Leaching of uranium,radium and thorium from vertisol soil by ground water

Shallow land burial is routinely used for the disposal of low-level radioactive waste. Natural processes causing leaching of radionuclides can lead to contamination of surrounding ground water and soil by the radionuclides. The comparative leachability of radionuclides U_(nat), ²²⁶Ra, ²²⁸Ra and Th_(nat) from the soil of a radioactive waste disposal site, by ground water was evaluated. The probability of leaching was obtained in the following order Ra (≈77%) > U (≈40%) > Th (≈20%). Observed ratios (OR) were calculated to correlate leachability of radionuclides to that of major cations Ca²⁺ and Mg²⁺. The leaching of the radionuclides was seen to be dependent on Ca²⁺ and SO₄²⁻ leached from the soil. This study provides sitespecific leachability of radionuclides, that can be used as indicator of the tendency for migration or retention in soil. It can play an important role during an unforeseen accident like breach of containment at the waste disposal site leading to contamination of soil and ground water and causing hazard to public via drinking water route.     

Separation of thorium from uranium ore

Thorium-230 has many research applications, but there is not a commercial source of this isotope. However, since ²³⁰Th is part of the ²³⁸U decay chain, it can be separated from naturally occurring uranium. In this work, a novel procedure was developed to separate thorium from uranium ore, consisting of leaching, liquid–liquid extraction, precipitations and ion exchange chromatography. The final product was 91.32?±?0.77 mg of thorium with a purity of 99.5?±?1.2 wt%. Of that, 7.65?±?0.10 mg was ²³⁰Th and the remainder ²³²Th. The total yield of ²³⁰Th was 71.1?±?5.4%. Ways to improve the yield by further processing the back-extraction solution are suggested.

     

Method of separating uranium from iron and thorium

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.     

A modified method for the determination of uranium in Nb/Ta minerals by LED fluorimetry

A modified LED fluorimetry determination of uranium in Nb/Ta minerals has been developed. The mineral is brought into solution by fusion with mixed phosphate flux (NaH₂PO₄, H₂O and Na₂HPO₄). Iron quenches uranium fluorescence when it is present above the ratio of (iron to uranium) 100. Uranium is separated in ethyl acetate by solvent extraction and then stripped back into pyrophosphate buffer (pH ~ 7) prior to its LED fluorimetry determination. This modified method has been applied for the determination of uranium in synthetic mixtures and Nb/Ta minerals including Certified Reference Materials (X1807) with high degree of accuracy and precision.

     

Electrodeposition of uranium and thorium

Cathodic depositions of uranium and thorium were carried out from a number of baths containing the metal salts, and complexing agents. A reducing agent was also present to prevent oxidation of the element. The deposition was also carried out at controlled pH. The current density ranged from 50 to 200 mA cm^–2. The purity of the deposited metals was better than 99.7%. The mechanism of formation of uranium and thorium is proposed and discussed.     

Chromatographic separation of rare earths and uranium from thorium

Ohne Zusammenfassung     

Anion-exchange separation of thorium and protactinium from uranium matrix

Summary The distribution behaviour of Th⁴⁺, Pa⁵⁺, and UO₂ ²⁺ ions between the anion-exchanger Amberlite IRA-400 and acetic acid-hydrochloric acid mixtures, has been investigated. It was found that the general behaviour of Th⁴⁺ ions is similar to that of UO₂ ²⁺ ions though the latter are much more highly adsorbed by the resin than Th⁴⁺. Protactinium exhibited a different behaviour from both Th⁴⁺ and UO₂ ²⁺ ions. The separation factors were calculated, and a Chromatographic procedure for sequential isolation of each element was developed.

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Zusammenfassung Das Verteilungsverhalten von Th⁴⁺, Pa⁵⁺ und UO₂ ²⁺ zwischen dem Anionenaustauscher Amberlit IRA-400 und Gemischen aus Essigsäure und Salzsäure wurde untersucht. Das allgemeine Verhalten von Th⁴⁺ ist ähnlich dem von Uranylionen, wenngleich letztere von dem Harz viel stärker adsorbiert werden als Th⁴⁺. Protactinium zeigt ein abweichendes Verhalten im Vergleich zu Th⁴⁺ und UO₂ ²⁺. Die Trennfaktoren wurden berechnet und ein chromatographisches Verfahren zur Isolierung der angeführten Ionen entwickelt.

     

Investigation of radioactive lead,uranium, and thorium in environmental waters by extraction chromatography resins

A time-saving and sensitive method for monitoring low concentration (activities) of ²¹⁰Pb, ²³²Th, and ²³⁰Th and ²³⁸U, ²³⁴U, and ²³⁵U in water samples has been developed. Through the combination of co-precipitation and extraction chromatography by 3M RAD disks and UTEVA (Eichrom) columns effective radiochemical separation of the analytes was carried out. Thorium and uranium activities were determined by alpha spectrometry and lead activity by LSC, respectively. The minimal detectable activities obtained were 0.6?Bq?m^?3 for uranium, 0.29?Bq?m^?3 for thorium, and 2.5?Bq?m^?3 for ²¹⁰Pb. More than 150 different waters were analysed for uranium content and only 30 for lead and thorium. The investigations are still in progress.     

Uranium, thorium and potassium contents and radioactive equilibrium states of the uranium and thorium series nuclides in phosphate rocks and phosphate fertilizers

Uranium, thorium and potassium contents and radioactive equilibrium states of the uranium and thorium series nuclides have been studied for 2 phosphate rocks and 7 phosphate fertilizers. Uranium contents were found to be rather high (39-117 ppm) except for phosphate rock from Kola. The uranium series nuclides were found to be in various equilibration states, which can be grouped into following three categories. Almost in the equilibrium state, 238U approximately 230Th greater than 210Pb greater than 226Ra and 238U greater than 230Th greater than 210Pb greater than 226Ra. Thorium contents were found to be, in general, low and appreciable disequilibrium of the thorium series nuclides was not observed except one sample. Potassium contents were also very low (less than 0.3% K2O) except for complex fertilizers. Based on the present data, discussions were made for the radiation exposure due to phosphate fertilizers.     

Study of scandium and thorium sorption from uranium leach liquors

Scandium and thorium sorption from simulated uranium leach liquors by phosphorous containing ion exchange resins was studied. Increase of thorium concentration resulted in a decrease of scandium sorption by 26–65%. Tulsion CH 93 resin was chosen for Sc separation from uranium leach liquors. It was shown that 180 g L^?1 Na₂CO₃ allowed for elution 94.1% of Sc and 98.9% of Th in dynamic conditions. Using (NH₄)₂SO₄ (50 g L^?1) + ACBM (180 g L^?1) mixture for primary Sc/Th separation at the resin/eluent ratio of 1:5 resulted in thorium desorption degree as high as 66–69%, whereas scandium loss did not exceed 10%.     

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.     

Determination of radioactive nuclides of uranium and thorium series and estimation of α-flux in LSI constituent materials

Gamma-rays of nuclides of uranium and thorium series in silicone resin and ceramics were measured with a Ge(Li) detector. The state of radioactive equilibrium was determined by comparing the concentrations of uranium and thorium with the radioactive concentrations of²¹⁴Pb and²¹²Pb. The radioactive equilibrium was attained in silicone resin but not in ceramics. The -flux was calculated from the concentrations of uranium and thorium and their daughter nuclides. The calculated values of -flux agreed with that of -flux measured.     

Determination of Nb and Ta in Nb/Ta minerals by inductively coupled plasmas optical emission spectrometry using slurry sample introduction

The determination of Nb and Ta in Nb–Ta minerals was accomplished by slurry nebulization inductively coupled plasma optical emission spectrometry (ICP-OES), using a clog-free V-groove ceramic nebulizer. Samples were first wet-ground to appropriate particle sizes with narrow size distribution and 90% of the particles in the slurry were smaller than 2.32 μm in diameter. Subsamples were then dispersed in pH 9 aqueous solutions, and agitated in an ultrasonic bath for 15 min prior to analysis. Due to the lack of slurry standards matching well with the samples, calibration was simply carried out using aqueous solution standards. Results were compared with those obtained from a conventional fusion decomposition procedure and acid digestion procedures and a good agreement between the measured and referred values was obtained. The technique provided a good alternative for the rapid determination of Nb and/or Ta in their corresponding minerals.     

Recovery of uranium and thorium from zirconium oxychloride by solvent extraction

A solvent extraction process is proposed to recover uranium and thorium from the crystal waste solutions of zirconium oxychloride. The extraction of iron from hydrochloride medium with P350, the extraction of uranium from hydrochloride with N235, and the extraction of thorium from the mixture solutions of nitric acid and the hydrochloric acid with P350 was investigated. The optimum extraction conditions were evaluated with synthetic solutions by studying the parameters of extractant concentration and acidity. The optimum separation conditions for Fe (III) are recognized as 30% P350 and 4.5 to 6.0 M HCl. The optimum extraction conditions for U (VI) are recognized as 25% N235 and 4.5 to 6.0 M HCl. And the optimum extraction conditions for Th (VI) are recognized as 30% P350 and 2.5 to 3.5 M HNO₃ in the mixture solutions. The recovery of uranium and thorium from the crystal waste solutions of zirconium oxychloride was investigated also. The results indicate that the recoveries of uranium and thorium are 92 and 86%, respectively.     

Separation of uranium from thorium on cryptomelane-type hydrous manganese dioxide

The distribution of UO ₂ ²⁺ and Th⁴⁺ in nitric acid media on crypomelane-type hydrous manganese dioxide (CRYMO) has been investigated by batch equilibrations and column break-through techniques. The parameters studied involve the media composition and concentrations of HNO₃, NaNO₃, UO ₂ ²⁺ and Th⁴⁺. It is found that Th⁴⁺ is more strongly adsorbed on CRYMO than UO ₂ ²⁺ with sufficient differences for chromatographic separation from each other. Uranium was quantitatively eluted from a CRYMO column with 0.1M HNO₃. Th⁴⁺ has been recovered by using 1M HNO₃ as eluent.     

Sorption of uranium and thorium from sulphuric acid using TVEX-PHOR resin

Summary Solid-liquid extraction has been used to study the uptake of uranium(VI) and thorium(IV) from sulphuric acid using a TVEX-PHOR resin. The experimental results were found to fit the BET isotherm and show a higher affinity of the TVEX-PHOR resin towards the extraction of uranium than thorium under similar experimental conditions. The best separation of uranium from thorium is obtained from 3M sulphuric acid at V/m ratio of 20 ml/g. Elution of loaded uranium and thorium was carried out with 1M sodium carbonate and 0.075M sulphuric acid, respectively. After the elution of both elements, the regenerated resin could be reused with high efficiency.     

Laser-induced breakdown spectroscopy measurements of uranium and thorium powders and uranium ore

Laser-induced breakdown spectroscopy (LIBS) was used to analyze depleted uranium and thorium oxide powders and uranium ore as a potential rapid in situ analysis technique in nuclear production facilities, environmental sampling, and in-field forensic applications. Material such as pressed pellets and metals, has been extensively studied using LIBS due to the high density of the material and more stable laser-induced plasma formation. Powders, on the other hand, are difficult to analyze using LIBS since ejection and removal of the powder occur in the laser interaction region. The capability of analyzing powders is important in allowing for rapid analysis of suspicious materials, environmental samples, or trace contamination on surfaces since it most closely represents field samples (soil, small particles, debris etc.). The rapid, in situ analysis of samples, including nuclear materials, also reduces costs in sample collection, transportation, sample preparation, and analysis time. Here we demonstrate the detection of actinides in oxide powders and within a uranium ore sample as both pressed pellets and powders on carbon adhesive discs for spectral comparison. The acquired LIBS spectra for both forms of the samples differ in overall intensity but yield a similar distribution of atomic emission spectral lines.     

Pollution characteristics and risk assessment of uranium and heavy metals of agricultural soil around the uranium tailing reservoir in Southern China

For the first time the pollution of the paddy soil within 2 km around the uranium tailing reservoir was investigated. The concentrations of U, Cd, Cr, Pb, Cu, Zn, Hg and As were determined by ICP-MS. The study showed that there was severe pollution in the first area (within 0–1 km of the tailing reservoir), which was caused by Cd, As, U and Hg. The pollution level of the second area (within 1–2 km) was relatively low. Hg and As were the main pollutants. In the first area, the contamination degree and risk of elements were positively correlated with the distance from the tailing reservoir. The second area was less polluted and influenced by mining and human activities because of mountain barriers.     

Ultratrace analysis of uranium and thorium in glass

It is today a most common phenomenon that ultratrace analyses for quality control have to be carried out in industrial laboratories far from optimum conditions and in spite of the lack of best suited equipment. It was against this setting that the development of a method for the photometric determination of uranium- and thorium-traces in glasses with arsenazo III was envisaged. The method basically consists of a digestion with HF/HClO₄/H₃BO₃, an extractive preseparation of interfering Ti- and Zr-traces with TTFA/hexanol/CCl₄, an extractive separation of U- and Th-traces with TTFA/TBP/toluene and a final determination of thorium alone (in the presence of photometrically inactive U(VI)) and the sum of Th+U(IV) with arsenazo III.The concentration of uranium is calculated from the difference of the sum of both traces minus the thorium content. Uranium can be determined with nearly the same sensitivity as thorium after reduction to uranium(IV). The most suitable reducing agent for uranium(VI) to uranium(IV) is a mixture of Na₂S₂O₄/CH₂O. An optimization of the arsenazo III concentration for the determination of thorium and uranium yielded an optimal concentration of 80 mg/L arsenazo III: For the reduction of uranium concentrations of 2 g/L of Na₂S₂O₄ and 3.2 g/L CH₂O proved to be optimal. Interferences of this photometric end determination by titanium, zirconium and scandium were investigated quantitatively. The permissible excess for these elements was found to be so low that a trace-trace separation method proved to be necessary. Separation methods were checked for the separation of the matrix components of the investigated glasses from thorium and uranium. One of these methods was suitable after optimization: thorium and uranium are extracted with TTFA/TBP/toluene from a solution containing hydrochloric acid. Back-extraction is carried out with HCl/KMnO₄. For the separation of titanium- and zirconium-cotraces an extra separation method had to be developed: they are extracted with TTFA/hexanol/CCl₄ before the separation of uranium- and thorium-traces from the matrix. The glasses were digested with HF/HX. Fluoride from the hydrofluoric acid is incompletely removed by evaporation and interferes with the extraction of uranium and thorium due to complex formation. Depending on the digestion variant used 162 to 0.23 mg F^– remain in the residue of the digestion of a 5 g sample. This interference was eliminated by a digestion with HF/HClO₄/H₃BO₃ and masking of residual fluoride with AlCl₃.Abbreviations used Arsenazo III 1,8-Dihydroxynaphthalene-3,6-disulphonic acid-2,7-bis [(azo-2)-phenylarsonic acid] - Arsenazo I 1,8-Dihydroxynaphthalene-3,6-disulphonic acid-2-[(azo-2)-phenylarsonic acid] - BPAP 2- (5-Bromo-2-pyridy] azo)-5-diethylaminophenol - EDTA Ethylenediaminetetraacetic acid - HX Designation for a high boiling mineral acid - FAAS Flame atomic absorption spectrometry - FOD 1,1,1,2,3,3,-Heptafluor-7, dimethyl-4,6-octanedione - GFAAS Graphite furnace atomic absorption spectrometry - ICP-MS Inductively coupled plasma — mass spectrometry - ICP-OES Inductively coupled plasma — optical emission spectrometry - LAS Liquid absorption spectrophotometry (classical photometry) - m(Th) Mass of thorium - NAA Neutron activation analysis - pK_Diss Negative logarithm to the base 10 of the dissociation constant of a complex - TBP Tri-(n-butyl)-phosphate - TOPO Tri(n-octyl)-phosphinoxide - TTFA 1-(2-Thenoyl)-3,3,3-trifluoroacetone     

Coprecipitation of uranium and thorium with barium sulfate

The coprecipitation behaviour of uranium or thorium with barium sulfate is investigated from the variation of yields with uranium or thorium concentration, acid and acidity, and amount of sodium and/or potassium sulfate. Uranium or thorium in quantities less than 1.5 mg is quantitatively coprecipitated with barium (5.9 mg) sulfate when using an optimum conditions. The chemical form of uranium in barium sulfate precipitates is discussed by determination of mole ratio of potassium to uranium.