Determination of sub-PPB contents of uranium and thorium in high-purity aluminium by RNAA

Aluminium samples, irradiated in a reactor, are dissolved in nitric acid²³³Pa and²³⁹Np are adsorbed on an anion exchange column and then separately eluted. The neptunium fraction is very pure and can be counted in a liquid scintillation counter with 100% efficiency. From the other fraction protactinium is extracted by trioctylphosphine oxide and measured by -ray spectrometry. With samples of 3 g, a thermal flux of 3·10¹³ n cm^–2s^–1 and an irradiation time of 24 hours detection limits are 0.0005 ng/g for U and 0.01 ng/g for Th.     

Determination of uranium, thorium, and 20 other elements in high-purity tungsten by radiochemical neutron activation analysis

A radiochemical neutron activation analysis method for the determination of 22 elements in high-purity tungsten has been developed. For the assay of indicator radionuclides with long half-lives, the radiochemical separation was performed from HF/H₂O₂, HF/NH₄F and HCl/H₂SO₄ media by a combination of cation and anion exchange on a Dowex 50 W × 8 and Dowex 1 × 8 column. An effective removal of the matrix-produced radionuclides of W and Re was achieved. U was determined via ¹⁴⁰La, the daughter nuclide of the fission product ¹⁴⁰Ba. Limits of detection of 2 ng/g for U and 0.02 ng/g for Th can be achieved. For the other elements, the limits of detection are between 0.004 ng/g (Sc) and 200 ng/g (Sr). The elements Hf, Ta and Sb could be determined by instrumental neutron activation analysis. This method was applied to the analysis of two tungsten powder samples of different purity grade. The results and limits of detection are compared with those of other methods. Received: 28 July 1997 / Revised: 29 October 1997 / Accepted: 1 November 1997     

Determination of uranium, thorium, and 20 other elements in high-purity tungsten by radiochemical neutron activation analysis

A radiochemical neutron activation analysis method for the determination of 22 elements in high-purity tungsten has been developed. For the assay of indicator radionuclides with long half-lives, the radiochemical separation was performed from HF/H₂O₂, HF/NH₄F and HCl/H₂SO₄ media by a combination of cation and anion exchange on a Dowex 50 W × 8 and Dowex 1 × 8 column. An effective removal of the matrix-produced radionuclides of W and Re was achieved. U was determined via ¹⁴⁰La, the daughter nuclide of the fission product ¹⁴⁰Ba. Limits of detection of 2 ng/g for U and 0.02 ng/g for Th can be achieved. For the other elements, the limits of detection are between 0.004 ng/g (Sc) and 200 ng/g (Sr). The elements Hf, Ta and Sb could be determined by instrumental neutron activation analysis. This method was applied to the analysis of two tungsten powder samples of different purity grade. The results and limits of detection are compared with those of other methods.     

Thermodynamic analysis and experimental study on the chlorination of uranium oxide by gas-solid reaction

In order to determine the operating condition of an uranium chlorination process with U₃O₈-C-Cl₂ system, the experimental conditions have been evaluated preliminarily by the thermochemical analysis and experimentally confirmed in this study. The dry-type chlorination of U₃O₈ occurs as irreversible and exothermic reaction and produces many kinds of chloride compounds such as UCl₃, UCl₄, UCl₅ and UCl₆ in the air and humidity controlled argon environment. Taking account of Gibbs free energy and vapor pressure for various chloride compounds, the proper temperature range of chlorination appears to be 863 to 953 K in aspects of increasing reaction rate and the yield of nonvolatile product. In the course of the experimental confirmation the powder of U₃O₈ is perfectly converted into uranium chlorides within 4 hours above 863K, and then the maximum fraction of uranium chloride remaining in the reactor is about 30% of total conversion mass.     

Determination of nickel,cobalt, copper and uranium in water by cathodic stripping chronopotentiometry with continuous flow

The potential of cathodic stripping chronopotentiometry for the determination of trace metals in a continuous-flow system is investigated. An automated analyzer with a fast rate of data acquisition (250 kHz) is described. The cathodic scans are preceded by adsorptive collection of surface-active metal complexes on the hanging mercury drop electrode. The scans are done by passing a constant current of between 0.8 (in deaerated solution) and 60 μA (in solutions saturated with air) through the working electrode. Copper, uranium, and nickel can be determined in the presence of dissolved oxygen, but the sensitivity for nickel is then much reduced. The sensitivity of stripping chronopotentiometry in the presence of dissolved oxygen is similar to that of fast linear-sweep voltammetry in the absence of dissolved oxygen. The limits of detection were 0.1 nM Ni, 0.1 nM Co, 1.8 nM Cu and 1.6 nM U, when the measurements were preceded by 60-s stirred adsorption; in the presence of dissolved oxygen the limit of detection for nickel was higher at 0.6 nM, and cobalt could not be determined, as its peak was located on top of the oxygen peak. The determinations of copper and uranium were not adversely affected by dissolved oxygen. The limits of detection can be lowered further by using a prolonged collection period (up to 300 s). The technique was successfully tested by measuring nickel with continuous flow in water pumped on board of a small vessel in the Tamar estuary.     

Chemical separation and electrothermal atomic-absorption spectrophotometric determination of Cd, Co, Cu and Ni in high-purity uranium

Summary An electrothermal atomic-absorption spectrophotometric method has been developed for the estimation of trace concentrations of Cd, Co, Cu and Ni in high-purity uranium after their chemical separation. The trace constituents from 100 mg of uranium sample in 3 M nitric acid solution were separated using 0.2 M di-n-octyl sulphoxide in xylene. The concentration of the analytes in the aqueous phase was determined by graphite furnace AAS. The detection limits were 0.001, 0.01, 0.025 and 0.05 ng for Cd, Co, Cu and Ni, respectively. The precision of the determinations was 7–14%. The effect on absorbances of the analytes due to the presence of Al, Ca, Fe, Mg, Pb, W and uranium was examined.

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Chemische Abtrennung und elektrothermische AAS-Bestimmung von Cd, Co, Cu und Ni in hochreinem Uran

Zusammenfassung Die Spuren werden aus einer 100 mg Uranprobe in 3 M salpetersaurer Lösung durch Extraktion des U mit Hilfe von 0.2 M Di-n-octylsulfoxid im Xylol abgetrennt und werden anschließend in der wäßrigen Phase durch Graphitofen-AAS bestimmt. Die Nachweisgrenzen betragen 0,001 ng (Cd), 0,01 ng (Co), 0,025 ng (Cu) und 0,05 ng (Ni). Die Reproduzierbarkeit beträgt 7–14%. Der Einfluß von Al, Ca, Fe, Mg, Pb, W sowie Resturan auf die Absorption der analysierten Elemente wurde untersucht.

     

Theoretical and experimental study of packed capillary columns in gas chromatography

Chromatographia - The coupling theories byGiddings andLittle-wood are reviewed and discussed. A practical method to derive the values of the constants involved in the plate height equation from...     

On-line extraction of polymers,oligomers, additives and monomers by multiple solvents on packed HPLC columns

Summary Extraction of monomers, additives, oligomers, and polymers from a blend is very time consuming and labor intensive. Now by use of a special guard column and multi-solvent gradient liquid chromatograph (HPLC), the extraction and analysis can be performed in one step.     

Thermodynamic analysis and experimental study on the reduction of mixed oxides including uranium oxide by lithium

In order to determine the operating conditions of an uranium reduction process with U₃O₈-Li-LiCl system, the operating conditions have been evaluated in thermodynamic aspects and the results were experimentally confirmed in this study. All the reduction experiments were conducted in an argon atmospheric glove box, and the resultant degree of reduction was determined by analyzing the product using XRD and TGA. In the results of this study, a reduction yield greater than 95% is achieved within about 3 hours of reaction. The effects of the added quantity of Li and LiCl to the reduction yield of U₃O₈ and the preferential removal of several metal oxides accompanying U₃O₈ in the course of reduction were discussed. For a greater reduction of U₃O₈, an additional 20% of Li is required when compared to the stoichiometric composition. The proper composition of LiCl is about 75% based on the weight of U₃O₈ charged.     

Investigation of radioactive lead,uranium, and thorium in environmental waters by extraction chromatography resins

A time-saving and sensitive method for monitoring low concentration (activities) of ²¹⁰Pb, ²³²Th, and ²³⁰Th and ²³⁸U, ²³⁴U, and ²³⁵U in water samples has been developed. Through the combination of co-precipitation and extraction chromatography by 3M RAD disks and UTEVA (Eichrom) columns effective radiochemical separation of the analytes was carried out. Thorium and uranium activities were determined by alpha spectrometry and lead activity by LSC, respectively. The minimal detectable activities obtained were 0.6?Bq?m^?3 for uranium, 0.29?Bq?m^?3 for thorium, and 2.5?Bq?m^?3 for ²¹⁰Pb. More than 150 different waters were analysed for uranium content and only 30 for lead and thorium. The investigations are still in progress.     

萃取反萃取法研究新峪焦精煤中有机硫的赋存规律

以高含有机硫的新裕焦精煤为研究对象,采用萃取反萃取和分级萃取的分离方法及XPS、GC/MS等分析技术,对原煤和各族组分内不同结构的有机硫分布情况进行了研究,重点考察了各类型有机硫在煤有机质本体结构及族组分中的赋存规律。结果表明,组分总硫基赋存分率则与复杂性程度正好相反;可溶性含硫组分在总溶出物中的分布,相对不同族组分而言总体均衡;可溶性的共轭结构类有机硫主要赋存于煤密中质组中,其次是疏中质组中且以噻吩类为主,较少赋存于煤重质组中;而可溶性的脂肪结构类有机硫则主要赋存于煤重质组和密中质组中,较少赋存于疏中质组中;各族组分内有机硫的萃取率随时间的变化规律具有明显的加和性,族组分内可溶含硫组分的溶出行为相互独立,符合煤嵌布结构模型的基本思想;煤中不同形态有机硫的赋存遵循"相似相溶"原理。     

Theoretical and experimental study of the adsorption on radioactive gases on continuous flow columns

A bimolecular reaction model was used to describe the adsorption process in continuous flow columns filled with solid adsorbents. The analytical solution of the model for low gas concentrations and a cascade-type numerical method for higher gas concentrations were developed. An air flow apparatus using activated carbon as adsorbent and methyl-iodide labelled with¹²⁵I as adsorbate was constructed for measuring breakthrough- and accumulation curves.     

Separation of thorium,uranium and neptunium on chromatographic columns loaded with ammonium 12-molybdophosphate

The separation of thorium, uranium and neptunium with chromatographic columns loaded with ammonium 12-molybdophosphate (AMP) was carried out in different media with variable amounts of the elements. Columns of different sizes were used. Good separation yields were obtained, and the recovery of the elements was always greater than 95%. The use of AMP columns appears to be a useful method in the analytical chemistry of these actinide elements and it is particularly valuable in the purification and recovery of actinides in the +4 oxidation state.     

Determination of traces of rare earth elements in high-purity uranium by ion-exchange separation and neutron activation γ-spectrometry

Neutron activation γ-spectrometry is sufficiently sensitive for the determination of traces of rare earth elements but quantitative separation from uranium is essential. The rare earth elements in 0.2 M ammonium carbonate medium are quantitatively retained on Chelex-100, and are quantitatively separated from uranium by recycling the eluate. When 10-g samples are used, neutron activation provides detection limits of 1–20 μg kg^?1. Recoveries of rare earths, checked by spiking with radiotracers, are essentially complete.     

Pre-concentration and separation of thorium, uranium, plutonium and americium in human soft tissues by extraction chromatography

An extraction chromatographic method is described for the pre-concentration and separation of thorium, uranium, plutonium and americium in human soft tissues. Tissues such as lung and liver are oven dried at 120°C, ashed at 450°C and the ashed sample is alternately wet (HNO₃/H₂O₂) and dry ashed, and then dissolved in 8M HCl. Because of the complex matrix and large sample samples (up to 1500 g), the actinides were preconcentrated from the tissue solution using the TRU^TM resin (EIChroM) prior to elemental separation by extraction chromatography and determination of americium, plutonium, uranium and thorium by alpha spectrometry. The actinides were eluted from the preconcentration column and each actinide was individually eluted on TEVA^TM and TRU^TM resin columns in a tandem configuration. Actinide activities were then determined by alpha spectrometry after electrodeposition from a sulfate medium. The method was validated by analyzing human tissue samples previously analyzed for americium, plutonium, uranium and thorium in the United States Transuranium and Uranium Registries (USTUR). Two National Institute of Standards and Technology (NIST) Standard Reference Materials, SRM 4351-Human Lung and SRM 4352-Human Liver were also analyzed. United States Transuranium and Uranium Registries, Washington State University, Pullman, WA, 99163, USA.     

Determination of uranium and thorium at the sub-ng/g-level in high-purity aluminium by radiochemical neutron activation analysis

Summary A radiochemical neutron activation analysis technique for the determination of uranium und thorium in highpurity aluminium via the indicator radionuclides ²³⁹Np and ²³³Pa, respectively, has been developed. The separation procedure is based on the removal of ²⁴Na on hydrated antimony pentoxide followed by ion-exchange on Dowex-1X8 from HCl/HF and HCl medium. The eluate fraction being of interest for the determination of uranium and thorium contains > 99% of ²³⁹Np and ²³³Pa and, in addition, 11±2% of hafnium and 29±5% of zirconium, and non-detectable fractions of other radionuclides. For a 3-day irradiation of a 100 mg sample at a thermal neutron flux of 10¹⁴cm^–2s^–1 and a decay time of 5 days, the attainable detection limit for both elements is 0.05 ng/g. The method was applied to the analysis of different high-purity aluminium samples, and the results are compared with those obtained in other laboratories.

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Bestimmung von Uran und Thorium in hochreinem Aluminium im sub-ng/g-Bereich durch radiochemische Neutronenaktivierungsanalyse

     

Separation and determination of uranium and thorium in zircon sands by extraction chromatography

An extraction chromatography method with a column of microporous polyethylene supporting tri-n-octylamine /TNOA/ was used to separate uranium and thorium from zircon sands. The two elements were determined both by physical-chemical techniques /fluorimetry and colorimetry/ and by radiometric techniques /alpha spectrometry/ after electrodeposition: their respective contents agreed well; furthermore, uranium and thorium isotopes resulted in secular equilibrium in the analyzed material.     

Determination of alpha-emitting uranium isotopes in soft tissues by solvent extraction and alpha-spectrometry

A radiochemical procedure has been developed for the determination of alpha-emitting isotopes of uranium ((238)U, (235)U and (234)U) in soft tissues. Known amounts of sample are spiked with (232)U internal tracer and wet-ashed. Uranium is co-precipitated with iron hydroxide as carrier, and extracted into 20% trilaurylamine solution in xylene after dissolution of the precipitate in 10M hydrochloric acid. The uranium, after stripping into an aqueous phase, is electro-deposited onto a platinum disc and counted by alpha-spectrometry. The radiochemical recovery ranges from 60 to 85% for bovine liver samples. The average radiochemical recoveries for human tissues vary from 53 to 78%.