Gamma-induced radiation polymerization of kaolin composite for sorption of lanthanum,europium and uranium ions from low-grade monazite leachate

Gamma radiation polymerization method was used for the modification of kaolin to produce (poly acrylamide-acrylic acid)-Kaolin (PAM-AA-K). Monazite ore is one of the main resources of uranium and lanthanide elements, therefore, this work focused on sorption of uranium, lanthanum and europium ions from low grade monazite leachate. The removal percent for Eu³⁺, La³⁺ and UO₂ ²⁺ are 94.6, 91.6 and 73.4%, respectively. Monolayer capacity of Eu³⁺, La³⁺ and UO₂ ²⁺ were found to be 54.64, 45.87 and 37.59 mg/g, respectively. The sorption mechanism of lanthanum and europium ions on PAM-AA-K composite mainly takes place as Ln(OH)²⁺, and for uranium as uranyl ion, UO₂ ²⁺.     

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).     

Oxo–Group‐14‐Element Bond Formation in Binuclear Uranium(V) Pacman Complexes

Simple and versatile routes to the functionalization of uranyl‐derived U^V–oxo groups are presented. The oxo‐lithiated, binuclear uranium(V)–oxo complexes [{(py)₃LiOUO}₂(L)] and [{(py)₃LiOUO}(OUOSiMe₃)(L)] were prepared by the direct combination of the uranyl(VI) silylamide “ate” complex [Li(py)₂][(OUO)(N”)₃] (N”=N(SiMe₃)₂) with the polypyrrolic macrocycle H₄L or the mononuclear uranyl (VI) Pacman complex [UO₂(py)(H₂L)], respectively. These oxo‐metalated complexes display distinct U? O single and multiple bonding patterns and an axial/equatorial arrangement of oxo ligands. Their ready availability allows the direct functionalization of the uranyl oxo group leading to the binuclear uranium(V) oxo–stannylated complexes [{(R₃Sn)OUO}₂(L)] (R=nBu, Ph), which represent rare examples of mixed uranium/tin complexes. Also, uranium–oxo‐group exchange occurred in reactions with [TiCl(OiPr)₃] to form U‐O? C bonds [{(py)₃LiOUO}(OUOiPr)(L)] and [(iPrOUO)₂(L)]. Overall, these represent the first family of uranium(V) complexes that are oxo‐functionalised by Group 14 elements.     

The luminescence of uranime-activated yttrium tungstate (Y2WO6)

The luminescence of uranium in Y₂WO₆ can be excited with long wavelength ultraviolet radiation at temperatures below room temperature. The emission consists of a fairly narrow band in the orange part of the spectrum. Its characteristics are comparable with the luminescence of uranium in MgWO₄ and the scheelites MWO₄ (M = Ca, Sr, Ba). It is possible to relate the thermal quenching temperature of the luminescence to spectral data. Energy transfer from the tungstate group to the uranate group is observed, but its efficiency is not very high compared with other systems.     

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     

The crystal and molecular structure of dioxo bis (2,2,6,6 - tetramethylheptane -3,5 dionato)methanol uranium (VI)

UO₂(thd)₂ CH₃OH (thd = tetramethylheptane-3,5-dione) is monoclinic, with a = 10.602(11), b = 22.883(20), c = 12.054(11) Å and β = 105.90(3)°, Z = 4 and space group P2₁/c. The structure, which is molecular, was solved by conventional Patterson and Fourier techniques with 3173 independent (hkl) reflexions collected with MoKα radiation (λ = 0.7107 Å), and refined to R = σ(|Fo|-|Fc|)/σ|Fo| = 0.093. The uranium coordination polyhedron is a pentagonal bipyramid, with UO (carbonyl) distances between 2.25 and 2.37 Å and a longer UO (methanol) distance of 2.50 Å. The uranyl group is linear (uranyl angle 179.3(8)°). The pentagon oxygen atoms and uranium do not form a planar system, as there are deviations of up to 0.17 Å from the mean plane. If the methanol oxygen atom O(7) is excluded from the plane calculation, the remaining atoms are more nearly planar. The four carbonyl oxygens are coplanar, with uranium 0.08 Å from their plane. The methanol oxygen is 0.28(4) Å from this second plane.The two (thd) molecules, excluding methyl carbons, are planar and are inclined at 43.6° to each other in a boat form and at 29.1 and 14.5° to the pentagonal plane. The methanol CO bond is inclined at 133° to the UO bond, confirming the ligand is the neutral CH₃OH molecule, and not CHO^?₃.     

Oxidation state and coordination environment of uranium in sodium iron aluminophosphate glasses

An analysis of the X-ray absorption near edge structure (XANES) and the extended X-ray absorption fine structure (EXAFS) of uranium determined the oxidation state and coordination environment of uranium atoms in glasses containing 40 mol % Na₂O, 10 mol % Al₂O₃, 10 mol % Fe₂O₃, and 40 mol % P₂O₅ to which uranium oxides were added to a concentration of 50 wt % (above 100%). If the added amount of UO₂ was small, uranium occurred as U(IV) in a near-octahedral oxygen environment with an average U–O distance in the first coordination sphere of 2.25 Å. At higher concentrations of uranium oxides introduced both as UO₂ and as UO₃, uranium occurred as U(V) and U(VI); the first coordination sphere is split; shorter (~1.7–1.8 Å) and longer (2.2–2.3 Å) distances were observed, which corresponded to the axial and equatorial U–O bonds in uranyl ions, respectively; and the redox equilibrium shifted toward U(VI). The glass with the maximal (~33 wt %) UO₃ concentration contained mainly U(VI). The existence of low-valence uranium species can be related to the presence of Fe(II) in glasses. The second coordination sphere of uranium manifests itself only at high concentrations of uranium oxides.     

Die Kristallstruktur einer triklinen Modifikation von Uranpentachlorid

The Crystal Structure of a Triclinic Modification of Uranium Pentachloride From solution uranium pentachloride crystallizes at room temperature in a triclinic modification belonging to the space group P1 . The unit cell contains one formula unit (UCl₅)₂ and has the dimensions a = 707, b = 965, c = 635 pm and α = 0.495 π, β = 0.652 π, γ = 0.603 π rad. The crystal structure was solved with the aid of X-ray diffraction data and was refined to a reliability index of R = 0.082. The structure consists of (UCl₅)₂ molecules having the point symmetry mmm in which the uranium atoms are linked with one another via two chlorine atoms. The crystal lattice can be derived from a hexagonal closest packing of chlorine atoms in which 1/5 of all octahedral holes are occupied by uranium atoms.     

Extraction of uranium with 2,3-dihydroxynaphthalene and cetyltrimethylammonium bromide, and its fluorimetric determination in silicate rocks

A novel procedure for the extraction of uranium has been described. UO₂ ²⁺ forms a 1:3 anionic complex with 2,3-dihydroxynaphthalene in the pH range, 4–12. This anionic complex is best extracted into ethyl acetate at pH 11–12 under the influence of a counter cation, cetyltrimethylammonium bromide. This extraction technique has been extended to the separation of uranium from silicate rock matrices for its determination by fluorimetry. Except Co, Cr, and Fe, most elements present in silicate rocks do not interfere. While the interferences of Co and Cr are suppressed by the addition of EDTA, iron is removed by prior extraction at pH 4–5 as its neutral complex with 2,3-dihydroxynaphthalene. The results compare favourably with those obtained from the conventional technique, i.e., extraction of uranium in ethyl acetate from NHO₃ medium under the influence of Al(NO₃)₃ ^.9H₂O as salting out agent. The extraction system under study is capable of separating even ultra-trace amounts of uranium quantitatively from complex matrices of rock samples. Besides, the method is simple, rapid, cost effective and precludes the use of reagents like nitric acid and aluminum nitrate (salting out agent) required in bulk quantities in the conventional system.     

Determination of uranium isotopes in environmental samples by alpha-spectrometry

A new and accurate method for the determination of uranium isotopes (²³⁸U, ²³⁴U and ²³⁵U) in environmental samples by alpha-spectrometry has been developed. Uranium is preconcentrated from filtered water samples by coprecipitation with iron(III) hydroxide at pH 9-10 using an ammonia solution and the precipitate is dissolved in HNO₃ and mineralized with H₂O₂ and HF; uranium in biological samples is ashed at 600 °C, leached with Na₂CO₃ solution and mineralised with HNO₃, HF and H₂O₂; uranium in soil samples is fused with Na₂CO₃ and Na₂O₂ at 600 °C and leached with HCl, HNO₃ and HF. The mineralized or leaching solution in 2M HNO₃ is passed through a Microthene-TOPO (tri-octyl-phosphine oxide) column; after washing, uranium is directly eluted into a cell with ammonium oxalate solution, electrodeposited on a stainless steel disk and measured by alpha-spectrometry. The lower limits of detection of the method is 0.37 Bq^.kg^-1 (soil) and 0.22 mBq^.l^-1 (water) for ²³⁸U and ²³⁴U and 0.038 Bq^.kg^-1 (soil) and 0.022 mBq^.l^-1 (water) for ²³⁵U if 0.5 g of soil and 1 litre of water are analyzed. Five reference materials supplied by the IAEA have been analyzed and reliable results are obtained. Sample analyses show that, the ²³⁸U, ²³⁴U and ²³⁵U concentrations are in the ranges of 0.30-103, 0.49-135 and 0.02-4.82 mBq^.l^-1 in waters, of 1.01-7.14, 0.85-7.69 and 0.04-0.32 Bq^.kg^-1 in mosses and lichens, and of 25.6-53.1, 26.4-53.8 and 1.18-2.48 Bq^.kg^-1 in sediments. The average uranium yields for waters, mosses, lichens and sediments are 74.5±9.0%, 80.5±8.3%, 77.8±4.9% and 89.4±9.7%, respectively.     

Analytical applications of a differential technique in laser-induced fluorimetry: accurate and precise determination of uranium in concentrates and for designing microchemielectronic devices for on-line determination in processing industries

A novel instrumental technique for the direct, fast, accurate, and precise determination of uranium in concentrates and other U-rich materials (as well as to mineralized rocks) is presented. The proposed technique is an absolute methodology, based on the comparison of the fluorescence of the accurately known standard with a sample of similar but unknown concentration in the low operational range of the instrument (on same sample-dilution basis), by the use of H₃PO₄-NH₄H₂PO₄ as a fluorescence-enhancing reagent. The relative standard deviation of the proposed technique was 0.5-0.9% (n=9) at 18.1, 36.2, 61.2, and 99.6% U₃O₈. The proposed technique is suitable for the determination of uranium in samples arising from exploration projects, ores from mining operations, mill process samples, uranium ore concentrates leading to fuel fabrication as well as samples from environmental monitoring containing up to 100% uranium. The results are in good agreement with those obtained by titrimetric, gravimetric, and TBP extraction-H₂O₂ spectrophotometric methods. The precision of the technique is within the acceptable ‘pure geochemistry’ type of analysis (R.S.D. ∼ 1.0%) and is comparable even those obtained with titrimetric and gravimetric assay. The proposed differential technique coupled with flow injection may open up new advancement in instrumentation leading to design and development of microchemielectronic devices for direct on-line determination, more compatible with the tools of computer age as also to help in handling of radioactive solutions in chemical laboratories in uranium processing industries.     

Role of Cyanex-272 as an extractant for uranium in the determination of rare earths by ICP-AES

A chemical separation procedure has been developed for the extraction of uranium from some of the crucially important rare earths using a novel extractant viz. Cyanex-272 (2,4,4-trimethyl pentyl phosphinic acid). The near total extraction of uranium and quantitative separation of rare earth elements has been validated using inductively coupled argon plasma - atomic emission spectrometry (ICP-AES). The recovery of some of the representative elements has been confirmed by radioactive tracer studies. The back extraction of uranium from the organic phase was carried out using a solution of 0.5M Na₂CO₃ which resulted in a near total recovery of uranium into the organic phase. These studies have enabled determination of sub ppm amounts of the analyte elements with a precision of 5% RSD utilizing prior chemical separation of rare earths from 1 g uranium samples in just three extractions with Cyanex-272.     

Optimization of a radioanalytical procedure for the determination of uranium isotopes in environmental samples

A radiochemical procedure is described for the fast and sensitive measurement of uranium isotopes in gaseous and liquid effluents of nuclear facilities. Equally, this procedure is suitable to measure uranium isotopes in all kinds of environmental samples. Uranium is leached from ashed sample materials with HNO₃, HF, and Al(NO₃)₃ solution and separated from matrix elements by extraction with trioctylphosphinic oxide and backextraction with NH₄F. After radiochemical cleaning by coprecipitation with LaF₃ and anion exchange, uranium isotopes are electroplated on stainless steel discs from HCl/oxalate solution. The preparation is measured by alpha-spectrometry using surface barrier detectors. The detection limit for 1000 minutes of counting time is 2 mBq per sample and nuclide, the chemical yield is in the range of 50 to 80%.     

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.

     

A gravimetric and an X-ray fluorescence method for the determination of rubidium in Rb2U(SO4)3

Chemical characterization of rubidium uranium(IV) trisulfate, Rb₂U(SO₄)₃, a new chemical assay standard for uranium requires accurate analysis of rubidium. A gravimetric and an X-ray fluorescence method (XRF) for the determination of rubidium in this compound are described. In the gravimetric method, rubidium is determined as Rb₂Na[Co(NO₂)₆].H₂O without separating uranium with a precision of the order of ±0.5%. In the XRF method, the concentration ratio of rubidium to uranium, C_Rb/C_U, is determined in the solid samples by the binary ratio method using calibration between intensity ratios (I_Rb/I_U) and concentration ratios (C_Rb/C_U). The concentration of rubidium is derived using the uranium value which is known with a precision better than ±0.05%. The XRF method has a precision better than ±0.8% for rubidium determination.     

Synthesis and characterization of uranium bromide phosphate UBrPO4·2H2O and uranium hydroxide phosphate U(OH)PO4

Uranium chloride phosphate tetrahydrate UClPO₄·4H₂O was obtained by mixing uranium (IV) hydrochloric solution and concentrated phosphoric acid [1]. From crystal structure studies its formula was determined as dihydrate [2]. Using the same method, i.e. starting from uranium (IV) hydrobromic solution and H₃PO₄, two crystal forms of a new compound, uranium bromide phosphate UBrPO₄·2H₂O were synthesized. Their XRD patterns, UV-visible and infrared spectra are presented in this paper. The hydrolysis process of the chloride and bromide phosphates leads to the amorphous uranium hydroxide phosphate U(OH)PO₄·6H₂O.     

Capillary zone electrophoretic (CZE) study of uranium(VI) complexation with humic acids

The interaction of UO₂ ²⁺ with various humic acids (HA's) has been studied by capillary zone electrophoresis (CZE). The experiments were done in 10 mM acetate buffer with pH 3.3 and 4.0, to avoid hydrolysis of uranium. It was found that in slightly acidic media and low HA concentration (<3 mM), two complexes with uranium(VI) are formed by fast kinetics and uranyl migrates as cationic species. Electrophoretic mobilities are decreasing with the increasing HA/uranium ratio and a low soluble neutral compound is also formed. In addition, it was found that at HA concentrations higher than 3 mM negatively charged species are formed. Similar results were obtained for HA's of different origin (soil, peat, coal derived, IHSS standards). Conditional stability constants of the complexes UO₂ ²⁺-HA for Fluka I HA, were estimated to be log ₁ = 4.18±0.06 and log ₂ = 7.28±0.18.     

Metallation of Ligands with Biological Activity: Synthesis and X‐Ray Characterization of [UO2(PN)2(H2O)]Cl2{PN = vitamin B6 pyridoxine[2‐methyl‐3‐hydroxy‐4, 5‐bis(hydroxymethyl) pyridine]}

Chloridrate of pyridoxine (vitamin B₆) reacts with UO₂(NO₃)₂·6H₂O in acetonitril containing triethylamine to give the complex salt [UO₂(PN)₂(H₂O)]Cl₂. The structure of the novel compound was analyzed by single crystal X‐ray diffraction affording the centrosymmetric triclinic space group . In [UO₂(PN)₂(H₂O)]²⁺ two zwitterionic pyridoxine molecules complex the uranium atom in a planar manner with a water molecule achieving the coordination of a semi planar pentagon. The two uranyl oxo ligands set the axis of a distorted pentagonal bipyramide. The ability of vitamin B₆ pyridoxine to react with UO₂²⁺ allowing the chelation of one uranium atom represents a very specific model of assimilation of uranium by living beings. It could also explain the serious damages caused by heavy or radioactive metals like uranium since their complexation “in vivo” by enzymatic systems like pyridoxal phosphate‐containing enzymes would lead to a modification of the prosthetic groups of the metalloenzymes with loss of their catalytic activities.     

Americium(III) coordination chemistry: An unexplored diversity of structure and bonding

The comparison of the physicochemical behavior of the actinides with that of the lanthanides can be justified by the analogy of their electronic structure, as each of the series is made up of elements corresponding to the filling of a given (n)f atomic shell. However relatively few points of comparison are available, given the lack of available structure for trans-plutonium(III) elements and the additional difficulty of stabilizing coordination complexes of uranium(III) to plutonium(III). This contribution is a focal point of trans-plutonium(III) chemistry and, more specifically, of some americium compounds that have been recently synthesized, all related with hard acid oxygen donor ligands that may be involved in the reprocessing chain of nuclear fuel. After a brief review of the solid hydrates and aquo species for the lanthanide and actinide families, we discuss two types of ligands that have in common three carboxylic goups, namely the aminotriacetic acid and the citric acid anions. The additional roles of the nitrogen atom for the first one and of the hydroxy function for the second one are discussed. Accordingly, five new complexes with either americium or lanthanides elements are described: [Co(NH₃)₆][M(NTA)₂(H₂O)]·8H₂O with M = Nd, Yb and Am, and [Co(NH₃)₆]₂K[M₃(Cit)₄(H₂O)₃]·18H₂O with Nd and Am cations. In all cases the americium complexes are isostructural with their lanthanide equivalents.     

Measurement of trace impurities in high purity materials

Neutron activation analysis was used for the determination of 29 trace impurities is high-purity semiconductor grade Ge and Si. In order to determine very low contents of uranium and thorium,²³⁹Np and²³³Pa activation products were separated using anion exchange and LaF₃ coprecipitation methods. The impurity contents were found to be very low, and therefore their adverse effects would be negligible.