Sorption coefficients and molecular mechanisms of Pu, U, Np, Am and Tc to Fe (hydr)oxides: A review

Li, Dien; Kaplan, Daniel I.

doi:10.1016/j.jhazmat.2012.09.011

Cited by 84 publications

(36 citation statements)

References 120 publications

(202 reference statements)

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“…The speciation in the bioaccumulation experiments typically followed a species distribution of Ca 2 UO 2 (CO 3 ) 3 , which is in general agreement with previous literature [9,10,46]. Many of the pH-dependent uranyl-carbonate complexes are only weakly sorbed to sediment binding phases such as Fe (hydr)oxides [61,62]. The weak sorption at high pH is often a result of the formation of weakly sorbing uranyl-carbonate complexes in the presence of carbonates and subsequent increase in total concentrations of U(VI) in solution, which is consistent with the lower sorption observed in the current and previous publications for more alkaline conditions [36,56].…”

Section: Application Of Whamsupporting

confidence: 87%

Predicting the bioavailability of sediment‐bound uranium to the freshwater midge (Chironomus dilutus) using physicochemical properties

Crawford

Lofts

Liber

2018

Enviro Toxic and Chemistry

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Assessment of uranium (U)-contaminated sediment is often hindered by the inability to accurately account for the physicochemical properties of sediment that modify U bioavailability. The present goal was to determine whether sediment-associated U bioavailability could be predicted over a wide range of conditions and sediment properties using simple regressions and a geochemical speciation model, the Windermere Humic Aqueous Model (WHAM7). Data from a U-contaminated field sediment bioaccumulation test, along with previously published bioaccumulation studies with U-spiked field and formulated sediments, were used to examine the models. Observed U concentrations in Chironomus dilutus larvae exposed to U-spiked and U-contaminated sediments correlated well (r > 0.74, p < 0.001) with the WHAM-calculated concentration of U bound to humic acid, indicating that humic acid may be a suitable surrogate for U binding sites (biotic ligands) in C. dilutus larvae. Subsequently, the concentration of U in C. dilutus was predicted with WHAM7 by numerically optimizing the equivalent mass of humic acid per gram of organism. The predicted concentrations of U in C. dilutus larvae exposed to U-spiked and U-contaminated field sediment compared well with the observed values, where one of the regression models provided a slightly better fit (mean absolute error = 18.1 mg U/kg dry wt) than WHAM7 (mean absolute error = 34.2 mg U/kg dry wt). The regression model provides a predictive capacity with a minimal number of variables, whereas WHAM7 provides additional complementary insight into the chemical variables influencing the speciation, sorption, and bioavailability of U in sediment. The present results indicate that physicochemical properties of sediment can be used to account for variability in U bioavailability as measured through bioaccumulation in chironomids exposed to U-contaminated sediments. Environ Toxicol Chem 2018;37:1146-1157. © 2017 SETAC.

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Section: Application Of Whamsupporting

confidence: 87%

Predicting the bioavailability of sediment‐bound uranium to the freshwater midge (Chironomus dilutus) using physicochemical properties

Crawford

Lofts

Liber

2018

Enviro Toxic and Chemistry

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“…In this context, understanding the behaviour of neptunium in the presence of Fe oxyhydroxides, including magnetite and green rust, informs prediction of the long-term behaviour of risk driving radionuclides in engineered and natural environments, including in radioactive waste disposal. Previous studies demonstrate that Np(V) can interact with phases such as ferrihydrite [18][19][20], lepidocrocite [21], goethite [19,20,22], hematite [19,20,23] and magnetite [12,16,20,24]. Here, for Fe(III) containing minerals, Np(V) typically forms inner sphere Np(V) complexes or, in the presence of carbonate, Np(V)-carbonate surface complexes [19,23,25].…”

Section: Introductionmentioning

confidence: 97%

Neptunium Reactivity During Co-Precipitation and Oxidation of Fe(II)/Fe(III) (Oxyhydr)oxides

et al. 2019

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Fe(II) bearing iron (oxyhydr)oxides were directly co-precipitated with Np(V)O2+ under anaerobic conditions to form Np doped magnetite and green rust. These environmentally relevant mineral phases were then characterised using geochemical and spectroscopic analyses. The Np doped mineral phases were then oxidised in air over 224 days with solution chemistry and end-point oxidation solid samples collected for further characterisation. Analysis using chemical extractions and X-ray absorption spectroscopy (XAS) techniques confirmed that Np(V) was initially reduced to Np(IV) during co-precipitation of both magnetite and green rust. Extended X-Ray Absorption Fine Structure (EXAFS) modelling suggested the Np(IV) formed a bidentate binuclear sorption complex to both minerals. Furthermore, following oxidation in air over several months, the sorbed Np(IV) was partially oxidised to Np(V), but very little remobilisation to solution occurred during oxidation. Here, linear combination fitting of the X-Ray Absorption Near Edge Structure (XANES) for the end-point oxidation samples for both mineral phases suggested approximately 50% oxidation to Np(V) had occurred over 7 months of oxidation in air. Both the reduction of Np(V) to Np(IV) and inner sphere sorption in association with iron (oxyhydr)oxides, and the strong retention of Np(IV) and Np(V) species with these phases under robust oxidation conditions, have important implications in understanding the mobility of neptunium in a range of engineered and natural environments.

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“…In natural and engineered environments iron oxide minerals are ubiquitous [9] and have the potential to affect the mobility of radionuclides significantly through both incorporation and surface complexation processes [10][11][12][13][14][15][16][17][18][19][20][21]. In aerobic environments the redox states of the actinides (U, Np and Pu) are dominated by relatively soluble hexa-and pentavalent species, while under anoxic and progressively more reducing conditions, poorly soluble tetra-and trivalent species dominate [22].…”

Section: Introductionmentioning

confidence: 99%

Neptunium(V) and Uranium(VI) Reactions at the Magnetite (111) Surface

et al. 2019

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Neptunium and uranium are important radionuclides in many aspects of the nuclear fuel cycle and are often present in radioactive wastes which require long term management. Understanding the environmental behaviour and mobility of these actinides is essential in underpinning remediation strategies and safety assessments for wastes containing these radionuclides. By combining state-of-the-art X-ray techniques (synchrotron-based Grazing Incidence XAS, and XPS) with wet chemistry techniques (ICP-MS, liquid scintillation counting and UV-Vis spectroscopy), we determined that contrary to uranium(VI), neptunium(V) interaction with magnetite is not significantly affected by the presence of bicarbonate. Uranium interactions with a magnetite surface resulted in XAS and XPS signals dominated by surface complexes of U(VI), while neptunium on the surface of magnetite was dominated by Np(IV) species. UV-Vis spectroscopy on the aqueous Np(V) species before and after interaction with magnetite showed different speciation due to the presence of carbonate. Interestingly, in the presence of bicarbonate after equilibration with magnetite, an unknown aqueous NpO2+ species was detected using UV-Vis spectroscopy, which we postulate is a ternary complex of Np(V) with carbonate and (likely) an iron species. Regardless, the Np speciation in the aqueous phase (Np(V)) and on the magnetite (111) surfaces (Np(IV)) indicate that with and without bicarbonate the interaction of Np(V) with magnetite proceeds via a surface mediated reduction mechanism. Overall, the results presented highlight the differences between uranium and neptunium interaction with magnetite, and reaffirm the potential importance of bicarbonate present in the aqueous phase.

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Sorption coefficients and molecular mechanisms of Pu, U, Np, Am and Tc to Fe (hydr)oxides: A review

Cited by 84 publications

References 120 publications

Predicting the bioavailability of sediment‐bound uranium to the freshwater midge (Chironomus dilutus) using physicochemical properties

Predicting the bioavailability of sediment‐bound uranium to the freshwater midge (Chironomus dilutus) using physicochemical properties

Neptunium Reactivity During Co-Precipitation and Oxidation of Fe(II)/Fe(III) (Oxyhydr)oxides

Neptunium(V) and Uranium(VI) Reactions at the Magnetite (111) Surface

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