-1762
Pan, Z., Roebbert, Y., Beck, A., Bartova, B., Vitova, T., Weyer, S., & Bernier-Latmani, R.
(See online at https://doi.org/10.1021/acs.est.1c06865)
