Estimation of distribution coefficient of uranium around a uranium mining site

Distribution coefficient (K _d) of uranium and its daughter products are very important for migration study around uranium mining sites. Since the distribution coefficient depends very much on the soil and groundwater chemistry, generation of site specific K _d is very important. In the literature there is a large variation of K _d values of uranium. For realistic prediction of contaminant migration, literature K _d value is not very effective. So site specific experimental K _d values are required. The present study emphasizes on the estimation of site specific distribution coefficient for uranium around a uranium mining site. The soil and groundwater parameters which affect the K _d value of uranium have also been estimated. Soil and groundwater samples from nine locations around Turamdih uranium mining site were collected and chemically characterized for various parameters. The distribution coefficient of uranium in top and one meter depth soil samples from above locations were estimated using laboratory batch method. The distribution coefficient of uranium varies from 69 ± 4 to 5524 ± 285 l/kg. No significant difference in uranium K _d values was observed for top and one meter depth soil samples. In the top and one meter depth soil samples uranium K _d values vary from 129 ± 8 to 5524 ± 285 and 69 ± 4 to 3862 ± 195 l/kg respectively. For the estimation of distribution coefficient of uranium different parameters like equilibration time, solid to solution ratio, method of tracer addition to solution, solid-solution separation method etc. have been optimized. The distribution coefficient of uranium determined in the present study will be used for the migration study of uranium around uranium mining sites.     

Natural radioactivity distribution in geological matrices around Kaiga environment

Summary The activity and absorbed dose rate of the naturally occurring radionuclides, viz. ²³⁸U, ²³² Th and ⁴⁰K were determined in soil and rock samples collected around Kaiga site. The mean activity levels (Kaiga soil) of naturally occurring ²³² Th are comparable with that in worldwide soil, while concentrations of ²³⁸U and ⁴⁰K are lower than those in worldwide soil. The absorbed dose rate in outdoor air ranged 20-58 nGy ^. h^-1 with a mean of 33.3 nGy ^. h^-1, which is below the world average of 60 nGy ^. h^-1. The total effective dose rate in outdoor air for soils ranged 25.6-74.4 mSv ^. y^-1 with a mean of 43.0 mSv ^. y^-1. The estimated dose rate at Kaiga is comparable with that estimated at Kakrapar and Rawatbhata and much less than that estimated at coastal sites of India.     

Radioanalytical assessment of environmental contamination around non-remediated uranium mining legacy site and radium mobility

During the past century extensive uranium mining took place in Portugal for radium and uranium production. One such uranium mine was the Boco Mine, in operation during the 1960s and 70s. Mining waste and open pits were left uncovered since mine closure. During the nineties a quarry for sand extraction was operated in the same site and water from a local stream was extensively used in sand sieving. Downstream the mine area, agriculture soil is used for cattle grazing. Water from the stream, water wells, soil, pasture and sheep meat were now analyzed for radionuclides of uranium natural series. The U-series radionuclide ²²⁶Ra was generally the highest in concentrations especially in soil, pasture, and in internal organs of sheep. ²²⁶Ra concentrations were 1,093 ± 96 Bq/kg (dry weight, dw) in soil, 43 ± 3 Bq/kg (dw) in pasture, and 193 ± 84 mBq/kg (wet weight, ww) in muscle tissue of sheep. Other sheep internal organs displayed much higher ²²⁶Ra concentrations, such as the brain and kidneys with 1,850 ± 613 mBq/kg (ww) and 6,043 ± 6,023 mBq/kg (ww), respectively. Results of analyses of tissue samples from sheep grown in a comparison area were 2 to 16 times lower, depending on the organ. Absorbed radiation doses for internal organs were computed and may exceed 5.2 mGy/y in the case of kidneys, near three times higher than in animals from the reference area, but below the threshold for biological effects. Radionuclide transfer in the terrestrial food chain and radiation exposure of the human population is discussed.     

Evaluation of the natural radioactivity in food and soil around uranium mining region

Journal of Radioanalytical and Nuclear Chemistry - To evaluate the radiological risk to human health associated with the ingestion of radionuclides in foods, some different plant foods cultivated...     

Antimony distribution in soils and plants near an abandoned mining site

A study about antimony distribution and mobility in soils located in the surroundings of an abandoned mining site is carried out. The mineralogical composition of the soils is obtained, and the samples classified into three groups attempting to correlate antimony level and behavior with the main mineral phases present. The total antimony concentrations are measured (5-40 mg kg⁻¹), and mobility of the metalloid is assessed by using selective extractants. Maximum mobility is obtained when extracting with a reducing-complexing medium which, taking into account the characteristics of the zone, means antimony availability to plants should be low. This is verified by analyzing both roots and leaves of vegetation growing in the area. The maximum level present in the leaves is 1.5 mg kg⁻¹ dry matter, but most of the samples show antimony concentrations below 0.5 mg kg⁻¹. The results indicate that plants represent an effective barrier to antimony that is incorporated only in small proportions, and so the risk posed to biota is low.     

Polarographic reduction of hexavalent uranium in sodium tripolyphosphate: Estimation of uranium

A polarographic method of estimating of uranium, based on the reduction of its tripolyphosphate complex at the dropping mercury electrode, has been developed and applied to uraniferous tantaloniobates and monazite. In the presence of elements such as copper, iron and vanadium which interfere with the cathodic step of the uranyl complex, a preliminary separation as uranyl ammonium phosphate in presence of EDTA is necessary.     

Inflow of polonium, uranium and plutonium radionuclides in Odra River catchment area assessment by environmetric expertise

The study deals with the application of cluster analysis (CA) and non-parametric tests (Shapiro–Wilk, Kruskal–Wallis, Dunn, U Mann–Whitney) to classify and interpret of a monitoring data set for Odra River water quality assessment based on concentration values of radiochemical parameters. The data set represents results for 3 alpha emitters (²¹⁰Po, ²³⁸U and ^239+240Pu) measured in surface water samples collected at 13 different sampling locations (5 in major Odra stream while 8 in Odra tributaries) within four seasons: winter, spring, summer and autumn, in the framework of 1 year-term quality monitoring research. The correlation analysis of polonium, uranium and plutonium data indicates that significant values of Spearman’s correlation coefficient appears between ²¹⁰Po and ^239+240Pu (r = 0.55 in autumn and 0.77 in winter as well as 0.49 in all year), while statistical significant correlation between uranium and plutonium as well as uranium and polonium were not found. In the Odra drainage basin, the biggest differences were observed in the case of ²³⁸U. The hypothesis about possible geographic and seasonal differences between concentration of ²¹⁰Po, ²³⁸U and ^239+240Pu in the Odra River catchment area was verified by cluster analysis (CA). Finally, to asses if there are statistically significant differences in mean concentration value of ²¹⁰Po, ²³⁸U and ^239+240Pu for Vistula and Odra Rivers drainage basins were obtained by used of the non-parametric tests. Comparing to Vistula catchment area, statistically different concentration of ²¹⁰Po and ^239+240Pu in all year was observed for river samples collected on Odra drainage basin.     

Separation of uranium from different uranium oxide matrices employing supercritical carbon dioxide extraction

Uranium from different uranium oxide matrices was extracted with tri-n-butyl phosphate–nitric acid (TBP–HNO₃) adduct using supercritical carbon dioxide (SC CO₂). While 30 min dissolution time at 323 K was sufficient for U₃O₈ and UO₂ powder, UO₂ 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–HNO₃ adduct, acidity of nitric acid used for preparing TBP–HNO₃ adduct and extraction time on uranium extraction efficiency was also investigated. For UO₂ powder, temperature of 323 K, pressure of 15.2 MPa, 1 mL TBP–HNO₃ 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 CO₂ alone which increased to 90% with the addition of 2.5% TBP in SC CO₂ 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.     

Alpha emitters from uranium mining in the environment

Uranium mining and milling activities usually generate an enhancement of radionuclide concentrations in the environment that may cause increased radiological exposure to mankind. For risk assessment and radiological protection of man and environment in these areas, usually, it is needed to implement radiological surveillance of water, soils, agricultural products, aerosols, and mining waste discharges as well. Radionuclides to be monitored in priority are alpha-emitting nuclides of the uranium natural series. Radioactivity analysis of materials from uranium mining areas of Portugal shows departure from secular radioactive equilibrium amongst uranium series radionuclides, thus rendering invalid the assumption of equilibrium and requiring the actual determination of each radionuclide. Radionuclide measurements performed with high resolution alphaspectrometry, as reported herein, produce accurate results on specific radionuclides that are essential in computing radiation doses to critical groups of the population.     

Advances in technologies for the measurement of uranium in diverse matrices

An overview of the advances in technologies, which can be used in the field as well as in a laboratory for the measurement of uranium in diverse matrices like, waters, minerals, mineralized rocks, and other beneficiation products for its exploration and processing industries is presented. Laser based technologies, ion chromatography, microsample X-ray analysis method followed by energy dispersive X-ray fluorescence technique (MXA-EDXRF), sensors for electrochemical detection followed by cyclic voltammogram and alpha liquid scintillation counting techniques are the most promising techniques. Among these techniques, laser fluorimetry/spectrofluorimetry, in particular, is the technique of choice because of its high performance qualification (PQ), inherent sensitivity, simplicity, cost effectiveness, minimum generation of analytical waste, rapidity, easy calibration and operation. It also fulfills the basic essential requirements of reliability, applicability and practicability (RAPs) for the analysis of uranium in solution of diverse matrices in entire nuclear fuel cycle. A very extensive range of uranium concentrations may be covered. Laser fluorimetry is suitable for direct determination of uranium in natural water systems within the μg L⁻¹ and mg L⁻¹ range while differential technique in laser fluorimetry (DT-LIF) is suitable for mineralized rocks and concentrates independent of matrix effects (uranium in samples containing >0.01% uranium). The most interesting feature of TRLIF is its capability of performing speciation of complexes directly in solution as well as remote determination via fiber optics and optrode. Future trend and advances in lasers, miniaturization and automation via flow injection analysis (FIA) has been discussed.     

Leaching dynamics of uranium in a contaminated soil site

Samples from a potentially contaminated industrial area were analyzed for uranium using neutron activation analysis (NAA). Uranium concentration values had a typical uncertainty of 2 % and a detection limit of 1 Bq/kg. To investigate the potential leaching dynamics into ground water two techniques were employed. The US EPA Toxicity Characterization Leaching Procedure (TCLP) and the Sequential Extraction Procedure (SEP) were used to determine the concentration of uranium in the leachates. TCLP and SEP showed that very little of the uranium leached into solution under different chemical conditions. Values of uranium leachates ranged from 0.05 to 3.5 Bq/L; a concentration much lower than the results found in the soil concentrations which ranged from 29 to 155 Bq/kg. NAA showed an 8 % uncertainty for leachates with a detection limit of 0.13 Bq/L. To mimic environmental conditions and acid rain, pH 4.3 water was used as the extraction solvent instead of the acetic acid routinely used in TCLP. Results confirmed that very low amounts of uranium leached with values ranging from 0.0002 to 0.0122 Bq/L. These values represent 0.01–1 % of the uranium in the soil samples. The distribution of uranium in soil according to particle size was also investigated to evaluate its potential movement and possible contamination of the water table. Particles below 250 μm in diameter showed a linear increase in uranium concentration whereas those with a larger diameter had constant uranium content.     

Estimation of trace impurities in reactor-grade uranium using ICP-AES

Estimation of impurities in reactor grade uranium is important from the point of view of neutron economy. For chemical separation, ion exchange and solvent extraction techniques have been employed although the latter is generally preferred. Amongst various extractants TBP (tri-n-butyl phosphate), TBP-TOPO (tri-n-octyl phosphine oxide), or TOPO only (in CCl(4), xylene, dodecane) is most often used. New reagents like Cyanex-923 (mixture of 4 tri-alkyl phosphine oxides)/TEHP (tri-ethylhexyl phosphoric acid) are also being used. This communication reports chemical separation of uranium by precipitation using 1,2-diaminocyclohexane NNN'N'-tetra acetic acid (CyDTA)/ammonium hydroxide in presence of 1,10-phenanthroline and estimation of impurities in the filtrate by ICP-AES. Quantitative separation of U, a high spectral interferent in plasma and recovery of impurities have been achieved. Recovery of Cd has been improved by using 1,10-phenanthroline. The method is accurate and precise, offering a relative standard deviation ranging from less than 4% (3.8% for Eu at the 10mug g(-1) level) to 12.9% (for Ce at the 2.5 mug g(-1) level) for all the elements studied.     

Estimation of 90Sr in reprocessed uranium oxide samples

Summary A method has been developed for the estimation of ⁹⁰Sr in reprocessed uranium oxide samples obtained from the Purex processing of natural uranium spent fuel discharged from the research reactor. The method employs a combination of precipitation and solvent extraction procedure to eliminate other beta-impurities prior to resorting to the estimation of ⁹⁰Sr by beta-counting. ¹⁰⁶Ru was eliminated by volatalizing with perchloric acid, uranium was removed by carrier precipitation with strontium as sulphate. The sulphate precipitate was converted to carbonate and dissolved in nitric acid. ²³⁴Th and ²³⁴Pa were eliminated by synergistic solvent extraction using tri-n-butyl phosphate and thenoyl trifluoroacetone extractant mixture in xylene. An iron scavenging step was included to remove any residual impurities. Finally, strontium is precipitated as SrC₂O₄^. H₂O. The separated ⁹⁰Sr activity was followed to check the equilibrium growth of ⁹⁰Y.     

Voltage-induced variation of distribution coefficient in electrochromatography

Upon application of an electric field along a column packed with anion exchange support materials, the output of a recorder jumps beyond the baseline, and with continued application a peak is obtained. If, instead, the electric field is applied in a pulsed manner, two peaks result. These observations are explained as caused by a change in the concentration of the solvent. Applying positive and negative voltages produces positive and negative peaks, respectively. The peak height depends on the value of applied voltage. Simulations using the plate height theory agree well with chromatograms obtained experimentally. The value of the local applied voltage is also estimated. Overall, the behavior is something like an injection arising from the pulsed application of an electric field. We suggest that voltage pulsing might be used as a new technique for sample injection.     

Determination of impurities in uranium matrices by time-of-flight ICP-MS using matrix-matched method

The analysis of impurities in uranium matrices is performed in a variety of fields, e.g., for quality control in the production stream converting uranium ores to fuels, as element signatures in nuclear forensics and safeguards, and for non-proliferation control. We have investigated the capabilities of time-of-flight ICP-MS for the analysis of impurities in uranium matrices using a matrix-matched method. The method was applied to the New Brunswick Laboratory CRM 124(1–7) series. For the seven certified reference materials, an overall precision and accuracy of approximately 5% and 14%, respectively, were obtained for 18 analyzed elements.     

Variation rules of the radon emanation coefficient in dump-leached uranium tailing sand

This study was intended to determine the variation rules of the radon emanation coefficient in dump-leached uranium tailing sand. A temperature and humidity controllable device for measuring the emanation coefficient was designed. Tailing sand with different grain sizes was selected from uranium tailings in southern China. An orthogonal experimental design was conducted to determine the radon emanation coefficient of the sand under different temperatures, humidities and grain sizes. Experimental results showed that the air temperature, humidity and grain size have significant effects on the emanation coefficient. The variation rules regarding the radon emanation coefficient showed significant reference value.