Determination of U and Th in tungsten by radiochemical neutron activation analysis

A radiochemical separation method using an anion exchange resin has been applied to 4N grade tungsten for determining U, Th and 4 other elements. While tungsten remained in the resin, Na, K and As were separated with 0.05M HCl and 1M HF and then U, Th and Cr were eluted with 1M HCl and 1M HF. The separation yield of neptunium (U) was influenced largely by the amount of thorium, but this influence could be neglected as the concentration of the thorium was below 0.5g/ml. The content of these elements were calculated by a single comparator method using monitors, gold and cobalt. The detection limits of U and Th are 4.0 and 1.2 ppb, respectively.     

Fluorimetric estimation of U(VI) in the presence of a large excess of Th(IV)

A fluorescence based method has been developed for the determination of trace amounts of uranium in thorium matrix using a mixture of phosphoric acid (H₃PO₄) and sulfuric acid (H₂SO₄), as fluorescence enhancing reagent for uranyl (UO₂ ²⁺) ion fluorescence. Synthetic samples mimicking the composition of ThO₂ fuel were prepared and the concentration of U(VI) was estimated. Satisfactory results are obtained when uranium is present at a concentration of 10 ppm in solid thorium samples with good precision.     

Extractive separation of Th(IV), U(VI), Ti(IV), La(III) and Fe(III) from Zarigan ore

In this study, the effects of various extraction parameters such as extractant types (Cyanex302, Cyanex272, TBP), acid type (nitric, sulfuric, hydrochloric) and their concentrations were studied on the thorium separation efficiency from uranium(VI), titanium(IV), lanthanum(III), iron(III) using Taguchi^??s method. Results showed that, all these variables had significant effects on the selective thorium separation. The optimum separations of thorium from uranium, titanium and iron were achieved by Cyanex302. The aqueous solutions of 0.01 and 1 M nitric acid were found as the best aqueous conditions for separating of thorium from titanium (or iron) and uranium, respectively. The combination of 0.01 M nitric acid and Cyanex272 were found that to be the optimum conditions for the selective separation of thorium from lanthanum. The results also showed that TBP could selectively extract all studied elements into organic phase leaving thorium behind in the aqueous phase. Detailed experiments showed that 0.5 M HNO₃ is the optimum acid concentration for separating of thorium from other elements with acidic extractants such as Cyanex272 and Cyanex302. The two-stage process containing TBP-Cyanex302 was proposed for separation thorium and uranium from Zarigan ore leachate.     

Adsorptive removal of U(VI) and Th(IV) from aqueous solutions using polymer-based electrospun PEO/PLLA fibrous membranes

Fibrous membranes based on poly(ethylene oxide) and poly(l-lactide) fabricated by electrospinning were evaluated for the first time as substrates for the adsorption of tetravalent thorium (Th(IV)) and hexavalent uranium (U(VI)) from aqueous media. The membranes consisted of microfibers with diameters of approximately 2 μm as revealed by scanning electron microscopy. The adsorption of Th(IV) and U(VI) on the membrane was investigated as a function of pH, ionic strength and initial metal concentration under normal atmospheric conditions. The experimental data indicated increased affinity of the membrane for Th(IV) and U(VI), which was pH depended and reaches maximum values (>90 %) for Th(IV) and U(VI) at pH 3 and pH 6.5, respectively. The maximum adsorption capacity (q _max) at optimum conditions was evaluated from the Langmuir isotherm and was found to amount 50.08 and 9.3 mmol kg^?1 for Th(IV) and U(VI), respectively. In addition, studies on the effect of ionic strength on the adsorption efficiency did not show any significant effect indicating that the adsorption of Th(IV) and U(VI) on the membrane was most probably based on specific interactions and the formation of inner-sphere surface complexes. The significantly higher adsorption efficiency of the membrane for Th(IV) in acidic media (pH ≤ 3) could be utilized for a pH-triggered, selective separation of Th(IV) from U(VI) from aqueous media.     

Preconcentration and determination of ultra-trace amounts of U(VI) and Th(IV) using titan yellow-impregnated Amberlite XAD-7 resin

A simple and sensitive method for the determination of ultra trace amounts of U(VI) and Th(IV) ions by spectrophotometric method after solid-phase extraction on a new extractant-impregnated resin (EIR) has been reported. The new EIR was synthesised by impregnating a weakly polar polymeric adsorbent, Amberlite XAD-7, with titan yellow (TY) as extractant. The analytical method is based on the simultaneous adsorption of analyte ions in a mini-column packed with TY/XAD-7 and performing sequential elution with 0.5% (w/v) Na₂CO₃ for uranium and 2.0 M HCl for thorium. The influences of the analytical parameters including pH, salting out agent and sample volume were investigated. The interference effects of foreign ions on the retention of the analyte ions were also explored. The limits of detection for U(VI) and Th(IV) were as low as 50 and 25 ng L^?1, respectively. Relative standard deviations (n = 7) for U(VI) and Th(IV) were 3.1% and 2.9%, respectively. The method was successfully applied to the determination of ultra trace amounts of U(VI) and Th(IV) in different real matrices including industrial wastewater samples and environmental waters. The proposed method was validated using three certified reference materials and the results were in good agreement with the certified values.     

Kinetic and thermodynamic aspects of U(VI) and Th(IV) sorption on a zeolitic volcanic tuff

Summary The sorption behavior of U(VI) and Th(IV) from simulated waste solutions on a zeolitic volcanic tuff from Nereju (Vrancea, Romania) has been studied in the absence of the ionic competition as a function of contact time, radioactive ions concentration, temperature and pH using a batch mode technique. The effect of the above-mentioned parameters on the sorption efficiency was discussed. The apparent thermodynamic parameters of the sorption of uranium and thorium onto the considered volcanic tuff were calculated, showing that the process is endothermic and higher temperatures favor the sorption process.     

A comparative study on the sorption and desorption of Hg,Th and U on clay

The sorption and desorption of uranium, thorium and mercury on a western Anatolian montmorillonite, obtained from the deposit located in Kula, were studied by application of a batch technique. The clay used is a tertiary clay originally found in a rather large geological formation of west Anatolia. It is nearly pure montmorillonite. Its cation exchange capacity (CEC) determination was performed for ammonium acetate by the Mehlich procedure. The mean CEC was found to be 83 meq/100 g, which, taking into account that CEC determinations were carried out on unfractionated material, is in good agreement with previously reported data. The concentration ranges were between 70–1500 ppm for mercury and 100–2000 ppm for thorium and uranium. The relative importance of test parameters, e.g., pH, clay particle size, groundwater composition, contact time and solid/water ratio, which determine the distribution coefficients was studied. The sorption coefficients varied between 2.7–6.4 ml/g for U, 0.22–1.59 ml/g for Th and 152.4–427.2 ml/g for Hg. The differences of distribution coefficients are discussed. The data could be fitted to Freundlich and Langmuir isotherms. The quantities of the sorbed and desorbed Th were much lower than its theoretical CEC's. This attitude was attributed to the blocking of montmorillonite by cation islands sorbed in the interlayer. Hg is sorbed most strongly. The experimental results indicate that the montmorillonites studied should be effective components of the buffer and backfill material and lead to eventual immobilization of these elements, which are environmentally dangerous.     

Comparison study of RNAA and ICP-MS for the determination of ultra-traces of Th and U in geological and cosmochemical samples

In order to determine thorium and uranium traces in geochemical and cosmochemical samples, we developed an ICP-MS procedure, in which an anion-exchange step was introduced after sample digestion to separate major matrix elements, leading to decrease the dilution factor and increase the sensitivity for Th and U. The ICP-MS procedure was compared to the RNAA procedure which we recently developed for the same purpose. Both ICP-MS and RNAA procedures developed were found to yield similar detection limits (sub ppb) for Th and U.     

Application of ion-exchange separations to determination of trace elements in natural waters-IX: simultaneous isolation and determination of uranium and thorium

A method is described for the determination of uranium and thorium in samples of natural waters. After acidification with citric acid the water sample is filtered and sodium citrate and ascorbic acid are added. The resulting solution of pH 3 is passed through a 4-g column of Dowex 1 x 8 (citrate form) on which both uranium and thorium are adsorbed as anionic citrate complexes. Thorium is eluted with 8M hydrochloric acid and separated from co-eluted substances by anion-exchange in 8M nitric acid medium on a separate 2-g column of the same resin in the nitrate form. After complete removal of iron by washing with a mixture consisting of IBMK, acetone and 1M hydrochloric acid (1:8:1 v v ) and treatment of the resin with 6M hydrochloric acid, the uranium is eluted from the 4-g column with 1M hydrochloric acid. In the eluate thorium is determined spectrophotometrically (arsenazo III method) while fluorimetry is employed for the assay of uranium. The procedure was used for the determination of uranium and thorium in numerous water samples collected in Austria, including samples of mineral-waters. The results indicate that a simple relationship exists between the uranium and thorium contents of waters which makes it possible to calculate the approximate thorium content of a sample on the basis of its uranium concentration and vice versa.     

Sorption and complexation of uranium(VI) and thorium(IV) with reagents Arsenazo III and Arsenazo M on fibrous filled sorbents

The possibility of the highly sensitive sorption-spectrometric determination of Th(IV) and U(VI) in the presence of each other on the solid phase of fibrous anion-exchange materials with Arsenazo M and Arsenazo III was examined. Polyacrylonitrile fiber filled with an exchanger AN-31, ANKB-50, or EDE-10p was used as the solid phase. It was demonstrated that the studied systems allow the selective determination of thorium in the presence of one-to twofold amounts of uranium. On PANV-EDE-10p with immobilized Arsenazo III, the detection limit of thorium in 2–10 M HCl is 0.002 μg/mL, and in 10 M HCl the presence of up to twofold amounts of uranium is permissible. A high sensitivity of the determination of uranium in 2–7 M HCl of 0.005 μg/mL, which has not been reported before, was attained. The time of the analysis of five or six samples is no longer than 20 min.     

Purification of 233U from Thorium and Iron in the Reprocessing of Irradiated Thorium Oxide Rods

A two step precipitation using ammonium carbonate and oxalic acid as the precipitants for thorium and iron is developed for the purification of ²³³U. Ammonium carbonate is added to the feed to increase the pH of the solution. The effect of pH on the solubility of U, Th and Fe in an excess of ammonium carbonate is studied. This indicates that the solubility of Th and Fe is minimum at pH 7 and the recovery of uranium is maximum. The effect of the concentration of thorium and iron on the recovery of uranium at pH 7 is studied. This indicates that the ammonium carbonate precipitation tolerates 2 g/l of thorium and 10 g/l of iron keeping losses of uranium to a minimum. If the feed solution contains more than a tolerable concentration of thorium the precipitation is followed in two steps: (1) Bulk of the thorium is removed by oxalate precipitation, (2) the remaining thorium and iron in the supernatant are removed by ammonium carbonate precipitation. A flow sheet is proposed for the purification of ²³³U from thorium and iron present in a strip product concentrate obtained during the reprocessing of irradiated thorium rods.     

Investigate the capability of INAA absolute method to determine the concentrations of 238U and 232Th in rock samples

This work aimed to study the capability of INAA absolute method in determining the elemental concentration of ²³⁸U and ²³²Th in the rock samples. The INAA absolute method was implemented in PUSPATI TRIGA Mark II research reactor, Malaysian Nuclear Agency (NM). The accuracy of INAA absolute method was performed by analyzing the IAEA certified reference material (CRM) Soil-7. The analytical results showed the deviations between experimental and certified values were mostly less than 10 % with Z-score in most cases less than 1. In general, the results of analysed CRM Soil-7 show a good agreement between certified and experimental results which mean that the INAA absolute method can be used accurately for elemental analysis of uranium and thorium in various types of samples. The concentration of ²³⁸U and ²³²Th ranged from 1.77 to 24.25 and 0.88 to 95.50 ppm respectively. The highest value of ²³⁸U and ²³²Th was recorded for granite rock sample G17 of ²³⁸U and sample G9 of ²³²Th, whereas the lower value was 1.77 ppm of ²³⁸U recorded in sandstone rock and 0.88 ppm of ²³²Th for gabbro. Moreover, a comparison of the ²³⁸U and ²³²Th results obtained by the INAA absolute method shows an acceptable level of consistency with those obtained by the INAA relative method.     

Reversed-phase liquid chromatography using mandelic acid as an eluent for the determination of uranium in presence of large amounts of thorium

Studies were carried out for the separation of uranium (U) and thorium (Th) on reversed-phase (RP) C₁₈ columns using mandelic acid as an eluent. Retention of thorium–mandelate on the unmodified stationary phase was found to be greater than that of uranyl–mandelate under the pH conditions employed. Th retention capacity of the stationary phase was determined as a function of pH and MeOH content of the mobile phase. The optimised parameters allowing U elution prior to Th were utilized for the determination of small amounts of U in the presence of large amounts of Th. The method has been used for the determination of U in synthetic samples with Th/U amount ratios up to 100,000 (10 μg/g of U) without any pre-separation, employing a particulate C₁₈ column. Effect of concentration of ion interaction reagents (IIRs) on the retention was studied to understand the mechanism of adsorption of their mandelate complexes onto the stationary phase. The experiments conducted unequivocally prove that thorium–mandelate complex is neutral whereas uranyl–mandelate complex is anionic in nature.     

Electronic structure, excited states, and photoelectron spectra of uranium, thorium, and zirconium bis(Ketimido) complexes (C5R5)2M[-NCPh2]2 (M = Th, U, Zr; R = H, CH3)

Organometallic actinide bis(ketimide) complexes (C5Me5)2An[-N=C(Ph)(R)]2 (where R = Ph, Me, and CH2Ph) of thorium(IV) and uranium(IV) have recently been synthesized that exhibit chemical, structural, and spectroscopic (UV-Visible, resonance-enhanced Raman) evidence for unusual actinide-ligand bonding. [Da Re et al., J. Am. Chem. Soc., 2005, 127, 682; Jantunen et al., Organometallics, 2004, 23, 4682; Morris et al., Organometallics, 2004, 23, 5142.] Similar evidence has been observed for the group 4 analogue (C5H5)2Zr[-N=CPh2]2. [Da Re et al., J. Am. Chem. Soc., 2005, 127, 682.] These compounds have important implications for the development of new heavy-element systems that possess novel electronic and magnetic properties. Here, we have investigated M-ketimido bonding (M = Th, U, Zr), as well as the spectroscopic properties of the highly colored bis-ketimido complexes, using density functional theory (DFT). Photoelectron spectroscopy (PES) has been used to experimentally elucidate the ground-state electronic structure of the thorium and uranium systems. Careful examination of the ground-state electronic structure, as well as a detailed modeling of the photoelectron spectra, reveals similar bonding interactions between the thorium and uranium compounds. Using time-dependent DFT (TDDFT), we have assigned the bands in the previously reported UV-Visible spectra for (C5Me5)2Th[-N=CPh2]2, (C5Me5)2U[-N=CPh2]2, and (C5H5)2Zr[-N=CPh2]2. The low-energy transitions are attributed to ligand-localized N p --> C=N pi excitations. These excited states may be either localized on a single ketimido unit or may be of the ligand-ligand charge-transfer type. Higher-energy transitions are cyclopentadienyl pi --> CN pi or cyclopentadienyl pi --> phenyl pi in character. The lowest-energy excitation in the (C5Me5)2U[-N=Ph2]2 compound is attributed to f-f and metal-ligand charge-transfer transitions that are not available in the thorium and zirconium analogues. Geometry optimization and vibrational analysis of the lowest-energy triplet state of the zirconium and thorium compounds also aids in the assignment and understanding of the resonance-enhanced Raman data that has recently been reported. [Da Re et al., J. Am. Chem. Soc., 2005, 127, 682.].     

Evaluation of adsorption behavior for U(VI) and Th(IV) ions onto solidified Mannich type material

Treatment of aqueous solution contaminated by uranium and thorium using a new Mannich type resin was studied. Different instrumental techniques such as elemental analysis, FTIR, and thermogravimetric analysis were employed for full characterization of the synthetic resin. Adsorption behavior was studied by batch experiments to determine the optimum conditions for U(VI) and Th(IV) ion removal. The adsorption studies showed the best fit with the second order rate equation and Langmuir model. The adsorption process is endothermic, spontaneous, and of increased disorder. The regeneration of sorbent was carried out using diluted HCl and the reuse of sorbent remains appreciable.     

Actinide metals with multiple bonds to carbon: synthesis, characterization, and reactivity of U(IV) and Th(IV) bis(iminophosphorano)methandiide pincer carbene complexes

Treatment of ThCl(4)(DME)(2) or UCl(4) with 1 equiv of dilithiumbis(iminophosphorano) methandiide, [Li(2)C(Ph(2)P═NSiMe(3))(2)] (1), afforded the chloro actinide carbene complexes [Cl(2)M(C(Ph(2)P═NSiMe(3))(2))] (2 (M = Th) and 3 (M = U)) in situ. Stable PCP metal-carbene complexes [Cp(2)Th(C(Ph(2)P═NSiMe(3))(2))] (4), [Cp(2)U(C(Ph(2)P═NSiMe(3))(2))] (5), [TpTh(C(Ph(2)P═NSiMe(3))(2))Cl] (6), and [TpU(C(Ph(2)P═NSiMe(3))(2))Cl] (7) were generated from 2 or 3 by further reaction with 2 equiv of thallium(I) cyclopentadienide (CpTl) in THF to yield 4 or 5 or with 1 equiv of potassium hydrotris(pyrazol-1-yl) borate (TpK) also in THF to give 6 or 7, respectively. The derivative complexes were isolated, and their crystal structures were determined by X-ray diffraction. All of these U (or Th)-carbene complexes (4-7) possess a very short M (Th or U)═carbene bond with evidence for multiple bond character. Gaussian 03 DFT calculations indicate that the M═C double bond is constructed by interaction of the 5f and 6d orbitals of the actinide metal with carbene 2p orbitals of both π and σ character. Complex 3 reacted with acetonitrile or benzonitrile to cyclo-add C≡N to the U═carbon double bond, thereby forming a new C-C bond in a new chelated quadridentate ligand in the bridged dimetallic complexes (9 and 10). A single carbon-U bond is retained. The newly coordinated uranium complex dimerizes with one equivalent of unconverted 3 using two chlorides and the newly formed imine derived from the nitrile as three connecting bridges. In addition, a new crystal structure of [CpUCl(3)(THF)(2)] (8) was determined by X-ray diffraction.     

Synthesis of N,N′-dimethyl-N,N′-dibutyl malonamide functionalized polymer and its sorption affinities towards U(VI) and Th(IV) ions

A novel chelating polymeric material was synthesized by chemical anchoring of N,N′-dimethyl-N,N′-dibutyl malonamide (DMDBMA) with chloromethylated polystyrene-divinyl benzene polymer. The polymeric material thus prepared was characterized by ¹³C NMR, FT-IR spectroscopy and CHN elemental analysis. The fabricated polymeric material exhibited superior binding for hexa-valent and tetra-valent metal ions such as U(VI) and Th(IV). Various physico-chemical properties of the functionalized polymer like phase adsorption kinetics, metal sorption mechanism and metal sorption capacity was studied in the static method. Adsorption kinetics studies show that <20 min was sufficient for >99.99% adsorption of Th(IV) and U(VI). The kinetics for adsorption of U(VI) and Th(IV) was found to follow the first order Lagergren rate kinetics. Adsorption of U(VI) on the malonamide functionalized polymer followed the Langmuir adsorption isotherm. The Langmuir monolayer adsorption phenomenon was also confirmed by the theoretical approach calculated based on the adsorption kinetics. The metal sorption capacities for uranium and thorium were found to be 18.78 ± 1.53 mg and 15.74 ± 1.59 mg/g of the chelating polymer at 3 M HNO₃, respectively.     

磷酸三丁酯萃淋树脂色层分离电感耦合等离子体质谱法测定富稀土样中微量铀和钍

研究了磷酸三丁酯萃淋树脂色层分离,电感耦合等离子体质谱法测定富稀土样中微量铀、钍的方法。样品经消解后,以磷酸三丁酯萃淋树脂为固定相、8 mol/L硝酸为流动相过柱分离,样品中的大部分稀土元素随流动相流出,而铀和钍则被固定相吸附,用去离子水洗脱后,再用电感耦合等离子体质谱仪测定。铀、钍的检出限分别为0.06,0.16μg/L,测定结果的相对标准偏差均小于10%(n=5),加标回收率为98%~105%。对稀土矿石标准物质进行测定,测定值与推荐值相符。该法操作简便,测定结果可靠,适于富稀土样中微量铀、钍的测定。     

Simultaneous determination of uranium(VI) and thorium(IV) with carminic acid by derivative spectrophotometry

The reactions of uranium(VI) and thorium(IV) ions with carminic acid have been investigated. These ions react with carminic acid in neutral medium, forming colored complexes. The dark purple or red wine complexes show a high absorption in the visible region (597 nm U(VI) and 616 nm Th(IV)). Chemical variables that affect the reaction have been optimized. The spectral overlapping of the color of complexes has been resolved by first-derivative spectrophotometry. The simultaneous determination of uranium(VI) and thorium(IV) mixtures is accomplished by taking the derivative signal (zero crossing) at 597 nm for U(VI) determination and at 616 nm for Th(IV) determination, respectively. The method has been applied to Tyuyamonite ore, containing in the matrix both ions.     

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.