Recent Advances in Aqueous Actinide Chemistry and Thermodynamics

Altmaier, M.; Gaona, Xavier; Fanghänel, Thomas

doi:10.1021/cr300379w

Cited by 180 publications

(155 citation statements)

References 164 publications

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“…In contrast to uranyl, protactinyl is not a stable species in solution but rather undergoes hydrolysis. 28,29 Accordingly, PaO 2 (C 2 O 4 ) − did not appear in the ESI mass spectrum. Instead, the gas-phase protactinyl complex was produced by CID of the Pa Both actinyls are distorted from linear, with that for protactinyl substantially more so.…”

Section: ■ Computational Methodsmentioning

confidence: 97%

Revealing Disparate Chemistries of Protactinium and Uranium. Synthesis of the Molecular Uranium Tetroxide Anion, UO₄^–

et al. 2017

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The synthesis, reactivity, structures, and bonding in gas-phase binary and complex oxide anion molecules of protactinium and uranium have been studied by experiment and theory. The oxalate ions, AnVO2(C2O4)−, where An = Pa or U, are essentially actinyl ions, AnVO2 +, coordinated by an oxalate dianion. Both react with water to yield the pentavalent hydroxides, AnVO(OH)2(C2O4)−. The chemistry of Pa and U becomes divergent for reactions that result in oxidation: whereas PaVI is inaccessible, UVI is very stable. The UVO2(C2O4)− complex exhibits a remarkable spontaneous exothermic replacement of the oxalate ligand by O2 to yield UO4 – and two CO2 molecules. The structure of the uranium tetroxide anion is computed to correspond to distorted uranyl, UVIO2 2+, coordinated in the equatorial plane by two equivalent O atoms each having formal charges of −1.5 and U–O bond orders intermediate between single and double. The unreactive nature of PaVO2(C2O4)− toward O2 is a manifestation of the resistance toward oxidation of PaV, and clearly reveals the disparate chemistries of Pa and U. The uranium tetroxide anion, UO4 –, reacts with water to yield UO5H2 –. Infrared spectra obtained for UO5H2 – confirm the computed lowest-energy structure, UO3(OH)2 –.

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Section: ■ Computational Methodsmentioning

confidence: 97%

Revealing Disparate Chemistries of Protactinium and Uranium. Synthesis of the Molecular Uranium Tetroxide Anion, UO₄^–

et al. 2017

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“…A comprehensive overview on several aspects related to actinide and Np solubility and speciation in aqueous media has been previously reported elsewhere [4][5][6]. Although in some cases kinetic factors can strongly hinder this type of reaction, solution thermodynamics remains as a very accurate approach to describe hydrolysis and solubility phenomena under given pH and ionic strength conditions.…”

Section: Introductionmentioning

confidence: 99%

Solubility and hydrolysis of Np(V) in dilute to concentrated alkaline NaCl solutions: formation of Na–Np(V)–OH solid phases at 22 °C

et al. 2016

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Abstract:The solubility of Np(V) was investigated at T = 22 ± 2 °C in alkaline NaCl solutions of different ionic strength (0.1-5.0 M). The solid phases controlling the solubility at different -log 10 m H +(pH m ) and NaCl concentration were characterized by XRD, quantitative chemical analysis, SEM-EDS and XAFS (both XANES and EXAFS). Aqueous phases in equilibrium with Np(V) solids were investigated for selected samples within 8.9 ≤ pH m ≤ 10.3 by UV-vis/NIR absorption spectroscopy. In 0.1 M NaCl, the experimental solubility of the initial greenish NpO 2 OH(am) solid phase is in good agreement with previous results obtained in NaClO 4 solutions, and is consistent with model calculations for fresh NpO 2 OH(am) using the thermodynamic data selection in NEA-TDB. Below pH m ~ 11.5 and for all NaCl concentrations studied, Np concentration in equilibrium with the solid phase remained constant during the timeframe of this study (~2 years). This observation is in contrast to the aging of the initial NpO 2 OH(am) into a more crystalline modification with the same stoichiometry, NpO 2 OH(am, aged), as reported in previous studies for concentrated NaClO 4 and NaCl. Instead, the greenish NpO 2 OH(am) transforms into a white solid phase in those systems with [NaCl] ≥ 1.0 M and pH m ≥ 11.5, and into two different pinkish phases above pH m ~ 13.2. The solid phase transformation is accompanied by a drop in Np solubility of 0.5-2 log 10 -units (depending upon NaCl concentration). XANES analyses of green, white and pink phases confirm the predominance of Np(V) in all cases. Quantitative chemical analysis shows the incorporation of Na + in the original NpO 2 OH(am) material, with Na:Np ≤ 0.3 for the greenish solids and 0.8 ≤ Na:Np ≤ 1.6 for the white and pinkish phases. XRD data confirms the amorphous character of the greenish phase, whereas white and pink solids show well-defined but discrepant XRD patterns. Furthermore, the XRD pattern collected for one of the pink solid phases match the data recently reported for NaNpO 2 (OH) 2 (cr). UV-vis/NIR spectra collected in 0.1-5.0 M NaCl solutions show the predominance of NpO 2 + ( ≥ 80%) at pH m ≤ 10.3. This observation is consistent with the Np(V) hydrolysis scheme currently selected in the NEA-TDB. This work provides sound evidences on the formation of ternary Na-Np(V)-OH solid phases in Na-rich hyperalkaline solutions and ambient temperature conditions. Given the unexpectedly high complexity of the system, further experimental efforts dedicated to assess the thermodynamic properties of these solid phases are needed, especially in view of their likely relevance as solubility controlling Np(V) solid phases in Na-rich systems such as saline and cementbased environments in the context of the safety assessment for nuclear waste disposal.

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“…For obvious reasons, metal ions with reasonable solubility (e.g., amphoteric ones) are most 50 intensely studied (e.g., Al(III) [7][8][9] , Ga(III) 10,11 , Cr(III) 12, 13 , Pb(II) 14 , Tl(I) 15,16 , etc.). Beside these, data for metal ions that are hardly soluble in alkaline conditions also emerge (e.g., Cu(II) 17 , Fe(III) 18 , actinides 19 , etc.) In the current paper, we will focus on the behaviour of the 55 amphoteric Sn(II) ion in hyperalkaline media.…”

Section: Introductionmentioning

confidence: 99%

Speciation and structure of tin(ii) in hyper-alkaline aqueous solution

et al. 2014

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5The structure of tin(II) hydroxido complex forming in hyperalkaline aqueous solutions (0.2  C NaOH  12 mol⋅dm -3 ) has been determined by EXAFS, Raman and Mössbauer spectroscopy, and the general composition by potentiometric titrations. Experimental work was supplemented by computational means. 10The mean Sn-O distance in the non-linear complex is remarkably short, 2.078 Å. From single crystal X-ray data of O-coordinated Sn(II) compounds, for the given coordination numbers of N = 2 and 3, the bond distances were found to cover a relatively wide range (much wider than normal). The experimentally

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Recent Advances in Aqueous Actinide Chemistry and Thermodynamics

Cited by 180 publications

References 164 publications

Revealing Disparate Chemistries of Protactinium and Uranium. Synthesis of the Molecular Uranium Tetroxide Anion, UO₄^–

Revealing Disparate Chemistries of Protactinium and Uranium. Synthesis of the Molecular Uranium Tetroxide Anion, UO₄^–

Solubility and hydrolysis of Np(V) in dilute to concentrated alkaline NaCl solutions: formation of Na–Np(V)–OH solid phases at 22 °C

Speciation and structure of tin(ii) in hyper-alkaline aqueous solution

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Recent Advances in Aqueous Actinide Chemistry and Thermodynamics

Cited by 180 publications

References 164 publications

Revealing Disparate Chemistries of Protactinium and Uranium. Synthesis of the Molecular Uranium Tetroxide Anion, UO4–

Revealing Disparate Chemistries of Protactinium and Uranium. Synthesis of the Molecular Uranium Tetroxide Anion, UO4–

Solubility and hydrolysis of Np(V) in dilute to concentrated alkaline NaCl solutions: formation of Na–Np(V)–OH solid phases at 22 °C

Speciation and structure of tin(ii) in hyper-alkaline aqueous solution

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Revealing Disparate Chemistries of Protactinium and Uranium. Synthesis of the Molecular Uranium Tetroxide Anion, UO₄^–

Revealing Disparate Chemistries of Protactinium and Uranium. Synthesis of the Molecular Uranium Tetroxide Anion, UO₄^–