Complex formation reactions of lanthanum(III), cerium(III), thorium(IV), dioxouranyl(IV) complexes with tricine

Equilibrium studies for the heavy metal ions La(III), Ce(III), Th(IV) and UO2(IV) (M) complexes of the zwitterionic buffer tricine (L) in aqueous solution are investigated. Stoichiometry and stability constants for the different complexes formed as well as hydrolysis products of the metal cations are determined at 25 degrees C and ionic strength 0.1 M NaNO3. The stability of the formed complexes are discussed in terms of the nature of the heavy metal cation. The solid complexes are synthesized and characterized by means of elemental analysis, FTIR, and TG analysis. The general molecular formulae of the obtained complexes is suggested to be [M(L)2](NO3)n-2(H2O)x, where n = the charge of the metal cation, x = no. of water molecules.     

Interaction of Aluminium (III) with the f-Family Ions Np(VI), Pu(VI), Np(V), Np(IV), Pu(IV), Nd(III), and Am(III) in the Course of Simultaneous Hydrolysis

The interaction of Np(VI), Pu(VI), Np(V), Np(IV), Pu(IV), Nd(III), and Am(III) with Al(III) in solutions at pH 0–4 was studied by the spectrophotometric method. It was shown that, in the range of pH 3–4, the hydrolyzed forms of neptunyl and plutonyl react with the hydrolyzed forms of aluminium. In the case of Pu(VI), the mixed hydroxoaqua complexes (H₂O)₃PuO₂(-OH)₂Al(OH)(H₂O)₃ ²⁺ or (H₂O)₄PuO₂OAl(OH)(H₂O)₄ ²⁺ are formed at the first stage of hydrolysis. Np(VI) also forms similar hydroxoaqua complexes with Al(III). The formation of the mixed hydroxoaqua complexes was also observed when Np(IV) or Pu(IV) was simultaneously hydrolyzed with Al(III) at pH 1.5–2.5. The Np(IV) complex with Al(III) has, most likely, the formula (H₂O) _n (OH)Np(-OH)₂Al(OH)(H₂O)₃ ³⁺. At pH from 2 to 4.1 (when aluminium hydroxide precipitates), the Np(V) or Nd(III) ions exist in solutions with or without Al(III) in similar forms. When pH is increased to 5–5.5, these ions are almost not captured by the aluminium hydroxide precipitate.     

Deviation between the chemistry of Ce(IV) and Pu(IV) and routes to ordered and disordered heterobimetallic 4f/5f and 5f/5f phosphonates

The heterobimetallic actinide compound UO(2)Ce(H(2)O)[C(6)H(4)(PO(3)H)(2)](2)·H(2)O was prepared via the hydrothermal reaction of U(VI) and Ce(IV) in the presence of 1,2-phenylenediphosphonic acid. We demonstrate that this is a kinetic product that is not stable with respect to decomposition to the monometallic compounds. Similar reactions have been explored with U(VI) and Ce(III), resulting in the oxidation of Ce(III) to Ce(IV) and the formation of the Ce(IV) phosphonate, Ce[C(6)H(4)(PO(3)H)(PO(3)H(2))][C(6)H(4)(PO(3)H)(PO(3))]·2H(2)O, UO(2)Ce(H(2)O)[C(6)H(4)(PO(3)H)(2)](2)·H(2)O, and UO(2)[C(6)H(4)(PO(3)H)(2)](H(2)O)·H(2)O. In comparison, the reaction of U(VI) with Np(VI) only yields Np[C(6)H(4)(PO(3)H)(2)](2)·2H(2)O and aqueous U(VI), whereas the reaction of U(VI) with Pu(VI) yields the disordered U(VI)/Pu(VI) compound, (U(0.9)Pu(0.1))O(2)[C(6)H(4)(PO(3)H)(2)](H(2)O)·H(2)O, and the Pu(IV) phosphonate, Pu[C(6)H(4)(PO(3)H)(PO(3)H(2))][C(6)H(4)(PO(3)H)(PO(3))]·2H(2)O. The reactions of Ce(IV) with Np(VI) yield disordered heterobimetallic phosphonates with both M[C(6)H(4)(PO(3)H)(PO(3)H(2))][C(6)H(4)(PO(3)H)(PO(3))]·2H(2)O (M = Ce, Np) and M[C(6)H(4)(PO(3)H)(2)](2)·2H(2)O (M = Ce, Np) structures, as well as the Ce(IV) phosphonate Ce[C(6)H(4)(PO(3)H)(PO(3)H(2))][C(6)H(4)(PO(3)H)(PO(3))]·2H(2)O. Ce(IV) reacts with Pu(IV) to yield the Pu(VI) compound, PuO(2)[C(6)H(4)(PO(3)H)(2)](H(2)O)·3H(2)O, and a disordered heterobimetallic Pu(IV)/Ce(IV) compound with the M[C(6)H(4)(PO(3)H)(PO(3)H(2))][C(6)H(4)(PO(3)H)(PO(3))]·2H(2)O (M = Ce, Pu) structure. Mixtures of Np(VI) and Pu(VI) yield disordered heterobimetallic Np(IV)/Pu(IV) phosphonates with both the An[C(6)H(4)(PO(3)H)(PO(3)H(2))][C(6)H(4)(PO(3)H)(PO(3))]·2H(2)O (M = Np, Pu) and An[C(6)H(4)(PO(3)H)(2)](2)·2H(2)O (M = Np, Pu) formulas.     

Spectrophotometric Studies of Cerium(III) and Thorium(IV) Chelates of Diethylenetriaminepentaacetic Acid (DTPA)

The interaction between diethylenetriaminepentaacetic acid (DTPA or H_sZ) and Ce(III) and Th(IV) ions has been investigated spectrophotometrically in aqueous solution at an ionic strength of 0.1 and for various temperatures. It has been found that the Ce(III)-DTPA chelate (1:1) exhibited a characteristic absorption maximum at 297 nm, and the optimum pH range is between 3.4 to 4.4. The absorption of Ce(III)-DTPA chelate is considerably diminished by adding small amounts of Th(IV) ions. This phenomenon was used to evaluate the formation constant of Th(IV)-DTPA chelate (1:1). The formation constants and the thermodynamic properties characterizing the formation of the chelates have been calculated at 25°. The results are as follows:      

Bicyclic and acyclic diamides: comparison of their aqueous phase binding constants with Nd(III), Am(III), Pu(IV), Np(V), Pu(VI), and U(VI)

This report describes affinity measurements for two, water-soluble, methyl-alkylated diamides incorporating the malonamide functionality, N,N,N',N' tetramethylmalonamide (TMMA) and a bicyclic diamide (1a), toward actinide metal cations (An) in acidic nitrate solutions. Ligand complexation to actinides possessing oxidation states ranging from +3 to +6 was monitored through optical absorbance spectroscopy, and formation constants were obtained from the refinement of the spectrophotometric titration data sets. Species analysis gives evidence for the formation of 1, 4, 1, and 2 spectrophotometrically observable complexes by TMMA to An(III, IV, V, and VI), respectively, while for 1a, the respective numbers are 3, 4, 2, and 2. Consistent with the preorganization of 1a toward actinide binding, a significant difference is found in the magnitudes of their respective formation constants at each complexation step. It has been found that the binding affinity for TMMA follows the well-established order An(V) < An(III) < An(VI) < An(IV). However, with 1a, Np(V) forms stronger complexes than Am(III). The complexation of 1a with Np(V) and Pu(VI) at an acidity of 1.0 M is followed by reduction to Np(IV) and Pu(IV), whereas TMMA does not perturb the initial oxidation state for these dioxocations. These measurements of diamide binding affinity mark the first time single-component optical absorbance spectra have been reported for a span of actinide-diamide complexes covering all common oxidation states in aqueous solution.     

Electromigration of Bk(IV) and some other tetravalent cations in nitric acid solutions

Electromigration of Bk(IV) and Ce(IV) in mixed HNO₃−HClO₄ solutions at constant total acid concentration of 6M has been investigated. Comparative electromigration of Bk(IV), Pu(IV), Th(IV) and Ce(IV) has been studied in nitric acid solutions at concentrations from 2M to 16M. Comparison of the obtained values of mobility shows that the ability to form negatively charged hexanitrato complexes in nitric acid solutions decreases with a decrease in ionic radius of the cations: Ce(IV), Th(IV), Pu(IV), Bk(IV). The mobility corresponding to negatively charged ions in the case of Bk(IV) appears only at HNO₃ concentrations higher than 10M. This fact allowed to explain the specific features of ion-exchange and solvent extraction behaviour of Bk(IV).     

Formation of soluble hexanuclear neptunium(IV) nanoclusters in aqueous solution: growth termination of actinide(IV) hydrous oxides by carboxylates

Complexation of Np(IV) with several carboxylates (RCOO(-); R = H, CH(3), or CHR'NH(2); R' = H, CH(3), or CH(2)SH) in moderately acidic aqueous solutions was studied by using UV-vis-NIR and X-ray absorption spectroscopy. As the pH increased, all investigated carboxylates initiated formation of water-soluble hexanuclear complexes, Np(6)(μ-RCOO)(12)(μ(3)-O)(4)(μ(3)-OH)(4), in which the neighboring Np atoms are connected by RCOO(-)syn-syn bridges and the triangular faces of the Np(6) octahedron are capped with μ(3)-O(2-)/μ(3)-OH(-). The structure information of Np(6)(μ-RCOO)(12)(μ(3)-O)(4)(μ(3)-OH)(4) in aqueous solution was extracted from the extended X-ray absorption fine structure data: Np-O(2-) = 2.22-2.23 ? (coordination number N = 1.9-2.2), Np-O(RCOO(-)) and Np-OH(-) = 2.42-2.43 ? (N = 5.6-6.7 in total), Np···C(RCOO(-)) = 3.43 ? (N = 3.3-3.9), Np···Np(neighbor) = 3.80-3.82 ? (N = 3.6-4.0), and Np···Np(terminal) = 5.39-5.41 ? (N = 1.0-1.2). For the simpler carboxylates, the gross stability constants of Np(6)(μ-RCOO)(12)(μ(3)-O)(4)(μ(3)-OH)(4) and related monomers, Np(RCOO)(OH)(2)(+), were determined from the UV-vis-NIR titration data: when R = H, log β(6,12,-12) = 42.7 ± 1.2 and log β(1,1,-2) = 2.51 ± 0.05 at I = 0.62 M and 295 K; when R = CH(3), log β(6,12,-12) = 52.0 ± 0.7 and log β(1,1,-2) = 3.86 ± 0.03 at I = 0.66 M and 295 K.     

Complexation of Pu(IV) with the natural siderophore desferrioxamine B and the redox properties of Pu(IV)(siderophore) complexes

The bioavailability and mobility of Pu species can be profoundly affected by siderophores and other oxygen-rich organic ligands. Pu(IV)(siderophore) complexes are generally soluble and may constitute with other soluble organo-Pu(IV) complexes the main fraction of soluble Pu(IV) in the environment. In order to understand the impact of siderophores on the behavior of Pu species, it is important to characterize the formation and redox behavior of Pu(siderophore) complexes. In this work, desferrioxamine B (DFO-B) was investigated for its capacity to bind Pu(IV) as a model siderophore and the properties of the complexes formed were characterized by optical spectroscopy measurements. In a 1:1 Pu(IV)/DFO-B ratio, the complexes Pu(IV)(H2DFO-B)4+, Pu(IV)(H1DFO-B)3+, Pu(IV)(DFO-B)2+, and Pu(IV)(DFO-B)(OH)+ form with corresponding thermodynamic stability constants log beta1,1,2 = 35.48, log beta1,1,1 = 34.87, log beta1,1,0 = 33.98, and log beta1,1,-1 = 27.33, respectively. In the presence of excess DFO-B, the complex Pu(IV)H2(DFO-B)22+ forms with the formation constant log beta2,1,2 = 62.30. The redox potential of the complex Pu(IV)H2(DFO-B)22+ was determined by cyclic voltammetry to be E1/2 = -0.509 V, and the redox potential of the complex Pu(IV)(DFO-B)2+ was estimated to be E1/2 = -0.269 V. The redox properties of Pu(IV)(DFO-B)2+ complexes indicate that Pu(III)(siderophore) complexes are more than 20 orders of magnitude less stable than their Pu(IV) analogues. This indicates that under reducing conditions, stable Pu(siderophore) complexes are unlikely to persist.     

Thermal decomposition of Np(IV) and Pu(III, IV) oxalates

Thermal decomposition of Pu(C₂O₄)₂·6H₂O, Pu₂(C₂O₄)₃·10H₂O and Np(C₂O₄)₂ ·6H₂O has been studied by using combination of gas chromatography, infrared spectroscopy, spectrophotometry and complex thermal analysis. We also investigated the decomposition of Pu oxalate under its -radiation. The reduction of Pu(IV) to Pu(III) has been confirmed. We found Np(V), which is formed from Np(IV), on the basis of infrared and absorption spectra of the intermediate compounds.     

Cerium(IV), neptunium(IV), and plutonium(IV) 1,2-phenylenediphosphonates: correlations and differences between early transuranium elements and their proposed surrogates

The in situ hydrothermal reduction of Np(VI) to Np(IV) and Pu(VI) to Pu(IV) in the presence of 1,2-phenylenediphosphonic acid (PhP2) results in the crystallization of Np[C(6)H(4)(PO(3)H)(2)](2)·2H(2)O (NpPhP2) and Pu[C(6)H(4)(PO(3)H)(PO(3)H(2))][C(6)H(4)(PO(3)H)(PO(3))]·2H(2)O (PuPhP2), respectively. Similar reactions have been explored with Ce(IV) resulting in the isolation of the Ce(IV) phenylenediphosphonate Ce[C(6)H(4)(PO(3)H)(PO(3)H(2))][C(6)H(4)(PO(3)H)(PO(3))]·2H(2)O (CePhP2). Single crystal diffraction studies reveal that although all these three compounds all crystallize in the triclinic space group P1?, only PuPhP2 and CePhP2 are isotypic, whereas NpPhP2 adopts a distinct structure. In the cerium and plutonium compounds edge-sharing dimers of MO(8) polyhedra are bridged by the diphosphonate ligand to create one-dimensional chains. NpPhP2 also forms chains. However, the NpO(8) units are monomeric. The protonation of the ligands is also different in the two structure types. Furthermore, the NpO(8) polyhedra are best described as square antiprisms (D(4d)), whereas the CeO(8) and PuO(8) units are trigonal dodecahedra (D(2d)). Bond-valence parameters of R(o) = 1.972 and b = 0.538 have been derived for Np(4+) using a combination of the data reported in this work with that available in crystallographic databases. The UV-vis-NIR absorption spectra of NpPhP2 and PuPhP2 are also reported and used to confirm the tetravalent oxidation states.     

Syntheses, Structures, and Spectroscopic Properties of Plutonium and Americium Phosphites and the Redetermination of the Ionic Radii of Pu(III) and Am(III)

A series of isotypic rare earth phosphites (RE = Ce(III), Pr(III), Nd(III), Pu(III), or Am(III)) with the general formulas RE(2)(HPO(3))(3)(H(2)O) along with a Pu(IV) phosphite, Pu[(HPO(3))(2)(H(2)O)(2)], have been prepared hydrothermally via reactions of RECl(3) with phosphorous acid. The structure of RE(2)(HPO(3))(3)(H(2)O) features a face-sharing interaction of eight- and nine-coordinate rare earth polyhedra. By use of the crystallographic data from the isotypic series along with data from previously reported isotypic series, the ionic radii for higher coordinate Pu(III) and Am(III) were calculated. The (VIII)Pu(III) radius was calculated as 1.112 ± 0.004 ?, and the (IX)Pu(III) radius was calculated to be 1.165 ± 0.002 ?. The (VIII)Am(III) radius was calculated as 1.108 ± 0.004 ?, and the (IX)Am(III) radius was calculated as 1.162 ± 0.002 ?.     

Specific Sequestering Agents for the Actinides. 29. Stability of the Thorium(IV) Complexes of Desferrioxamine B (DFO) and Three Octadentate Catecholate or Hydroxypyridinonate DFO Derivatives: DFOMTA, DFOCAMC, and DFO-1,2-HOPO. Comparative Stability of the Plutonium(IV) DFOMTA Complex(1)

The metal complex stability constants of Th(IV) with desferrioxamine B (DFO) and three octadentate derivatives [N-(2,3-dihydroxy-4-carboxybenzoyl)desferrioxamine B (DFOCAMC), N-(1,2-dihydro-1-hydroxy-2-oxopyridin-6-yl)carbonyl)desferrioxamine B (DFO-1,2-HOPO) and N-(2,3-dihydroxy-4-(methylamido)benzoyl)desferrioxamine B (DFOMTA)] have been determined. The formation constant of the Pu(IV)/DFOMTA complex has also been determined, and the formation constants have been estimated for the other Pu(IV) complexes of octadentate DFO derivatives. The DFO derivatives form 1:1 complexes with Th(IV) in aqueous solution. The solution chemistry of the Th(IV) complexes has been studied by spectrophotometric, potentiometric and proton NMR titrations. The Th(IV) formation constants are as follows (log K(f) values and esd's): DFO, 26.6(1); DFOMTA, 38.55(5); DFOCAMC, 37.2(3); DFO-1,2-HOPO, 33.7(4). The Pu(IV)/DFOMTA formation constant, determined by competitive spectrophotometric titration is (log K(f) value) 41.7(2). The estimation of the other Pu(IV) formation constants are as follows (log K(f) values): DFOCAMC, 40.4; DFO-1,2-HOPO, 36.9. The selectivity of DFO and the three derivatives for actinide(IV) ions is discussed.     

Thermodynamics of substituted rhodanine II: Binary complexes of Th(IV), UO2(II), Ce(III), and La(III) with 3-benzamidorhodanine and its derivatives

Summary Th(IV), UO₂(II), Ce(III) and La(III) chelates with 3-benzamidorhodanine and its derivatives have been investigated potentiometrically in 0.1M KCl and 20% (v/v) ethanol-water medium. The stability of the formed complexes increases in the order Th(IV)>UO₂(II)>Ce(III)>La(III). For the same metal ion, the stability of the chelates is found to increase with decreasing temperature, ionic strength, dielectric constant of the medium and by increasing the electron repelling property of the substituent. The thermodynamic parameters (G, H and S) for complexation are evaluated and discussed. The formation of the complexes has been found to be spontaneous, exothermic and entropically favourable.

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Thermodynamik von substituiertem Rhodanin II: Binäre Komplexe von Th(IV), UO₂(II), Ce(III) und La(III) mit 3-Benzamidorhodanin und seinen Derivaten

Zusammenfassung Th(IV)-, UO₂(II)-, Ce(III)- und La(III)-Chelate mit 3-Benzamidorhodanin und seinen Derivaten wurden in 0.1M KCl und 20% (/) Ethanol-Wasser potentiometrisch untersucht. Die Stabilität der gebildeten Komplexe steigt in der Reihenfolge Th(IV)>UO₂(II)>Ce(III)>La(III). Für ein- und dasselbe Metallion steigt die Stabilität der Chelate mit sinkender Temperatur, Ionenstärke und Dielektrizitätskonstante des Mediums und mit steigender Elektronenabstoßungsfähigkeit des Substituenten. Die thermodynamischen Parameter (G, H und S) für die Komplexbildungsreaktion werden bestimmt und diskutiert. Die Bildung der Komplexe erweist sich als spontan, exotherm und entropisch begünstigt.

     

Solvent extraction behaviour of lanthanum(III), cerium(III), europium(III), thorium(IV) and uranium(VI) with 3-phenyl-4-benzoyl-5-isoxazolone

The extraction behaviour of La(III), Ce(III), Eu(III), Th(IV) and U(VI) with 3-phenyl-4- benzoyl-5-isoxazolone (HPBI) in chloroform has been studied. The mechanism of extraction and the species extracted have been identified. Extraction constants for each system have been calculated. The system has been used to separate Th(IV) from U(VI) and from La(III), Ce(III) and Eu(III). A comparison of the extraction constants with those for the 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (HPMBP) and thenoyltrifluoroacetone (HTTA) systems indicates that HPBI extracts these metal species better than HPMBP and HTTA do.     

Absorption spectroscopic properties for Pu(III,IV and VI) in nitric and hydrochloric acid media

Absorption spectroscopic properties for various Pu oxidation states in nitric and hydrochloric acid solutions were investigated with UV-Visible spectrophotometry. As a result, it was confirmed that the intensities of the major absorption peaks had a tendency to decrease for Pu(III), Pu(IV) and Pu(VI) in HCl and HNO₃ media, and the major peak positions were shifted to longer or shorter wavelengths depending on the complexforming abilities of Pu(III), Pu(IV) and Pu(VI) with the chloride or nitrate ion with increasing acid concentrations. The values of the wavelength and the molar absorptivity for the principal peaks of Pu(III), Pu(IV) and Pu(VI) in NHO₃ and HCl solutions were similar to those reported in other works. The values of the molar absorptivity for the principal peaks of Pu(III), Pu(IV) and Pu(VI) in the HNO₃ solution were a little higher than those in the HCl solution.     

Electrochemical and spectroscopic studies of Pu(IV) and Pu(III) in nitric acid solutions

Electrochemical and absorption spectroscopic properties of Pu(IV) and Pu(III) in nitric acid have been investigated by using cyclic voltammetry (CV) and UV–Visible spectroscopy. CV using a glassy carbon electrode suggested that the electrochemical reaction of Pu(IV) nitrate complexes were found to be a quasi-reversible reduction to Pu(III) species. The formal redox potentials (E ⁰) for Pu(IV)/Pu(III) couples were +0.721, +0.712, +0.706, +0.705, +0.704, 0.694, and +0.696 V (vs. Ag/AgCl) when nitric acid concentrations are 1–7 M nitric acid solutions, respectively. These results indicate that the reduction product of Pu(IV) is only Pu(III). Further details for reaction mechanism of Pu(IV) were discussed on the basis of digital simulation of the experimental cyclic voltammograms. The absorption spectroscopic properties of Pu(III) and Pu(IV) in nitric acid solutions were investigated with UV–Visible spectrophotometry. As a result, it was founds that the intensities of the characteristic absorption peaks of Pu(III) and Pu(IV) tend to decrease with increasing nitric acid concentration for 1–8 M, and the peaks positions shifted longer or shorter wavelengths depending on the complex-forming abilities of Pu(III) and Pu(IV) with an increase in the nitric acid concentration.     

Modeling Speciation and Solubility in Aqueous Systems Containing U(IV,VI), Np(IV,V, VI), Pu(III,IV, V,VI), Am(III), and Cm(III)

A comprehensive thermodynamic model, referred to as the Mixed-Solvent Electrolyte model, has been applied to calculate phase equilibria and chemical speciation in selected aqueous actinide systems. The solution chemistry of U(IV, VI), Np(IV, V, VI), Pu(III, IV, V, VI), Am(III), and Cm(III) has been analyzed to develop the parameters of the model. These parameters include the standard-state thermochemical properties of aqueous and solid actinide species as well as the ion interaction parameters that reflect the solution’s nonideality. The model reproduces the solubility behavior and accurately predicts the formation of competing solid phases as a function of pH (from 0 to 14 and higher), temperature (up to 573 K), partial pressure of CO₂ (up to \( p_{{{\text{CO}}_{2} }} \)  = 1 bar), and concentrations of acids (to 127 mol·kg^?1), bases (to 18 mol·kg^?1), carbonates (to 6 mol·kg^?1) and other ionic components (i.e., Na⁺, Ca²⁺, Mg²⁺, OH^?, Cl^?, \( {\text{ClO}}_{4}^{ - } \), and \( {\text{NO}}_{3}^{ - } \)). Redox effects on solubility and speciation have been incorporated into the model, as exemplified by the reductive and oxidative dissolution of Np(VI) and Pu(IV) solids, respectively. Thus, the model can be used to elucidate the phase and chemical equilibria for radionuclides in natural aquatic systems or in nuclear waste repository environments as a function of environmental conditions. Additionally, the model has been applied to systems relevant to nuclear fuel processing, in which nitric acid and nitrate salts of plutonium and uranium are present at high concentrations. The model reproduces speciation and solubility in the U(VI) + HNO₃ + H₂O and Pu(IV, VI) + HNO₃ + H₂O systems up to very high nitric acid concentrations (\( x_{{{\text{HNO}}_{3} }} \approx 0.70 \)). Furthermore, the similarities and differences in the solubility behavior of the actinides have been analyzed in terms of aqueous speciation.     

Carbonate extraction-based refining of uranium. Separation of U(VI), Ce(IV), and Ln(III) from aqueous carbonate solutions with methyltrioctylammonium carbonate

The extraction of U(VI), Ce(IV), La(III), Nd(III), Sm(III), and Y(III) from an aqueous solution of Na₂CO₃ (0.25 mol/L) resulting from oxidative dissolution of U(IV) in the presence of H₂O₂ into a solution of methyltrioctylammonium carbonate (0.25 mol/L) in toluene. It was found that β_{U(VI)/Ln(III)} values vary from ~8 to 3290 as the O : W ratio changes from 2 : 1 to 10 : 1, while β_U(VI)/Ce(IV) varies from ~1.5 to 10, which allows for the extraction separation of U(VI) from Ce(IV) in a 8- to 10-stage counter-current extraction cascade and from Ln(III) in 2- to 3-stage cascade under the same conditions.     

Studies on the HTTA extraction of tetravalent actinides

The data on the extraction of Np(IV) and Pu(IV) from aqueous perchloric and nitric acid into benzene solution of thenoyl-trifluoro-acetone (HTTA) have been obtained at different temperatures. From these data the equilibrium constant for their extraction and the values of enthalpy for the extraction of Np(IV) and Pu(IV) were calculated. The absorption spectra of HTTA extracts containing Th(IV), U(IV), Np(IV) and Pu(IV) have been recorded to explore their analytical applications.     

Electrochemistry and Spectroelectrochemistry of the Pu (III/IV) and (IV/VI) Couples in Nitric Acid Systems

The solution chemistry of Pu in nitric acid is explored via electrochemistry and spectroelectrochemistry. By utilizing and comparing these techniques, an improved understanding of Pu behavior and its dependence on nitric acid concentration can be achieved. Here the Pu (III/IV) couple is characterized using cyclic voltammetry, square wave voltammetry, and a spectroelectrochemical Nernst step. Results indicate the formal reduction potential of the couple shifts negative with increasing acid concentration and reversible electrochemistry is no longer attainable above 6 M HNO₃. Spectroelectrochemistry is also used to explore the irreversible oxidation of Pu(IV) to Pu(VI) and shine light on the mechanism and acid dependence of the redox reaction.