Ab initio X-ray absorption spectroscopy study of the solvation structure of Th(IV), U(IV), and Np(IV) in aqueous solution

The coordination structures of U(IV), Np(IV), and Th(IV) in aqueous solution have been determined by studying the X-ray absorption near edge structure (XANES) of the actinide (An) L(3)-edge absorption spectra. The high sensitivity of XANES to the bonding geometry provides an unambiguous determination of the coordination polyhedron. On the basis of the comparison of ab initio computations with the experimental data we conclude that the hydration sphere of the three An(IV) aqua-ions studied is best modeled by 9 water molecules forming a tricapped trigonal prism.     

Acetylenic β-keto Ester of Th(IV), U(IV), and U(VI) Compounds

Acetylenic β-keto ester (L) compounds ML₄ (M = Th and U), and UO₂L₂ · EtOH have been prepared by reactions in non-aqueous solvents. The infrared spectra of these compounds are reported together with some of their chemical properties.     

Comparative EXAFS investigation of uranium(VI) and -(IV) aquo chloro complexes in solution using a newly developed spectroelectrochemical cell

The coordination of the U(IV) and U(VI) ions as a function of the chloride concentration in aqueous solution has been studied by U L(III)-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The oxidation state of uranium was changed in situ using a gastight spectroelectrochemical cell, specifically designed for the safe use with radioactive solutions. For U(VI) we observed the complexes UO2(H2O)5(2+), UO2(H2O)4Cl+, UO2(H2O)3Cl2(0), and UO2(H2O)2Cl3- with [Cl-] increasing from 0 to 9 M, and for U(IV) we observed the complexes U(H2O)9(4+), U(H2O)8Cl3+, U(H2O)(6-7)Cl2(2+), and U(H2O)5Cl3+. The distances in the U(VI) coordination sphere are U-Oax = 1.76+/-0.02 A, Oeq = 2.41 +/- 0.02 A, and U-Cl = 2.71 +/- 0.02 A; the distances in the U(IV) coordination sphere are U-O = 2.41 +/- 0.02 A and U-Cl = 2.71 +/- 0.02 A.     

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.     

Halloysite nanotubes: an eco-friendly adsorbent for the adsorption of Th(IV)/U(VI) ions from aqueous solution

Journal of Radioanalytical and Nuclear Chemistry - In this study, the halloysite nanotubes was characterized and the adsorption of Th(IV) and U(VI) on halloysite nanotubes was investigated as a...     

Extraction of U(VI), Zr(IV) and Th(IV) from perchlorate media, by PC-88A

Extraction of U(VI), Zr(IV) and Th(IV) has been investigated from perchlorate media using 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC-88A) dissolved in toluene. The extraction of U(VI), Zr(IV) and Th(IV) was found to be quantitative in the pH range 1.6 to 3.2, 2.0 to 4.7 and 2.3 to 3.8, respectively, with 3.0^.10^-3, 5.6^.10^-4 and 1.0^.10^-2M PC-88A dissolved in toluene. U(VI) was stripped with 4.0M HCl, Zr(IV) with 2.5M NaF and Th(IV) with 8.0M HCl from the metal loaded organic phase containing PC-88A dissolved in toluene. The probable extracted species have been ascertained by plotting log D vs. log [HR] as UO₂R₂ ^.2HR, ZrR₄ ^.2HR and ThR₄ ^.4HR, respectively. U(VI) was separated from Zr(IV) and Th(IV) and from other associated metals. This method was proved by the determination of U(VI) in some real samples.     

Stability constants of U(VI) and U(IV)-humic acid complexes

Summary Conditional stability constants have been determined for U(IV) and U(VI) Boom Clay humic acid (BCHA) and Aldrich humic acid (AHA) complexes, under anaerobic and carbonate free conditions. The constants are needed for nuclear waste repository performance assessment purposes. The U(IV) constants were obtained by developing an approach based on the solubility product of amorphous U(OH)₄. The U(VI) constants were obtained by applying the Schubert ion-exchange approach.     

Synergistic extraction of Am(III), Th(IV) and U(VI) by PMBP and crown ethers

The extraction of UO ₂ ²⁺ , Am³⁺, and Th⁴⁺ by 1-phenyl-3-methyl-4-benzylpyrazolone with crown ethers was studies using 0.1M (NaClO₄) aqueous phase and toluene. The crown ethers were 12C4, 15C5, 18C6, DB18C6 and DCH18C6. The synergic equilibrium constant did not show correlation between the cationic radii and the ether cavity size nor did the values follow a simple order of ether basicity. The ether basicity, steric effects, and the number of ether oxygens bound to the cation are the combined factors which seemingly determine the pattern of M(PMBP)_n—CE interaction.     

Ion exchange separation of Eu(III), Th(IV), U(VI) and Pu(IV) ions on Amberlyst A-15 in non-aqueous solutions

Distribution ratios of europium(III), thorium(IV), uranium(VI) and plutonium(IV) ions on Amberlyst A-15, a macroreticular polystyrene sulfonate resin, after extraction in HTTA-TBP-Shell Sol-T and HTTA-TOPO-benzene solutions have been determined as a function of the aqueous acidity. The affinity orders were EuPu>Th>U and Eu>Th>Pu>U in the former and the latter solutions, respectively. Separation factors were computed from the observed K_d values. A procedure for the separation of a mixture of Eu(III), Th(IV), and U(VI) ions in HTTA-TOPO-benzene solution in an ion-exchange column is described.     

Ion exchange studies of U(VI), Th(IV), Pu(IV) and Eu(III) on a macroreticular resin in TBP-Shell Sol-T solutions

Ion exchange studies of uranium(VI), thorium(IV), plutonium(IV) and europium(III) ions on a macroreticular cation exchange resin, Amberlyst A-15, from solutions of 30% and 5% TBP—Shell Sol-T have been carried out. The metal ions were extracted into TBP Shell Sol-T phase from 8M NH₄NO₃ at different nitric acid concentrations. Ion exchange distribution ratios as a function of organic phase acidity of 30% and 5% TBP have been computed. Separation factors computed from the observed Kd values are plotted as a function of organic phase acidity.     

Studies on the extraction behavior of Zr(IV), Ce(III), Th(IV) and U(VI) from aqueous solutions of Arsenazo-I with HDEHP,HTTA, TDA and TCMA

The extraction behavior of Zr(IV), Ce(III), Th(IV) and U(VI) from aqueous solutions containing Arsenazo-I with the organic solvents tridodecylamine (TDA), 1-[thenoyl-(2)]-3-3-3-trifluoroacetone (HTTA), di(2-ethylhexyl) phosphoric acid (HDEHP) and tricaprylmethylammonium chloride (TCMA) in xylene has been investigated. Effect of hydrogen ion concentration in the aqueous phase, Arsenazo-I concentration, as well as the effect of solvent concentration on the extraction was studied. Some alternatives for separation of the elements studied were recommended enabling the spectrophotometric determination of these elements using Arsenazo-I without interference.     

Extraction and thermodynamic behavior of U(VI) and Th(IV) from nitric acid solution with tri-isoamyl phosphate

The extraction behavior of U(VI) and Th(IV) with tri-isoamyl phosphate–kerosene (TiAP–KO) from nitric acid medium was investigated in detail using the batch extraction method as a function of aqueous-phase acidity, TiAP concentration and temperature, then the thermodynamic parameters associated with the extraction were derived by the second-law method. It could be noted that the distribution ratios of U(VI) or Th(IV) increased with increasing HNO₃ concentration until 6 or 5 M from 0.1 M. However, a good separation factor (D _U(VI)/D _Th(IV)) of 88.25 was achieved at 6 M HNO₃, and the stripping of U(VI) from TiAP–KO with deionized water or diluted nitric acid was easier than that of Th(IV). The probable extracted species were deduced by log D-log c plot at different temperatures as UO₂(NO₃)₂·(TiAP)_(1–2) and Th(NO₃)₄·(TiAP)_(2–3), respectively. Additionally, △H, △G and △S for the extraction of U(VI) and Th(IV) revealed that the extraction of U(VI) by TiAP was an exothermic process and was counteracted by entropy change, while the extraction of Th(IV) was an endothermic process and was driven by entropy change.     

Synthesis and Characterization of Th(IV) and U(VI) Complexes with O-Vanillin-P-Phenylenediamine

Two new solid complexes, [ThL(NO₃)₂](NO₃)₂, [UO₂L(NO₃)]NO₃ (L=o-vanillin-p-phenylenediamine) have been synthesized and characterized by elemental analyses, DTA-TG, IR spectra, UV spectra and molar conductance. Possible structures of the two complexes are proposed.     

Pulse radiolysis studies of U(VI) complexes in aqueous media

The rate constants for the reaction between the hydrated electron and dioxouranium(VI) complexes with carbonate IMDA, NTA, oxalate and chloride ion range from 2 to 4 × 10¹⁰ M⁻¹ sec⁻¹. The insensitivity of the reaction rate to formal charge, potential, and number of water molecules in the equatorial coordination sphere of uranium is interpreted in terms of an electron tunneling mechanism for the reaction. Spectroscopic and structural data are cited to provide evidence consistent with such a mechanism.     

The effect of previous gamma-irradiation on the extraction of U(VI), Th(IV), Zr(IV), Eu(III) and Am(III) by various amides

The extraction behavior of U(VI), Th(IV), Zr(IV), Eu(III) and Am(III) from 3.5M nitric acid with a series of gamma-pre-irradiated symmetrical and unsymmetrical monoamides in benzene has been investigated up to a dose of 100 Mrad. The results indicated that the radiolytic stability is influenced by the structure of amides. Symmetrical monoamides seem to be less affected by radiation compared with unsymmetrical monoamides. Infrared studies identify the final products of radiolysis as the respective carboxylic acids and amines. The radiolytic degradation of the investigated monoamides has been estimated by quantitative IR spectroscopy. Extraction data obtained under similar experimental conditions for U(VI), Th(IV) and Zr(IV) with the TBP/benzene system have also been compared. This revised version was published online in August 2006 with corrections to the Cover Date.     

UO<Subscript>2</Subscript>(VI), Sn(IV), Th(IV) and Li(I) complexes of 4-azomalononitrile antipyrine

UO₂(VI), Sn(IV), Th(IV) and Li(I) complexes of 4-azomalononitrile antipyrine (L) have been isolated and characterized based on IR spectra, ¹H NMR, elemental analyses, molar conductance and thermal analysis (DTA/TG). The study revealed that the ligand behaves as a neutral bidentate one and coordination takes place via the carbonyl atom of pyrazolone ring >C=O and the azomethine nitrogen >C=N. The thermal stability of the metal complexes were investigated by thermogravimetry (TG), differential thermal analysis (DTA) techniques and infrared spectra, and correlated to their structure. The thermal study revealed that Th(IV) complexes show lower thermal stability than both UO₂(VI) and Sn(IV) complexes.     

Photoelectron spectra of uranium(IV), (V) and (VI) complexes

Satellites were observed on 4f photoelectron spectra of uranium (IV) complexes, while none was seen for diamagnetic uranyl complexes. Photoelectron lines of oxygen 1s coordinated to the uranium ion were broad for NaUO₃ and uranyl complexes.     

Differential estimation of U(VI) and U(IV) ions in aqueous solutions by Arsenazo 1

The spectrophotometric determination of pure U(IV) or U(VI) ions in solution with Arsenazo I is greatly dependant on the pH of the solutions. The experimental conditions for the differential estimation of the different oxidation states of U ions, in the same sample, using Arsenazo I have been identified and implemented. The results showed that the applied method is rather rapid and accurate.