Cyclic Voltammetric Behavior of Uranyl ion in Sulfuric Acid Solutions. Application to Some Nuclear Materials Characterization

Casadio, S.; Lorenzinl, L.

doi:10.1080/00032717308058737

Cited by 12 publications

(14 citation statements)

References 7 publications

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“…Noting the strong influence of solvent H + on disproportionation kinetics − and assuming a first-order relationship to H + concentrations, ,,− it is entirely plausible that the rate constant of homogeneous U(V) disproportionation at pH 7–8 could be 5–7 orders of magnitude slower than that experimentally reported to occur at pH values <2. The predicted stability of U(V) is not unprecedented as it has previously been shown that U(V) can remain as a stable surface species on magnetite for at least 56 days or as an aqueous UO 2 (CO 3 ) 3 5– complex for at least 14 days .…”

Section: Resultsmentioning

confidence: 98%

“…However, they only considered internal rearrangements to achieve proton transfer within the encounter complexes. Given the overwhelming evidence of the role of solvent H + in accelerating U(V) disproportionation, − the PCET proposed by Wander et al may not accurately reflect the disproportionation ET pathway. The PCET rate constant that we obtained, which requires two protonation steps of axial oxygens by solvent H + , is consistent with the assertions in Steele and Taylor and Kubicki et al that acid attack of axial oxygens is a necessary process to stabilize the product states of U(IV) and U(VI).…”

Section: Resultsmentioning

confidence: 99%

“…Because of the tendency of the system to continue to U(IV) precipitation in relevant experiments, U(V) has been notoriously difficult to isolate and its elimination by disproportionation has long been considered fast. However, almost all of the experimental studies examining the kinetics of homogeneous U(V) disproportionation have necessarily been conducted in extremely acid conditions (i.e., pH <2) to avoid condensation of U(IV) species. − Reported disproportionation rate constants in these studies have varied from ∼1 to 11 600 M –1 s –1 , being strongly influenced by concentrations of H + , U(VI), and complexing anions, such as sulfate and chloride. While some of the pioneering studies observed a first-order rate relationship with respect to H + , later studies did not observe such a phenomenon. , Nevertheless, it is generally agreed that solvent H + promotes U(V) disproportionation though the mechanism(s) through which it does so have not been clearly articulated .…”

Section: Introductionmentioning

confidence: 99%

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Mechanisms and Rates of U(VI) Reduction by Fe(II) in Homogeneous Aqueous Solution and the Role of U(V) Disproportionation

Collins

Rosso

2017

J. Phys. Chem. A

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Molecular-level pathways in the aqueous redox transformation of uranium by iron remain unclear, despite the importance of this knowledge for predicting uranium transport and distribution in natural and engineered environments. As the relative importance of homogeneous versus heterogeneous pathways is difficult to probe experimentally, here we apply computational molecular simulation to isolate rates of key one electron transfer reactions in the homogeneous pathway. By comparison to experimental observations the role of the heterogeneous pathway also becomes clear. Density functional theory (DFT) and Marcus theory calculations for all primary monomeric species at pH values ≤7 show for UO and its hydrolysis species UOOH and UO(OH) that reduction by Fe is thermodynamically favorable, though kinetically limited for UO. An inner-sphere encounter complex between UOOH and Fe was the most stable for the first hydrolysis species and displayed an electron transfer rate constant k = 4.3 × 10 s. Three stable inner- and outer-sphere encounter complexes between UO(OH) and Fe were found, with electron transfer rate constants ranging from k = 7.6 × 10 to 7.2 × 10 s. Homogeneous reduction of these U(VI) hydrolysis species to U(V) is, therefore, predicted to be facile. In contrast, homogeneous reduction of UO by Fe was found to be thermodynamically unfavorable, suggesting the possible importance of U(V)-U(V) disproportionation as a route to U(IV). Calculations on homogeneous disproportionation, however, while yielding a stable outer-sphere U(V)-U(V) encounter complex, indicate that this electron transfer reaction is not feasible at circumneutral pH. Protonation of both axial O atoms of acceptor U(V) (i.e., by HO) was found to be a prerequisite to stabilize U(IV), consistent with the experimental observation that the rate of this reaction is inversely correlated with pH. Thus, despite prevailing notions that U(V) is rapidly eliminated by homogeneous disproportionation, this pathway is irrelevant at environmental conditions.

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Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Mechanisms and Rates of U(VI) Reduction by Fe(II) in Homogeneous Aqueous Solution and the Role of U(V) Disproportionation

Collins

Rosso

2017

J. Phys. Chem. A

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“…In the present study, Box‐Behnken design, which is a common response surface method for experimental design, was used to evaluate and optimize the effects of independent variables on the USAEME process, to obtain more quantity of extract from the experiments performed. Many methods have been developed for determination of uranium and thorium, such as fluorimetry, electrochemistry, inductively coupled plasma mass spectrometry, and spectrophotometry . UV‐Vis spectrometry is widely applied to metal complexes in solution for its availability, simplicity, speed, accuracy, and cost‐effectiveness.…”

Section: Introductionmentioning

confidence: 99%

Moving window partial least squares after orthogonal signal correction as a coupling method for determination of uranium and thorium by ultrasound‐assisted emulsification microextraction

Khorshidi

Ниази

2018

Journal of Chemometrics

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This study, a fast, simple, and efficient ultrasound-assisted emulsification microextraction coupled with orthogonal signal correction-moving window partial least squares (OSC-MWPLS) was successfully used to preconcentration and simultaneous spectrophotometric determination of uranium and thorium in water samples. Response surface methodology based on a Box-Behnken design was used to optimize the extraction conditions. The analysis of variance and some statistical tests such as lack-of-fit and coefficient of determination (R 2 ) showed good fit of the experimental data with the second-order polynomial model. Under the optimum conditions, the calibration graphs were linear in the range of 10.0 to 230.0 and 10.0 to 250.0 ng mL −1 with detection limits of 3.11 and 3.56 ng mL −1 (3S b /m) for uranium and thorium, respectively. The preconcentration factor of this method for uranium and thorium reached 192. Repeatability (intra-day) and reproducibility (inter-day) were obtained 1.23% and 2.18% for uranium and 1.34% and 1.95% for thorium, respectively. The OSC was used for preprocessing of data matrices, and also MWPLS regression has been proposed for the selection of informative spectral intervals. In this paper, ultrasound-assisted emulsification microextraction coupled with OSC-MWPLS method was presented for the first time. The root mean square error of prediction for uranium and thorium with PLS, OSC-PLS, and OSC-MWPLS were 11.755, 10.335 and 5.301, 5.399 and 0.974, 0.986 ng mL −1 , respectively. The results indicated that practical and environmentally friendly proposed method could be successfully used to the simultaneous determination of uranium and thorium in different environmental water samples.

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“…The reduction of U(V1) has been extensively studied in aqueous media by different electrochemical methods (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14).2 Most of these studies have been carried out in acidic (HCIO,, HCl, H2S04, HN03) media (2-1 1). In sufficiently acidic solution, the reduction mechanism (12) is that uranyl is reduced in a one-electron step and that the resulting U(V) species disproportionates, regenerating U(W).…”

Section: Introductionmentioning

confidence: 99%

Electroreduction of uranyl ion in aqueous calcium nitrate solutions

Bansal¹,

Plambeck²

1981

Can. J. Chem.

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This paper is dedicated to Professor W . E. Harris on the occasion of his retirement jkom the University of Alberta NAROTTAM P. BANSAL and JAMES A. PLAMBECK. Can. J. Chem. 59, 1515Chem. 59, (1981. The electroreduction of uranyl ions in buffered and unbuffered 0.5 M calcium nitrate has been studied using polarography, cyclic voltammetry, chronopotentiometry, and chronoamperometry. The results are compared with those in molten calcium nitrate tetrahydrate.NAROTTAM P. BANSAL et JAMES A. PLAMBECK. Can. J. Chem. 59, 1515Chem. 59, (1981. Faisant appel a la polarographie, la voltametrie cyclique, la chronopotentiometrie et la chronoampCrometrie, on a CtudiC la reduction Clectrolytique des ions uranyles dans des solutions 0,s M de nitrate de calcium tamponnees et non tamponnees. On a compare les rksultats a ceux obtenus dans du nitrate de calcium tetrahydrate fondu.

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Cyclic Voltammetric Behavior of Uranyl ion in Sulfuric Acid Solutions. Application to Some Nuclear Materials Characterization

Cited by 12 publications

References 7 publications

Mechanisms and Rates of U(VI) Reduction by Fe(II) in Homogeneous Aqueous Solution and the Role of U(V) Disproportionation

Mechanisms and Rates of U(VI) Reduction by Fe(II) in Homogeneous Aqueous Solution and the Role of U(V) Disproportionation

Moving window partial least squares after orthogonal signal correction as a coupling method for determination of uranium and thorium by ultrasound‐assisted emulsification microextraction

Electroreduction of uranyl ion in aqueous calcium nitrate solutions

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