The micro volumetric determination of uranium with application to bismuth base alloy analysis

The macro volumetric method for the determination of uranium by titration against standard ceric sulphate after reduction on a lead column has been successfully applied on the micro scale Microgram amounts of uranium can be determined by this method, the lowest amount determinable being about 1 microgram. The procedure is accurate to within ±1% at the 100 μg level of uranium Although bismuth and iron cause difficulty, there is no interference from zirconium or thorium.This method for uranium has been applied to the analysis of bismuth base alloys containing uranium in concentrations from 0.005 to 0.1% by weight.     

Sorption of uranium (VI) species on zircon: structural investigation of the solid/solution interface

This work is an investigation of the mechanisms of interaction between uranium (VI) ions and zirconium silicate. The speciation of uranium (VI) sorbed on zircon was studied using four complementary techniques as probes of the local structure around the uranium atom: laser spectrofluorimetry, X-ray photoelectron spectroscopy (XPS), diffuse reflectance infrared Fourier-transformed (DRIFT) spectroscopy, and EXAFS spectroscopy. The sorption of uranyl on zirconium oxide was also studied to allow structural comparisons. Spectrofluorimetry and XPS results allowed an identification of the silicate sorption sites on the solid. These methods associated with spectrofluorimetry and DRIFT led to a characterization of the sorbed surface complexes, taking into account the influence of the nature of the background salt and of the pH on the structure of the U(VI) surface species. EXAFS measurements, either on air-dried samples or in situ, were then carried out on well-characterized samples and allowed identification of the sorption mechanism on zircon as the formation of an inner-sphere polydentate surface complex.     

The determination of zirconium in fluoride-containing solutions

In the recommended procedure the zirconium is first precipitated from solution as the insoluble barium fluozirconate. After separation, the precipitate is dissolved in a mixture of nitric and boric acids and the zirconium is then precipitated as its hydroxide. This precipitate is separated, dissolved in hydrochloric acid and this solution is evaporated to fumes of perchloric acid to remove completely fluoride ions. The zirconium content is then determined volumetrically by adding a slight excess of a standard solution of ethylenediaminetetra-acetic acid and back titrating with a standard iron solution at pH 2.3 using potassium benzohydroxamate as indicator and the photometric technique for end-point detection. This method is applicable to the determination of milligram amounts of zirconium in fluoride-containing nitric or hydrochloric acid solutions provided that the concentration of these acids is below 3N. It is also suitable for the determination of zirconium in the presence of any of the following elements - uranium, titanium, niobium, tantalum, molybdenum, tungsten, lead, iron, copper and tin.     

Simultaneous spectrophotometric determination of trace amounts of uranium, thorium, and zirconium using the partial least squares method after their preconcentration by α-benzoin oxime modified Amberlite XAD-2000 resin

A new solid phase extraction method for separation and preconcentration of trace amounts of uranium, thorium, and zirconium in water samples is proposed. The procedure is based on the adsorption of U(VI), Th(IV) and Zr(IV) ions on a column of Amberlite XAD-2000 resin loaded with α-benzoin oxime prior to their simultaneous spectrophotometric determination with Arsenazo III using orthogonal signal correction partial least squares method. The enrichment factor for preconcentration of uranium, thorium, and zirconium was found to be 100. The detection limits for U(VI), Th(IV) and Zr(IV) were 0.50, 0.54, and 0.48 μg L⁻¹, respectively. The precision of the method, evaluated as the relative standard deviation obtained by analyzing a series of 10 replicates, was below 4% for all elements. The practical applicability of the developed sorbent was examined using synthetic seawater, natural waters and ceramic samples.     

Electronic structure of a uranium impurity center in zircon

The electronic structure of a large fragment of the crystal lattice of zircon ZrSiO₄ with a uranium impurity atom replacing the zirconium atom was investigated using the completely relativistic discrete variation (DV) cluster method. The results are compared with the data of a similar calculation of the ideal ZrSiO₄ crystal. An analysis of the overlap populations and effective charges on the atoms of the matrix and impurity showed that chemical binding of uranium with the environment is covalent, and the electron density redistribution caused by this substitution changes not only the impurity and the nearest environment, but also the atoms of the next coordination spheres.     

Determination of small amounts of uranium in hafnium,zirconium and zircaloy-2

To meet specification requirements, selected methods for determining uranium have been examined and two satisfactory procedures have been developed for application to the analysis of reactor-grades of hafnium, zirconium and Zircaloy-2.These procedures are based on extraction of uranyl ions from a solution of the sample with a tri-n-butyl phosphate-iso-octane mixture. Following this extraction, uranium over the range 10–150 p.p.m. is determined by a spectrophotometric method, using dibenzoylmethane. For smaller amounts of uranium, down to about 0.5 p.p.m., the determination is completed by squarewave polarography.     

The determination of uranium in alloy systems

A procedure is described for the determination of the uranium content of metallurgical alloys containing this element as a minor constituent. The uranium is first separated from the sample solution by precipitation as uranyl ammonium phosphate in the presence of ethylenediamine-totra-acetic acid. By this means the uranium is separated from many elements including iron, chromium, copper, nickel, vanadium, cerium, ncodymium and bismuth. Tho uranyl ammonium phosphate precipitate is dissolved in hydrochloric acid and the resulting solution is passed through a lead reductor. The tetravalent uranium is titrated with a standard cerie sulphate solution, using ferroin as the indicator. This procedure has proved very suitable for the analysis of bismuthuranium binary alloys containing uranium in amounts up to approximately 20%.     

Characterization of hot particles in surface soil around the Chernobyl NPP

An ICP-AES method for the analysis of trace amounts of lanthanides and yttrium in sodium or magnesium diuranate samples (yellow cake) and other beneficiation product generated during the uranium extraction process (hydrometallurgy) from its ores is described. Most of the matrix elements are removed by an initial oxalate precipitation of lanthanides using calcium as carrier. A solvent extraction procedure using a mixture of mono 2-ethylhexyl dihydrogen phosphate (H₂MEHP) and bis (2-ethylhexyl) hydrogen phosphate (HDEHP) is used for the removal of calcium, iron and the occluded uranium. A combination of oxalate precipitation and solvent extraction procedure is applied for the selective separation and preconcentration of traces of lanthanides from yellow cake and iron cake samples. The solvent extraction procedure is directly applied for the separation of lanthanides from the uranium leach liquor and lime cake. The accuracy of the method is checked by analyzing synthetic mixture containing known amounts of traces of lanthanides and also by comparing with another standard separation procedure like ion exchange method, and the recovery was better than 95%. The method is rapid, simple, accurate and suitable for the separation of lanthanides from uranium, iron and calcium rich materials. The precision of the method is characterized by an RSD of 2 to 4%.     

Solvent extraction separations with bpha. applications to the microanalysis of niobium and zirconium in uranium

A detailed study of the benzoylphenylhydroxylamine (BPHA)-chloroform-hydrochloric acid solvent extraction system with 52 elements is described with emphasis placed on extraction of the easily hydrolyzed transition metals from strong hydrochloric acid. From this study, a separation procedure for hafnium, niobium, tantalum, titanium, vanadium, and zirconium from uranium was developed, and procedures are given for the microanalysis of niobium and zirconium in uranium. Niobium and zirconium are separated from uranium by extraction into BPHA-chloroform from 10-N HCl.The separated elements are then measured colorimetrically as the niobium-4-(2-pyridylazo)resorcinol and zirconium-arsenazo III complexes. The limit of detection is 1 μg/g U.     

Polarometrische bestimmung von zirkonium(IV) mit tartrazin

A new polarimetric procedure has been developed for the rapid determination of zirconium in the presence of tartrazin as reagent This determination is possible in the presence of uranium.     

Determination of uranium, thorium and rare-earth elements in zircon samples using ICP-MS

Zircon is an accessory mineral, which occurs at low concentrations in a wide variety of rocks and is a host for hafnium, rare-earth elements (REE) and radio active elements like uranium and thorium. The presence of uranium in zircon has led to its increased use in the age determination of rocks. Zirconium is also considered as a strategic, hi-tech element because of its various applications, especially in the manufacturing, nuclear and aerospace industries. Analysis of zircon constitutes one of the tough tasks in analytical chemistry as it is a highly resistant mineral and it is extremely difficult to achieve its complete decomposition. In the present work, inductively coupled plasma mass spectrometry has been applied to the determination of hafnium, REE, uranium and thorium in zircon samples using two different sample dissolution procedures, one employing sodium peroxide fusion and another using a fusion mixture of KHF₂ and NaF in 3:1 ratio. Some selected zircon samples originating from different places on the eastern coast of India have been analysed by both the methods and values obtained by both methods were found to be in good agreement with each other. Though a number of international zircon reference materials are available, certified or even proposed values are available only for a very few elements in them. Two zircon reference materials have also been analysed by both methods and usable values have been proposed in this paper. The values obtained by both methods were found to compare well with each other and as well with those reported in literature. The % RSD for all the estimated elements varied from 1.0 to 12.0% at different concentration levels.     

Separation of protactinium from uranium and other reaction products in the reaction of 60 MeV/nucleon 18O with natural uranium

Protactinium was produced by the reaction of 60 MeV/nucleon ¹⁸O with natural uranium. A simple, relatively fast radiochemical procedure was developed, which can be used for the extraction separation of protactinium from uranium and from the complex reaction products using 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone and tri-iso-octylamine as extractants. Measurements of the gamma-ray spectra for the separated protactinium fractions were performed with a HPGe detector. The measured g-ray spectrum of protactinium shows that the decontamination from the main impurity elements, especially zirconium and niobium, is quite satisfactory.     

Separation of uranium from complex nuclear reaction product mixtures

A solvent extraction procedure for rapid separation of uranium from complex nuclear reaction product mixtures is suggested. The procedure has been tested in batch experiments with tracer amounts of representative elements. It has also been tested with fission products and uranium tracer using the continuous chemical separation system SISAK at the Mainz TRIGA reactor.     

Simultaneous determination of uranium and thorium with Arsenazo III by second-derivative spectrophotometry

A derivative spectrophotometric method has been developed for the simultaneous determination of microgram quantities of uranium and thorium with Arsenazo III in hydrochloric acid medium. The second-derivative absorbances of the uranium and thorium Arsenazo III complexes at 679.5 and 684.4 nm are used for their quantification. Uranium and thorium, both in the range 0.1-0.7 mug/ml have been determined simultaneously with good precision. The procedure does not require separation of uranium and thorium, and allows the determination of both metals in the presence of alkaline-earth metals and zirconium, but lanthanides interfere.     

Spectrophotometric determination of zirconium, uranium, thorium and rare earths with arsenazo III after extractions with thenoyltrifluoroacetone and tri-n-octylamine

A method is described for the spectrophotometric determination of microgram amounts of zirconium, uranium(VI), thorium and rare earths with Arsenazo III after systematic separation by extraction. First zirconium is extracted into a xylene solution of thenoyltrifluoroacetone (TTA) from about 4M hydrochloric acid. Uranium(VI) is then extracted into a xylene solution of tri-n-octy lamine from about 4M hydrochloric acid. Thorium is next extracted into TTA solution at pH about 1.5, and finally rare earths are extracted into TTA solution at pH about 4.7. Each metal is back-extracted from the organic phase before determination.     

Role of Cyanex-272 as an extractant for uranium in the determination of rare earths by ICP-AES

A chemical separation procedure has been developed for the extraction of uranium from some of the crucially important rare earths using a novel extractant viz. Cyanex-272 (2,4,4-trimethyl pentyl phosphinic acid). The near total extraction of uranium and quantitative separation of rare earth elements has been validated using inductively coupled argon plasma - atomic emission spectrometry (ICP-AES). The recovery of some of the representative elements has been confirmed by radioactive tracer studies. The back extraction of uranium from the organic phase was carried out using a solution of 0.5M Na₂CO₃ which resulted in a near total recovery of uranium into the organic phase. These studies have enabled determination of sub ppm amounts of the analyte elements with a precision of 5% RSD utilizing prior chemical separation of rare earths from 1 g uranium samples in just three extractions with Cyanex-272.     

Extraction Preconcentration of Uranium and Thorium Traces in the Analysis of Bottom Sediments by Inductively Coupled Plasma Mass Spectrometry

A procedure was developed for determining trace amounts of uranium and thorium isotopes in bottom sediments from Lake Baikal. This procedure involves sample decomposition, the coextraction of uranium and thorium with trioctylphosphine oxide, the quantitative back extraction after diluting the extract with caprylic acid, and the ICP MS analysis of the back extract. The procedure was verified by analyzing a BIL-1 Lake Baikal bottom silt standard reference material using the developed procedure and independent methods. The detection limits of abundant uranium and thorium isotopes are restricted by blank measures and equal to 1 × 10^–7 mass %. The detection limits for²³⁴U and ²³⁰Th are 4 × 10^–10 and 6 × 10^–10 mass %, respectively.     

Fine-scale determination of OH in radiation-damaged zircon using Synchrotron Fourier Transform Infra Red spectroscopy (FTIR) and Attenuated Total Reflectance (ATR)

The crystal structure of zircon is gradually broken down by the decay of small amounts of U and Th present in zirconium lattice sites. It has been observed that, with increasing radiation damage, zircon can lose radiogenic Pb and at the same time gain water from the environment. The disturbance of the U-Pb system is a major problem in zircon U-Pb geochronology. Water penetration appears to be an important factor in Pb loss but to explore this further a technique is needed for making fine-scale in situ measurements of water on the polished surface of radiation damaged zircons. Our research has shown that Attenuated Total Reflectance Fourier Transform Infra Red (ATR-FTIR) spectroscopy with a synchrotron source and thermal analysis can be successfully used to map the fine-scale distribution of OH/H₂O in radiation damaged zircons. The radiation damaged zircons were found to have an OH/H₂O content varying from 0.4% to 5% with maxima occurring in the heavily damaged (metamict) zones noted for their disturbed U-Pb systems. Whilst thermal analysis confirmed the presence of OH and possibly H₂O the infrared spectra did not distinguish between them.     

Separation of antimony from uranium using zirconium phosphate

Summary The distribution behaviour of antimony and uranium between zirconium phosphate and hydrochloric acid solutions of different concentrations has been determined. The effect of organic solvent addition to the aqueous phase on the distribution data has been investigated. In all cases, the separation factors are evaluated and discussed. The best separation factor was achieved using 1M HCl over all organic-aqueous solvent mixtures. Based on these findings, a procedure has been developed for the separation of antimony from uranium using a Chromatographic column loaded with zirconium phosphate and 1M HCl as eluant.

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Zusammenfassung Das Verteilungsverhalten von Antimon und Uran zwischen Zirkonium-phosphat und Salzsäure verschiedener Konzentration wurde bestimmt. Der Einfluß zugesetzten organischen Lösungsmittels auf die Verteilungsdaten wurde untersucht. Die besten Trennungsergebnisse wurden mit 1-n Salzsäure ohne jeden organischen Zusatz erzielt. Auf dieser Grundlage wurde ein Verfahren ausgearbeitet, um mit Hilfe einer mit Zirkoniumphosphat beladenen chromatographischen Säule und mit 1-n Salzsäure als Elutionsmittel Antimon von Uran zu trennen.

     

Integrated Utilization of Silicon Tetrafluoride and Zirconium Dioxide

The reaction of silicon tetrafluoride with zirconium dioxide was studied. A technological scheme was suggested for utilization of silicon tetrafluoride and reprocessing of spent zirconium dioxide to obtain zircon and zirconium tetrafluoride.