Biological Reduction of a U(V)–Organic Ligand Complex

Microbial reduction of soluble hexavalent uranium (U(VI)) to sparingly soluble tetravalent uranium (U(IV)) has been explored as an in situ strategy to immobilize U. Organic ligands might pose a potential hindrance to the success of such remediation efforts. In the current study, a set of structurally diverse organic ligands were shown to enhance the dissolution of crystalline uraninite (UO 2 ) for a wide range of ligand concentrations under anoxic conditions at pH 7.0. Comparisons were made to ligand-induced U mobilization from noncrystalline U(IV). For both U phases, aqueous U concentrations remained low in the absence of organic ligands (<25 nM for UO 2 ; 300 nM for noncrystalline U(IV)). The tested organic ligands (2,6-pyridinedicarboxylic acid (DPA), desferrioxamine B (DFOB), N , N ′-di(2-hydroxybenzyl)ethylene-diamine- N , N ′-diacetic acid (HBED), and citrate) enhanced U mobilization to varying extents. Over 45 days, the ligands mobilized only up to 0.3% of the 370 μM UO 2 , while a much larger extent of the 300 μM of biomass-bound noncrystalline U(IV) was mobilized (up to 57%) within only 2 days (>500 times more U mobilization). This work shows the potential of numerous organic ligands present in the environment to mobilize both recalcitrant and labile U forms under anoxic conditions to hazardous levels and, in doing so, undermine the stability of immobilized U(IV) sources.

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“…Several studies including noncrystalline U(IV) with organic ligands have previously used the method. 33 , 50 …”

Section: Methodsmentioning

confidence: 99%

Ligand-Induced U Mobilization from Chemogenic Uraninite and Biogenic Noncrystalline U(IV) under Anoxic Conditions

Chardi

Satpathy

Schenkeveld

et al. 2022

Environ. Sci. Technol.

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“…Thus, we expect that little to no active biomass will be present, especially given the removal of the electron donor. 61 After washing, the noncrystalline U(IV) product was resuspended in NaCl and MOPS. Previous work has shown that this product is stable in a simple buffered medium (e.g., PIPES−bicarbonate 38 ), indicating that these washing steps do not alter the U(IV) speciation.…”

Section: Methodsmentioning

confidence: 99%

Uranium Isotope Fractionation during the Anoxic Mobilization of Noncrystalline U(IV) by Ligand Complexation

Roebbert

Rosendahl

Brown

et al. 2021

Environ. Sci. Technol.

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Uranium (U) isotopes are suggested as a tool to trace U reduction. However, noncrystalline U(IV), formed predominantly in near-surface environments, may be complexed and remobilized using ligands under anoxic conditions. This may cause additional U isotope fractionation and alter the signatures generated by U reduction. Here, we investigate the efficacy of noncrystalline U(IV) mobilization by ligand complexation and the associated U isotope fractionation. Noncrystalline U(IV) was produced via the reduction of U(VI) (400 μM) by Shewanella oneidensis MR-1 and was subsequently mobilized with EDTA (1 mM), citrate (1 mM), or bicarbonate (500 mM) in batch experiments. Complexation with all investigated ligands resulted in significant mobilization of U(IV) and led to an enrichment of 238 U in the mobilized fraction (δ 238 U = 0.4−0.7 ‰ for EDTA; 0.3 ‰ for citrate; 0.2−0.3 ‰ for bicarbonate). For mobilization with bicarbonate, a Rayleigh approach was the most suitable isotope fractionation model, yielding a fractionation factor α of 1.00026− 1.00036. Mobilization with EDTA could be modeled with equilibrium isotope fractionation (α: 1.00039−1.00049). The results show that U isotope fractionation associated with U(IV) mobilization under anoxic conditions is significant and needs to be considered when applying U isotopes in remediation monitoring or as a paleo-redox proxy.

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“…Moreover, the proposed PEC method opens a new avenue toward the facile synthesis of U(V), an often “overlooked” U oxidation state. U(V) chemistry is important for elucidating the biogeochemical behaviors of U in the environment and understanding the properties of the f electrons of actinide ions ( Molinas et al., 2021 ; Chen et al., 2005 ). And a facile U(V) synthesis method is useful for assisting future studies on the U(V) chemistry.…”

Section: Discussionmentioning

confidence: 99%

Efficient and durable uranium extraction from uranium mine tailings seepage water via a photoelectrochemical method

Jin

Liang

et al. 2021

iScience

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Summary Current photocatalytic uranium (U) extraction methods have intrinsic obstacles, such as the recombination of charge carriers, and the deactivation of catalysts by extracted U. Here we show that, by applying a bias potential on the photocatalyst, the photoelectrochemical (PEC) method can address these limitations. We demonstrate that, owing to efficient spatial charge-carriers separation driven by the applied bias, the PEC method enables efficient and durable U extraction. The effects of multiple operation conditions are investigated. The U extraction proceeds via single-step one-electron reduction, resulting in the formation of pentavalent U, which can facilitate future studies on this often-overlooked U species. In real seepage water the PEC method achieves an extraction capacity of 0.67 gU m −3 ·h −1 without deactivation for 156 h continuous operation, which is 17 times faster than the photocatalytic method. This work provides an alternative tool for U resource recovery and facilitates future studies on U(V) chemistry.

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Biological Reduction of a U(V)–Organic Ligand Complex

Cited by 23 publications

References 48 publications

Ligand-Induced U Mobilization from Chemogenic Uraninite and Biogenic Noncrystalline U(IV) under Anoxic Conditions

Ligand-Induced U Mobilization from Chemogenic Uraninite and Biogenic Noncrystalline U(IV) under Anoxic Conditions

Uranium Isotope Fractionation during the Anoxic Mobilization of Noncrystalline U(IV) by Ligand Complexation

Efficient and durable uranium extraction from uranium mine tailings seepage water via a photoelectrochemical method

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