Low Uranium Concentrations Research Articles

Simultaneous determination of uranium and thorium in high grade thorium ores

A routine procedure has been developed for the simultaneous determination of uranium and thorium in high concentration thorium ores. INAA is used to determine the uranium and thorium concentration. However, for very low concentrations of uranium a radiochemical procedure based on the use of NPy/benzene as an extractant has to be employed. The precision and accuracy of the method has been determined by analyzing IAEA and NBL standard thorium/uranium ores.

Investigations in Special "High Radon Areas" In Germany

The main source of high radon concentration indoors is the exhalation of radon from the soil. In the western part of Germany, two interesting regions, “Eifel” and “Hunsruck”, are selected for these radon investigations. The first region is an area with silt and sandstone of low uranium content but with tectonic fractures caused by postvolcanic activity, whereas in the part of the “Hunsruck” under consideration, the uranium concentration in the ground formerly allowed the extraction of uranium ores. An electrostatic deposit of the first radon daughter (Polonium-218-ion) onto a surface barrier detector and the subsequent analysis of the measured alpha spectra enables the determination of the concentration of radon in dwellings, its diffusion through and its exhalation rate from the soil. A maximum indoor concentration of radon of 8 kBq★m−3 in a bedroom and approximately 35 kBq★m−3 in a cellar room were determined in a house built in 1976. The daily variation between the minimum and the maximum concentration indoors amounts to a factor of ten. In these regions the radon concentration outdoors varies between 20 and 150 Bq★m−3. The exhalation rates of radon from the soil are found to range from 0.002 to 1 Bq★m−2★S−1 The effects of sealing the ground slab with polyurethane and removing the air under the ground slab by suction will be presented.

Recoil and Transmutation Effects in the Migration Behaviour of Actinides

Most actinide nuclides decay by {alpha} emission with the formation of kinetically and electronically excited daughters. The behaviour of heavy recoil atoms can be inferred from the observation of rupture of equilibrium in the natural radioactive series, from hot atom chemistry and from computer simulation of collision dynamics. On the basis of these sources of information, a new chemical model is established for {alpha} recoil chemistry. It postulates that the chemical state of the daughter atom is determined by redox reactions with oxygen interstitials at the end of the trajectory of the recoil atom. The model predicts that in minerals with low uranium content, {sup 234}U tends toward a leachable, oxidized form; on the other hand, in an environment with high uranium content, {sup 234}U is less amenable to oxidation, complex formation and leaching. These findings suggest that the disposal of radwaste would be more appropriate in 'reducing' organic solids than in ceramic matter or glassy material. (orig.).

Neutron activation analysis for ultra low contents of uranium and thorium in aluminium and silica

Highly sensitive neutron activation analysis of uranium and thorium in high quality silica and aluminium has been investigated using the Japan Materials Testing Reactor (JMTR), having a thermal neutron flux higher than 1014 n/cm2/s. In order to determine ultra-low contents of uranium and thorium,239Np and233Pa as activation products were separated by using anion exchange and LaF3 coprecipitation methods. As a result, a number of interfering radioactive isotopes containing double neutron capture product such as183Ta were removed completely from the isolated239Np and233Pa fraction and the detection limits for uranium and thorium were found to be 2·10−12 g and 4·10−13 g, respectively.

Polybenzimidazole resin based new chelating agents uranyl ion selectivity of resins with immobilized glyoxal-bis-2-hydroxyanil and salicylaldehyde-ethylenediimine

Microporous polybenzimidazole (PBI) of 250–500 μm spherical bead size from Celanese has been reacted with epichlorohydrin and sodium hydroxide and the resulting epoxidized product (EPBI) further reacted with glyoxal-bis-2-hydroxyanil (GHA) and salicylaldehyde-ethylenediimine (SED) at ordinary temperatures, using a quaternary ammonium salt as the phase-transfer catalyst. The resulting new sorbents EPBI(GHA) and EPBI(SED) have been compared with the base resin PBI and the conventional ion-exchange resins Dowex 50W-X8(H +) and Dowex 1-X8(SO 4 2−) in respect of uranyl sorption in sulfate system. In UO 2SO 4 solution at pH 4.7, the saturation capacities (mmol U/g dry wt. of resin) of the five resins, in the aforesaid order, are 1.03, 1.20, 2.79, 2.10 and 1.35, respectively. Both EPBI(GHA) and EPBI(SED), however, show greater sorption capacities than PBI at low substrate concentrations of uranium (< 60 mg U/L) due to their significantly higher binding constants than PBI. Both PBI and its derivatives EPBI(GHA) and EPBI(SED) have considerably greater salt tolerance than the Dowex resins. Thus, in the presence of twenty fold molar equivalents of sodium ions, the uranium selectivities of Dowex 50W-X8(H +) and Dowex 1-X8(SO 4 2−) are, respectively, 0.32 and 0.50 in NaCl solution and 0.15 and 0.87 in Na 2SO 4 solution. In comparison, PBI and its derivatives have selectivities of 1.0 in NaCl and 0.75–0.80 in Na 2SO 4, thus yielding greater uranium sorptions than the Dowex resins against a high salt background.

Determination of uranium in solution at the ng 1 −1 level by time-resolved laser-induced spectrofluorimetry: application to geological samples

Time-resolved laser-induced spectrofluorimetry was used for the determination of uranium at the ng 1 −1 level in alkaline water with high chloride and sulphide contents in order to obtain a better understanding of uranium mobilization under natural reducing conditions. The optimum complexing medium, limit of detection and results obtained for several waters from different localities in the Pyrenees are presented. These data seem to confirm that even at very low uranium concentrations, thermodynamic control by a mineral phase takes place.

Effects of Chlorite Alteration on Uranium Redistribution in Koongarra, Australia

ABSTRACTThe relevance of alteration of chlorite, one of the major constituent minerals of the host rock to uranium ore at Koongarra, to the redistribution of uranium in the vicinity of the ore deposit has been examined. The chlorite alteration is produced by weathering; chlorite is transformed to vermiculite, through regularly interstratified chlorite/vermiculite. The Fe released from chlorite reprecipitates to form iron minerals, possibly ferrihydrite. Vermiculite is then replaced by kaolinite (and possibly smectite), further releasing Fe. On the millimeter scale, an alpha autoradiography study has shown that uranium concentrations are qualitatively proportional to the extent of the alteration; altered chlorite grains having higher uranium concentration. On the meter scale, the X-ray diffraction study has revealed that the abundances of chlorite, vermiculite, and kaolinite correspond well to the low, intermediate, and high uranium concentration zones, respectively. These suggest that the interaction of the uraniferous solution with chlorite causes the alteration of chlorite and the precipitation and sorption of uranium in the alteration products from the solution, and thus, the uranium migration is retarded at Koongarra.

Application and limitation of fission-track geochronology to quarternary tephras

Zircon and glass are the principal materials used for fission-track dating of Quaternary tephras. This is because zircon is a common accessory mineral in rhyolitic tephras, and it usually contains sufficient uranium to produce detectable quantities of spontaneous fission tracks over the time span of the Quaternary. Volcanic glass, though uranium-poor, is typically the dominant component of rhyolitic tephras, comprising up to 99% of some distal tephra-fall deposits. Low uranium contents, however, result in low spontaneous track densities that make the age measurement difficult and laborious, a condition exacerbated by very young glasses. In addition, fission tracks in glass shards are unstable and can partially anneal at ambient temperatures. Therefore, unless the glass age is corrected by plateau or isothermal heating experiments, partial annealing causes a reduction in the measured age compared to the true age of the sample. Fission-track dating has a large subjective component that can contribute systematic errors to the analysis; microlite inclusions and some structural defects resemble fission tracks, and if misidentified and included in the count of spontaneous tracks the calculated age would be too old. The most prevalent source of systematic error is contamination in the natural environment, for many tephras in the stratigraphic record are reworked tuffaceous sediments. These deposits may contain detrital components that could mask the primary age of the tephra. However, by using the external detector fission-track method it is possible to calculate ages of single mineral grains, and to distinguish contaminants from primary phases on the basis of their age distribution. This ‘grain-discrete’ capability is the major advantage of the fission-track method over ‘bulk’ geochronological systems.

Determination of low levels of uranium impurity by fission track registration using mica and polycarbonate detectors

A first attempt to determine low levels of uranium by fission track registration was made by optical counting over wide fields in mica and polycarbonate detectors under high magnification. Homogeneous distribution of fission tracks was achieved by registrations using liquid ampoules and powder pellets. Extremely low uranium concentration in twofold distilled water was determined to be 0.039 ± 0.002 ppb (i.e. ng g-1). Low levels of uranium in solids were well determined by mica and Lexan detectors, viz., 1.42 ± 0.27 ppm (μg g-1) in a photoelectric semiconductor; 0.11 ± 0.03 ppm and 0.06 ± 0.02 ppm in different types of toothpaste. The background uranium content of track detectors and binding material were primarily estimated to be 1.18 ± 0.01 ppb in annealed muscovites (Brazilian Clear Ruby Mica), 1.02 ± 0.23 ppb in Lexan polycarbonate, and 2.20 ± 0.93 ppb in methyl cellulose. Repeated results of uranium determination by duplicate detection, using mica and Lexan on identical samples irradiated at different neutron fluences, were seen to be very consistent. These homogenized track registration techniques can be applied reliably to the determination of low concentrations of uranium impurity, between 10-2 ppb and 10 ppm.

Stripping voltammetric determination of trace levels of uranium by synergic adsorption

A voltammetric method is reported for the determination of low uranium concentrations in natural waters. A very strongly adsorbed mixed complex of uranyl ion with 2-thenoyltrifluoroacetone and tri-n-butyl phosphate is applied. Synergic adsorption is obtained compared with the adsorption obtained with either ligand alone. In 0.55 mol dm −3 sodium chloride, the detection limit was 10 −10 mol dm −3 uranyl ion after accumulation for 10 min at −0.1 V vs. Ag/AgCl. For the natural level of uranium in sea water (about 10 −8 mol dm −3), accumulation for 2 min was sufficient.

Assessment of natural and man-made alpha emitting radionuclides

Abstract Damage track detectors have unique capabilities for measuring low concentrations of natural and man-made alpha emitters in biological and environmental samples. With electronic devices such as surface-barrier detectors, zinc-sulphide screen counters and large area grid ionization chambers, the detection sensitivity is limited by the duration of exposure or the stability of electronic counting systems. Damage track detectors can be used for sufficiently long exposure periods so that the intrinsic background of the detector material can be ignored. In particular, the applications of damage track detectors, described in this paper, refer to the assessment of low concentrations of Uranium, Plutonium and radon, using the registration of alpha-particle and fission- fragment tracks. The sensitivity and the simplicity of track counting can be greatly enhanced by using the spark counter.

Spectrophotometric study of analytical reactions of triphenylmethane dyes with uranyl in the presence of cationic surfactants

Numerical analysis of absorbance data for the analytically significant UO22+ - Chromazurol B, UO22+ - Chromazurol S, and UO22+ - Eriochromcyanine R systems in the presence of the cationic surfactant SeptonexR revealed that also in micellar medium, complex equilibria establish and several complexes are formed in dependence on pH and concentration of uranyl ions, reagent, and surfactant. Based on the results, optimum conditions are found for the spectrophotometric determination of low concentration of uranium.

Behavior of uranium-238 and its daughter nuclides in the Masutomi spring, Yamanashi Prefecture, central Japan.

The geochemical behavior of uranium, radium and radon in the Masutomi spring district, Yamanashi Prefecture, central Japan, was studied. The uranium concentrations in the spring waters range from 0.01 to 2.07 ppb (average 0.27 ppb). The 234U/238U activity ratios in the spring waters range from 0.98 to 2.42, and show an inverse correlation with the 238U concentrations. The measurement of redox potentials of the waters shows that the waters are reductive. This may be the reason for the low uranium concentrations. Alpha recoil dissolution of 234Th explains the behavior of 234U. Radioactive disequilibria are also observed in 226Ra/238U, 222Rn/238U, and 222Rn/226Ra ratios. Highly exess radon is attributed to both the source granite rocks and the radium rich precipitates near the surface. On the other hand, the behavior of radium as well as other general ions such as sodium is explained by mixing or dilution of a deep water with surface waters.

Uranium in pore waters from North Atlantic (GME and Southern Nares Abyssal Plain) sediments

A central question to be addressed by the international sub-seabed radioactive waste disposal program is the mobility of radionu-clides through sediments, which are the most important barrier to the transfer to the ocean and eventually to man. The major component of high-level radioactive waste is uranium. Here we report the measurement of low uranium concentrations in composite pore-water samples from the uppermost 20–30 m of deep-sea abyssal plain sediments from the Great Meteor East and Southern Nares Abyssal Plains Area. Many values are between 0.1 and 0.5 p.p.b. (parts per 109) which are the lowest uranium concentrations ever measured in the pore waters of deep-sea sediments. Our lowest value, 0.05±0.01 p.p.b., is orders of magnitude lower than the predicted solubility of UO2 or U4O9, probably indicating solubility control of U(IV) by an adsorbed phase. The uranium concentrations obtained from both sites correlate closely with measured redox potentials (Eh) in the sediments. The low mobility of uranium in pore waters from turbiditic deep-sea abyssal plain sediments, which can be deduced from these measurements, has important implications for the sub-seabed disposal of high-level radioactive waste, and for marine geochemistry of uranium.

A study of234U/238U ratios in groundwaters of Taiyuan area, Shanxi Province

Uranium contents and234U/238U ratios have been determined on 29 water samples from the Taiyuan area, Shanxi Province. The results show that the same artesian aquifer has similar uranium contents and234U/238U activity ratios, and the deeper aquifers have higher A. R. values but lower uranium contents. The A. R. values increase slightly towards groundwater flow in the artesian aquifers dominated by oxidizing ground waters.The Lancun Spring and the famous Jinci Spring belong to two different karst groundwater systems, i.e., the east and west karst groundwater systems. The recharge area of the Lancun Spring should cover the wide limestone outcrops of middle Ordovician in the northeast. The Ordovician fissure-karst ground water to the Jinci Spring is extensively mixed with fissure water in Carboniferous-Jurassic formations and seepage water from the Fenhe River.

Ultrastructural localization of uranium biosorption in Penicillium digitatum by stem X-ray microanalysis

When Penicillium digitatum Saccardo cultures are exposed to aqueous solutions containing soluble uranium salts, considerable amounts of this element are accumulated in the fungal mycelium. The accumulated uranium is retained after thorough rinsing with distilled water but is removed by alkali carbonate solutions. Analysis of thick sections (0·5 μm) of the fungal hyphae with TEM, after incubation in UO 2Cl 2 solutions of varying concentrations under both light and dark conditions, revealed conspicuous crystal-like deposits in UO 2Cl 2-exposed hyphae, but none in the control hyphae. Thick sections were necessary for crystal visualization. Using energy-dispersive X-ray analysis, uranium was detected as the only heavy element in these crystals. Uranium crystal biosorption was localized on the outside surface of the hyphal cell wall (following short exposures to relatively low uranium concentrations) or inside the cell wall (following long exposure to relatively high uranium concentrations). In some cases, crystal-like deposits of uranium salts were located on the outside surface as well as inside the cell.

The recovery of uranium from the waste solution of fission 99Mo production

A procedure is described for the solvent extraction of enriched uranium from the waste solution of fission 99Mo production. An extraction process has been developed for recovering residual uranium from waste solutions of the fission 99Mo production. The procedure and the apparatus meet the very low uranium concentrations (∼10 g U/L) by using special air lift extractors which work satisfactorily at low organic/aqueous phase ratios. The design of the plant is briefly described.

Xps and Xrd Studies of Uranium Rich Minerals from Cigar Lake, Saskatchewan

AbstractSamples of uranium ore from the 1,300 million year old Cigar Lake deposits in northern Saskatchewan have been investigated using X ray Photoelectron Spectroscopy (XPS) and X ray Diffraction (XRD). The XPS spectra showed the peaks for U, Pb, 0, C, Si, Ca and Mg. Analysis of highresolution XPS spectra showed that the oxidation state of uranium in these minerals is equal to, or lower than, that of U3O7. The XRD data confirm the presence of an oxidized phase, most likely α U3O7., in addition to UO2. The low U(VI)/U(IV) ratio in these minerals is consistent with the low uranium concentration found in groundwater in contact with these uranium minerals. The relevance of these results to the disposal concept of used nuclear fuel in the Canadian Nuclear Fuel Waste Management Program is discussed.

Luminescence and energy migration in the garnet Gd 3Li 3Te 2O 12 doped with several rare earths and uranium

Energy transfer phenomena have been observed by activating the garnet host-lattice Gd 3Li 3Te 2O 12 with Eu 3+, Dy 3+, Tm 3+, and U 6+. Eu 3+ acts as an effective trap for Gd 3+ excitons. Even at very low europium concentrations emission from Eu 3+ ions can be observed showing both energy migration among the Gd 3+ ions and efficient transfer to Eu 3+. Also Dy 3+ is an effective activator for Gd 3+ excitons, transfer being possible both from the Gd 3+ 6 I and 6 P levels. Tm 3+ is not very effective in picking up energy from the Gd 3+ sublattice. The weak transfer occurs mainly from the Gd 3+ 6 I levels which are in close resonance with the Tm 3+( 3P) levels. U 6+, occupying Te 6+ sites in the host-lattice, is a very effective trap for Gd 3+ excitons. Even very low (≤10 ppm) uranium concentrations are sufficient to pick up almost all excitation energy from the Gd 3+ sublattice. The spectral data indicate a high energy transfer probability from Gd 3+ to U 6+ ions, based to a large extent on an exchange interaction.

Organic geochemical analysis of sedimentary organic matter associated with uranium

Samples of sedimentary organic matter from several geologic environments and ages which are enriched in uranium (56 ppm to 12%) have been characterized. The three analytical techniqyes used to study the samples were Rock-Eval pyrolysis, pyrolysis-gas chromatography-mass spectrometry, and solid-state C-13 nuclear magnetic resonance (NMR) spectroscopy. In samples with low uranium content, the pyrolysis-gas chromatography products contain oxygenated functional groups (as hydroxyl) and molecules with both aliphatic and aromatic carbon atoms. These samples with low uranium content give measurable Rock-Eval hydrocarbon and organic-CO 2 yields, and C-13 NMR values of > 30% aliphatic carbon. In contrast, uranium-rich samples have few hydrocarbon pyrolysis products, increased Rock-Eval organic-CO 2 contents and > 70% aromatic carbon contents from C-13 NMR. The increase in aromaticity and decrease in hydrocarbon pyrolysis yield are related to the amount of uranium and the age of the uranium minerals, which correspond to the degree of radiation damage. The three analytical techniques give complementary results. Increase in Rock-Eval organic-CO 2 yield correlates with uranium content for samples from the Grants uranium region. Calculations show that the amount of organic-CO 2 corresponds to the quantity of uranium chemically reduced by the organic matter for the Grants uranium region samples.