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Journal of Radioanalytical and Nuclear Chemistry
Authors: M. Olguin, M. Solache-Rios, D. Acosta, P. Bosch, and S. Bulbulian

Abstract  

The capacity of bentonite and purified bentonite to remove UO 2 2+ ions from aqueous solutions has been investigated. The UO 2 2+ uptake in these clays was determined for 0.2 and 0.002M uranyl nitrate solutions. It was found that under these conditions (0.2M) the maximum UO 2 2+ uptake was 1.010±0.070 meq UO 2 2+ /g of bentonite and 0.787±0.020 meq UO 2 2+ /g of purified bentonite. In purified bentonite UO 2 2+ sorption is irreversible up to 50 hours as no desorption was observed. Such is not the case in the natural bentonite. X-ray diffraction, thermal analyses, and transmission electron microscopy were used to characterize the solids. The uranium content was determined by neutron activation analysis.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: M. Olguin, J. Duque, R. Pomés, M. Villafuerte-Castrejón, L. Sansores, P. Bosch, and S. Bulbulian

Abstract  

The present study discusses the incorporation of uranyl ion into Y-zeolite framework. The UO 2 2+ sorption was measured by neutron activation analyses. The Y-zeolite framework distorts in response to the cations present in the structure. Hence, depending on the amount and the location of the exchanged cations, the features of the X-ray diffraction pattern may vary. From the Rietveld analysis of these patterns, the positions occupied by the UO 2 2+ cations in the zeolite network were determined.

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Abstract  

The extraction of UO 2 2+ from nitrate solution has been carried out using DHDECMP. Different parameters affecting the distribution coefficient of UO 2 2+ have been determined. The extraction of UO 2 2+ was found to have second order dependency on both extractant and H+ concentrations. Addition of some bases as TBP and TOPO to the phosphonate extractant increased the distribution of UO 2 2+ to a great extent. LogD for UO 2 2+ with respect to both synergistic bases was found to be a first order dependent. The thermodynamic parameters have been calculated and the extraction mechanisms have been suggested.

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Abstract  

The behavior of (UO2)2(OH) 2 2+ has been investigated in solid-liquid equilibria under 100%, 8%, 1%, 0.3% and 0.03% CO2 partial pressure as well as in undersaturated systems in equilibrium with air at 24±2°C in 0.1M NaClO4 solutions. From spectroscopic investigations by UV-Vis-and time-resolved laser-induced fluorescence (TRLF) spectroscopies, single component absorption and emission spectra are suggested for the (UO2)2 (OH) 2 2+ species. The lifetime 22 of the fluorescence emitting electronically excited state of (UO2)2(OH) 2 2+ was determined as 22 = 2.9 ± 0.9 s. The formation constant of (UO2)2(OH) 2 2+ was found to be log K22=–5.97 ± 0.06. Interpretation of the experimental data was also made assuming the species (UO2)2(OH) 2 2+ , but unsatisfactory results have been obtained.

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Abstract  

The scavenging of UO2 2+ using 4-sulfonic calix[6]arene in the presence of a strong adsorbent was studied as a function of pH. The adsorbent selected was goethite because of its strong affinity for UO2 2+ and its abundance in natural soils. In order to understand the underlying chemistry of the scavenging process, the adsorption of UO2 2+ and 4-sulfonic calix[6]arene onto goethite, respectively, and the extraction of adsorbed UO2 2+ from goethite surface were modeled using the triple-layer model. The model well explained the pH dependence of the adsorption and extraction processes. This work showed that maximum extraction was obtained around pH 10.5 in the presence of 12g/l goethite in the case of a 1:3T U(VI):T calixareneratio.

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Abstract  

The kinetics of particle-diffusion controlled ion exchange in the ternary system of cations UO 2 2+ –Na+–H+–001×7 strong acidic resin has been studied. In the [R–H+]/(Na++UO 2 2+ ) system, the change of the amount of Na+ in the resin phase with time showed a high peak. In the [R–Na+]/(H++UO 2 2+ ) system, the change of the amount of H+ in the resin phase with time also showed a high peak. In the [R2–UO 2 2+ ]/(H++Na+) system, the change of amount of H+ in the resin phase with time showed merely a small peak. This kinetic character of the ternary ion exchange system in the finite solution volume has been analyzed according to the Nerst-Planck equation, and on the whole, the trend of the experimental results is consistent with the resulting numerical solution of the set of Nerst-Planck equations.

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Abstract  

A series of UO2 2+ complex with monoamide ligand was isolated. The complexes have been characterized with the aid of 13C and 1HNMR spectroscopic studies. The result shows that the amide ligand directly coordinates to the uranyl(VI) ion through its carbonyl group. The change of the value of the chemical shift due to the complexation has been discussed.

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Abstract  

The study was undertaken to evaluate the feasibility of functionalized multi-walled carbon nanotubes (MWCNTs) for the removal of UO2 2+ from aqueous solutions. The MWCNTs was treated by oxygen plasma and characterized by FTIR and XPS. The characterization indicates that MWCNTs is successfully functionalized of oxygen groups such as –COOH on its surface (denote as P-MWCNTs). The sorption of UO2 2+ from aqueous solution on P-MWCNTs was studied as a function of contact time, solid contents, pH, ionic strength and temperature under ambient conditions using batch experiment. Two simplified kinetic models of pseudo-first-order and pseudo-second-order were tested to determine kinetic parameters such as rate constants, equilibrium sorption capacities and related correlation coefficients for kinetic models of the sorption process. It can be seen that the UO2 2+ sorption on P-MWCNTs could be described more favorably by the pseudo-second-order model. The thermodynamic parameters (∆G°, ∆S°, ∆H°) calculated from the temperature-dependent sorption isotherms indicated that the sorption of UO2 2+ on P-MWCNTs were an endothermic and spontaneous processes. The results of the present study suggest that P-MWCNTs can be used beneficially in treating industrial effluents containing radioactive and heavy metal ions.

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Abstract  

We report on the bimolecular quenching rate constants (k q) of the *UO2 2+ with 1-naphthol, 2-naphthol and dihydroxynaphthols compounds in 1M H3PO4 medium and describe the appearance of stable photoproducts which is attributed to the photodegradation of the naphtholic compounds.

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Abstract  

The present paper deals with an experimental study on the bioleaching of a poor uranium ore by means of hydrophytic plants Lemna minor and Riccia fluitans, under various operating conditions. The maximum degree of bioleaching (42%) of the reduced uranium species to U(VI) has been attained for the ore-Lemna minor-alkaline carbonate solution system. The UO2 2+ ions amount accumulated in the plants is negligible as compared to the dissolved quantity, owing to the ionic competition between uranyl ions and the cations necessary to the mineral nutrition. The X-ray diffraction patterns prove that the uranium species in pyrochlore mineral are completely oxidized to U(VI), while thucolite is only partially turned into UO2 2+ ions, in the presence of living plants.

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