Determination of trace level impurities in uranium compounds by ICP-AES after organic extraction

The determination was studied of Al, B, Be, Cd, Ca, Co, Cu, Mg, Mn, Mo, Pb, Si, Sn, V, Cr, Ni, and Fe as trace level impurities in uranium compounds by ICP-AES after extraction of uranium with three different mixtures of di-(2-ethyl-hexyl) phosphate (D2EHP) and tri-(2-ethyl-hexyl)-phosphate (T2EHP) in solvents like toluene, carbon tetrachloride, hexane and cyclohexane. The study was carried out in presence of different concentrations of HCl and HNO₃. A single extraction with D2EHP in cyclohexane using nitric acid as matrix was sufficient to reduce the U₃O₈ concentration from 100 g/l to 100 g/ml. The ICP-AES instrumentation applied, allowed the determination of metal concentrations ten-times lower than those usually found in nuclear grade U₃O₈. To check the efficiency of the extraction and the accuracy of the proposed method, Certified Reference Materials were used in the dissolution and extraction steps. The method described can be used for the determination of trace metals in nuclear grade U₃O₈.     

色谱分离ICP-AES法测定高纯度八氧化三铀中的13种微量杂质

采用磷酸三丁酯（TBP）萃淋树脂色层分离铀，用电感耦合等离子体-原子发射光谱法测定分离后的离纯度铀氧化物的杂质元素Al、Ca、Cr、Cu、Fu、Mn、Mo、Ni、P、Ti、V、Zn、Zr，除Al、Fe、Mo外的其余10种元素的测定结果符合标准物质定值的要求。     

Analytical application of DHOA for the determination of trace metallic constituents in U based fuel materials by ICP-AES

DHOA (Di-n-hexyl-octanamide) is one of the alternative extractants to TBP (tri-n-butyl phosphate) known for the extraction of uranium from moderate nitric acid medium without significant extraction of the fission products. Analytical application of DHOA was explored to develop a methodology for determination of trace metallic constituents in uranium based nuclear materials. This involved the separation of uranium matrix by 1.1 M DHOA-dodecane followed by the analysis of the raffinate for trace constituents by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). A systematic study showed that four contacts of 1.1 M DHOA-dodecane were required for quantitative extraction of U from 4 M HNO₃ feed for the sample size of 1 g in 10 mL. The feasibility of using DHOA for extraction of U from trace metallic constituents in U based fuel materials without losing trace quantities of analytes of interest was studied by using synthetic samples after appropriate spiking of common impurities and critical elements at their required specification limits (common elements—5 ppm, critical elements—1 ppm). A systematic study was carried out to compare the analytical performance of DHOA with TBP, which revealed that DHOA could successfully be employed for the determination of 19 trace constituents with lower estimation limits of 5 ppm for common impurities and 1 ppm for critical elements.     

Determination of analytes at trace level in uranium matrix by ICP-AES without chemical/physical separation

Determination of trace metallic constituents in nuclear materials e.g. U, Pu, Am, Zr etc. by Atomic Emission Spectroscopy requires the separation of the major matrix without the loss of analytes at trace level. For DC Arc carrier distillation technique, carrier is used to separate the matrix physically according to the volatility of the analytes while appropriate extractant in suitable diluent is used for chemical separation in inductively coupled plasma atomic emission spectroscopy (ICP-AES). In the present study an attempt was made to develop a methodology for the determination of B, Cd, Mg, Zn, Al, Sr and Sc at trace level (up to 0.1 μg/mL) in uranium matrix without any chemical or physical separation. It involves identification of suitable analytical lines of uranium for its ICP-AES determination; study the spectral interference of uranium to choose interference free analytical lines, optimization of instrumental and experimental parameters etc. The method was validated using synthetic samples.     

Solid phase separation and ICP-OES/ICP-MS determination of rare earth impurities in nuclear grade uranium oxide

A simple, effective and low cost solid phase extraction procedure was standardized for the trace and ultra-trace level determination of rare earth impurities, such as, Ce, Dy, Sm, Gd, Eu, Er etc. which act as neutron poisons, in nuclear grade uranium oxide (U₃O₈?>?99.9% by weight). The method involves selective separation of these elements as their fluorides with the help of activated charcoal from major uranium matrix followed by determination by ICP-MS and high resolution ICP-OES. The residual uranium content of the solution was <10???g/mL. The recovery of REEs ranges from 85 to 105%. The method was validated with nuclear grade uranium oxide standards CRM-I to CRM-V (BARC, Mumbai, India) in addition to some synthetic standards. The RSD of the method was ±12% (n?=?3).     

Extraction of uranium(IV) from phosphoric acid solutions with 1-phenyl-3-methyl-4-benzoylpyrazolone-5 (PMBP)

The extraction of uranium(IV) from phosphoric acid solutions with PMBP and PMBP-TOPO mixtures has been studied. The synergic extraction with PMBP-TOPO is more effective than the simple chelate extraction with PMBP and both systems are more effective than the synergic extraction of uranium(VI) with DEHPA-TOPO. It is established that the complexes extracted are U(PMBP)(4) and U(PMBP)(4).TOPO for the chelate and synergic extraction respectively. The most probable uranium(VI) species in the aqueous phase (2.9-6.33M H(3)PO(4)) is the neutral complex U(H(5)P(2)O(8))(4). Analytical methods suitable for determination of uranium in phosphoric acid solutions have been developed. The highest sensitivity is achieved by combining the synergic extraction with the uranium(IV)-arsenazo III colour reaction.     

Chemical separation and ICP-AES determination of 22 metallic elements in U and Pu matrices using cyanex-923 extractant and studies on stripping of U and Pu

Comprehensive studies have been carried out on the extraction behavior of uranium and plutonium matrices using cyanex-923 extractant. The near total extraction of U/Pu and quantitative separation of 22 metallic elements at trace levels has been established using inductively coupled plasma-atomic emission spectrometry (ICP-AES). The studies carried out on back extraction of U/Pu from organic phase have established the near total recovery of these matrices into the aqueous phase using 1 M Na(2)CO(3) and saturated oxalic acid, respectively.     

Spectrophotometric determination of the oxygen to uranium ratio in uranium oxides based on dissolution in sulphuric acid

The oxygen to uranium ratio in uranium oxides such as U(3)O(8), UO(2+x) powders and UO(2) fuel pellets has been determined by a new spectrophotometric method. The method can be used for determination of O/U ratio in UO(2) pellets and powders on a routine basis. In the described method, uranium oxides in the powder form are dissolved in 2M sulphuric acid containing a few drops of HF. The concentrations of U(IV) and U(VI) are directly determined by means of the absorbances of these species at different wavelengths. For determination of the O/U ratio in U(3)O(8) powder samples, 630 and 310 nm are the wavelengths chosen for U(IV) and U(VI), respectively. For UO(2+x) powder, where the O/U ratio lies between 2.04 to 2.15, U(IV) and U(VI) are determined at 630 and 300 nm respectively, whereas for UO(2) fuel pellets, where the O/U ratio is less than 2.01, 535 and 285 nm are used. The molar absorptivity of U(IV) at 630 and 535 nm is 21.4 and 6.8 l.mole(-1).cm(-1) and that of U(VI) at 310, 300 and 285 nm is 178.1, 278.6 and 585 l.mole(-1).cm(-1), respectively. Standard deviations of +/-0.002 O/U ratio units for pellets and +/-0.004 O/U ratio units for powders have been achieved.     

电感耦合等离子体发射光谱法测定二氧化铀中痕量磷和硅元素

研究了电感偶合等离子体发射光谱法测定二氧化铀(UO2)中痕量磷和硅元素含量的方法。经过对HNO3,H2O等试剂的多级纯化,获得超低空白的高纯试剂。对样品溶解、待测杂质元素与铀基体分离等过程从机理方面进行了研究。在分离铀基体与硅元素时用磷酸三丁酯(TBP)作萃取剂,二甲苯作为稀释剂;在分离铀基体与磷元素时用三辛胺(TOA)作萃取剂,二甲苯作稀释剂。二氧化铀中磷、硅元素检出限分别为0.012,0.078μg/g,加标回收率分别为98%,96%,相对标准偏差小于4%(n=6)。该方法重现性好、检出限低,满足生产和科研检测要求。     

Simple radiochemical neutron-activation method for the determination of uranium in ultramafic rocks

A radiochemical neutron-activation method for the determination of trace concentrations of uranium in rocks is described. The method is based on separation of 23·5-min ²³⁹U after alkaline fusion by extraction with tri-n-butyl phosphate from moderately concentrated nitric acid, followed by measurement of the 74-keV γ-ray with a Ge(Li) detector. The limit of detection is 0·2 ng of U under the present conditions, and the precision at the 0·005 ppm level is about 10%. The method is especially useful for determination of uranium in ultramafic rocks.     

Synthesis of salicylaldehyde-modified mesoporous silica and its application as a new sorbent for separation, preconcentration and determination of uranium by inductively coupled plasma atomic emission spectrometry

A new functionalized mesoporous silica (MCM-41) using salicylaldehyde was utilized for the separation, preconcentration and determination of uranium in natural water by inductively coupled plasma atomic emission spectrometry (ICP-AES).Experimental conditions for effective adsorption of trace levels of U(VI) were optimized. The preconcentration factor was 100 (1.0 mL of elution for a 100 mL sample volume). The analytical curve was linear in the range 2-1000 μg L⁻¹ and the detection limit was 0.5 ng mL⁻¹. The relative standard deviation (R.S.D.) under optimum conditions was 2.5% (n = 10). Common coexisting ions did not interfere with the separation and determination of uranium at pH 5. The sorbent exhibited excellent stability and its sorption capacity under optimum conditions has been found to be 10 mg of uranium per gram of sorbent. The method was applied for the recovery and determination of uranium in different water samples.     

An extractive pellet fluorimetric determination of trace uranium in thorium rich samples

An extractive pellet fluorimetry determination of trace uranium in thorium rich samples has been developed. This is based upon a solvent extraction system which completely separates both the elements uranium and thorium from each other. Thorium as a neutral complex with 2,3-dihydroxynaphthalene at pH 4–6 is extracted into ethylacetate and then uranium-2,3-dihydroxynaphthalene anionic complex is extracted into another batch of ethylacetate at pH 11–12 under the influence of a counter cation, cetyltrimethylammonium ion. This method has been applied for the determination of trace uranium in synthetic nuclear grade thorium oxide and thorium rich mineralized rock with high degree of accuracy and precision.     

Synthesis of chitosan resin possessing a phenylarsonic acid moiety for collection/concentration of uranium and its determination by ICP-AES

A chitosan resin possessing a phenylarsonic acid moiety (phenylarsonic acid type chitosan resin) was developed for the collection and concentration of trace uranium prior to inductively coupled plasma (ICP) atomic emission spectrometry (AES) measurement. The adsorption behavior of 52 elements was systematically examined by packing it in a minicolumn and measuring the elements in the effluent by ICP mass spectrometry. The resin could adsorb several cationic species by a chelating mechanism, and several oxo acids, such as Ti(IV), V(V), Mo(VI), and W(VI), by an anion-exchange mechanism and/or a chelating mechanism. Especially, U(VI) could be adsorbed almost 100% over a wide pH region from pH 4 to 8. Uranium adsorbed was easily eluted with 1 M nitric acid (10 mL), and the 25-fold preconcentration of uranium was achieved by using a proposed column procedure, which could be applied to the determination of trace uranium in seawater by ICP-AES. The limit of detection was 0.1 ng mL⁻¹ for measurement by ICP-AES coupled with 25-fold column preconcentration.     

Selective ion exchange separation of uranium from concomitant impurities in uranium materials and subsequent determination of the impurities by ICP-OES

An ion exchange method has been developed for the separation of uranium from trace level metallic impurities prior to their determination by inductively coupled plasma optical emission spectrometry (ICP-OES) in uranium materials. Selective separation of uranium from trace level metallic impurities consisting Cr, Co, Cu, Fe, Mn, Cd, Gd, Dy, Ni, and Ca was achieved on anion exchange resin Dowex 1 × 8 in sulphate medium. The resin (100–200 mesh, in chloride form) was packed in a small Teflon column (7.8 cm × 0.8 cm I.D.) and brought into sulphate form by passing 0.2 N ammonium sulphate solution. Optimum experimental conditions including pH and concentration of sulphate in the liquid phase were investigated for the effective uptake of uranium by the column. Uranium was selectively retained on the column as anionic complex with sulphate, while impurities were passed through the column. Post column solution was collected and analyzed by ICP-OES for the determination of metallic impurities. Up to 2,500 μg/mL of uranium was retained with >99% efficiency after passing 25 mL sample through the column at pH 3. Percentage recoveries obtained for most of the metallic impurities were >95% with relative standard deviations <5%. The method established was applied for the determination of gadolinium in urania–gadolinia (UO₂–Gd₂O₃) ceramic nuclear fuel and excellent results were achieved. Solvent extraction method using tributylphosphate (TBP) as extractant was also applied for the separation of uranium in urania–gadolinia nuclear fuel samples prior to the determination of gadolinium by ICP-OES. The results obtained with the present method were found very comparable with those of the solvent extraction method.     

Spectral interference study of uranium on other analytes by using CCD based ICP-AES

Due to the multi-electronic nature, uranium is having line rich emission spectra and is expected to interfere during the determination of analytes at the trace level in uranium matrix. Therefore, chemical separation of uranium followed by the determination of trace metallic impurities in the raffinate by ICP-AES is generally adopted procedure in nuclear industries. There is restriction on choosing alternate analytical lines of elements by photomultiplier tube based ICP-AES associated with the polychromator while monochromator needs significant time to scan different analytical lines of all the elements. Since charged coupled detector (CCD) consists of array of pixels, it is having more option in choosing alternative analytical lines of the analytes. Therefore, an attempt was made to study the spectral interference of uranium on different analytical lines of analytes viz. Al, Ga, In, Si, Li, Ti, Mg, Sr, K, Ce, Nd, Lu, Sc, V, Er, Y, Ba, Bi, Pb, W, La, Tl, Sn, Yb, Mo, Sb, Pr and Zr; and the correction factors were evaluated (where ever necessary) using CCD based ICP-AES technique. The sensitivity and the detection limits of the analytical channels of the elements in presence of uranium matrix were calculated. The present study also deals with the identification of suitable analytical lines of uranium and its detection limits.     

Polarographic behaviour of uranium (VI) in organic solutions

Polarographic determination of uranium (VI) has been studied in the organic extraction phase TBP—diluent along with a selected aprotic solvent (i. e. dimethyl sulfoxide or N,N-dimethylformamide). DMF was found more suitable because it dissolves the organic extraction phase better than DMSO. U (VI) extracted in TBP-kerosene, n-hexane, cyclohexane, n-dodecane, benzene, from nitric acid medium can be determined in an organic solution (e. g. 50% DMF-30% TBP-20% kerosene) where it gives a well defined wave. In the organic solution, nitric acid added and/or extracted from the aqueous phase was found as an excellent supporting electrolyte for uranium determination.     

Preconcentration of trace uranium from seawater with solid phase extraction followed by differential pulse polarographic determination in chloroform eluate

In the present study, an effective method is presented for the separation and preconcentration of uranium (VI) by solid phase extraction (SPE). For this purpose, U(VI) oxinate is formed by the reaction of U(VI) with 8-hydroxyquinoline and adsorbed onto the octylsilane (C-8) SPE cartridge. The analyte is completely eluted with chloroform and determined by differential pulse polarography. The SPE conditions were optimized by evaluating the effective factors such as pH, oxine concentration, type and concentration of buffer and masking agent. By the proposed method a preconcentration factor more than 100 was achieved. The average recovery of uranium (VI) oxinate (0.1 mg l(-1)) was 99.8%. The relative standard deviation was 1.6% for seven replicate determinations of uranyl ion in the solution with a concentration 20 mug l(-1). Some concomitant ions such as Ca(+2), Mg(+2) and Fe(+3) which interfere in extraction or determination process of uranium were masked with EDTA in aqueous phase during the extraction process. The proposed method was successfully used for the determination of uranium in Caspian Sea and Persian Gulf water samples.     

Dissolution Extraction of Uranium Oxides and Cerium Oxide with TBP-HNO3 Complex in Supercritical CO2

Dissolution extraction of uranium oxides, CeO2 and (U, Ce)O2 solid solution with TBP-HNO3 complex in supercritical CO2 (SC-CO2) was investigated. It is difficult to dissolve and extract directly UO2 pellets and CeO2 with TBP-HNO3 complex in SC-CO2. After UO2 pellets spontaneously turns into U3O8 powders under O2 flow and 600 °C, the extraction efficiency can reach more than 98%. For dissolution extraction of (U, Ce)O2 solid solution with TBP-HNO3 complex in SC-CO2 under 60 and 20 MPa, the extraction efficiency of U and Ce is 98.61% and 98.1% respectively.     

The Simultaneous Determination of Trace Dy,Eu, Gd and Sm in Nuclear Grade Uranium Oxide by Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES)

A method for the simultaneous determination of trace Dy, Eu, Gd and Sm in nuclear grade uranium oxide by Inductively Coupled Plasma Atomic Emission Spectrometry has been developed. The process of uranium extraction and ICP/AES optimization are investigated. The detection limits of Dy, Eu, Gd and Sm are 0.003, 0.002, 0.006 and 0.010 μg/ml respectively, and more than 90% recovery can be obtained.     

Determination of sulphur in uranium matrix by total reflection X-ray fluorescence spectrometry

The possibility of sulphur determination in uranium matrix by total reflection x-ray fluorescence spectrometry (TXRF) has been studied. Calibration solutions and samples of sulphur in uranium matrix were prepared by mixing uranium in form of a standard uranyl nitrate solution and sulphur in the form of Na₂SO₄ standard solution, prepared by dissolving Na₂SO₄ in Milli-Q water. For major element analysis of sulphur, it was determined without separation of uranium whereas for the trace level determinations, uranium was first separated by solvent extraction using 30% tri-n-butyl phosphate (TBP) in dodecane as an extractant. In order to countercheck the TXRF results, a few samples of Rb₂U(SO₄)₃, a chemical assay standard for uranium, were diluted to different dilutions and sulphur content in these solutions were determined. The TXRF determined results for trace determinations of sulphur in these diluted solutions were counterchecked after addition of another uranium solution, so that sulphur is at trace level compared to uranium, separating uranium from these solution mixtures using TBP extraction and determining sulphur in aqueous phase by TXRF. For such TXRF determinations, Co was used as internal standard and W Lα was used as excitation source. The precision and accuracy of the method was assessed for trace and major element determinations and was found to be better than 8% (1σ RSD) and 15% at a concentration level of 1 μg/mL of sulphur measured in solutions whereas for Rb₂U(SO₄)₃, these values were found to be better than 4 and 13%, respectively.