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Abstract  

Heavy metals like the actinides possess a high risk potential to the environment not only because of their radiotoxicity but also due to their chemical toxicology. Uranium as one of the major actinide elements has to be considered in particular. Under reducing conditions, tetravalent uranium occurs primarily in the environment. To date, a lack of appropriate analytical techniques that featured sufficient sensitivity made it difficult to study the aqueous phosphate chemistry of uranium(IV) as such complexes show only low solubility. A novel time-resolved laser fluorescence spectroscopy system was set up recently and optimized to do research on uranium(IV). By application of this laser system we could successfully study uranium(IV) phosphate in concentration ranges where no precipitation or formation of colloids occurred. At pH = 1.0, U4+ and one uranium(IV) phosphate complex existed in parallel in aqueous solution. The complex could be identified as [U(H2PO4)]3+. Determination of its corresponding complex formation constant via two different evaluation methods resulted in the finding of (1)
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\log \beta_{121}^{ \circ } = 2 6. 3 7 \pm 0. 7 6$$ \end{document}
and (2)
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\log \beta_{121}^{ \circ } = 2 6. 4 3 \pm 0. 2 3$$ \end{document}
. Both values prove that [U(H2PO4)]3+ is a very stable complex in solution under experimental conditions. As they are in very good agreement with each other, the total complex formation constant was determined by means of the weighted average out of (1) and (2). It was calculated to be
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\log \beta_{121}^{ \circ } = 2 6. 4 2 \pm 0. 2 2$$ \end{document}
.
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Abstract  

Uranium is a toxic element due to its radioactivity. Developing analytical methods of uranium for avoiding its damage is necessary. In this study, we found that the catalytic effect of mercury(II) on the precipitation reaction of potassium ferrocyanide with potassium ferricyanide could be inhibited strongly by uranium(IV). The sediment produced from the reaction could be deposited on a magnetoelastic foil, resulting in a resonance frequency shift of the foil due to its mass change. The resonance frequency shift of the foil could be wirelessly detected with a detection system. Based on these facts, a wireless magnetoelastic sensing method for the determination of uranium(IV) has been developed based on the inhibitory effect of uranium(IV) on the catalytic precipitation reaction. The influence of manifold variables on the determination was investigated in details. A linear range was found to be 0.9–15.0 μg/L under optimal conditions with a detection limit of 0.46 μg/L. The method offers an opportunity for remote measurement of radioactive samples containing uranium in sealed vessels, which is beneficial to protecting operator health. The method was applied to determine uranium(IV) in real samples with satisfactory results.

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Abstract  

Two tris(oxouranium)-substituted Keggin and Dawson sandwich-type tungstophosphate heteropolyanions Na12[(UO)3(H2O)6(PW9O34)2]·21 H2O (1) and Na18[(UO)3(H2O)6(P2W15O56)2]·27 H2O (2) have been prepared by reaction of uranium sulphate with [PW9O34]9− and [P2W15O56]12−, respectively, in aqueous media at 4.7 pH. The products were characterized by elemental and thermal analyses, IR, UV-Vis spectroscopy and magnetical susceptibility. The results of these studies suggest that the compounds obtained from Keggin and Dawson trilacunary anions are 2∶3 sandwich-type complexes and both exhibit a square antiprismatic stereochemistry for uranium(IV) with retention of polyoxometallate parent structure.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: M. Rusu, D. Rusu, C. Roşu, C. Crăciun, L. David, A.R. Tomşa, and Gh. Marcu

Abstract  

A new uranium tungstoborate heteropolyanion K12[U(BW11O39H)2]·23 H2O has been prepared and investigated by thermal analyses, IR, UV-Vis spectroscopy and magnetic susceptibility measurements. The compound obtained from Keggin monolacunary anions is 1:2 sandwich-type and exhibits a square antiprismatic stereochemistry for uranium (IV) ion.

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Summary  

Six sandwich-type uranium(IV)-polyoxometalates (UIV-POM) were prepared and investigated by FT-IR and UV-VIS spectroscopy. Changes in position and shape of antisymmetric stretching vibration bands in the 640-1000 cm-1 region were identified in all UIV-POM FT-IR spectra. These changes are related to coordination of U(IV) to the trilacunary Keggin units. Visible electronic spectra of aqueous solutions of UIV-POM complexes correspond to uranium 3H4 electronic ground state, having a quasicubic configuration. Presence of electronic transitions were identified by UV spectroscopy of UIV-POM complexes in aqueous solutions.

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Abstract  

The polyoxotungstate K19[U2KAs4W40O140].42H2O was synthesized and investigated by spectroscopic and magnetic susceptibility measurements. The IR spectrum of the complex contains the nas(U–O)»1133 cm–1 band due to the uranium coordination at {AsW9} units and WO6 binding octahedra. Electronic spectra indicate a 3H4 ground state for the uranium(IV) in a quasicubic configuration. ESR spectra show a small orthorhombic distortion from the cubic symmetry (g x = 2.045, g y = 2.050, g z = 2.085, D = 18.31.10–4 .cm–1, E = 5.99.10–4 .cm–1). The uranium ions are antiferromagnetically coupled for T>200 K (meff = 1.3 mB at room temperature).

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A study was made of the thermal decompositions of the hydrates of 5 neutral sulphate complexes and 5 hydroxy-sulphate complexes of uranium(IV). The hydrates did not yield corresponding stable anhydrous compounds. After dehydration, the complexes decomposed in endothermic reactions involving progressive substitution of sulphur trioxide (that is liberated) by oxygen, giving oxy-sulphates and other compunds.

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Abstract  

A simple analytical procedure for the sequential determination of uranium (IV), free acidity and hydrazine in presence of hydrolysable ions is developed and described. In this method, first, uranium (IV) is determined using fiber optic aided spectrophotometry then same solution is used for determination of free acidity and hydrazine. Free acid is titrated with standard sodium carbonate solution after uranium (IV) is masked with EDTA. Once the end point for the free acid is determined at pH 3.0, an aliquot of formaldehyde is added to liberate the acid equivalent to hydrazine which is then titrated with the same standard sodium carbonate solution using an automatic titration system. The described method is simple, accurate and reproducible. The overall recovery of uranium (IV), nitric acid and hydrazine is 98% with 3% relative standard deviation respectively. The major advantage of the method is that it uses sodium carbonate a primary standard as titrant and generation of corrosive analytical wastes containing oxalate or sulphate is avoided. Valuable metals like uranium and plutonium can easily be recovered from analytical waste before final disposal.

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Abstract  

A kinetic spectrophotometric method has been developed for the determination of trace amounts of uranium(IV) based on its catalytic effect on the phosphomolybdic acid iodide reaction. A significant feature of the proposed procedure is the selectivity for uranium(IV); it enables the determination of trace amount of uranium in the presence of large excess of rare metalions and other cations and anions. The method can be applied to the determination of uranium within the concentration range of 0–12g· cm–3, and the detection limit of the method is 0.02g·cm–3. Trace amounts of uranium in thorium nitrate and scandium oxide had been determined by the procedure and the results are satisfactory.

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Abstract  

The kinetics of stripping of thorium(IV) and uranium(IV) from tributylphosphate (TBP)-kerosene with dilute nitic acid solution has been studied using the Lewis cell technique. The effects of concentrations of Th(IV), U(IV), nitric acid, TBP, temperature and stirring speed on the stripping rate have been examined. The result show that the stripping rates of Th(IV) and U(IV) are all controlled by diffusion process.

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