Journal•ISSN: 0033-8230
Radiochimica Acta
R. Oldenbourg Verlag
About: Radiochimica Acta is an academic journal published by R. Oldenbourg Verlag. The journal publishes majorly in the area(s): Sorption & Uranium. It has an ISSN identifier of 0033-8230. Over the lifetime, 5644 publications have been published receiving 81868 citations. The journal is also known as: Radiochimica acta (Print).
Topics: Sorption, Uranium, Extraction (chemistry), Aqueous solution, Adsorption
Papers published on a yearly basis
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TL;DR: The Nagra/PSI Chemical Thermodynamic Data Base has been updated to support performance assessments of the planned Swiss repositories for radioactive waste as discussed by the authors, and more than 70% of the database contents have been revised.
Abstract: The Nagra/PSI Chemical Thermodynamic Data Base has been updated to support performance assessments of the planned Swiss repositories for radioactive waste. The update from version 05/92 to 01/01 involved major revisions for most of the actinides and fission products. Altogether, more than 70% of the database contents have been revised. Data for U, Np, Pu, Am and Tc recommended by the NEA TDB project were considered in the update. Thermodynamic data for Th, Sn, Eu, Pd, Al, and solubility and metal complexation of sulphides and silicates were extensively reviewed. Data for Zr, Ni and Se were examined less rigorously as these elements are currently being reviewed in phase II of the NEA TDB project. Our experiences from this two year team effort can be summarised as follows. Detailed in-house reviews and critical appraisal of NEA recommendations greatly improved the chemical consistency and quality of the selected data. On the other hand, we could discern major gaps in the data, especially missing carbonate complexes. In some systems, e.g. Th(IV)-H 2 O and U(IV)-H 2 O, experimental data could not be described by a unique set of thermodynamic constants. There, a pragmatic approach based on solubility data was chosen for application to performance assessment. The electronic version of our database and information concerning its full documentation is available on our PSI web site (http://www.psi.ch/les).
614 citations
TL;DR: In this paper, the solubility and hydrolysis properties of actinide ions were reviewed and a comprehen presented by applying a semi-empirical electrostatic model and an empirical correlation with the known constants of other actinides.
Abstract: Summary. The solubility and hydrolysis of Th(IV), U(IV), Np(IV), and Pu(IV) are critically reviewed and a comprehenpresented. The hydrolysis constants are selected preferentially from experimental studies at actinide trace concentrations, where the interference of colloid formation can be excluded. Unknown formation constants of mononuclear complexes An(OH)n 42n are estimated by applying a semi-empirical electrostatic model and an empirical correlation with the known constants of other actinide ions. Based on the known and estimated hydrolysis constants, the solubility products of An(OH)4(am) or AnO2 2 imental solubility data available in the literature. The SIT is used for ionic strength corrections. The solubilities of U(IV), Np(IV), and Pu(IV) hydroxides or hydrous oxides can be calculated by accounting only for mononuclear hydrolysis species. The considerably higher solubilities of amorphous Th(IV) precipitates at pH , 5 include major contributions of polynuclear species. The solubility data in acidic solutions depend strongly on the preparation and crystallinity of the solid phase. In neutral and alkaline solutions, where An(OH)4(aq) are the predominant aqueous species, the solubilities of AnO 2(cr) become equal to those of the amorphous solids. This indicates that the crystalline dioxides are covered by amorphous hydroxide layers.
501 citations
TL;DR: In this article, the authors reported a further validation of the stoichiometry and the formation constant of this complex using two analytical approaches with time-resolved laser-induced fluorescence spectroscopy (TRLFS) species detection: i) titration of a nonfluorescent uranyl tricarbonate complex solution with calcium ions, and quantitative determination of the produced fluorescent calcium complex via TRLFS; and ii) variation of the calcium concentration in the complex by competitive calcium complexation with EDTA 4−.
Abstract: Summary. We recently discovered a neutral dicalcium uranyl tricarbonate complex, Ca2UO2(CO3)3(aq.), in uranium mining related waters [1]. We are now reporting a further validation of the stoichiometry and the formation constant of this complex using two analytical approaches with time-resolved laser-induced fluorescence spectroscopy (TRLFS) species detection: i) titration of a non-fluorescent uranyl tricarbonate complex solution with calcium ions, and quantitative determination of the produced fluorescent calcium complex via TRLFS; and ii) variation of the calcium concentration in the complex by competitive calcium complexation with EDTA 4− . Slope analysis of the log (fluorescence intensity) versus log [Ca 2+ ] with both methods have shown that two calcium ions are bound to form the complex Ca2UO2(CO3)3(aq.) .T he formation constants determined from the two independent methods are: i) log β ◦ 213 = 30.45 ± 0.35 and ii) log β ◦ 213 = 30.77 ± 0.25. A bathochrome shift of 0.35 nm between the UO2(CO3)3 4− complex and the Ca2UO2(CO3)3(aq.) complex is observed in the laser-induced photoacoustic spectrum (LIPAS), giving additional evidence for the formation of the calcium uranyl carbonate complex. EXAFS spectra at the LII and LIII-edges of uranium in uranyl carbonate solutions with and without calcium do not differ significantly. A somewhat better fit to the EXAFS of the Ca2UO2(CO3)3(aq.) complex is obtained by including the U-Ca shell. From the similarities between the EXAFS of the Ca2UO2(CO3)3(aq.) species in solution and the natural mineral liebigite, we conclude that the calcium atoms are likely to be in the same positions both in the solution complex and in the solid. This complex influences considerably the speciation of uranium in the pH region from 6 to 10 in calcium-rich uranium-mining-related waters.
409 citations
TL;DR: In this article, four important processes that can occur with the actinide cations are: precipitation, complexation, sorption and colloid formation, and the degree to which these four processes progress is strongly dependent on the oxidation state of actinides.
Abstract: In order to predict release and transport rates, as well as design cleanup and containment methods, it is essential to understand the chemical reactions and forms of the actinides under aqueous environmental conditions. Four important processes that can occur with the actinide cations are: precipitation, complexation, sorption and colloid formation. Precipitation of a solid phase will limit the amount of actinide in solution near the solid phase and have a retarding effect on release and transport rates. Complexation increases the amount of actinide in solution and tends to increase release and migration rates. Actinides can sorb on to mineral or rock surfaces which tends to retard migration. Actinide ions can form or become associated with colloidal sized particles which can, depending on the nature of the colloid and the solution conditions, enhance or retard migration of the actinide. The degree to which these four processes progress is strongly dependent on the oxidation state of the actinide and tends to be similar for actinides in the same oxidation state.
258 citations
TL;DR: In this article, a time-resolved laser-induced fluorescence spectroscopy (TRLFS) was used to investigate the chemical speciation of U(VI) in natural seepage water and corresponding model solutions.
Abstract: Chemical speciation of U(VI) in natural seepage water and corresponding model solutions was investigated by time-resolved laser-induced fluorescence spectroscopy. Calculations of uranium speciation in this medium show that U02(C03)3~ and U02(C03) |\" should be the major individual components. Due to the very low fluorescence intensity, the pure uranyl carbonato complexes could not be measured directly by TRLFS. However, a uranium fluorescence spectrum was recorded from seepage water samples. The TRLFS investigations show that the main component of uranium in this seepage water is a calcium uranium carbonato complex. The main fluorescence wavelengths of this complex are at 463.9, 483.6, 502.8, 524.3 and 555.4 nm. The fluorescence lifetime of the species is 64±17 ns. This study shows that the calcium content of the water has a great influence on the uranium speciation. For the first time, the existence of a calcium uranium carbonato complex — (Ca2[U02(C03)3] |
246 citations