A Comparison Between Unirradiated UO<sub>2</sub>(s) and Schoepite Solubilities in 1 Μ NaCl Medium

Torrero, M.E.; Casas, I.; Pablo, Joan de; Sandino, M. C. A.; Grambow, Bernd

doi:10.1524/ract.1994.6667.special-issue.29

Cited by 38 publications

(18 citation statements)

References 15 publications

(22 reference statements)

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“…This agrees with studies showing the formation of U colloids in solutions where polynuclear aqueous U(VI) species pre-exist ( Fig. 2) and of meta-stable uranyl oxide hydrates in super-saturated solutions (Dent et al, 1992;Torrero et al, 1994;DiazArocas and Grambow, 1998). The major assessment of our experimental work is that sorption onto large surface areas of Al-hydroxide controls the removal of U from aqueous phase for such unstable solutions at ½U I AQ P 10 lM, as well as for the stable uranyl solutions.…”

Section: Macroscopic Uranyl Uptakesupporting

confidence: 91%

“…Note that low U coverage samples were obtained over ranges of ½U I AQ values (1-100 lM). Torrero et al (1994) Values are at 298 K and at infinite dilution standard state. a Value selected in the thermodynamic data compilation of Grenthe et al (1992) and confirmed in the revised selection of Guillaumont et al (2003).…”

Section: Presentation Of the Spectroscopic Samplesmentioning

confidence: 99%

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Uranyl sorption species at low coverage on Al-hydroxide: TRLFS and XAFS studies

Froideval

Nero

Gaillard

et al. 2006

Geochimica et Cosmochimica Acta

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International audienceDetailed understanding of the respective roles of solution and surface parameters on the reactions at uranyl solution/Al-(hydr)oxide interfaces is crucial to model accurately the behaviour of U in nature. We report studies on the effects of the initial aqueous uranyl speciation in moderately acidic solutions, e.g. of mononuclear, polynuclear uranyl species and/or (potential) U(VI) colloids, on the sorption of U by large surface areas of amorphous Al-hydroxide. Investigations by Extended X-ray Absorption Fine Structure (EXAFS) and Time-Resolved Laser-induced Fluorescence Spectroscopy (TRLFS) reveal similar U coordination environments on Al-hydroxide for low to moderate U loadings of sorption samples obtained at pH 4–5, independently of the presence of mononuclear or polynuclear aqueous species, or of the potential instability of initial solutions favoring true U-colloids formation. EXAFS data can be interpreted in terms of a dimeric, bidentate, inner-sphere uranyl surface complex as an average of the U surface structures. TRLFS data, however, provide valuable insights into the complex U surface speciation. They indicate multiple uranyl surface species under moderately acidic conditions, as predominant mononuclear and/or dinuclear, inner-sphere surface complexes and as additional minor species having U atoms in a uranyl (hydr)oxide-like coordination environment. The additional species probably occur as surface polymers and/or as adsorbed true U colloids, depending on the aqueous U concentration level (1–100 μM). These results are of importance because they suggest that Al-hydroxide surface characteristics strongly control uranyl surface species in moderately acidic systems

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Section: Macroscopic Uranyl Uptakesupporting

confidence: 91%

Section: Presentation Of the Spectroscopic Samplesmentioning

confidence: 99%

Uranyl sorption species at low coverage on Al-hydroxide: TRLFS and XAFS studies

Froideval

Nero

Gaillard

et al. 2006

Geochimica et Cosmochimica Acta

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“…The value of the solubility product of schoepite at 25°C was experimentally determined by Torrero et al (1994): K schoepite = 10 5.38 . In order to calculate saturation indices with respect to schoepite using equation (2), it is necessary to know the activity of the uranyl cation, a(UO 2+ 2 ), and the pH of the solutions.…”

Section: Identification Of Minerals On the Surface Of Calcitementioning

confidence: 99%

Crystal Growth of Schoepite on the (104) Surface of Calcite

Schindler

Putnis

2004

The Canadian Mineralogist

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12 , cristallise suite à une interaction de solutions uranylées acides ou basiques avec la calcite. Ces solutions uranylées possèdent une concentration de (UO 2 ) 2+ entre 1.5 et 50 mmol L -1 , et une valeur initiale de pH de 2.5, 4.5 ou 10.0. Un examen des cristaux avec le microscope à force atomique (AFM) révèle les morphologies distinctes des cristaux de schoepite formés sur la surface (104) de la calcite. Les cristaux formés au cours des expériences in situ avec une solution de nitrate uranylée (pH initial = 2.5) ont une morphologie en plaquettes, et leur face proéminente (001) est définie par des arêtes [210]. Les cristaux formés au cours des expériences in situ avec une solution d'acétate uranylée (pH initial = 4.5) semblent plus trappus, avec des faces rectangulaires (001) de piètre qualité. Un examen des surfaces de calcite suite à une interaction avec une solution légèrement acide pour trois jours (pH final entre 5.5 et 6.5) montre des cristaux en plaquettes assymétriques avec des faces (001) proéminentes définies par les arêtes [100], [010], [120], et [110]. Des expériences avec des solutions basiques après trois semaines (pH final entre 7.5 et 8.0) révèlent de gros cristaux rectangulaires de schoepite, dans lesquels la face (001) est surtout définie par les arêtes [100] et [010]. Les épaisseurs différentes des cristaux de schoepite dans les expériences in situ seraient dues aux taux de croissance différents des faces S et F des solutions ayant des indices de saturation différents par rapport à la schoepite. La présence d'arêtes sur la face (001) des cristaux de schoepite dépendrait des paramètres structuraux des chaînes de polyèdres parallèles aux arêtes et au pH de la solution.(Traduit par la Rédaction)

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“…Thermodynamic data for aqueous uranyl species and solubility constants of U-bearing solid phases were adjusted to be consistent with the NEA database [27]. The formation constant of UO 2 (OH) 2 [28] and solubility constant of "amorphous" schoepite from Torrero et al [29] were also added to the database. Calculation of U speciation shows that more than 96% of the U VI occur as uranyl ions (UO 2+ 2 ) in the experimental suspensions over the entire range of U concentration.…”

Section: The Removed Quantity Of Uranyl Ion (Uo 2+mentioning

confidence: 99%

A simplified method to estimate kinetic and thermodynamic parameters on the solid–liquid separation of pollutants

Montes-Hernandez¹,

Rihs²

2006

Journal of Colloid and Interface Science

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The aim of the present study was to propose a simplified experimental-theoretical method for estimating the kinetic and thermodynamic parameters for the solid-liquid separation of pollutants by using kinetic studies with batch reactors, i.e., the removed quantity of dissolved ion as a function of time at different initial concentration. This method was applied to the removal of uranyl ion (UO(2+)(2)) from aqueous solutions onto synthetic manganese oxide (birnessite). The pseudo-second-order kinetics and one-site saturation models were proposed to fit the experimental and calculated data, the fitting parameters being estimated by nonlinear regression, using the least-squares method. For initial concentration range 0.2-11.8 microM, the results showed that the uranyl removal process in dispersed batch reactors can be efficiently modeled by the proposed models. Then, several kinetic and thermodynamic parameters were calculated, such as maximal removed quantity of uranyl, q(r,max), half-removal time, t(1/2), initial rate of uranyl-ion removal, v(0), initial uranyl-removal coefficient, K, maximal rate of uranyl removal, v(0,max), mass transfer coefficient, D(transfer), equilibrium Langmuir constant, K(L), and constant separation factor, K(s). These parameters make it possible to demonstrate that the removal of U onto birnessite is favorable, and that the maximum surface coverage of the uranyl ions represents about 3% of vacant sites in the Mn layer.

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A Comparison Between Unirradiated UO₂(s) and Schoepite Solubilities in 1 Μ NaCl Medium

Cited by 38 publications

References 15 publications

Uranyl sorption species at low coverage on Al-hydroxide: TRLFS and XAFS studies

Uranyl sorption species at low coverage on Al-hydroxide: TRLFS and XAFS studies

Crystal Growth of Schoepite on the (104) Surface of Calcite

A simplified method to estimate kinetic and thermodynamic parameters on the solid–liquid separation of pollutants

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A Comparison Between Unirradiated UO2(s) and Schoepite Solubilities in 1 Μ NaCl Medium

Cited by 38 publications

References 15 publications

Uranyl sorption species at low coverage on Al-hydroxide: TRLFS and XAFS studies

Uranyl sorption species at low coverage on Al-hydroxide: TRLFS and XAFS studies

Crystal Growth of Schoepite on the (104) Surface of Calcite

A simplified method to estimate kinetic and thermodynamic parameters on the solid–liquid separation of pollutants

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Product

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A Comparison Between Unirradiated UO₂(s) and Schoepite Solubilities in 1 Μ NaCl Medium