Effect of Carbonate on the Solubility of Neptunium in Natural Granitic Groundwater

Kim, B.Y.; Oh, Jy; Baik, Min Hoon; Yun, Jong-Il

doi:10.5516/net.2010.42.5.552

Cited by 8 publications

(7 citation statements)

References 24 publications

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“…Interestingly, this lower solubility coincides with a higher static order as reflected by lower Debye–Waller factor of the Np-Np paths as compared to the 1 day sample (Table ). Even addition of a high concentration of carbonate (0.1 M) had only a relatively small influence on Np retention, in line with previous results. , …”

Section: Environmental Implicationssupporting

confidence: 92%

“…Even addition of a high concentration of carbonate (0.1 M) had only a relatively small influence on Np retention, in line with previous results. 58,59 The observed high retention of Np by siderite across a relatively wide pH range is encouraging. However, the potential mobilization of the formed NpO 2 −like nanoparticles as colloids may significantly raise the risk of Np migration away from the waste disposal site.…”

Section: ■ Environmental Implicationsmentioning

confidence: 74%

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Neptunium^V Retention by Siderite under Anoxic Conditions: Precipitation of NpO₂–Like Nanoparticles and of Np^IV Pentacarbonate

Scheinost

Steudtner

Hübner

et al. 2016

Environ. Sci. Technol.

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The Np retention by siderite, an Fe carbonate mineral with relevance for the near-field of high-level radioactive waste repositories, was investigated under anoxic conditions. Batch sorption experiments show that siderite has a high affinity for aqueous NpO across pH 7 to 13 as expressed by solid-water distribution coefficients, log R > 5, similar to the log R determined for the (solely) tetravalent actinide Th on calcite, suggesting reduction of Np to Np by siderite. Np L-edge X-ray absorption near edge (XANES) spectroscopy conducted in a pH range typical for siderite-containing host rocks (7-8), confirmed the tetravalent Np oxidation state. Extended X-ray absorption fine-structure (EXAFS) spectroscopy revealed a local structure in line with NpO-like nanoparticles with diameter < 1 nm, a result further corroborated by high-resolution transmission electron microscopy (HRTEM). The low solubility of these NpO-like nanoparticles (∼10 M), along with their negligible surface charge at neutral pH conditions which favors particle aggregation, suggest an efficient retention of Np in the near-field of radioactive waste repositories. When Np was added to ferrous carbonate solution, the subsequent precipitation of siderite did not lead to a structural incorporation of Np by siderite, but caused precipitation of a Np pentacarbonate phase.

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Section: Environmental Implicationssupporting

confidence: 92%

Section: ■ Environmental Implicationsmentioning

confidence: 74%

Neptunium^V Retention by Siderite under Anoxic Conditions: Precipitation of NpO₂–Like Nanoparticles and of Np^IV Pentacarbonate

Scheinost

Steudtner

Hübner

et al. 2016

Environ. Sci. Technol.

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“…It remains unclear in these low Np microcosm studies whether Np(V) removal is linked to microbial metabolism or the result of abiotic reaction with Mn(II/III) minerals produced during microbial Mn(IV) reduction. The formation of Np-carbonatohydroxo complexes has been shown to increase the solubility of Np(IV) (Kitamura and Kohara, 2002;Kim et al, 2010). However, in these systems under end point sulfate reducing conditions (pE -4), and taking into account the increase in inorganic carbon expected from acetate utilization (2 mM), solution modelling in PHREEQC-2 (SIT database) predicted that Np would be speciated as Np(OH)4 (see supporting information S2).…”

Section: Neptunium Behaviour During Progressive Bioreductionmentioning

confidence: 99%

Neptunium and manganese biocycling in nuclear legacy sediment systems

Thorpe

Morris

Lloyd

et al. 2015

Applied Geochemistry

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Understanding the behaviour of the highly radiotoxic, long half-life radionuclide neptunium in the environment is important for the management of radioactively contaminated land and the safe disposal of radioactive wastes. Recent studies have identified that microbial reduction can reduce the mobility of neptunium via reduction of soluble Np(V) to poorly soluble Np(IV), with coupling to both Mn- and Fe(III)- reduction implicated in neptunyl reduction. To further explore these processes Mn(IV) as δMnO2 was added to sediment microcosms to create a sediment microcosm experiment "poised" under Mn-reducing conditions. Enhanced removal of Np(V) from solution occurred during Mn-reduction, and parallel X-ray absorption spectroscopy (XAS) studies confirmed Np(V) reduction to Np(IV) commensurate with microbially-mediated Mn-reduction. Molecular ecology analysis of the XAS systems, which contained up to 0.2 mM Np showed no significant impact of elevated Np concentrations on the microbial population. These results demonstrate the importance of Mn cycling on Np biogeochemistry, and clearly highlight new pathways to reductive immobilisation for this highly radiotoxic actinide

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“…The H 2 O 2 decomposition mechanism is dependent on U oxidation and so can also be investigated using U 3 O 8 for comparison with UO 2 . The concentration of bicarbonate in groundwater is dependent on the location of the deep geological repository, and can range from ∼10 −4 M (Tono, Japan), 24 to ∼10 −3 M (Daejeon, South Korea), 25,26 to ∼10 −2 M (Forsmark, Sweden) 27 and so it is necessary to understand U dissolution and H 2 O 2 decomposition at uranium oxide surfaces over a range of bicarbonate concentrations.…”

Section: Introductionmentioning

confidence: 99%

The kinetics and mechanism of H₂O₂ decomposition at the U₃O₈ surface in bicarbonate solution

et al. 2021

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Effect of Carbonate on the Solubility of Neptunium in Natural Granitic Groundwater

Cited by 8 publications

References 24 publications

Neptunium^V Retention by Siderite under Anoxic Conditions: Precipitation of NpO₂–Like Nanoparticles and of Np^IV Pentacarbonate

Neptunium^V Retention by Siderite under Anoxic Conditions: Precipitation of NpO₂–Like Nanoparticles and of Np^IV Pentacarbonate

Neptunium and manganese biocycling in nuclear legacy sediment systems

The kinetics and mechanism of H₂O₂ decomposition at the U₃O₈ surface in bicarbonate solution

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Effect of Carbonate on the Solubility of Neptunium in Natural Granitic Groundwater

Cited by 8 publications

References 24 publications

NeptuniumV Retention by Siderite under Anoxic Conditions: Precipitation of NpO2–Like Nanoparticles and of NpIV Pentacarbonate

NeptuniumV Retention by Siderite under Anoxic Conditions: Precipitation of NpO2–Like Nanoparticles and of NpIV Pentacarbonate

Neptunium and manganese biocycling in nuclear legacy sediment systems

The kinetics and mechanism of H2O2 decomposition at the U3O8 surface in bicarbonate solution

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Neptunium^V Retention by Siderite under Anoxic Conditions: Precipitation of NpO₂–Like Nanoparticles and of Np^IV Pentacarbonate

Neptunium^V Retention by Siderite under Anoxic Conditions: Precipitation of NpO₂–Like Nanoparticles and of Np^IV Pentacarbonate

The kinetics and mechanism of H₂O₂ decomposition at the U₃O₈ surface in bicarbonate solution