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1.
In order to develop a production process of 99Mo by fission of low-enriched uranium, the first purification step, which consists of dissolution of a uranium metal foil target, was studied. It was found that alkaline NaClO gave good results, reaching the dissolution of up to 300 m of uranium foil. The different conditions for the dissolution were studied and the optimum ones were found. The influence of NaClO and NaOH concentration, temperature, dissolving solution volume per unit of surface and dissolution time were investigated. During this step, a gas, identified as H 2, was generated, and a precipitate characterized as Na 2U 2O 7 was observed. A stoichiometric reaction for this uranium dissolution is proposed. 相似文献
2.
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. 相似文献
3.
Microbial column flotation using Thiobacillus ferrooxidans was applied for desulfurization of Pittsburgh coal of CWM (Coal-Water Mixture) size between 38 μm and 75 μm. The coal contained
ferrous ion which would interfere separation of pyrite from coal by microbial flotation. The wash-out of ferrous ion with
0.5N HC1 solution enabled pyrite removal from coal. The coal was divided into two parts, the small-size coal between 38 μm
and 53 μm, and the large-size coal between 53 μm and 75 μm. The pyritic sulfur content was decreased from 2.88% of the feed
coal to 0.98% of the product coal for the largesize coal and from 2.77% of the feed coal to 1.12% of the product coal for
the small-size coal by microbial flotation. The decrease was based on removal of liberated pyrite particles (between 20 μm
and 70 μm). However, the fine particles (less than 20 μm) could not be removed even though the pyrite particles were liberated
from coal particles. The microbial column flotation was more effective for desulfurization of the large liberated pyrite particle
than that of the small. It was not effective for desulfurization of the locked pyrite particles that were buried in coal particles.
Both the pyrite liberation from coal and its particle size are important factors for the pyrite removal by microbial column
flotation. 相似文献
4.
A derivative spectrophotometric method has been developed for the simultaneous determination of uranium and plutonium at trace
levels in various process streams in 3M HNO 3 medium using Arsenazo III. The method was developed with the objective of measuring both uranium and plutonium in the same
aliquot in fairly high burn-up fuels. The first derivative absorbances of the uranium and plutonium Arsenazo III complexes
at 632 nm and 606.5 nm, respectively, were used for their quantification. Mixed aliquots of uranium (20–28 μg/ml) and plutonium
(0.5–1.5 μg/ml) with U/Pu ratio varying from 25 to 40 were analysed using this technique. A relative error of about 5% was
obtained for uranium and plutonium. The method is simple, fast and does not require separation of uranium and plutonium. The
effect of presence of many fission products, corrosion products and complexing anions on determination of uranium and plutonium
was also studied. 相似文献
5.
A continuous flow-through reactor with a thin layer of solid particles (size ranging from 100 to 300 μm) was used to obtain a deeper knowledge on the mechanism of dissolution of UO 2 under oxidizing conditions. Using this methodology the dissolution rate of uranium dioxide was determined at three different oxygen partial pressures (5, 21, and 100% in nitrogen) and as a function of pH (between 3 and 12) in a noncomplexing medium. From the results of these experiments the following rate equation was derived: In addition, XPS characterizations were performed to determine the U(IV)/U(VI) ratio on the solid surface at different experimental times and conditions. These results showed that at acidic conditions (pH below 6.7) the final solid surface presents a stoichiometry close to UO 2, while at alkaline conditions the final solid surface average composition is close to UO 2.25. This information was integrated with the results of the leaching experiments to present a model for the mechanism of dissolution of uranium dioxide under the experimental conditions. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 261–267, 1997. 相似文献
6.
Uranium from different uranium oxide matrices was extracted with tri- n-butyl phosphate–nitric acid (TBP–HNO 3) adduct using supercritical carbon dioxide (SC CO 2). While 30 min dissolution time at 323 K was sufficient for U 3O 8 and UO 2 powder, UO 2 granule (at 333 K) and crushed green pellet (at 353 K) required 40 min. Crushed sintered pellet required 60 min at 353 K
for complete dissolution. Influence of various experimental parameters such as temperature, pressure, volume of TBP–HNO 3 adduct, acidity of nitric acid used for preparing TBP–HNO 3 adduct and extraction time on uranium extraction efficiency was also investigated. For UO 2 powder, temperature of 323 K, pressure of 15.2 MPa, 1 mL TBP–HNO 3 adduct, 10 M nitric acid and 30 min extraction time was found to be optimum. ~70% uranium extraction efficiency was obtained
on extraction with SC CO 2 alone which increased to 90% with the addition of 2.5% TBP in SC CO 2 stream. Extraction efficiency was found to vary linearly with TBP percentage and nearly complete uranium extraction (~99%)
was observed with 20% TBP. Nearly complete extraction was also achieved with addition of 2.5% thenoyltrifluoroacetylacetone
(TTA) in methanol. The optimized procedure was extended to remove uranium from simulated tissue paper waste matrix smeared
with uranium oxide solids. 相似文献
7.
Two complimentary spectroscopic techniques, X-ray absorption and fluorescence spectroscopy have been conducted at spatial
scales of 1 to 25 μm on uranium contaminated soil sediments collected from two former nuclear materials processing facilities
of the DOE: Fernald, OH and Savannah River Site, SC. A method of imbedding particles in a non-reactive Si polymer was developed
such that individual particles could be examined before and after extraction with a wide range of chemicals typically used
in sequential extraction techniques and others proposed for ex situ chemical intervention technologies. Using both the micro-X-ray fluorescence (XRF) and micro-X-ray Absorption Near Edge Structure
(XANES) techniques, both elemental and oxidation state distribution maps were generated on individual particles before and
following chemical extraction. XANES can determine the relative proportion of U(VI) and U(IV) in phases comprising individual
particles before and after extraction and showed that greater than 85% of the uranium existed as hexavalent U(VI). Fluorescence
spectra of contaminated particles containing mainly U(VI) revealed populations of uranyl hydroxide phases and demonstrated
the relative efficacy and specificity of each extraction method. Correlation of XAS and fluorescence data at micron scales
provides information of U oxidation state as well as chemical form in heterogeneous samples. 相似文献
8.
Secondary ion mass spectrometry (SIMS) was optimised for characterisation of uranium- and plutonium-containing particles
in soils, swipes and forensic samples. This was done by analysing in-house produced spherical UO 2-particles. Screening techniques as α-autoradiography together with SIMS analysis were employed to detect UO 2-particles in a soil sample from Chernobyl.
The use of SIMS was exploited for the identification of uranium- and plutonium-containing particles and for the determination
of their isotopic composition. The particles collected on swipe samples were transferred to a special adhesive support for
the analysis by SIMS. Particles containing highly enriched uranium with diameters up to 10 μm were also detected in a forensic
sample. For the measurements of the isotopic ratios a mass resolution of 1000 was used. At this resolution flat-top peaks
were obtained which greatly improve the accuracy of the measurement. The isotopic composition of the particles was measured
with a typical accuracy and precision of 0.5%. Statistically meaningful results can be obtained, for instance, from a specimen
containing as few as 10 10 atoms/μm 3 of uranium in particles of UO 2 weighing a few picograms. 相似文献
9.
Samples of orange, yellow, beige, ivory and blue-green ceramic dinnerware glazed with uranium compounds have been examined.
Measurements at glaze surfaces yielded exposure rates of 3.8–16 mR/h (1–4 μC/kgh) for orange glazes and rates of 0.04–1.3
mR/h (0.01–0.3 μC/kgh) for ivory beige, and yellow glazes. Whole body exposure from a shelf display of 40 orange dishes was
estimated to be 0.1–0.5 mR/h (0.03–0.13 μC/kgh), or up to 50 times the room background radiation level, at a distance of 1
meter. Twenty-four hour leaching tests of orange, yellow, and ivory dishes were carried out with various concentrations of
acetic and citric acids. Uranium concentrations in leachates of some orange dishes exceeded 450 mg/l. Uranium is a chemical
nephrotoxin and the United States Environmental Protection Agency has proposed a maximum contaminant level for drinking water
of 0.020 mg/l. Based on this value a person consuming, 2.2 l of drinking water per day would ingest 0.31 mg of uranium per
week. A person eating once a week from an orange glazed dish could easily ingest 10 or more times this amount. 相似文献
10.
Uranium shows relatively conservative behaviour in seawater because of the formation of stable carbonato complexes, whereas particulate uranium, involved in suspended particles with the particle size of more than 0.45 m, is a minor constituent. It was found that particulate uranium, with a range from 0.24 to 39 Bq·1 –1, varies spatially and temporally. Its highest concentration occurs in the tropical region of the western North Pacific during the winter of 1983, corresponding to the 1983 El Nifio event. A leaching experiment revealed that major species of particulate uranium are labile organic complexes. Mass balance considerations suggest that particulate uranium in open ocean waters correlates with the presence of particulate organic matter (POM). A high peak of particulate uranium in 1983 may indicate that POM, i.e., primary productivity, increased in the western tropical Pacific during the El Niño event. 相似文献
11.
A set of natural matrix Standard Reference Materials were developed by the National Bureau of Standards for analytical methods
evaluation. These materials were analyzed using a KF fusion procedure and an acid dissolution procedure. The latter method
yielded radioactive concentrations that were 15–20% lower then that of the former. This was thought to be due to a fraction
of the sample, “resistates,” that did not dissolve during the dissolution. In this study, HF dissolutions were conducted on
NIST natural matrix SRMs, in which ~0.08% of total sample mass remained after dissolution. The acid resistant residual materials
were concentrated, then dissolved using a LiBO 2 fusion procedure and were found to contain a considerable fraction of the uranium and thorium. 相似文献
12.
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 (UO 2–Gd 2O 3) 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. 相似文献
13.
A well-characterized low-grade fluoritized uranium samples from new occurrence in Gabal El-Missikat prospect, Eastern Desert, Egypt was subjected to sulfuric acid leaching. The effects of leaching parameters on uranium dissolution mechanism were investigated. The shrinking core model was used to model leaching reactions. The kinetics equations indicates that the reactions appear to be controlled by layer diffusion process. The activation energy for uranium dissolution was evaluated. Low activation energy value (2.54 kJ mol−1) confirm the diffusion layer mechanism. The presence of fluoride ions in the solution increases the dissolution of uranium. The optimum process operating parameters were: sulfuric acid concentration: 1.5 M, solid–liquid ratio: 1:3, contact time 8 h; agitation speed rate 200 rpm; and ore particle size − 75 µm at temperature 60 °C, in the absence of an external oxidant. Under these experimental conditions, the extraction efficiency of uranium was about 91%. 相似文献
14.
Undisturbed, non-fertilized woodland soil (“loamy sandy soil” type) from 1 m below surface was dry and wet sieved. Sieving
fractions of <10–1000 μm were analyzed for total alpha-activity. Thorium and uranium contents were determined by alpha-spectrometry
after radiochemical separation. Soluble and insoluble parts of thorium and uranium were determined in the sieved fractions
indicating that the isotope distribution in soil correlates with the particle size distribution: The smaller the size fraction
the higher the isotope content. Isotope ratios of 228Th/ 232Th, and 234U/ 238U are discussed. 相似文献
15.
Electrospun ultrafine silica fibers were calcined at 150–800 °C. The relation of calcination temperature to the ability to
form biomimetic apatite in a simulated body fluid solution (SBF) was evaluated. The largest apatite particles, formed on non-calcined
fibers after 1 week of soaking in SBF, were 10 μm in diameter, had a narrow size distribution (coefficient of variation 9%),
and were similar to pearls on string. The particles size decreased with increasing calcination temperature below 250 °C and
the particles formed on the fibers calcined at 250 °C were 4.5 μm in diameter. No particles were found on those calcined above
500 °C. By using a concentrated SBF at 1.5-times higher ionic concentrations than SBF, the size of apatite microparticles
increased about 50%. The fibrous substrate covered with apatite particles was effective for osteoblastic differentiation of
pre-osteoblastic cells. 相似文献
16.
Irradiated uranium metal fuel was stored underwater in the K East and K West storage basins at the US Department of Energy Hanford Site. The uranium metal under damaged cladding reacted with water to generate hydrogen gas, uranium oxides, and spalled uranium metal particles which intermingled with other particulates to form sludge. While the fuel has been removed, uranium metal in the sludge remains hazardous. An expeditious routine method to analyze 0.03 wt% uranium metal in the presence of >30 wt% total uranium was needed to support safe sludge management and processing. A selective dissolution method was designed based on the rapid uranium oxide dissolution but very low uranium metal corrosion rates in hot concentrated phosphoric acid. The uranium metal-bearing heel from the phosphoric acid step then is rinsed before the uranium metal is dissolved in hot concentrated nitric acid for analysis. Technical underpinnings of the selective dissolution method, including the influence of sludge components, were investigated to design the steps and define the reagents, quantities, concentrations, temperatures, and times within the selective dissolution analysis. Tests with simulant sludge proved the technique feasible. Tests with genuine sludge showed a 0.0028 ± 0.0037 wt% (at one standard deviation) uranium metal analytical background, a 0.011 wt% detection limit, and a 0.030 wt% quantitation limit in settled (wet) sludge. In tests using genuine K Basin sludge spiked with uranium metal at concentrations above the 0.030 wt% ± 25 % (relative) quantitation limit, uranium metal recoveries averaged 99.5 % with a relative standard deviation of 3.5 %. 相似文献
17.
Atomization processes for uranium in aqueous media and in the presence of a plutonium matrix have been studied and a chemical
mechanism is proposed. These studies have been utilized for the determination of uranium in plutonium by Electrothermal Atomization-
Atomic Absorption Spectrometry (ETA-AAS) within the constraints of its stable carbide forming tendency and complexity caused
by formation of plutonium suboxide at high temperatures. In spite of these limitations the analytical range obtained for determination
of uranium is 2.5–100 ng with a sample aliquot of 5 μL containing 5 mg/mL plutonium concentration. The precision of the method
is evaluated as 9% RSD.
Received: 9 September 1997 / Revised: 29 December 1997 / Accepted: 31 December 1997 相似文献
18.
During this work the determination of uranium in the range of μg·L −1 to tens of μg·L −1 was done by alpha-spectrometry after electroplating the aliquots of water sample using (NH 4) 2SO 4 as an electrolyte. In general, the determination of uranium by alpha-spectrometry needs its separation from other transuranics
specially thorium. The process described here does not involve any sample digestion and radiochemical separation of uranium
from other transuranics. In this method an aliquot (1 to 3 mL) of the sample was dried and dissolve in (NH 4) 2SO 4 and thereafter the sample was electroplated on a stainless steel (SS) planchet by using an electrochemical cell of special
design. The proposed techniques have a distinct advantage over the determination of uranium by adsorptive stripping voltammetry
(AdSV) in which uranium-chloranilic (2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone) acid complex was used for concentrating
the uranium from the solution. Since in the case of AdSv, the determination of uranium was not possible for samples having
dissolved organic carbon (DOC) more than 15 mg·L −1 and Cl − concentration is in the range of 40,000 μ·g −1. In the case of spike experiments with 232U the recovery was observed in the range of 90–95% in aqueous medium having higher concentration of Cl − and DOC as indicated above. 相似文献
19.
In situ leaching of uranium ores with sulfuric acid during active uranium mining activity on the Gessenheap has caused longstanding
environmental problems of acid mine drainage and elevated concentrations of uranium. To study there remediation measures the
test site Gessenwiese, a recultivated former uranium mining heap near Ronnenburg/East Thuringia/Germany, was installed as
a part of a research program of the Friedrich-Schiller University Jena to study, among other techniques, the phytoremediation
capacity of native and selected plants towards uranium. In the first step the uranium speciation in surface seepage and soil
pore waters from Gessenwiese, ranging in pH from 3.2 to 4.0, were studied by time-resolved laser-induced fluorescence spectroscopy
(TRLFS). Both types of water samples showed mono-exponential luminescence decay, indicating the presence of only one major
species. The detected emission bands were found at 477.5, 491.8, 513.0, 537.2, 562.3, and 590.7 nm in case of the surface
water samples, and were found at 477.2, 493.2, 513.8, 537.0, 562.4, and 590.0 nm in case of the soil water samples. These
characteristic peak maxima together with the observed mono-exponential decay indicated that the uranium speciation in the
seepage and soil pore waters is dominated by the uranium (VI) sulfate species UO 2SO 4(aq). Due to the presence of luminescence quenchers in the natural water samples the measured luminescence lifetimes of the UO 2SO 4(aq) species of 1.0–2.6 μs were reduced in comparison to pure uranium sulfate solutions, which show a luminescence lifetime of
4.7 μs. These results convincingly show that in the pH range of 3.2–4.0 TRLFS is a suitable and very useful technique to study
the uranium speciation in naturally occurring water samples. 相似文献
20.
Highly monodisperse polystyrene (PS) microspheres in the size range of 3.75–7.09 μm were synthesized by dispersion polymerization
with dropwise monomer feeding procedure. The morphology, size, and particle size distribution (PSD) of the PS microspheres
obtained by different monomer feeding modes, including batch polymerization and various feeding rates, were investigated.
The PSD of particles showed a close dependence on feeding rate. The PS microspheres with low coefficient of variation (CV)
values all less than 4.8% obtained by the optimum feeding rates revealed better uniformity than those by batch polymerization
(CV values all more than 8.2%). According to the time courses of monomer conversion and particle numbers, the effects of monomer
feeding modes on the polymerization reaction of the large-sized PS microspheres were clarified. It is found that the dropwise
monomer feeding procedure is promising for the synthesis of large-sized monodisperse PS particles in 3.75–7.09 μm. 相似文献
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