Galvanochemical treatment of solutions from nitric acid process of uranium refining

A procedure was developed for galvanochemical treatment of solutions from nitric acid process of uranium refining at nuclear fuel cycle enterprises. The main features of galvanochemical treatment of uranium-containing process solutions, followed by leaching and recycling of uranium, were determined.     

Characterization and remediation of soils contaminated with uranium

Environmental contamination caused by radionuclides, in particular by uranium and its decay products is a serious problem worldwide. The development of nuclear science and technology has led to increasing nuclear waste containing uranium being released and disposed in the environment. The objective of this paper is to develop a better understanding of the techniques for the remediation of soils polluted with radionuclides (uranium in particular), considering: the chemical forms of uranium, including depleted uranium (DU) in soil and other environmental media, their characteristics and concentrations, and some of the effects on environmental and human health; research issues concerning the remediation process, the benefits and results; a better understanding of the range of uses and situations for which each is most appropriate. The paper addresses the main features of the following techniques for uranium remediation: natural attenuation, physical methods, chemical processes (chemical extraction methods from contaminated soils assisted by various suitable chelators (sodium bicarbonate, citric acid, two-stage acid leaching procedure), extraction using supercritical fluids such as solvents, permeable reactive barriers), biological processes (biomineralization and microbial reduction, phytoremediation, biosorption), and electrokinetic methods. In addition, factors affecting uranium removal from soils are furthermore reviewed including soil characteristics, pH and reagent concentration, retention time.     

Leaching of Uranium from Its Mineralization and Experimental Design of the Process

The central composite design (CCD) of experiments was used to study the leaching of uranium and iron from the mineralized Gabal Al-Aglab uranium ore sample using sulfuric acid solution. The leaching factors were sulfuric acid concentration, contact time, particle size, temperature, solid to liquid ratio, and stirring rate. The uranium and iron leaching efficiencies were 71.6 and 10.8%, respectively. Three factors were taken into consideration in the experimental planning: leaching time, solid/liquid ratio, and stirring rate. The obtained results were statistically analyzed using analysis of variances (ANOVA) to determine the main effects and interactions between the investigated factors.     

Selective recovery of uranium from multicomponent salt systems on inorganic sorbents

The recovery of uranium from highly saline process solutions from extraction refining of uranium on Termoksid inorganic sorbents was studied under static and dynamic conditions. The isotherms of uranium sorption on these sorbents are described by the Freundlich equation. Termoksid inorganic sorbents proved to be efficient for exhaustive removal of uranium from process solutions from extraction refining of uranium.     

Hair analysis as an indicator of exposure to uranium

Medical examinations performed on four monks of a monastery in the northern Greece revealed heavy metal contamination. Hair analysis, performed by a toxicological laboratory abroad, indicated, among other, the presence of uranium. The uranium concentrations determined in a laboratory of "Elemental Hair Analysis' indicated a uranium level that was about five times the maximum value of the reference range, which has been adopted by the measuring laboratory. After these diagnostic findings, on request of 10 monks, uranium determination in hair and urine samples was performed by means of alpha spectrometry in GAEC's laboratory. The measured uranium concentrations in hair varied from 0.15 to 2.10 mBq g(-1), which correspond to 12.1 and 170 ng g(-1), respectively. The uranium concentrations in urine were between 41 and 174 ng d(-1). For comparison purposes, urine and non-dyed hair samples from the staff of the laboratory were analysed. Because one of the major sources of uranium intake is through drinking water, water samples were also analysed. The mean value of the uranium concentration in the two drinking water samples collected from the residence area was found to be 2.35 μg l(-1).     

Content of uranium in urine of uranium miners as a tool for estimation of intakes of long-lived alpha radionuclides

Uranium in the urine of 10 uranium miners (hewers), 27 members of general population and 11 family members of miners was determined by the High-Resolution ICP-MS method. Concentration of uranium in urine of the miners was converted to daily excretion of (238)U under the assumption that the daily excretion of urine is 2 l and compared with the modelled excretion of (238)U. Daily excretion of (238)U was modelled using input data from personal dosemeters from a component for measurement of intake of long-lived alpha radionuclides. A reasonable agreement between evaluated and measured values was found. The uncertainty of inhalation intakes, derived from measurements of filters from personal dosemeters, and uncertainty of concentration of uranium in urine are discussed.     

Estimation of uranium GI absorption fractions for children and adults

Uranium is ubiquitously found in drinking water and food. The gastrointestinal tract absorption fraction (f(1)) is an important parameter in risk assessment of uranium burdens from ingestion. Although absorption of uranium from ingestion has been studied extensively in the past, human data concerning children and adults are still limited. In a previous study based on measurements of uranium concentration in 73 bone-ash samples collected by Health Canada, the absorption fractions for uranium ingestion were determined to be 0.093 ± 0.113 for infants, and 0.050 ± 0.032 for young children ranging from 1 to 7 y of age. To extend the study, a total of 69 bone-ash samples were selected for children and adults ranging from 7 to 25 y of age and residing in the same Canadian community that is known to have an elevated level of uranium in its drinking water supply. For each bone-ash sample, the total uranium concentration was measured by inductively coupled plasma mass spectrometry. To solve uranium transfer in the biokinetic model for uranium given in International Commission of Radiological Protection (ICRP) Publication 69 with estimated daily uranium intake, the program WinSAAM v3.0.1 was used. The absorption fractions were determined to be 0.030 ± 0.022 for children (7-18 y) and 0.021 ± 0.015 for adults (18-25 y). For anyone more than 18 y of age, the estimated f(1) value for uranium agree well with the ICRP recommended value of 0.02.     

Hydrolytic durability of uranium-containing sodium aluminum (iron) phosphate glasses

Normalized mass loss and leach rates of elements from the synthesized sodium aluminum phosphate and sodium aluminum iron phosphate glasses in relation to the content of uranium introduced into the glass-forming charge in the form of uranium dioxide or uranyl nitrate were determined by the РСТ procedure (variant А). The relationship between the element leaching parameters and the structure of the anionic motif of the glass network, up to the formation of a polyanionic structure from aluminum (iron)–phosphorus–oxygen network and uranium–oxygen polyanions, was determined. The resistance of the glasses to leaching of elements is on the same level as that of reference iron phosphate glasses.     

Assessment of exposure to depleted uranium

In most circumstances, measurement of uranium excreted in urine at known times after exposure is potentially the most sensitive method for determining the amount of depleted uranium (DU) incorporated. The problems associated with this approach are that natural uranium is always present in urine because of the ingestion of natural uranium in food and drink, and that the uncertainties in the intakes as assessed from excretion measurements can be quite large, because many assumptions concerning the exposure characteristics (time pattern of exposure, route of intake, chemical form, solubility, biokinetics within the body) must be made. Applying currently available methods and instruments for the measurement of uranium in urine samples, DU incorporations of levels relevant with respect to potential health hazards can be detected reliably, even a long time after exposure.     

Evaluation of uranium incorporation from contaminated areas using teeth as bioindicators--a case study

The Southwest region of the Bahia state in Brazil hosts thelargest uranium reserve of the country (100 kton in uranium,only), plus the cities of Caetité, Lagoa Real and Igaporã.In this work, aim was at the investigation of uranium burdenson residents of these cities by using teeth as bioindicators,as a contribution for possible radiation protection measures.Thus, a total of 41 human teeth were collected, plus 50 froman allegedly uranium free area (the control region). Concentrationsof uranium in teeth from residents of 5- to 87-y old were determinedby means of a high-resolution inductively coupled plasma massspectrometer (ICP-MS). The highest uranium concentration inteeth was measured from samples belonging to residents of Caetité(median equal to 16 ppb). Assuming that the uranium concentrationsin teeth and bones are similar within 10–20% (for childrenand young adults), it concluded that uranium body levels inresidents of Caetité are at least one order of magnitudehigher than the worldwide average. This finding led to concludethat daily ingestion of uranium, from food and water, is equallyhigh.     

中国铀矿采冶技术发展与展望

对中国铀矿采冶工业的发展作了全面的回顾,重点介绍了中国铀矿地浸、堆浸、原地爆破浸出技术的研究进展与应用水平;在对中国铀矿采冶形势和存在的问题分析的基础上,结合矿床资源的特点,指出了中国铀矿采冶技术发展的方向。21世纪中国铀矿冶工业面临新的发展机遇和挑战,只有开发新的采、选、冶技术,提高铀资源的利用水平,减少铀矿采冶对环境的影响,才能实现铀矿冶的可持续发展和经济与环境的协调发展。     

Distribution of uranium in Dounreay workers due to uptake from the environment

At Dounreay, there are a number of facilities in which the main radiological hazard is the intake of uranium. The hazard is managed through the implementation of controls and contamination surveys in order to reduce the risk of intake. In order to provide reassurance that radiological significant intakes are not taking place, a routine urine sample programme is in place. As well as being exposed to work place sources of uranium workers are also exposed to the intake of uranium from foodstuffs and water, which are not associated with their work at Dounreay. In order to characterise the intake of the radionuclides from the environment, urine samples were collected from a group of Dounreay personnel who are not exposed to uranium in their workplace. The distribution of the uranium isotopes 234U, 235U and 238U has been assessed for these workers. The distributions will be used to assess the likelihood of uranium detected in urine for a uranium worker being due to an intake in the workplace. The best match to distributions of 234U and 238U was found to be a combination of normal and lognormal distributions.     

Radiogenic uranium in paragenetic mineral associations

Isotope composition of U in minerals of two mineral associations based on aeschynite and pyrochlore was studied. Although the ratio of U isotopes in the mineral associations as a whole is equilibrium (or close to equilibrium), the distribution of the radiogenic ²³⁴U isotope between separate parts of these associations is essentially nonuniform. Two models of the disturbance of the radioactive equilibrium are discussed: dependence of the ²³⁴U/²³⁸U ratio on the U concentration in the mineral (Adloff-Roessler model) and transfer of ²³⁴Th recoil atoms from one phase to another (Sheng-Kuroda model). It is impossible within the framework of any of the models to consistently account for the observed distribution of the radiogenic U between different mineral phases. For the quasi-closed mineral system based on aeschynite, a model of the redistribution of the radiogenic U under the action of natural solutions mainly within the mineral association is suggested; for the open system involving pyrochlore, the effects of natural leaching are explained taking into account the valence and chemical state of uranium in the minerals.     

Study of uranium transfer across the blood-brain barrier

Uranium is a heavy metal which, following accidental exposure, may potentially be deposited in human tissues and target organs, the kidneys and bones. A few published studies have described the distribution of this element after chronic exposure and one of them has demonstrated an accumulation in the brain. In the present study, using inductively coupled plasma mass spectrometry (ICP-MS) for the quantification of uranium, uranium transfer across the blood-brain barrier (BBB) has been assessed using the in situ brain perfusion technique in the rat. For this purpose, a physiological buffered bicarbonate saline at pH 7.4 containing natural uranium at a given concentration was perfused. After checking the integrity of the BBB during the perfusion, the background measurement of uranium in control rats without uranium in the perfusate was determined. The quantity of uranium in the exposed rat hemisphere, which appeared to be significantly higher than that in the control rats, was measured. Finally, the possible transfer of the perfused uranium not only in the vascular space but also in the brain parenchyma is discussed.     

Combined SEM/EDX and micro-Raman spectroscopy analysis of uranium minerals from a former uranium mine

Samples of the secondary uranium minerals collected in the abandoned uranium mine at Pecs (Hungary) were investigated by two micro-techniques: scanning electron microscopy (SEM/EDX) and micro-Raman spectroscopy (MRS). They were applied to locate U-rich particles and identify the chemical form and oxidation state of the uranium compounds. The most abundant mineral was a K and/or Na uranyl sulphate (zippeite group). U(VI) was also present in the form showing intensive Raman scattering at 860 cm⁻¹ which can be attributed to uranium trioxide. This research has shown the successful application of micro-Raman spectroscopy for the identification of uranyl mineral species on the level of individual particles.     

Development and Prospect of China Uranium Mining and Metallurgy

The development of industry of uranium mining and metallurgy in China has been reviewed generally, emphasizing on investigation approaches and application levels of uranium mining technologies such as insitu leaching, heap leaching, stope leaching: on the basis of analysis on status of uranium mining and metallurgy and problems existed, also considering the specific features of deposit resources, the development orientation of uranium mining and metallurgy in China is pointed out. The industry of China uranium mining and metallurgy is faced to new opportunity of development and challenge in 21st century, the only way to realize sustainable development of uranium mining and metallurgy and harmonious development between economy and environment is to develop new technology on mining, ore beneficiation and metallurgy, increase the utilization level of uranium resources, low down impact on environment caused by mining and metallurgy.     

Mechanism of uranium removal from the aqueous solution by elemental iron

The effectiveness of elemental iron (Fe(0)) to remove uranium (U) from the aqueous phase has been demonstrated. While the mitigation effect is sure, discrepancies in the removal mechanism have been reported. The objective of this study was to investigate the mechanism of U(VI) removal from aqueous phases by Fe(0). For this purpose, a systematic sequence of bulk experiments was conducted to characterize the effects of the availability and the abundance of corrosion products on U(VI) removal. Results indicated that U(VI) removal reactions did not primary occur at the surface of the metallic iron. It is determined that U(VI) co-precipitation with aging corrosion products is a plausible explanation for the irreversible fixation under experimental conditions. Results of XRD analyses did no show any U phases, whereas SEM-EDX analyses showed that U tended to associate with rusted areas on the surface of Fe(0). Recovering U with different leaching solutions varied upon the dissolution capacity of the individual solutions for corrosion products, showing that the irreversibility of the removal depends on the stability of the corrosion products. U(VI) co-precipitation as removal mechanism enables a better discussion of reported discrepancies.     

Sorption of uranium from carbonate solutions on various ion exchangers

Sorption of uranium from model carbonate solutions on ion-exchange resins of various types was studied. Highly basic anion exchangers (PFA-300, A-560, and AV-17 × 8) and ampholytes (S-930, S-922, S-957, and ANKB-35) exhibit the best sorption properties. The dependences of the static exchange capacity of PFA-300, A-560, and S-922 resins for uranium on the pH of the carbonate solution were evaluated, and the conditions of uranium desorption were determined.     

Sorption of uranium from nitric acid solutions on various ion exchangers

Sorption of uranium from model nitric acid solutions on ion-exchange resins of various types was studied. Phosphoric acid cation exchanger KRF-20, an ampholyte with iminodiphosphonic groups (S-950), and a cation exchanger with phosphonic and sulfonic groups (S-957) exhibit the best sorption properties. The dependences of the static exchange capacity of the above resins for uranium on the HNO₃ concentration, the sorption isotherms in 1 and 3 M solution of HNO₃, and the capacity for uranium to breakthrough were determined. The possibility of uranium desorption with a hot solution o Na₂CO₃ was demonstrated.     

The distribution of uranium and thorium in samples taken from different polluted marine environment

Concentrations of uranium and thorium in seawater, sediment and some marine species taken from along the coastal areas of Malaysia were determined spectrophotometrically. The uranium and thorium concentrations in seawater were found to vary ranging from 1.80 to 4.1 and 0.14 to 0.88 microg/L, respectively. The concentration of uranium in sediment samples was reported to range from 3.00 to 6.60 microg/g while those of thorium were slightly lower ranging from 0.01 to 0.68 microg/g. The uptake of uranium and thorium in marine species was found to be rather low. Similar variations in total alpha activities in samples were also observed with the total alpha activities relatively lower than the beta activities in most samples.