In Situ Anchoring of Pyrrhotite on Graphitic Carbon Nitride Nanosheet for Efficient Immobilization of Uranium

Enrichment of U^VI is an urgent project for nuclear energy development. Herein, magnetic graphitic carbon nitride nanosheets were successfully prepared by in situ anchoring of pyrrhotite (Fe₇S₈) on the graphitic carbon nitride nanosheet (CNNS), which were used for capturing U^VI. The structural characterizations of Fe₇S₈/CNNS-1 indicated that the CNNS could prevent the aggregation of Fe₇S₈ and the saturation magnetization was 4.69 emu g⁻¹, which meant that it was easy to separate the adsorbent from the solution. Adsorption experiments were performed to investigate the sorption properties. The results disclosed that the sorption data conformed to the Langmuir isotherm model with the maximum adsorption capacity of 572.78 mg g⁻¹ at 298 K. The results of X-ray photoelectron spectroscopy (XPS) demonstrated that the main adsorption mechanism are as follows: U^VI is adsorbed on the surface of Fe₇S₈/CNNS-1 through surface complexation initially, then it was reduced to insoluble U^IV. Thereby, this work provided an efficient and easy to handle sorbent material for extraction of U^VI.     

Ligand-Supported Facile Conversion of Uranyl(VI) into Uranium(IV) in Organic and Aqueous Media

Reduction of uranyl(VI) to U^V and to U^IV is important in uranium environmental migration and remediation processes. The anaerobic reduction of a uranyl U^VI complex supported by a picolinate ligand in both organic and aqueous media is presented. The [U^VIO₂(dpaea)] complex is readily converted into the cis-boroxide U^IV species via diborane-mediated reductive functionalization in organic media. Remarkably, in aqueous media the uranyl(VI) complex is rapidly converted, by Na₂S₂O₄, a reductant relevant for chemical remediation processes, into the stable uranyl(V) analogue, which is then slowly reduced to yield a water-insoluble trinuclear U^IV oxo-hydroxo cluster. This report provides the first example of direct conversion of a uranyl(VI) compound into a well-defined molecular U^IV species in aqueous conditions.     

Ligand‐Supported Facile Conversion of Uranyl(VI) into Uranium(IV) in Organic and Aqueous Media

Reduction of uranyl(VI) to U^V and to U^IV is important in uranium environmental migration and remediation processes. The anaerobic reduction of a uranyl U^VI complex supported by a picolinate ligand in both organic and aqueous media is presented. The [U^VIO₂(dpaea)] complex is readily converted into the cis‐boroxide U^IV species via diborane‐mediated reductive functionalization in organic media. Remarkably, in aqueous media the uranyl(VI) complex is rapidly converted, by Na₂S₂O₄, a reductant relevant for chemical remediation processes, into the stable uranyl(V) analogue, which is then slowly reduced to yield a water‐insoluble trinuclear U^IV oxo‐hydroxo cluster. This report provides the first example of direct conversion of a uranyl(VI) compound into a well‐defined molecular U^IV species in aqueous conditions.     

Backbonding in Thorium(IV) and Uranium(IV) Diarsenido Complexes with tBuNC and CO

The coordination of tBuNC and CO with the diarsenido complexes (C₅Me₅)₂An(η²-As₂Mes₂), An=Th, U, has been investigated. For the first time, a comparison between isostructural complexes of Th^IV and U^IV has been possible with CO; density functional calculations indicated an appreciable amount of π backbonding that originates from charge transfer from an actinide-arsenic sigma bond. The calculated CO stretching frequencies in the Th^IV and U^IV diarsenido complexes are consistent with the experimental measurements, both show large shifts to lower frequency. We demonstrate that the π backbonding is crucial to explaining the red shifts of CO frequency upon An^IV complex formation. Interestingly, this interaction essentially correlates to the parallel orientation of π*(C−O) orbitals relative to the An−As bond.     

Regenerable Covalent Organic Frameworks for Photo-enhanced Uranium Adsorption from Seawater

Uranium is a key resource for the development of the nuclear industry, and extracting uranium from the natural seawater is one of the most promising ways to address the shortage of uranium resources. Herein, a semiconducting covalent organic framework (named NDA-TN-AO) with excellent photocatalytic and photoelectric activities was synthesized. The excellent photocatalytic effect endowed NDA-TN-AO with a high anti-biofouling activity by generating biotoxic reactive oxygen species and promoting photoelectrons to reduce the adsorbed U^VI to insoluble U^IV, thereby increasing the uranium extraction capacity. Owing to the photoinduced effect, the adsorption capacity of NDA-TN-AO to uranium in seawater reaches 6.07 mg g⁻¹, which is 1.33 times of that in dark. The NDA-TN-AO with enhanced adsorption capacity is a promising material for extracting uranium from the natural seawater.     

Regenerable Covalent Organic Frameworks for Photo‐enhanced Uranium Adsorption from Seawater

Uranium is a key resource for the development of the nuclear industry, and extracting uranium from the natural seawater is one of the most promising ways to address the shortage of uranium resources. Herein, a semiconducting covalent organic framework (named NDA‐TN‐AO) with excellent photocatalytic and photoelectric activities was synthesized. The excellent photocatalytic effect endowed NDA‐TN‐AO with a high anti‐biofouling activity by generating biotoxic reactive oxygen species and promoting photoelectrons to reduce the adsorbed U^VI to insoluble U^IV, thereby increasing the uranium extraction capacity. Owing to the photoinduced effect, the adsorption capacity of NDA‐TN‐AO to uranium in seawater reaches 6.07 mg g^?1, which is 1.33 times of that in dark. The NDA‐TN‐AO with enhanced adsorption capacity is a promising material for extracting uranium from the natural seawater.     

IR and <Superscript>31</Superscript>P NMR spectroscopic study of complexation of carbamoyl methyl phosphinates with U<Superscript>VI</Superscript> and Th<Superscript>IV</Superscript> in nitric acid solutions

The composition of complexes formed upon the extraction of U^VI and Th^IV nitrates with O-n-nonyl(N,N-dibutylcarbamoylmethyl) methyl phosphinate (L) from solutions of nitric acid without additional solvent was determined by ³¹P NMR spectroscopy. The structures of the complexes formed were studied by IR spectroscopy. Uranium(VI) is extracted from 3 and 5 M solutions of HNO₃ as the [UO₂(L)₂(NO₃)₂] complex, while thorium(IV) is extracted from 5 M HNO₃ as the [Th(L)₃(NO₃)₃]⁺·NO ₃ ⁻ complex. In both cases, ligand L has bidentate coordination. Ligand L contacts with 3 and 5 M nitric acid to form adducts L·HNO₃ and L· (HNO₃)₂, respectively. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2460–2464, November, 2005.     

Interaction of AnVI with Isothiocyanate Ion in Water‐Organic Media (An = U,Np, Pu)

Behavior of U^VI, Np^VI and Pu^VI in water‐acetonitrile solutions was studied spectrophotometrically with the successive addition of the polar organic ligands (dimethyl sulfoxide or hexamethylphosphoric triamide) and the NCS^– ion. The detected spectral effects – changes in the absorption intensity, bathochromic shifts in the absorption bands, the absence of isosbestic points, a change in the color of the solution – indicate complex competitive processes occurring in the studied solutions. In the case of Np^VI, its partial reduction to Np^IV by NCS^– ion is observed. Solid U^VI complex, [UO₂(HMPA)₂(NCS)₂], was isolated, its crystal structure was determined using X‐ray diffraction. In contrast to known AnO₂²⁺ compounds with the NCS^– ion, this complex exhibits tetragonal bipyramidal environment of the U atom. [UO₂(HMPA)₂(NCS)₂] is also characterized by UV/Vis, IR and luminescence spectroscopy.     

Isolation of a Star‐Shaped Uranium(V/VI) Cluster from the Anaerobic Photochemical Reduction of Uranyl(VI)

Actinide oxo clusters are an important class of compounds due to their impact on actinide migration in the environment. The photolytic reduction of uranyl(VI) has potential application in catalysis and spent nuclear fuel reprocessing, but the intermediate species involved in this reduction have not yet been elucidated. Here we show that the photolysis of partially hydrated uranyl(VI) in anaerobic conditions leads to the reduction of uranyl(VI), and to the incorporation of the resulting U^V species into the stable mixed‐valent star‐shaped U^VI/U^V oxo cluster [U(UO₂)₅(μ₃‐O)₅(PhCOO)₅(Py)₇] ( 1 ). This cluster is only the second example of a U^VI/U^V cluster and the first one associating uranyl groups to a non‐uranyl(V) center. The U^V center in 1 is stable, while the reaction of uranyl(V) iodide with potassium benzoate leads to immediate disproportionation and formation of the U₁₂^IVU₄^VO₂₄ cluster {[K(Py)₂]₂[K(Py)]₂[U₁₆O₂₄(PhCOO)₂₄(Py)₂]} ( 5 ).     

Polarographic analysis. II

Summary The polarography of hexavalent uranium in sulphuric acid solutions of different concentrations and solutions containing sodium sulphate is studied. In 0.01 M H₂SO₄ three waves are obtained corresponding to the successive reduction of U^VI to U^V, U^V to U^IV and U^IV to U^III. The second and third waves intermingle by increasing the H₂SO₄ concentration up to 0.055 M or by adding Na₂SO₄ or sulphosalicylic acid. In 0.25 M H₂SO₄ or in the presence of EDTA the second wave shifts to less negative potentials and intermingles with the first wave, forming a single wave along which reduction of U^VI gives a mixture of U^V and U^IV. The diffusion current of this wave increases up to 1 M H₂SO₄ and then decreases above this acidity. The diffusion current measured at –0.6 V is proportional to the U^VI concentration in the presence of 0.25–0.6 M H₂SO₄. This is not the case in the presence of EDTA. The proportionality is better at lower than at higher acidity.Part I: See Z. analyt. Chem.174, 4 (1960).     

Recovery of Uranium(VI) from Sulfate Leach Liquor using Modified Duolite

Silicate mercapto Duolite composite ( SMDC ) and activated Duolite A 101 D ( AD ) were prepared, characterized, and tested for uranium removal from sulfate solution using batch experiment technique. The capability of newly adsorbents for sorption of uranium was estimated and optimized under different controlling variables, including the impact of uranium initial concentration, pH of the medium, equilibrium time, temperatures, dose and interfering ions. Testing of different adsorbents for adsorption isotherms revealed that the achieved experimental data were fitting well with the Langmuir isotherm model with 68.02 mg · g^–1 and 208.33 mg · g^–1 as theoretical capacity for AD and SMDC , respectively. Thermodynamic parameters have been resulted in negative values for ΔH and ΔS indicating an exothermic and decreased randomness behavior for uranium(VI) adsorption, while negative values of ΔG indicate spontaneous uranium adsorption. The kinetics studies showed that the adsorption process was controlled expressed by pseudo-second order model. Finally, the optimized factors have been applied for uranium(VI) recovery from Gattar leach liquor producing a uranium concentrate (Na₂U₂O₇) with uranium concentration of 70 % and purity of 93.33 %.     

Determination of the Uranium(VI) and ‐(IV) Species in Uranium Ores

The determination of the two species of uranium(VI and IV) present in 6 uranium ores was studied in relation to the chemical and mineralogical composition, humidity, and pH of the samples taken over from the mine. X‐ray diffraction studies, performed on the uranium ores in powder form allowed to establish their mineralogical composition. Thechemical analysis pointed out the presence, besides the two uranium species, of some microelements able to influence the U^VI/U^IV ratio in minerals and to leach out U^VI as uranyl ions from the corresponding minerals.     

Chitin-based magnetic composite for the removal of contaminating substances from aqueous media

A method of obtaining multipurpose magnetic chitin, which combines the magnetic properties of magnetite and the adsorption properties of polysaccharide, was proposed. The possibility of using chitin-(CT) and chitosan (CS)-containing magnetic composites for the adsorption of inorganic ions Co^II and Cr^VI and organic substances (2- and 4-nitrophenols) from aqueous media was analyzed. It was shown that the adsorption capacity of magnetic chitin with respect to Co^II and Cr^VI ions reached 41 mg g^?1 and 15 mg g^?1, respectively. The maximum adsorption capacity for 4-nitrophenol (19 mg g^?1 per CT-containing magnetic composite or 56 mg g^?1 per chitin component) was about three times higher than for 2-nitrophenol. The obtained adsorbent Fe₃O₄/CT is environmentally friendly and reusable.

     

Synthesis,structural and catalytic activity of binaphthyl macrocyclic complexes

The binaphthyl macrocyclic ligand, N,N′-diethyl-[3,3′-(2,2′-dihydroxy-1,1′-binaphthyl)carboxamide]-2,2′-dihydroxy-1,1′-binaphthyl-3,3′-dicarboxylic acid (DDCDB), has been synthesized and investigated. The ligand (DDCDB) and its metal complexes involving Cu^II, Zn^II, UO ₂ ^II , Th^IV, Ce^III, Mo^VI and W^VI ions have been prepared and characterized by spectral (i.r., u.v.–vis.), elemental analyses, magnetic moments and thermal analyses measurements. DDCDB behaves as a tridentate ligand towards Cu^II, Zn^II and UO ₂ ^II ions coordinating via CO, NH and the deprotonated naphthyl OH groups in a ratio of 2:1 (M:L). On the other hand, DDCDB behaves in a bidentate manner coordinatingvia the NH and the deprotonated naphthyl OH groups only in case of the Th^IV, Ce^III, Mo^VI, and W^IV ions and in ratio 1:1 (M:L). Results of thermal measurements confirm the existence of solvent molecules inside and outside the coordination sphere. Th^VI complex has been applied for the hydrolysis of phosphodiester and the results show a significant rate enhancement of ~5.8 million fold with respect to the auto-hydrolysis of bis-(p-nitrophenyl) phosphate (BNPP) under the same conditions Also, Cu^II complex accelerates the photodegradation of the hazardous pollutant (acid green dye) in the presence of hydrogen peroxide by degrading 90% of the dye within 23 min.     

A Mixed‐Valent Uranium Phosphonate Framework Containing UIV,UV, and UVI

It is shown that U^VO₂⁺ ions can reside at U^VIO₂²⁺ lattice sites during mild reduction and crystallization process under solvothermal conditions, yielding a complicated and rare mixed‐valent uranium phosphonate compound that simultaneously contains U^IV, U^V, and U^VI. The presence of uranium with three oxidation states was confirmed by various characterization techniques, including X‐ray crystallography, X‐ray photoelectron, electron paramagnetic resonance, FTIR, UV/Vis‐NIR absorption, and synchrotron radiation X‐ray absorption spectroscopy, and magnetism measurements.     

Atranes

Genetal methods are described for the preparation of metalloatrane-3,7,10-triones, containing an atom of a ter-, quarter-, or quinquevalent metal (mainly in the form of hydrates). Seven intramolecular compounds of this type (with M = Nd^III, ClTi^IV, ClZr^IV, Ce^III, HOPb^IV, HOMn^IV, HOOU^VI), have been prepared, of which only two (with M = Nd^III and HOOU^VI) were known previously. Compounds with the composition N (CH₂COO)₃M · mN (CH₂COO)₃ · nH₂O with M = Nd^III, Th^IV, CO^III and Ni^III (m=1) and with M = Sb (m=3 and 4) have also been obtained.For part XVIII, see [1].     

Trinuclear Schiff base complexes with uranium(V) and copper(II) or zinc(II) ions

Treatment of the uranium(IV) complexes [{ML¹(py)}₂U^IV] (M = Cu, Zn; L¹ = N,N′-bis(3-hydroxysalicylidene)-1,3-propanediamine) with silver nitrate in pyridine led to the formation of the corresponding cationic uranium(V) species which were found to be thermally unstable and were converted back into the parent U^IV complexes; no electron transfer was observed in solution between the U^IV and U^V compounds. In the crystals of [{ML¹(py)}₂U^IV][{ML¹(py)}₂U^V][NO₃], the neutral U^IV and cationic U^V species are clearly identified by the distinct U–O distances. Similar reaction of [{ZnL²(py)}₂U^IV] [L² = N,N′-bis(3-hydroxysalicylidene)-1,4-butanediamine] with AgNO₃ gave crystals of [{ZnL²(py)}U^V{ZnL²(py)₂}][NO₃] but the copper counterpart was not isolated. Crystals of [{ZnL¹(py)}₂U^V][OTf] · THF (OTf = OSO₂CF₃) were obtained fortuitously from the reaction of [Zn(H₂L¹)] and U(OTf)₃.     

Complexes of a tridentate ONS Schiff base. Synthesis and biological properties

Several new complexes of a tridentate ONS Schiff base derived from the condensation of S-benzyldithiocarbazate with salicylaldehyde have been characterised by elemental analyses, molar conductivity measurements and by i.r. and electronic spectra. The Schiff base (HONSH) behaves as a dinegatively charged ligand coordinating through the thiolo sulphur, the azomethine nitrogen and the hydroxyl oxygen. It forms mono-ligand complexes: [M(ONS)X], [M=Ni^II, Cu^II, Cr^III, Sb^III, Zn^II, Zr^IV or U^VI with X = H₂O, Cl]. The ligand produced a bis-chelated complex of composition [Th(ONS)₂] with Th^IV. Square-planar structures are proposed for the Ni^II and Cu^II complexes. Antimicrobial tests indicate that the Schiff base and five of the metal complexes of Cu^II, Ni^II, U^VI, Zn^II and Sb^III are strongly active against bacteria. Ni^II and Sb^III complexes were the most effective against Pseudomonas aeruginosa (gram negative), while the Cu^II complex proved to be best against Bacillus cereus (gram positive bacteria). Antifungal activities were also noted with the Schiff base and the U^VI complex. These compounds showed positive results against Candida albicans fungi, however, none of them were effective against Aspergillus ochraceous fungi. The Schiff base and its zinc and antimony complexes are strongly active against leukemic cells (CD₅₀ = 2.3–4.3 μg cm⁻³) while the copper, uranium and thorium complexes are moderately active (CD₅₀ = 6.9–9.5 μg cm⁻³). The nickel, zirconium and chromium complexes were found to be inactive. This revised version was published online in June 2006 with corrections to the Cover Date.     

Solvent extraction and spectrophotometric determination of uranium (VI)

Summary Solvent extraction of uranium-sodium diethyldithiocarbamate with ethylmethyl ketone and separation from titanium, zirconium, thorium, lanthanum and cerium has been described. It has been found that 11.75 to 47.00 mg of uranium can be extracted from a binary mixture containing 4.78 to 19.04 mg of titanium, 9.12 to 36.48 mg of zirconium, 116.0 to 460.0 mg of thorium, 6.95 to 27.8 mg of lanthanum or 7.06 to 28.24 mg of cerium at pH 3.0. The pH range between which the separations may be carried out successfully is 2.0 to 3.5. The following cations interfere in the separations: Cu^II, Fe^III, Co^II, Bi^III, Ni^II, Cr^VI, Te^IV, Se^IV, Ag^I, Hg^II, As^III, Sn^IV, Pb^IV, Cd^II, Mo^VI, Mn^II, V^V, Zn^II, In^III, Tl^I, W^VI, Os^VIII and Nb^V.

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Zusammenfassung Uran kann durch Extraktion als Diäthyldithiocarbamidat mit Methyläthylketon von Ti, Zr, Th, La oder Ce getrennt werden. Der günstigste pH-Bereich liegt zwischen 2,0 und 3,5. Die Trennungen wurden mit folgenden Mengen durchgeführt: U (11,75–47,00 mg); Ti (4,78 bis 19,04 mg), Zr (9,12–36,48 mg) Th (116,0–460,0 mg), La (6,95–27,8 mg), Ce (7,06–28,24 mg). Folgende Ionen verursachen Störungen: Cu^II, Fe^III, Co^II, Bi^III, Ni^II, Cr^VI, Te^IV, Se^IV, Ag^I, Hg^II, As^III, Sn^IV, Pb^IV, Cd^II, Mo^VI, Mn^II, V^VI, Zn^II, In^III, Tl^I, W^VI, Os^VIII sowie Nb^V.

     

Adsorption recovery of thorium(IV) by Myrica rubra tannin and larch tannin immobilized onto collagen fibres

Novel adsorbents which can concentrate Th(IV) in aqueous solution were prepared by immobilizingMyrica rubra tannin and larch tannin onto collagen fibre matrices. The adsorption capacities of the immobilized tannins to Th(IV) are related to temperature and pH value of the adsorption process. For example, when the initial concentration of Th(IV) was 116.0 mg·l^-1 and the immobilized tannin was 100 mg, the adsorption capacities of immobilized Myrica rubra tannin and larch tannin were 55.98 mg Th(IV)·g^-1 and 13.19 mg Th(IV)·g^-1, respectively at 303 K, and 73.67 mg Th(IV)·g^-1 and 18.19 mg Th(IV)·g^-1 at 323 K. It was also found that the higher adsorption capacity was obtained at higher pH value. The adsorption equilibrium data of the immobilized tannins for Th(IV) can be well fitted by the Langmuir model and the mechanism of the adsorption was found to be a chemical adsorption. In general, the adsorption capacity of immobilized Myrica rubra tannin to Th(IV) is significantly higher than that of immobilized larch tannin, probably due to the fact that the B ring of Myrica rubra tannin has a pyrogallol structure which has higher reaction activity with metal ions. The breakthrough point of the adsorption column of immobilized Myrica rubra tannin was at 33 bed volumes for the experimental system. The mass transfer coefficient of adsorption column determined by Adams-Bohart equation was 1.61·10^-4 l·mg^-1.min^-1. The adsorption column can be easily regenerated by 0.1 mol·l^-1 HNO₃ solution, showing outstanding ability of concentrating Th(IV). This revised version was published online in July 2006 with corrections to the Cover Date.