Electrochemical and spectrophotometric investigations of neptunium in alkaline media

Gelis, Artem V.; Vanýsek, Petr; Jensen, Mark P.; Nash, K.L.

doi:10.1524/ract.2001.89.9.565

Cited by 18 publications

(24 citation statements)

References 10 publications

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“…Our prior work on neptunium speciation [17] has established the comparative redox stability and solubility of the respective tetrahydroxides of penta-and hexavalent actinides in concentrated base solutions.…”

Section: Leaching Methodsmentioning

confidence: 99%

Oxidative Alkaline Leaching of Americium from Simulated High‐Level Nuclear Waste Sludges

Reed

Garnov

Rao

et al. 2005

Separation Science and Technology

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Oxidative alkaline leaching has been proposed to pre-treat the high-level nuclear waste sludges to remove some of the problematic (e.g., Cr) and/or non-radioactive (e.g., Na, Al) constituents before vitrification. It is critical to understand the behavior of actinides, americium and plutonium in particular, in oxidative alkaline leaching. We have studied the leaching behavior of americium from four different sludge simulants (BiPO 4 , BiPO 4 modified , Redox, PUREX) using potassium permanganate and potassium persulfate in * Corresponding author phone: 510-486-5427; fax: 510-486-5596; e-mail: LRao@lbl.gov

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Section: Leaching Methodsmentioning

confidence: 99%

Oxidative Alkaline Leaching of Americium from Simulated High‐Level Nuclear Waste Sludges

Reed

Garnov

Rao

et al. 2005

Separation Science and Technology

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“…In ~0.1 M solutions of Np(IV) in 0.05-0.1 M HClO 4 , HCl, or HNO 3 , no less than 10 -4 M Np(III) and Np(V) should be present in equilibrium. Reaction (26) was not yet observed. This may be due to its low rate.…”

Section: Second the Np(vii) Ions Undergo Protonationmentioning

confidence: 96%

“…At almost the same potential close to 0.59 V, with a decrease in the charge from 3-for NpO 4 (OH) 2 3-to 1-for RuO 4 -and MnO 4 -the stability of the ion decreases. A decrease in the Н + concentration leads to Np(IV) hydrolysis and to a decrease in the potentials of both (26) Np(IV)/(III) and Np(V)/(IV) couples. In ~0.1 M solutions of Np(IV) in 0.05-0.1 M HClO 4 , HCl, or HNO 3 , no less than 10 -4 M Np(III) and Np(V) should be present in equilibrium.…”

Section: Second the Np(vii) Ions Undergo Protonationmentioning

confidence: 99%

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Speciation, stability, and reactions of Np(III–VII) in aqueous solutions

2012

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Published data on the structure of Np ions in acid and alkali solutions, on hydrolysis of Np ions and their complexation with anions and cations, on their redox reactions with water and with each other (disproportionation, reproportionation), and on the effect of anions on this process are analyzed. Possible directions of research in chemistry of Np ions are outlined.The behavior of Np in various oxidation states in aqueous solutions is of interest for several reasons. First, 237 Np can be recovered from spent fuel of energy nuclear reactors and purified to remove impurities of actinides and other elements by extraction, ion exchange, and precipitation. Second, 237 Np is the starting material for the 238 Pu production. In the course of 237 Np and 238 Pu separation in solutions, these ions are subjected to intense α-radiation from 238 Pu. Third, Np is present in radioactive waste repositories. Fourth, Np migrates in the environment and is taken up by living bodies. Fifth, among actinides and other elements only Np is characterized by high stability of the pentavalent state in a wide pH range and by the heptavalent state stable in alkaline solutions.In solutions, Np exists in oxidation states from +3 to +7. The procedures for preparing Np in the required oxidation states, speciation of Np ions, and their hydrolysis, complexation, and certain redox reactions are described in [1][2][3]. However, these reviews do not discuss the stability of Np(VII) in a wide pH range, the behavior of Np ions in aqueous solutions of heteropoly compounds, silicates, and a number of organic substances, and other problems.Below we consider the structure of Np ions in various oxidation states, their speciation in aqueous solutions, and redox reactions with water and with each other. The data were taken from [1-3] and from original papers.In noncomplexing media, Np(III) and (IV) exist in the form of hydrated cations Np 3+ ·9H 2 O [3] and Np 4+ · (8-10)Н 2 О [4]. Neptunium(V) and (VI) exist as aqua complexes NpO 2 + ·5H 2 O and NpO 2 2+ ·5H 2 O [ [4][5][6], whose coordination polyhedron is a pentagonal bipyramid [5]. The report [7] that Np(VI) chloride complexes containing the NpO 3+ group can be prepared from aqueous hydrochloric acid solutions appeared to be erroneous [8,9]. For Np(VII), the form Np(ОН) 6 + [10] or its equivalent, NpO 2 (ОН) 2 + ·2H 2 O, is suggested. Unfortunately, none of them was confirmed experimentally.All the actinide ions, including Np, undergo hydrolysis in aqueous solutions. The susceptibility to hydrolysis decreases in the order Np 4+ > NpO 2 2+ > Np 3+ > NpO 2 + , in accordance with a decrease in the effective charge of the ion [2]. The NpO 2 + aq ion is not hydrolyzed up to рН 7. The NpO 2 2+ aq and Np 3+ aq ions prevail up to pH 5 and 6-7, respectively. The Np 4+ aq ion is hydrolyzed strongly, and hydrolyzed species appear at pH 1.The hydrolysis reactions can be described by the general equationThe hydrolysis constants K nq determined in solutions with a definite ionic strength and the calculated quantities f...

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“…[ [48][49][50] Curium has a barely accessible tetravalent oxidation state, but does not appear in the penta-or hexavalent oxidation states in aqueous solutions. [51] Likewise only a very small number of the lanthanides can be oxidized to the tetravalent oxidation state; all Ln(IV) are strong oxidants.…”

Section: Task 3 Am/ln Separation With Oxidation State Adjustment Andmentioning

confidence: 99%

Selective Separation of Trivalent Actinides from Lanthanides by Aqueous Processing with Introduction of Soft Donor Atoms

Nash¹,

Clark²,

Lumetta³

2009

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With increased application of MOX fuels and longer burnup times for conventional fuels, higher concentrations of the transplutonium actinides Am and Cm (and even heavier species like Bk and Cf) will be produced. The half-lives of the Am isotopes ( 241 Am, 433 yrs; 243 Am, 7370 yrs) are significantly longer than those of the most important long-lived, high specific activity lanthanides or the most common Cm, Bk and Cf isotopes, thus the greatest concern as regards long-term radiotoxicity. With the removal and transmutation of Am isotopes, radiation levels of high level wastes are reduced to near uranium mineral levels within less than 1000 years as opposed to the 10 4

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Electrochemical and spectrophotometric investigations of neptunium in alkaline media

Cited by 18 publications

References 10 publications

Oxidative Alkaline Leaching of Americium from Simulated High‐Level Nuclear Waste Sludges

Oxidative Alkaline Leaching of Americium from Simulated High‐Level Nuclear Waste Sludges

Speciation, stability, and reactions of Np(III–VII) in aqueous solutions

Selective Separation of Trivalent Actinides from Lanthanides by Aqueous Processing with Introduction of Soft Donor Atoms

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