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Journal of Radioanalytical and Nuclear Chemistry
Authors: Frederic Poineau, Charles Yeamans, G. Silva, Gary Cerefice, Alfred Sattelberger, and Kenneth Czerwinski

Abstract  

Uranium mononitride (UN), sesquinitride (U2N3) and dinitride (UN2) were characterized by extended X-Ray absorption fine structure spectroscopy. Analysis on UN indicate the presence of three uranium shells at distances of 3.46(3), 4.89(5) and 6.01(6) Å and a nitrogen shell at a distance of 2.46(2) Å. For U2N3, two absorbing uranium atoms at different crystallographic positions are present in the structure. One of the uranium atoms is surrounded by nitrogen atoms at 2.28(2) Å and by uranium atoms at 3.66(4) and 3.95(4) Å. The second type of uranium atom is surrounded by nitrogen atoms at 2.33(2) and 2.64(3) Å and by uranium atoms at 3.66(4), 3.95(4) and 5.31(5) Å. Results on UN2 indicate two uranium shells at 3.71(4) and 5.32(5) Å and two nitrogen shells at 2.28(2) and 4.34(4) Å. The lattice parameters of UN, U2N3 and UN2 unit cells were respectively determined to be 4.89(5), 10.62(10) and 5.32(5) Å. Those results are well in agreement with those obtained by X-Ray diffraction analysis.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: A. Efstathopoulos, K. Karfopoulos, D. Karangelos, N. Petropoulos, E. Hinis, and S. Simopoulos

Abstract  

Phosphorimetry is an analytical technique for the determination of elemental uranium concentration in aqueous environmental or biological samples. Uranium phosphorescence from aqueous samples at room temperature is practically undetectable without the addition of a uranium complexant, i.e., a solution whose molecules bind to the uranyl ions present in the sample under measurement and protect them from non-luminescent de-excitation. Procurement of commercially available and proprietary in nature complexant solutions can prove cost in-effective. On the other hand, phosphoric acid is known for its phosphorescence protecting capabilities. This study investigates the optimisation of phosphoric acid use as uranium complexant, and assesses it in terms of accuracy, precision and longevity, with rather encouraging results.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: Stefan Bister, Florian Koenn, Maruta Bunka, Jonny Birkhan, Torben Lüllau, Beate Riebe, and Rolf Michel

Abstract  

The Mulde River is a left side tributary of the Elbe River and mainly situated in Saxony. The river system consists of the Freiberger Mulde River and the Zwickauer Mulde River, which merge to form the Vereinigte Mulde River. The Zwickauer Mulde River drains the former uranium mining and milling areas in Saxony. This research project was established to quantify the long-term effect of the former uranium mining and milling activities by investigating the content of uranium of the water of the Mulde River. The activity concentration of uranium in samples from the Zwickauer Mulde River is still high compared with the natural background. The values measured in the water of the Vereinigte Mulde River are also elevated, but to a lesser extent due to the dilution effect caused by the merging with the uncontaminated Freiberger Mulde River. Furthermore, the level of contamination of the river water decreased by at least a factor of three as compared to the early 1990s.

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Abstract  

The adsorption of uranium from crude phosphoric acid has been investigated using conventional activated carbons. It was found that treatment with nitric acid oxidized the surface of activated carbon and significantly increased the adsorption capacity for uranium in acidic solutions. The parameters that affect the uranium(VI) adsorption, such as contact time, solution pH, initial uranium(VI) concentration, and temperature, have been investigated. Equilibrium data were fitted to a simplified Langmuir and Freundlich isotherms for the oxidized samples which indicate that the uranium adsorption onto the activated carbon fitted well with Langmuir isotherm than Freundlich isotherm. Equilibrium studies evaluate the theoretical capacity of activated carbon to be 45.24 g kg−1.

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Abstract  

Immobilized Saccharomyces cerevisiae (ISC) was prepared by the sodium alginate–gelatin embedding method after dry cells had been cross-linked by formaldehyde. Adsorption of uranium(VI) by incompletely and completely dry ISC was studied. The results indicated that incompletely dry ISC had greater adsorption capacity for U(VI), with physical adsorption being the primary mechanism, whereas completely dry ISC exhibited much greater rigidity and much smaller volume. Therefore, initial absorption of U(VI) by incompletely dry ISC followed by heating could be compared with glass solidification for disposal of radioactive waste. The influence of solution pH, temperature, and contact time on U(VI) absorption was also studied, with pH being found to be the main influencing factor. The adsorption mechanism of completely dry ISC was explored by scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) spectroscopy, indicating that the main adsorption mechanism is chemical adsorption.

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Abstract  

The activity concentrations of 238U and 234U have been determined in groundwater samples of hot springs and deep wells in Northern Greece. The analysis was performed by alpha spectroscopy after pre-concentration and separation of uranium by cation exchange (Chelex 100 resin) and finally its electro-deposition on stainless steel discs. The uranium concentration in deep wells and springs varies strongly between 0.15 and 7.66 μg L−1 and the corresponding 238U and 234U activity concentrations between 1.82–95.3 and 1.70–160.1 mBq L−1, respectively. The obtained isotopic ratio 234U/238U varies between 0.95 and 1.74 indicating a disturbed radioactive equilibrium between the two uranium isotopes. In the studied waters uranium concentrations in solution decrease with increasing pH in the pH range between 7 and 9. This is attributed to the fact that at lower pH dissolution of soil minerals occurs and uranium which is adsorbed or forms solid solution with the geological matrix enters the aqueous phase. The strong dependence of the uranium concentration in the studied waters from the dissolution of the geological matrix is corroborated by the strong correlation of the uranium concentration with the electrical conductivity measured in the ground waters under investigation.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: Jorge Guzmán Mar, Leticia López Martínez, Pedro López de Alba, Nancy Ornelas Soto, and Víctor Cerdà Martín

Abstract  

A multisyringe flow injection analysis method for the determination of uranium in water samples was developed. The methodology was based on the complexation reaction of uranium with arsenazo (III) at pH 2.0. Uranium concentrations were spectrophotometrically detected at 649 nm using a light emitting diode. Under the optimized conditions, a linear dynamic range from 0.1 to 4.0 μg mL−1, a 3σ detection limit of 0.04 μg mL−1, and a 10σ quantification limit of 0.10 μg mL−1 were obtained. The reproducibility (%) at 0.5, 2.5, and 4.0 μg mL−1 was 2.5, 0.9, and 0.6%, respectively (n = 10). The interference effect of some ions was tested. The proposed method was successfully applied to the determination of uranium in water samples.

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Abstract  

Urine assay is the preferred method for monitoring accidental or chronic internal intake of uranium into the human body. A new radiochemical separation procedure has been developed to provide isotopic uranium analysis in urine samples. In the procedure, uranium is co-precipitated with hydrous titanium oxide (HTiO) from urine matrix, and is then purified by anion exchange chromatographic column. Alpha spectrometry is used for isotopic uranium analysis after preparation of a thin-layer counting source by cerium fluoride micro-precipitation. Replicate spike and procedural blank samples were prepared and measured to validate the procedure. The 232U tracer was utilized for chemical recovery correction, and an average recovery of 76.2 ± 8.1% was found for 1400 mL urine samples. With 48 h of counting, the minimum detectable activity concentrations were determined to be 0.43, 0.21 and 0.42 mBq/L for 238U, 235U and 234U, respectively.

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Abstract  

In order to understand the mobility of uranium it is very important to know about its sorption kinetics and the thermodynamics behind the sorption process on soil. In the present study the sorption kinetics of uranium was studied in soil and the influence parameters to the sorption process, such as initial uranium concentration, pH, contact time and temperature were investigated. Distribution coefficient of uranium on soil was measured by laboratory batch method. Experimental isotherms evaluated from the distribution coefficients were fit to Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models. The sorption energy for uranium from the D–R adsorption isotherm was calculated to be 7.07 kJ mol−1.The values of ΔH and ΔS were calculated to be 37.33 kJ mol−1 and 162 J K−1 mol−1, respectively. ΔG at 30 °C was estimated to be −11.76 kJ mol−1. From sorption kinetics of uranium the reaction rate was calculated to be 1.6 × 10−3 min−1.

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Abstract  

An ion exchange method has been developed for the separation of uranium from trace level metallic impurities prior to their determination by inductively coupled plasma optical emission spectrometry (ICP-OES) in uranium materials. Selective separation of uranium from trace level metallic impurities consisting Cr, Co, Cu, Fe, Mn, Cd, Gd, Dy, Ni, and Ca was achieved on anion exchange resin Dowex 1 × 8 in sulphate medium. The resin (100–200 mesh, in chloride form) was packed in a small Teflon column (7.8 cm × 0.8 cm I.D.) and brought into sulphate form by passing 0.2 N ammonium sulphate solution. Optimum experimental conditions including pH and concentration of sulphate in the liquid phase were investigated for the effective uptake of uranium by the column. Uranium was selectively retained on the column as anionic complex with sulphate, while impurities were passed through the column. Post column solution was collected and analyzed by ICP-OES for the determination of metallic impurities. Up to 2,500 μg/mL of uranium was retained with >99% efficiency after passing 25 mL sample through the column at pH 3. Percentage recoveries obtained for most of the metallic impurities were >95% with relative standard deviations <5%. The method established was applied for the determination of gadolinium in urania–gadolinia (UO2–Gd2O3) ceramic nuclear fuel and excellent results were achieved. Solvent extraction method using tributylphosphate (TBP) as extractant was also applied for the separation of uranium in urania–gadolinia nuclear fuel samples prior to the determination of gadolinium by ICP-OES. The results obtained with the present method were found very comparable with those of the solvent extraction method.

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