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Journal of Radioanalytical and Nuclear Chemistry
Authors:
Sung Park
,
Dong Cho
,
Gyu Oh
,
Jong Lee
,
Sung Hwang
,
Young Kang
,
Hansoo Lee
,
Eung Kim
, and
Seong-Won Park

Abstract  

From an electrorefining process, uranium deposits were recovered at the solid cathode of an electrorefining system. The uranium deposits from the electrorefiner contained about 30–40 wt% salts. In order to recover pure uranium and transform it into metal ingots, these salts have to be removed. A salt distiller was adapted for a salt evaporation. A batch operation for the salt removal was carried out by a heating and a vacuum evaporation. The operational conditions were a 700–1,000 °C hold temperature and less than a 1 Torr under Argon atmosphere, respectively. The behaviors of the salt evaporations were investigated by focusing on the effects of the pressure and the holding temperature for the salt distillation. The removal efficiencies of the salts were obtained with regard to the operational conditions. The experimental results of the salt evaporations were evaluated by using the Hertz-Langmuir relation. The effective evaporation coefficients of this relation were obtained with regards to the vacuum pressures and the hold temperatures. The higher the vacuum pressure and the higher the holding temperature were, the higher the removal efficiencies of the salts were.

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Abstract  

It is important to increase a throughput of the salt removal process from uranium deposits which is generated on the solid cathode of electro-refiner in pyroprocess. In this study, it was proposed to increase the throughput of the salt removal process by the separation of the liquid salt prior to the distillation of the LiCl–KCl eutectic salt from the uranium deposits. The feasibility of liquid salt separation was examined by salt separation experiments on a stainless steel sieve. It was found that the amount of salt to be distilled could be reduced by the liquid salt separation prior to the salt distillation. The residual salt remained in the deposits after the liquid salt separation was successfully removed further by the vacuum distillation. It was concluded that the combination of a liquid salt separation and a vacuum distillation is an effective route for the achievement of a high throughput performance in the salt separation process.

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Abstract  

Recovered salt can be reused in the electrorefining process and the final removed salt from uranium (U) deposits can be fed into a following U casting process to prepare ingot. Therefore, salt distillation process is very important to increase the throughput of the salt separation system due to the high U content of spent nuclear fuel and high salt fraction of U dendrites. Yields on salt recovered by a batch type vacuum distiller transfer device were processed for obtaining pure eutectic salt and U. In this study, the influence of the various temperature slopes of each zones on salt evaporation and recovery rate are discussed. From the experimental results, the optimal temperature of each zones appear at the Top Zone and Zone 1 is 850 °C, Zone 2 is 650 °C and Zone 3 is 600 °C, respectively. In these conditions, the complete evaporation of pure salt in 1.4 h occurred and the amount of recovered salt was about 99 wt%. The adhered salt in U deposits was separated by a temperature slope zone of salt distillation equipment. From the experimental results using U deposits, the amount of salt evaporation was achieved more than 99 wt% and the salt evaporation rate was about 1.16 g/min. Also, the mount of recovered salt was about 99.5 wt%.

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Abstract  

Uranium dendrites which were deposited at a solid cathode of an electrorefiner contained a certain amount of salts. These salts should be removed for the recovery of pure metal using a cathode processor. In the uranium deposits from the electrorefining process, there are actinide chlorides and rare earth chlorides in addition to uranium chloride in the LiCl–KCl eutectic salt. The evaporation behaviors of the actinides and rare earth chlorides in the salts should be investigated for the removal of salts in the deposits. Experiments on the salt evaporation of rare earth chlorides in a LiCl–KCl eutectic salt were carried out. Though the vapor pressures of the rare earth chlorides were lower than those of the LiCl and KCl, the rare earth chlorides were co-evaporized with the LiCl–KCl eutectic salt. The Hertz–Langmuir relation was applied for this evaporation, and also the evaporation rates of the salt were obtained. The co-evaporation of the rare earth chlorides and LiCl–KCl eutectic were also discussed.

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Journal of Radioanalytical and Nuclear Chemistry
Authors:
E. Tóth
,
F. Deák
,
Cs. Gyurkócza
,
Zs. Kasztovszky
,
R. Kuczi
,
G. Marx
,
B. Nagy
,
S. Oberstedt
,
L. Sajó-Bohus
,
Cs. Sükösd
,
G. Tóth
, and
N. Vajda

Abstract  

For the public, indoor radon is the main source of exposure from ionizing radiation. Radon gas originates from the radioactive decay chain of uranium deposited in rocks or in building materials. In the reviews mostly a rather steady radon exhalation has been assumed. In a village of North-East Hungary, however, high radon concentrations have been measured, differing strongly in neighbouring houses and varying in time, due to the interplay of several geochemical phenomena.

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Abstract  

Sample of fresh and weathered quartz pebble conglomerates of the West Rand Group of the 2.5–2.8 Ga Witwatersrand gold-uranium deposit (South Africa) were investigated. Uranium and thorium element and isotope analyses were carried out by -spectrometry. Two different kinds of sample treatment were presented: bulk rock analysis and leaching process, and a detailed description of data evaluation from the -spectrometric measurements were given. Radioactive disequilibrium found in bulk rocks and leached solutions of all weathered samples indicate U redistribution processes, mainly U loss in the weathered zone of conglomerates. It could be shown that the use of -spectrometry and in addition the use of two kinds of sample treatment is a good method for studying the behaviour of uranium during weathering processes.

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Geochemical Prospecting for Thorium and Uranium Deposits, vol. 16 Elsevier Science Amsterdam . [3]. P. Henderson 1984

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Abstract  

Acid leaching of uranium deposits is not a selective process. Sulfuric acid solubilizes iron(III) and half or more of the thorium depending on the mineralog of this element. In uranium recovery by solvent extraction process, uranium is separated from iron by an organic phase consisting of 10 vol% tributylphosphate(TBP) in kerosine diluent. Provided that the aqueous phase is saturated with ammonium nitrate or made 4–5 M in nitric acid prior to extraction. Nitric acid or ammonium nitrate is added to the leach solution in order to obtain a uranyl nitrate product. Leach solutions containing thorium(IV) besides iron are treated in an analogous fashion. Uranium can be extracted away from thorium using 10 vol% TBP in kerosine diluent. The aqueous phase should be saturated with ammonium nitrate and the pH of the solution lowered to 0.5 with sufficient amount of sulfuric acid. In other words, the separation of uranium and thorium depends on the way the relative distributions of the two materials between aqueous solutions and TBP vary with sulfuric acid concentration. Thorium is later recovered from the waste leach liquor, after removal of sulfate ions. Uranium can be stripped from the organic phase by distilled water, and precipitated as ammonium diuranate.

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Abstract  

The prediction of the adsorption behavior of natural composite materials was studied by a single mineral approach. The adsorption of U(VI) on single minerals such as goethite, hematite, kaolinite and quartz was fully modeled using the diffuse-layer model in various experimental conditions. A quasi-thermodynamic database of surface complexation constants for single minerals was established in a consistent manner. In a preliminary work, the adsorption of a synthetic mixture of goethite and kaolinite was simulated using the model established for a single mineral system. The competitive adsorption of U(VI) between goethite and kaolinite can be well explained by the model. The adsorption behavior of natural composite materials taken from the Koongarra uranium deposit (Australia) was predicted in a similar manner. In comparison with the synthetic mixture, the prediction was less successful in the acidic pH range. However, the model predicted well the adsorption behavior in the neutral to alkaline pH range. Furthermore, the model reasonably explained the role of iron oxide minerals in the adsorption of U(VI) on natural composite materials.

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