Aqueous uranyl complexes. 3. Potentiometric measurements of the hydrolysis of uranyl(VI) ion at 25�C

Palmer, Donald A.; Nguyen-Trung, C.

doi:10.1007/bf00972833

Cited by 52 publications

(67 citation statements)

References 17 publications

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“…The inorganic uranium thermodynamic database employed in the geochemical simulations was derived primarily from the ΝΕΑ critical review series [10,11], but also from more recent original research publications [12,13], where data were deemed to be internally consistent. The uranyl-organic thermodynamic database was derived from a critical review of the literature following the ΝΕΑ protocol [14].…”

Section: Methodsmentioning

confidence: 99%

The Use of Geochemical Speciation Modelling to Predict the Impact of Uranium to Freshwater Biota

1996

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Uranium is the prime potential contaminant in mine waste waters that may be released from the Ranger Uranium Mine (RUM) into the receiving waters of the Magela Creek, Alligator Rivers Region, Northern Australia. The potential ecological impact of the migration of uranium, that would result from an elevation in its concentration above background, in the Magela Creek downstream of the RUM, has been experimentally investigated by integrating biomonitoring with geochemical speciation modelling. The freshwater bivalve Velesunio angasi, abundant throughout the Magela Creek catchment, was exposed to a variety of uranium concentrations in a synthetic Magela Creek water, at four pH levels (5.0, 5.3, 5.5 and 6.0), in the presence (3.05 and 7.50 mg Γ') and absence of a model fulvic acid (FA), and its behavioural response was measured. Speciation modelling, using the HARPHRQ code, provided evidence that UO| + and U0 2 0H + are the uranium species most responsible (ca. 96%) for eliciting an adverse behavioural response when UO| + is assigned twice the toxic effect of U0 2 0H + . This finding rejects the notion that biota respond specifically to the sum total of inorganic uranyl species.

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Section: Methodsmentioning

confidence: 99%

The Use of Geochemical Speciation Modelling to Predict the Impact of Uranium to Freshwater Biota

1996

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“…[40][41][42] This species is never observed as the sole soluble complex because it is in thermodynamic equilibrium with monomeric U(VI)O 2 2+ and (U(VI)O 2 )(OH) + forms. 40 contain complexed alcohol groups, suggesting that these species will also exhibit a resistance to biodegradation by microbes. Single-Crystal X-ray Diffractometry.…”

Section: Relationships To Aqueous Solutionsmentioning

confidence: 99%

Structural characterization of environmentally relevant ternary uranyl citrate complexes present in aqueous solutions and solid state materials

et al. 2015

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Organic acids are important metal chelators in environmental systems and tend to form soluble complexes in aqueous solutions, ultimately influencing the transport and bioavailability of contaminants in surface and subsurface waters. This is particularly true for the formation of uranyl citrate complexes, which have been utilized in advanced photo- and bioremediation strategies for soils contaminated with nuclear materials. Given the complexity of environmental systems, the formation of ternary or heterometallic uranyl species in aqueous solutions are also expected, particularly with Al(iii) and Fe(iii) cations. These ternary forms are reported to be more stable in aqueous solutions, potentially enhancing contaminant mobility and uptake by organisms, but the exact coordination geometries of these soluble molecular complexes have not been elucidated. To provide insight into the nature of these species, we have developed a series of geochemical model compounds ([(UO(2))(2)Al(2)(C(6)H(4)O(7))(4)](6-) (U(2)Al(2)), [(UO(2))(2)Fe(2)(C(6)H(4)O(7))(4)](6-) (U(2)Fe(2)-1) and [(UO(2))(2)Fe(2)(C(6)H(4)O(7))(4)(H(2)O)(2)](6-) (U(2)Fe(2)-2) and [(UO(2))(2)Fe(4)(OH)(4)(C(6)H(4)O(7))(4)](8-) (U(2)Fe(4))) that were characterized by single-crystal X-ray diffraction and vibrational spectroscopy. Mass spectroscopy was then employed to compare the model compounds to species present in aqueous solutions to provide an enhanced understanding of the ternary uranyl citrate complexes that could be relevant in natural systems.

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“…Five water ligands are coordinated in acidic solution, a mixture of water and hydroxide ligands in neutral solution, and four or five hydroxide ligands in highly alkaline solution. Actinyl complexes in aqueous solution, particularly those at low pH, have been studied experimentally [1][2][3][4][5][6][7][8][9][10][11][12][13] and theoretically. [13][14][15][16][17][18][19][20][21][22][23] The actinyl ions exist in different oxidation states in the environment but UO 2 2+ , NpO 2 + , and PuO 2 2+ are the most abundant and thus the complexes formed by these species under different pH conditions are of considerable interest.…”

Section: Introductionmentioning

confidence: 99%

Theoretical studies of UO2(OH)(H2O)n+, UO2(OH)2(H2O)n, NpO2(OH)(H2O)n, and PuO2(OH)(H2O)n+ (n≤21) complexes in aqueous solution

Cao

Balasubramanian

2009

The Journal of Chemical Physics

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Extensive ab initio calculations have been carried out to study equilibrium structures, vibrational frequencies, and the nature of chemical bonds of hydrated UO(2)(OH)(+), UO(2)(OH)(2), NpO(2)(OH), and PuO(2)(OH)(+) complexes that contain up to 21 water molecules both in first and second hydration spheres in both aqueous solution and the gas phase. The structures have been further optimized by considering long-range solvent effects through a polarizable continuum dielectric model. The hydrolysis reaction Gibbs free energy of UO(2)(H(2)O)(5) (2+) is computed to be 8.11 kcal/mol at the MP2 level in good agreement with experiments. Our results reveal that it is necessary to include water molecules bound to the complex in the first hydration sphere for proper treatment of the hydrated complex and the dielectric cavity although water molecules in the second hydration sphere do not change the coordination complex. Structural reoptimization of the complex in a dielectric cavity seems inevitable to seek subtle structural variations in the solvent and to correlate with the observed spectra and thermodynamic properties in the aqueous environment. Our computations reveal dramatically different equilibrium structures in the gas phase and solution and also confirm the observed facile exchanges between the complex and bulk solvent. Complete active space multiconfiguration self-consistent field followed by multireference singles+doubles CI (MRSDCI) computations on smaller complexes confirm predominantly single-configurational nature of these species and the validity of B3LYP and MP2 techniques for these complexes in their ground states.

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Aqueous uranyl complexes. 3. Potentiometric measurements of the hydrolysis of uranyl(VI) ion at 25�C

Cited by 52 publications

References 17 publications

The Use of Geochemical Speciation Modelling to Predict the Impact of Uranium to Freshwater Biota

The Use of Geochemical Speciation Modelling to Predict the Impact of Uranium to Freshwater Biota

Structural characterization of environmentally relevant ternary uranyl citrate complexes present in aqueous solutions and solid state materials

Theoretical studies of UO2(OH)(H2O)n+, UO2(OH)2(H2O)n, NpO2(OH)(H2O)n, and PuO2(OH)(H2O)n+ (n≤21) complexes in aqueous solution

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