Sodium Diuranate Research Articles

Capabilities of micro-Raman spectrometry for the identification of uranium ore concentrates from analysis of single particles

It has been proven, by the analysis of macroscopic amount of materiel pressed into pellets, that Raman spectrometry is a well suited technique to determine precisely the chemical compositions of uranium ore concentrates (UOCs), which is useful information for nuclear forensics and safeguards. However, as in some cases, only low amounts of UOC are available or the sample is a mixture of different UOCs, there is a need to carry out the identification at the individual grain or particle’s level. To evaluate the capability of micro-Raman spectrometry (MRS) for this purpose, 15–30 particles with typical sizes of a few micrometers from five UOCs of known bulk chemical compositions (uranyl peroxide – UP, sodium di-uranate – SDU, ammonium di-uranate – ADU, tri-uranium octo-oxide – TUO, and uranyl hydroxide – UH), production process and origins, were analyzed. Spectra were also compared with the ones obtained with macroscopic amounts of material pressed into pellets. Results show that for some UOCs (SDU, ADU, UH), micro-Raman spectra are reproducible from one particle to another and in good agreement on one side with available bibliographic data and on the other side with Raman spectra performed on macroscopic amounts of UOC. However, spectra of particles from the UP and TUO UOCs show that these compounds are mixtures of three species which were identified. In these cases, an acceptable agreement is obtained between the average Raman spectrum on compressed pellets and the one of most abundant species in analyzed particles. Consequently, an UOC compound or components of a mixture of UOCs can be reliably identified by the analyses of a limited number of isolated particles of a few μm in size by means of MRS.

Uranium oxide synthetic pathway discernment through thermal decomposition and morphological analysis

Abstract Many commercial processes exist for converting uranium from ore to the desired uranium compound for use in nuclear power or nuclear weapons. Accurately determining the processing history of the uranium ore concentrates (UOCs) and their calcination products, can greatly aid a nuclear forensics investigation of unknown or interdicted nuclear materials. In this study, two novel forensic signatures, based on nuclear materials synthesis, were pursued. Thermogravimetric analysis – mass spectrometry (TGA-MS) was utilized for its ability to discern UOCs based on mass changes and evolved gas species; while scanning electron microscopy (SEM), in conjunction with particle segmentation, was performed to identify microfeatures present in the calcination and reduction products (i.e. UO3, U3O8, and UO2) that are unique to the starting UOC. In total, five UOCs from common commercial processing routes including: ammonium diuranate (ADU), uranyl peroxide (UO4), sodium diuranate (SDU), uranyl hydroxide (UH), and ammonium uranyl carbonate (AUC), were synthesized from uranyl nitrate solutions. Samples of these materials were calcined in air at 400 °C and 800 °C. The 800 °C calcination product was subsequently reduced with hydrogen gas at 510 °C. The starting UOCs were investigated using TGA-MS; while SEM quantitative morphological analysis was used to identify signatures in the calcination products. Powder X-ray diffractometry (p-XRD) was used to identify the composition of each UOC and the subsequent calcination products. TGA-MS of the starting UOCs indicate temperature-dependent dehydration, volatilization, and reduction events that were unique to each material; thus making this a quantifiable signature of the initial material in the processing history. In addition, p-XRD, in conjunction with quantitative morphological analysis, was capable of discriminating calcination products of each processing history at the 99 % confidence level. Quantifying these nuclear material properties, enables nuclear forensics scientists to better identify the origin of unknown or interdicted nuclear materials.

Uranium-bearing phases in Hanford nuclear waste

Uranium is the most prevalent radioactive element in the 210 million liters of nuclear waste at the Hanford Site but the uranium speciation has not been determined in the waste tanks. The present study determined the common uranium-bearing solid phases in Hanford Site tank waste with X-ray diffraction and scanning electron microscopy. Sodium uranates were the most common species but uranium was also routinely co-precipitated with iron oxides. Na–U–O–P-bearing species were occasionally present. Two morphologies of sodium uranates were observed, long acicular and small spherical agglomerates up to 50 μm in size.

Application of Commercial Adsorbent for Rare earth elements - Uranium Mutual Separation and Purification

The treatment of rare earths sulfate liquor contaminated with traces of uranium as radioactive contaminates utilizing lewatit mono plus M500 was studied. Adsorption behavior was studied by batch experiments to determine the optimum conditions for uranium removal. The obtained equilibrium data were found to be satisfactory fitted with Langmuir isotherm and the second order rate equation. Also, elution process was achieved by 2M NaCl/1M HCl solution and the reuse of sorbent remains appreciable. A marketable pure product of rare earth oxide was prepared in addition to pure sodium diuranate containing total uranium content of the starting REEs cake.

Determination of uranium in uranyl nitrate raffinate generated through sodium di-uranate process

The paper discusses a method developed for the determination of uranium in uranyl nitrate raffinate (UNR) generated through sodium di-uranate (SDU) process using inductively coupled plasma atomic emission spectrometer (ICP-AES). High concentration of Na in UNR limits the direct determination of uranium in ICP-AES. Therefore, selective extraction of uranium from UNR using tri-n-octyl-phosphine oxide (TOPO) and stripping by ammonium carbonate was followed. Effect of sodium on estimation of uranium is discussed. The method has been validated by standard recovery of spiked real time UNR samples with known amounts of uranium CRM (Merck-HC42984673). The developed method compared well with EDXRFS and Redox titrimetric methods.

Process for recovery of uranium from low grade SDU of phosphoric acid/D2EHPA-TBP plant origin using DHOA/n-dodecane solvent

Abstract A process is described for separation and recovery of uranium from low grade sodium diuranate (SDU) obtained from processing of phosphatic uranium with D2EHPA-TBP solvent. SDU containing impurities of rare earths mostly heavier fraction (Y, Dy, Er, Yb) and Fe, Al, Cr, Mn, Ca, etc. was dissolved in nitric acid and contacted with N,N-dihexyl octanamide (DHOA)/n-dodecane solvent for selective separation of uranium from rest of the impurities. The average separation factor of uranium with respect to the heavy rare earths and base metals was obtained was 30 and 1000 respectively. Effect of different experimental parameters like aqueous nitric acid concentration, DHOA concentration, uranium concentration, phase ratio of extraction, scrubbing and stripping was optimized to obtain high purity uranium product solution. The extraction of uranium by DHOA follows solvation mechanism, at low uranium loading the combining ratio of U to DHOA determined by slope analysis method suggests complex formation as [UO2(NO3)2·2DHOA]. A 8-stage counter current extraction of 70 g/L uranium feed solution obtained on dissolving SDU in 3 M HNO3 with 1 M DHOA/n-dodecane solvent at O/A = 1 and scrubbing with 80 g/L pure uranium solution in 3 M HNO3 at O/A = 4:1 was found appropriate to obtain uranium of purity above 99.9%.

Synthesis and characterization of sodium and potassium uranates with the compositions Na2[(UO2)6O4(OH)6] · 8H2 and K2[(UO2)6O4(OH)6] · 8H2

Sodium and potassium uranates with the compositions M2[(UO2)6O4(OH)6] · 8Н2 (M = Na, K) have been synthesized by reacting schoepite (UO3 · 2.25H2O) with aqueous sodium hydroxide and potassium hydroxide solutions (pH 10–12) under hydrothermal conditions at 100°C for 15 days. Chemical analysis, X-ray diffraction, IR spectroscopy, and thermogravimetry data demonstrate that these compounds are perfect compositional and crystallographic analogs.

Solubility of U(VI) in chloride solutions. I. The stable oxides/hydroxides in NaCl systems, solubility products, hydrolysis constants and SIT coefficients

The solubility of uranium(VI) is studied at T=(22±2)°C in carbonate-free 0.03–5.61mol·kgw−1 NaCl solutions at pHm=4–14.5 (pHm=−log [H+]). The solid phases metaschoepite UO3·2H2O(cr) and sodium uranate Na2U2O7·H2O(cr) (or NaUO2O(OH)(cr)) are characterized by XRD, SEM–EDS, thermogravimetry and quantitative chemical analysis. UO3·2H2O(cr) controls the solubility of U(VI) in acidic to near neutral pH conditions regardless of NaCl concentration. Na2U2O7·H2O(cr) forms in alkaline systems and is stable at pHm≥7 over the complete range of NaCl concentrations investigated.The solubility of UO3·2H2O(cr) at pHm<7 in NaCl solutions is very well described with the hydrolysis constants recommended by the NEA–TDB, a set of SIT coefficients evaluated in the present study and a solubility product of log*K°s,0{UO3·2H2O(cr)}=(5.35±0.13). Titration experiments and UV–vis absorption spectra of saturated solutions at pHm=4–5 in dilute to concentrated NaCl solutions confirm the speciation calculated in the present study and show the predominance of the trinuclear hydroxide complex (UO2)3(OH)42+ at high chloride concentrations. Solubility data obtained at 7≤pHm≤14.5 with Na2U2O7·H2O(cr) and in solutions equilibrated simultaneously with Na2U2O7·H2O(cr) and UO3·2H2O(cr) yield a solubility product of log*K°s,0{0.5 Na2U2O7·H2O(cr)}=(12.2±0.2) and the formation constants of the anionic hydrolysis species UO2(OH)3− (log*β°(1,3)=−(20.7±0.4)) and UO2(OH)42− (log*β°(1,4)=−(31.9±0.2)). SIT coefficients for these species are derived based on the solubility data obtained in dilute to concentrated NaCl systems.The chemical, thermodynamic and SIT activity models provided in this work for the system UVI–Na+–H+–Cl−–OH−–H2O(l) represent an accurate and robust tool for the calculation of U(VI) solubility and aqueous speciation in a variety of geochemical conditions relevant in the context of nuclear waste disposal.

Purification of uranium from zirconium-rich crude sodium di-uranate using counter-current solvent extraction

Solvent extraction studies on the purification of uranium from zirconium rich sodium diuranate (SDU) feed was carried out using n-tri butyl phosphate (TBP) as extractant and n-decanol as phase modifier. The presence of Zr in SDU leached solution leads to the formation of third phase during liquid–liquid extraction of uranium which was successfully prevented by addition of n-decanol in 30% (v/v) TBP/n-dodecane mixture. A seven stage counter current extraction of SDU feed solution followed by five stage stripping were carried out using optimum concentration of phase modifier 15% n-decanol-30% TBP in n-dodecane as solvent. Based on the findings a process flow-sheet has been developed for the purification of SDU to nuclear grade ammonium diuranate.

Thermodynamic assessment of the Na-O and Na-U-O systems: Margin to the safe operation of SFRs

A thermodynamic model for the Na-O system was developed for the first time using the CALPHAD method after review of the structural, thermodynamic, and phase diagram data available on this system. Differential Scanning Calorimetry measurements were moreover performed to assess the phase equilibria and liquidus temperature in the Na2O-Na2O2 composition range. A CALPHAD model for the Na-U-O system was furthermore developed on the basis of both reviewed experimental data, and thermodynamic functions of the sodium uranates derived by combining ab initio calculations and a quasi-harmonic statistical model. The phase equilibria in this ternary system are particularly relevant for the safety assessment of the nuclear fuel-sodium coolant interaction in Sodium-cooled Fast reactors (SFRs). The model predicts the stability of the ternary phase field UO2-Na3UO4-Na4UO5, which is consistent with the most recent literature data. Further optimization was moreover performed to fit the sodium partial pressures measured experimentally in the NaUO3-Na2U2O7-UO2 and NaUO3-Na2UO4-Na2U2O7 phase fields, yielding an overall consistent description. Finally, the oxygen content required to form pentavalent Na3UO4 and hexavalent Na4UO5 in liquid sodium at 900K were calculated to be 0.7 and 1.5wppm, respectively, which are levels typically encountered in SFRs.

ナトリウムウラネートの合成

ナトリウムウラネートの合成

Supercritical fluid extraction and purification of uranium from crude sodium diuranate

Supercritical Fluid Extraction (SFE) and purification of uranium, from crude sodium diuranate (SDU) containing uranium (53%), iron (22.2% of U) and rare earth impurities (4% of U), has been studied. Adduct of tri-butyl phosphate (TBP) and nitric acid (HNO3) has been used for uranium dissolution and extraction. Carbon dioxide has been used as supercritical fluid. For 200mg of crude SDU, operating parameters such as temperature, pressure, quantity of TBP·HNO3 adduct, static and collection time have been optimized at 323K temperature, 15.20MPa pressure, 1mL of TBP·HNO3 adduct, 20min. static time and 20min. collection time. Under these conditions, uranium extraction efficiency was 95±5%. Addition of free nitric acid leads to improvement in purity of uranium. Uranium was stripped from SFE extract and precipitated as ammonium diuranate (ADU), which was then subjected to second cycle of SFE. After two cycles of SFE, purification factor of uranium was found to be 4970, 90, 110 and 60 with respect to iron, yttrium, ytterbium and erbium respectively.

Study of crystal growth and effect of temperature and mixing on properties of sodium diuranate

Almost 30–40% of total uranium deposits in India are in the form of carbonate and bicarbonate. Uranium in the ore is leached by alkali and then precipitated with NaOH as sodium diuranate (SDU). Morphology of SDU particle has been observed using high resolution SEM and it has been observed that the SDU particles consist of nano scale circular platelets, which are connected with each other to form primary agglomerates and further connected to form secondary agglomerate. Effect of temperature and mixing on SDU particle size distribution (PSD) and crystal structure have been studied. It was observed that the mean particle size reduces with an increase in the impeller power number. But no changes were observed in crystal structure with a change in the impeller design. Further, the mean particle size was found to be reduced with an increase in temperature.

Synthesis and study of sodium uranate Na2U2O7·6H2O and of products of its dehydration and thermal decomposition

Previously unknown sodium uranate of the composition Na2U2O7·6H2O was synthesized by precipitation from solution under hydrothermal conditions at 200°С. The composition and structure of this compound were determined by chemical analysis, X-ray diffraction, IR spectroscopy, and thermal analysis. The dehydration and thermal decomposition of the compound were studied.

Comparison of Uranium Recovery by Ion Exchange from Sulfuric Acid Liquor in Iodide and Chloride Media

ABSTRACTUranium is normally leached from its ores with sulfuric acid, separated from impurities using solvent extraction or ion exchange, and precipitated to yield a commercial product known as “yellow cake.” This research has investigated the use of sodium chloride and potassium iodide with the sulfuric acid leach to recover the uranium, mercury and cesium from the cemented waste. Sulfuric leaching using KI improves the solubilization of Hg by a combination of acidification, complexation, and oxidation and form a mercury tetraiodide complex. Mercury and cesium were recovered selectively using thiourea resin and solid potassium cobalt hexacyanoferrate respectively with removal efficiencies reaching 99%. The U recovery from sulfuric liquor using the chelating resin Lewatit TP260 is very efficient. The loading curve for U recovery in iodide media shows a better uptake than in chloride media and the resulting breakthrough is delayed. High purity yellow cake was obtained by precipitation as sodium diuranate.

Potentiality of uranium adsorption from wet phosphoric acid using amine-impregnated cellulose

The prepared amine-impregnated cellulose (AIC) was found to be an efficient adsorbent for uranium originated from El-Sebaiya phosphate ore. The impregenation process was carried out by copolymerization between pretreated cellulose and a mixture of (tri-ethyl amine and epi-chorohydrine).In the present work, two working solutions were used. The first solution was a synthesized phosphoric acid (35% P2O5 and 100 ppm U) used for optimizing the loading process of uranium. The second one was used as a case study for adsorption of uranium from a real phosphoric acid (WPPA) prepared from El-Sebaiya phosphate ore (P2O5 35%, 100 ppm U). The obtained equilibrium data were found to be satisfactory fitted with Langmuir isotherm. A maximum-metal uptake of 56.5 mgU/g AIC was observed at the obtained optimum conditions. Also, elution process of uranium has been achieved at 1 M of 30 ml Na2CO3 solution/g AIC after 15 min contact time. From the latter, a marketable product of sodium di-uranate was prepared.

An investigation of kinetic reaction and decomposition of sodium uranate

For the management of severe accidents of sodium-cooled fast breeder reactor, the coolability of the fuel debris bed on a core support plate is a key concern during the post-accident heat removal phase. In an air ingress scenario, the reactions between the fuel and highly oxidized sodium are likely to form sodium uranoplutonate. This would negatively influence the coolability of the fuel debris bed due to a lowering of the thermal conductivity and density. This study has focused on the formation kinetics of sodium uranate from UO2 and liquid sodium including oxygen at a high concentration. In this paper, the experiments on reaction initiation temperatures, reaction rates, and the decomposition of sodium uranate are reported.

Assessing hand-held Raman spectrometer FirstDefender RM for nuclear safeguards applications

The performance and applicability of the hand-held Raman spectrometer FirstDefender RM (Thermo Scientific) to nuclear safeguards field were assessed. More than 100 different uranium ore concentrates, frequently referred to as yellow cake, were measured and wherever applicable library scans were collected. A subset of the samples was then used to test the identification capability of the instrument. The accuracy of identification was shown to be sound for uranyl peroxide, sodium diuranate, ammonium diuranate, uranium trioxide and ammonium uranyl carbonate. The study also demonstrated the instrument’s potential for a quick quantitative determination of the uranium concentration in uranyl nitrate solutions.

Raman spectroscopy of uranium compounds and the use of multivariate analysis for visualization and classification

Raman spectroscopy was used on 95 samples comprising mainly of uranium ore concentrates as well as some UF4 and UO2 samples, in order to classify uranium compounds for nuclear forensic purposes, for the first time. This technique was selected as it is non-destructive and rapid. The spectra obtained from 9 different classes of chemical compounds were subjected to multivariate data analysis such as principal component analysis (PCA), partial least square-discriminant analysis (PLS-DA) and Fisher Discriminant Analysis (FDA). These classes were ammonium diuranate (ADU), sodium diuranate (SDU), ammonium uranyl carbonate (AUC), uranyl hydroxide (UH), UO2, UO3, UO4, U3O8 and UF4. Unsupervised PCA of full spectra shows fairly good distinction among the classes with some overlaps observed with ADU and UH. These overlaps are also reflected in the poorer specificities determined by PLS-DA. Higher values of sensitivities and specificities of remaining compounds were obtained. Supervised FDA based on reduced dataset of only 40 variables shows similar results to that of PCA but with closer clustering of ADU, UH, SDU, AUC. As a rapid and non-destructive technique, Raman spectroscopy is useful and complements existing techniques in multi-faceted nuclear forensics.

Thermal studies on the interaction behavior of ternary nitrate mixtures of UO2(NO3)2⋅6H2O–NaNO3–Sr(NO3)2 at elevated temperatures

Thermal and X-ray diffraction measurements have been used to study the formation of various nitrato-complexes as intermediates and mixed oxides as end products using different mol ratios of the ternary mixtures of UO2(NO3)2⋅6H2O, NaNO3 and Sr(NO3)2 at high temperatures. These results indicate the interaction of UO2(NO3)2⋅6H2O and NaNO3 in equimolar ratio to form sodium uranyl nitrate monohydrate (Na[UO2(NO3)3]⋅H2O), dimerized sodium uranyl oxynitrate (Na2[(UO2NO3)2(O)2]) and sodium diuranate (Na2U2O7). The decomposition temperature of Sr(NO3)2 decreased by 60°C in the presence of in-situ formed Na2U2O7. The uranium of Na2U2O7 intermediate reacts with Sr(NO3)2 to form various strontium uranium mixed oxides depending on Sr to U ratio in the initial mixtures. During the interaction of Sr(NO3)2 with Na2U2O7, sodium separates out as amorphous Na2O in the mixtures, containing Sr to U ratio ⩾1. Na2O phase is not formed in the uranium rich ternary mixture.