Phase equilibria in ternary liquid systems containing solvates of lutetium(III) and uranyl(VI) nitrates with tri-n-butyl phosphate and tetradecane at various temperatures

The phase diagram has been studied for the ternary liquid system (TLS) [Lu(NO₃)₃(TBP)₃]-[UO₂(NO₃)₂(TBP)₂]-tetradecane at T = 298.15–333.15 K. There are fields of homogeneous and two-phase solutions in the system. One phase (phase I) is enriched in [Lu(NO₃)₃(TBP)₃] and [UO₂(NO₃)₂(TBP)₂]; the other (phase II) is enriched in tetradecane. Critical compositions in the system depend on temperature. [UO₂(NO₃)₂(TBP)₂] tends to be distributed to phase I, despite the fact that the binary system [UO₂(NO₃)₂(TBP)₂[-tetradecane is a single phase at all temperatures studied.     

Phase equilibria at various temperatures in the ternary liquid system containing solvates of thorium(IV) and uranyl(VI) nitrates with tri-n-butyl phosphate and tetradecane

The phase diagram of the ternary liquid system [Th(NO₃)₄(TBP)₂]-[UO₂(NO₃)₂(TBP)₂]-tetradecane (where TBP stands for tri-n-butyl phosphate) has been investigated at temperatures from 298.15 to 333.15 K. The ternary liquid system is characterized by a region of homogeneous solutions and a region of two-phase liquid systems (stratified systems). One phase is enriched with solvates [Th(NO₃)₄(TBP)₃] and [UO₂(NO₃)₂(TBP)₂] (phase I), and the other is enriched with tetradecane (phase II). The temperature (T = 298.15–333.15 K) does not substantially affect the two-phase region. In the two-phase systems, the preferential distribution of [UO₂(NO₃)₂(TBP)₂] into phase I is observed in spite of the fact that the binary system [UO₂(NO₃)₂(TBP)₂]-tetradecane is a single phase at all temperatures investigated. The distribution of [UO₂(NO₃)₂(TBP)₂] into phase I leads to the redistribution of [Th(NO₃)₄(TBP)₂] into phase II. At all temperatures investigated, the critical solution points of the ternary liquid system have compositions with close contents of the solvates [Th(NO₃)₄(TBP)₂] and [UO₂(NO₃)₂(TBP)₂].     

Use of the Wilson equation to calculate solid-liquid phase equilibria in binary and ternary systems

Generalized formulation is presented for calculating simple eutectic type solid-liquid phase diagrams for binary and ternary systems by using the Wilson equation for molar excess Gibbs energy in the liquid phase. The liquidus surface and eutectic points of molten salt mixtures with a common ion were calculated and compared with experimental values. The average error in the estimation of ternary eutectic composition was ± 0.013 (mole fraction) for the two ternary systems tested. The agreement was generally better than that obtained with the regular solution approximation.     

Molecular dynamics simulation of uranyl(VI) adsorption equilibria onto an external montmorillonite surface

We used molecular dynamics simulations to study the adsorption of aqueous uranyl species (UO(2)(2+)) onto clay mineral surfaces in the presence of sodium counterions and carbonato ligands. The large system size (10,000 atoms) and long simulation times (10 ns) allowed us to investigate the thermodynamics of ion adsorption, and the atomistic detail provided clues for the observed adsorption behavior. The model system consisted of the basal surface of a low-charge Na-montmorillonite clay in contact with aqueous uranyl carbonate solutions with concentrations of 0.027 M, 0.081 M, and 0.162 M. Periodic boundary conditions were used in the simulations to better represent an aqueous solution interacting with an external clay surface. Uranyl adsorption tendency was found to decrease as the aqueous uranyl carbonate concentration was increased, while sodium adsorption remained constant. The observed behavior is explained by physical and chemical effects. As the ionic strength of the aqueous solution was increased, electrostatic factors prevented further uranyl adsorption once the surface charge had been neutralized. Additionally, the formation of aqueous uranyl carbonate complexes, including uranyl carbonato oligomers, contributed to the decreased uranyl adsorption tendency.     

Prediction of ternary phase equilibria from binary data

The two-parameter UNIQUAC equation is modified to give better results of vapor—liquid and liquid—liquid equilibria for a variety of binary systems. The proposed equation is easily extended to a multicomponent system without including any ternary (or multicomponent) parameters. The good capability of the equation in data reduction is shown by many illustrative examples for various kinds of strongly nonideal binary and ternary mixtures.     

Phase equilibria analysis of the binary N2-NH3 and H2-NH3 systems and prediction of ternary phase equilibria

The high-pressure phase equilibria of binary mixtures, hydrogen-ammonia and nitrogen-ammonia, have been analyzed. A combined Chemical Association + Redlich–Kwong Equation of State (A + RKEOS) approach is adopted to represent gas-phase non-idealities while the liquid phase non-idealities are modeled using the NRTL equations. The proposed approach gave better representation as compared to other modified Redlich–Kwong Equations of State. The new approach was satisfactorily used to predict the phase equilibria of the ternary system of hydrogen–nitrogen–ammonia.     

Potentiometric and multinuclear NMR study of the binary and ternary uranium(VI)-L-fluoride systems, where L is alpha-hydroxycarboxylate or glycine

Equilibria, structures, and ligand-exchange dynamics in binary and ternary U(VI)-L-F- systems, where L is glycolate, alpha-hydroxyisobutyrate, or glycine, have been investigated in 1.0 M NaClO4 by potentiometry and 1H, 17O, and 19F NMR spectroscopy. L may be bonded in two ways: either through the carboxylate end or by the formation of a chelate. In the glycolate system, the chelate is formed by proton dissociation from the alpha-hydroxy group at around pH 3, indicating a dramatic increase, a factor of at least 10(13), of its dissociation constant on coordination to uranium(VI). The L exchange in carboxylate-coordinated UO2LF3(2-) follows an Eigen-Wilkins mechanism, as previously found for acetate. The water exchange rate, k(aq) = 4.2 x 10(5) s(-1), is in excellent agreement with the value determined earlier for UO2(2+)(aq). The ligand-exchange dynamics of UO2(O-CH2-COO)2F3- and the activation parameters for the fluoride exchange in D2O (k(obs) = 12 s(-1), deltaH(double dagger) = 45.8 +/- 2.2 kJ mo(-1), and deltaS(double dagger) = -55.8 +/- 3.6 J K(-1) mol(-1)) are very similar to those in the corresponding oxalate complex, with two parallel pathways, one for fluoride and one for the alpha-oxocarboxylate. The same is true for the L exchange in UO2(O-CH2-COO)2(2-) and UO2(oxalate)2(2-). The exchange of alpha-oxocarboxylate takes place by a proton-assisted chelate ring opening followed by dissociation. Because we cannot decide if there is also a parallel H+-independent pathway, only an upper limit for the rate constant, k1 < 1.2 s(-1), can be given. This value is smaller than those in previously studied ternary systems. Equilibria and dynamics in the ternary uranium(VI)-glycine-fluoride system, investigated by 19F NMR spectroscopy, indicate the formation of one major ternary complex, UO2LF3(2-), and one binary complex, UO2L2 (L = H2N-CH2COO-), with chelate-bonded glycine; log beta(9) = 13.80 +/- 0.05 for the equilibrium UO2(2+) + H2N-CH2COO- + 3F- = UO2(H2N-CH2COO)F3(2-) and log beta(11) = 13.0 +/- 0.05 for the reaction UO2(2+) + 2H2N-CH2COO- = UO2(H2N-CH2COO)2. The glycinate exchange consists of a ring opening followed by proton-assisted steps. The rate of ring opening, 139 +/- 9 s(-1), is independent of both the concentration of H+ and the solvent, H2O or D2O.     

Chemical equilibria in the uranyl(vi)-peroxide-carbonate system; identification of precursors for the formation of poly-peroxometallates

The focus of this study is on the identification of precursors in solution that might act as building blocks when solid uranyl(vi) poly-peroxometallate clusters containing peroxide and hydroxide bridges are formed. The precursors could be identified by using carbonate as an auxiliary ligand that prevented the formation of large clusters, such as the ones found in solids of fullerene type. Using data from potentiometric and NMR ((17)O and (13)C) experiments we identified the following complexes and determined their equilibrium constants: (UO(2))(2)(O(2))(CO(3))(4)(6-), UO(2)(O(2))CO(3)(2-), UO(2)(O(2))(CO(3))(2)(4-), (UO(2))(2)(O(2))(CO(3))(2)(2-), (UO(2))(2)(O(2))(2)(CO(3))(2-) and [UO(2)(O(2))(CO(3))](5)(10-). The NMR spectra of the pentamer show that all uranyl and carbonate sites are equivalent, which is only consistent with a ring structure built from uranyl units linked by peroxide bridges with the carbonate coordinated "outside" the ring; this proposed structure is very similar to [UO(2)(O(2))(oxalate)](5)(10-) identified by Burns et al. (J. Am. Chem. Soc., 2009, 131, 16648; Inorg. Chem., 2012, 51, 2403) in K(10)[UO(2)(O(2))(oxalate)](5)·(H(2)O)(13); similar ring structures where oxalate or carbonate has been replaced by hydroxide are important structure elements in solid poly-peroxometallate complexes. The equivalent uranyl sites in (UO(2))(2)(O(2))(2)(CO(3))(2-) suggest that the uranyl-units are linked by the carbonate ion and not by peroxide.     

RP-HPLC study of redox equilibria in vanadium-PAR binary and ternary systems: Direct determination of vanadium in steel

The reversed-phase high-performance liquid Chromatographic (RP-HPLC) behaviour of the binary chelates of V(V) and V(IV) with 4-(2-pyridylazo) resorcinol (PAR) and ternary chelates of vanadium with PAR and auxiliary ligands: hydrogen peroxide, hydroxylamine, tartrate and citrate were studied using a C₁₈ column. The complex double-peak chromatograms of V(IV)/V(V)-PAR systems were studied and the origin of each peak was proved. Vanadium in ternary systems with PAR and hydrogen peroxide was found exclusively in V(V)-H₂O₂-PAR complex (single peak on the chromatogram) despite its initial oxidation state. The double role of hydroxylamine (complex agent and reductor) in vanadium systems with PAR was confirmed: in the V(V) system three species were identified (V(V)-PAR, V(V)-NH₂OH-PAR and V(IV)-PAR), but in the V(IV) system only two: V(IV)-PAR and V(V)-NH₂OH-PAR. Citrate and tartrate giving single peak were found as auxiliary ligands in ternary V(V) systems of analytical importance. Due to its masking potential towards iron (III) ions, citrate was chosen as the most suitable third component of a ternary vanadium system with PAR, to form the basis of an RP-HPLC method for direct determination of V in steel.     

Chemical binding in ternary chalcogenides AiBIIIC 2 VI

The semiconductors a^IB^IIIc ₂ ^Vi (A^I = Cu, Ag; B111 = Ga, In; CVI = 5, Se) have found wide use in quantum electronics and nonlinear optics. Some of them show great promise as materials for solar batteries. The valence and vacant states of the components of A^IB^IIIC ₂ ^VI were studied experimentally (SK X-ray emission and absorption spectra in sulfides) and theoretically using the cluster version of the local coherent potential. For this study, experimental literature data are used. The calculations were performed with inclusion of the d states of the noble metal lying at the top of the valence band and determining the nature of the chemical bond (p— d hybridization). Also included is the structural factor (anion shift from the equilibrium positions in a sphalerite structure), whose effect on the forbidden gap E_g is comparable to that of p— d hybridization. Lattice parameters a and c and anion shifts u are calculated in terms of Jaffe and Zunger theory using Pauling's tetrahedral radii. The calculated density of state curves agree well in shape and satisfactorily in energy with the corresponding X-ray and X-ray photoelectron spectra. Our results confirm that Bragg's idea on transferability and conservation of elementary bonds is applicable to the compounds under study. The estimated forbidden gaps Eg proved to be close to the experimental ones to an accuracy of approximately 0.2 eV for all compounds A^IB^IIIC ₂ ^VI . Translated fromZhurnal Strukturnoi Khimii, Vol. 41, No. 3, pp. 515-524, May–June, 2000.     

U(VI) uranyl cation-cation interactions in framework germanates

The isomorphous compounds NH(4)[(UO(6))(2)(UO(2))(9)(GeO(4))(GeO(3)(OH))] (1), K[(UO(6))(2)(UO(2))(9)(GeO(4))(GeO(3)(OH))] (2), Li(3)O[(UO(6))(2)(UO(2))(9)(GeO(4))(GeO(3)(OH))] (3), and Ba[(UO(6))(2)(UO(2))(9)(GeO(4))(2)] (4) were synthesized by hydrothermal reaction at 220 °C. The structures were determined using single crystal X-ray diffraction and refined to R(1) = 0.0349 (1), 0.0232 (2), 0.0236 (3), 0.0267 (4). Each are trigonal, P(3)1c. 1: a = 10.2525(5), c = 17.3972(13), V = 1583.69(16) ?(3), Z = 2; 2: a = 10.226(4), c = 17.150(9), V = 1553.1(12) ?(3), Z = 2; 3: a = 10.2668(5), c = 17.0558(11), V = 1556.94(15) ?(3), Z = 2; 4: a = 10.2012(5), c = 17.1570(12), V = 1546.23(15) ?(3), Z = 2. There are three symmetrically independent U sites in each structure, two of which correspond to typical (UO(2))(2+) uranyl ions and the other of which is octahedrally coordinated by six O atoms. One of the uranyl ions donates a cation-cation interaction, and accepts a different cation-cation interaction. The linkages between the U-centered polyhedra result in a relatively dense three-dimensional framework. Ge and low-valence sites are located within cavities in the framework of U-polyhedra. Chemical, thermal, and spectroscopic characterizations are provided.     

Coordination environment of aqueous uranyl(VI) ion

Water dissociation from [UO2(OH2)5]2+ is studied with Car-Parrinello molecular dynamics simulations (using the BLYP density functional) in the gas phase and in aqueous solution. Free energies, DeltaA, are estimated from pointwise thermodynamic integration using one U-O(H2) distance as a reaction coordinate. While an isomeric, four-coordinate complex, [UO2(OH2)4]2+.H2O, is more stable than the five-coordinate reactant in the gas phase (DeltaA = -2.2 kcal/mol), the former is strongly disfavored in water (DeltaA = +8.7 kcal/mol).     

Phase diagrams for ternary systems having clathrate hydrates and vapor-liquid equilibria (simulation and experiment)

Models of T-x ₁-x ₂ phase diagrams where binary and ternary intermediate phases of stoichiometric or variable composition are formed by vapor-liquid syntectic reactions were considered. Phase transformation schemes for such the systems are presented, as well as vertical sections and isothermal sections in various interinvariant ranges.     

Calculating binary and ternary multiphase equilibria: extensions of the integral area method

The area method was proposed in 1992 to calculate binary and ternary 2-phase equilibria. In its integral form, the method provides both the necessary and sufficient conditions required for the determination of the global minimum reduced Gibbs energy of mixing (Φ). The method has since been applied to the calculation of both pure component and ternary multiphase equilibria in a differential form. However, the extension of the original (2 point) integral area method to the direct calculation of both binary and ternary multiphase equilibria has not been completed. Direct 3 point and modified 2 point search methods have therefore been developed here and used to estimate the phase compositions of a representative binary vapour-liquid-liquid system. The 2 point area method principle has been extended and applied to the calculation of ternary multiphase equilibria using a net volume approach. However, this volume method was found to fail due to an underlying inconsistency in the bounding of the integrated Φ surface by the trial 3-phase region. A new method is proposed that overcomes this problem by minimising the area of intersection between a tangent plane and the Φ surface. This new method has successfully calculated the 3-phase compositions of two simple test systems from a variety of initial mixture starting points.     

Isothermal (vapour + liquid) equilibria in the binary and ternary systems composed of 2-propanol, 2,2,4-trimethylpentane,and 2,4-dimethyl-3-pentanone

(Vapour + liquid) equilibrium data in the three binary (2-propanol + 2,2,4-trimethylpentane), (2-propanol + 2,4-dimethyl-3-pentanone), (2,2,4-trimethylpentane + 2,4-dimethyl-3-pentanone) systems, and in the ternary (2-propanol + 2,2,4-trimethylpentane + 2,4-dimethyl-3-pentanone) system are reported. The data were measured isothermally at (330.00 and 340.00) K covering the pressure range (8 to 70) kPa. The binary (vapour + liquid) equilibrium data were correlated using the Wilson and NRTL equations by means of a robust algorithm for processing all isotherms together; resulting parameters were then used for calculation of phase behaviour in the ternary system and for subsequent comparison with experimental data. Azeotropic behaviour of the (2-propanol + 2,2,4-trimethylpentane) system was evaluated together with all available published data.