Calorimetric studies on the thermal decomposition of tri n-butyl phosphate-nitric acid systems

Thermal decomposition of neat TBP, acid-solvates (TBP·1.1HNO₃, TBP·2.4HNO₃) (prepared by equilibrating neat TBP with 8 and 15.6?M nitric acid) with and without the presence of additives such as uranyl nitrate, sodium nitrate and sodium nitrite, mixtures of neat TBP and nitric acid of different acidities, 1.1?M TBP solutions in diluents such as n-dodecane (n-DD), n-octane and isooctane has been studied using an adiabatic calorimeter. Enthalpy change and the activation energy for the decomposition reaction derived from the calorimetric data wherever possible are reported in this article. Neat TBP was found to be stable up to 255?°C, whereas the acid-solvates TBP·1.1HNO₃ and TBP·2.4HNO₃ decomposed at 120 and 111?°C, respectively, with a decomposition enthalpy of ?495.8?±?10.9 and ?1115.5?±?8.2?kJ?mol^?1 of TBP. Activation energy and pre exponential factor derived from the calorimetric data for the decomposition of these acid-solvates were found be 108.8?±?3.7, 103.5?±?1.4?kJ?mol^?1 of TBP and 6.1?×?10¹⁰ and 5.6?×?10⁹?S^?1, respectively. The thermochemical parameters such as, the onset temperature, enthalpy of decomposition, activation energy and the pre-exponential factor were found to strongly depend on acid-solvate stoichiometry. Heat capacity (C _p ), of neat TBP and the acid-solvates (TBP·1.1HNO₃ and TBP·2.4HNO₃) were measured at constant pressure using heat flux type differential scanning calorimeter (DSC) in the temperature range 32?C67?°C. The values obtained at 32?°C for neat TBP, acid-solvates TBP·1.1HNO₃ and TBP·2.4HNO₃ are 1.8, 1.76 and 1.63?J?g^?1?K^?1, respectively. C _p of neat TBP, 1.82?J?g^?1?K^?1, was also measured at 27?°C using ??hot disk?? method and was found to agree well with the values obtained by DSC method.     

Study on Properties of TBP-HNO3 Complex Used for Direct Dissolution of Lanthanide and Actinide Oxides in Supercritical Fluid CO2

The tri-n-butyl phosphate-nitric acid （TBP-HNO3） complex prepared by contacting the pure TBP with the concentrated HNO3 can be used for direct dissolution of lanthanide and actinide oxides in the supercritical fluid carbon dioxide （SCF-CO2）. Properties of the TBP-HNO3 complex have been studied. Experimental results showed that when the initial HNO3/TBP volume ratio was varied from 1 ： 7 to 5 ： 1, the concentration of HNO3 in the TBP-HNO3 complex changed from 1.95 to 5.89 mol/L, the [HNO3]/[TBP] ratio of the TBP-HNO3 complex changed from 0.61 to 2.22, and the content of H20 in the TBP-HNO3 complex changed from 2.02% to 4.19%. All of the density, viscosity and surface tension of the TBP-HNO3 complex changed with the concentration of HNO3 in the complex, and were higher than those of the pure TBE The protons of HNO3 and H2O in the complex underwent rapid exchange to exhibit a singlet resonance peak in nuclear magnetic resonance spectra. When the TBP-HNO3 complex was dissolved in a low dielectric constant solvent, small droplets of HNO3 were formed that can be detected by NMR.     

Kinetics of reductive stripping of Pu(IV) in the tributylphosphate-kerosene/nitric acid-water system using dihydroxyurea

The kinetics of the reductive stripping of plutonium(IV) by dihydroxyurea (DHU) in 30% TBP/kerosene-HNO₃ system was studied with a constant interfacial area cell. The stripping rate of plutonium(IV) increases with the increase of the stirring speed of two phases and the interfacial area. The activation energy of this process is 28.4 kJ/mol. Under the given experimental conditions, the mass transfer of Pu is not controlled by redox reaction, but controlled by molecular diffusion from the organic phase to organic film layer and from the aqueous film layer to aqueous phase. The rate equation of reductive stripping (process is controlled by diffusion) was obtained as: r ₀ = k′[Pu(IV)]₀[DHU]_a ^0.16[HNO₃]_a ^−0.34. The rate constant k′ is (5.0±0.4)·10⁻² (mol/L)^0.18·min⁻¹ at 18.0°C.     

Extraction chemistry of uranyl nitrate and nitric acid in high concentration systems

HNO₃ is extracted in significant quantities by uranyl nitrate solvates with different extractants: TBP (tributyl phosphate), TOPO (trioctyl phosphine oxide) and TDA (tetradecyl ammonium). The effect of diluent nature is not observed on extracting HNO₃ and TBP saturated by uranium at equilibrium with its salt using the diluents (CCl₄, C₆H₅Cl, C₁₂H₂₆, CHCl₃) which are less polar than UO₂(NO₃)₂(TBP)₂. HNO₃ occurs in organic phase as undissociated form and its state is similar to pure anhydrous HNO₃. Solvates of TBP and TDA with uranyl nitrate dissolve HNO₃ without displacement of uranium from organic phase.     

N235萃取HCl体系中TBP消除第三相的作用机理

通过测定萃取有机相的电导率变化研究叔胺N₂₃₅(三烷基胺)萃取盐酸体系中第三相的形成及改性剂消除第三相的作用机理。实验结果表明，无改性剂时萃取体系在各种条件下均出现第三相。第三相组成为R₃NH⁺(H₂O)₃·Cl^-，具有导电性。加改性剂TBP(磷酸三丁酯)后，第三相消失。本文认为改性剂TBP消除第三相的作用机理是TBP能够将萃合物R₃NH+(H₂O)₃·Cl^-拆分为可溶于惰性稀释剂的R₃NH⁺(H₂O)₃·O=P(OC₄H₉)₃大阳离子，Cl^-离子则以抗衡离子分散于稀释剂中。     

Thermoanalytical investigation of the synthesis of pyrazine and bipyrazine via the pyrolysis of the bis(pyrazinecarboxylate)copper(II) complex

The pyrolysis of hydrated bis(pyrazinecarboxylate)copper(II) under an argon atmosphere proceeds via the loss of the water molecules at 84–95°C, ΔH=40.4 kJ (mol H₂O)^?1 followed by the thermal decomposition of the complex at 284–325°C, ΔH=97.0 kJ·mol^?1, yielding 0.72 mole of pyrazine, 0.28 mole of bipyrazine, and 2 mole of CO₂ per mole of complex.     

Polarographic waves of tri-n-butyl phosphate and polarographic determination of uranium in the presence of tri-n-butyl phosphate

The results of a study on the polarographic behaviour of TBP and its influence on the determination of uranyl ions is presented. The half-wave potential of the adsorption wave of TBP depends on the concentration of TBP, type of supporting elec trolyte and its concentration. In the presence of TBP the polarographic wave of U(VI) ion is changed. Below 7·10^?5 M TBP the polarographic wave of U(VI) is not affected, between 7·10^?5 and 2·10^?4 M TBP the shape, height and half-wave potential of U(VI) waves are changed and above 2·10^?4 M, up to saturated solution of TBP, the waves of U(VI) do, not change further. The bes supporting electrolytes for the determination of U(VI) are KNO₃ or NaClO₄ in concentrations of 0.1 to 0.5 M, pH 1–2 and TBP concentrations from 3·10^?4 to 1.2·10^?3 M.     

Microwave-assisted dissolution of ceramic uranium dioxide in TBP–HNO3 complex

Microwave-assisted dissolution of ceramic uranium dioxide in tri-n-butyl phosphate (TBP)–HNO₃ complex was investigated. The research on dissolution of ceramic uranium dioxide in TBP–HNO₃ inclusion complex under microwave heating showed the efficiency of the use of this method. Nitric acid present in the inclusion complex participates both dissolution of UO₂, and oxidation of U(IV)–U(VI), the resulting UO₂(NO₃)₂ extracted with tri-n-butyl phosphate. Dissolution rate depends on both temperature of microwave dissolution process, and concentration of nitric acid present in the inclusion complex. The most intensive dissolution process is when the concentration of nitric acid ≥2 mol/L and the temperature of 120 °C. From the experimental data obtained by two kinetic models activation energies were calculated. At the average activation energy of UO₂ dissolution in TBP–HNO₃ complex equal 70 kJ/mol, and reaction order is close to one, i.e. the reaction takes place in an area close to kinetic.     

Extraction of pertechnetate anion as a ligand in metal complexes with tributylphosphate

The extraction of the pertechnetate anion has been investigated in the systems tributylphosphate (TBP)—solvent (carbon tetrachloride, n-heptane, chloroform)—metal salt (uranyl nitrate and chloride, thorium nitrate)—ammonium salt. In the absence of a metal, the solvates HTeO₄. iTBP (i=4) are extracted, while in the presence of uranium and thorium, the distribution of technetium corresponds to the formation of the mixed complexes: UO₂(NO₃)(TeO₄)·2TBP, UO₂Cl(TcO₄)·2TBP and Th(NO₃)₃ (TcO₁)·2TBP. The effective constants of the reactions H⁺+TcO ₄ ⁻ +i(TBP)_org←(HTcO₁·iTBP)_org, and (ML_n·2TBP)_org+TcO ₄ ⁻ ←(ML_n−1TcO₄·2TBP)_org+L were established in the above systems. The extraction of pertechnetate ion is more effective when it is coordinated to a cation solvated by TBP than the extraction in the form of pertechnetate acid solvated by TBP.     

NMR study of the interaction between water and tributyl phosphate in the TBP-CCl4-H2O system

Hydrogen bonding between water and tributyl phosphate (TBP) in TBP? CCl₄? H₂O system has been studied by ¹H NMR. A new model and an empirical equation have been established on the basis of Li's model and the parameters of hydrogen bond between water and TBP are determined by nonlinear optimization method. In TBP? CCl₄? H₂O system change of ¹H chemical shift of water can be satisfactorily explained by the new model and the empirical equation in the whole concentration range. When the concentration of water in the organic phase is very low, the main existing forms of water are H₂O · TBP and H₂O · 2TBP. When the concentration of water reaches saturation, the main existing form is associated water, but there are still about 20% of water existing in the forms of H₂O · TBP and H₂O · 2TBP.     

Radiolytic degradation of TBP-HNO3 system: Gas chromatographic determination of radiation chemical yields of n-Butanol and nitrobutane

Radiolytic degradation of the TBP-HNO₃ system has been studied for the radiation dose range of 19.8 to 262 kGy by the gas chromatographic method. n-Butanol and nitrobutane formed due to irradiation have been identified and estimated in pure TBP, TBP-3M HNO₃ extract and TBP-5M HNO₃ extract. The G-values (radiation chemical yields) of n-butanol are determined to be 0.28, 0.77 and 0.47 for a pure TBP, TBP-3M HNO₃ extract and TBP-5M HNO₃ extract, respectively. The G-values of nitrobutane (1-nitrobutane) are 0.55 and 1.09 for TBP-3M HNO₃ extract and TBP-5M HNO₃ extract. It is found than G(n-butanol) is less for TBP-5M HNO₃ extract than for TBP-3M HNO₃ extract, while G(nitrobutane) is grater for TBP-5M HNO₃ extract than for TBP-3M HNO₃ extract. This is explained on the basis of the formation of TBP.HNO₃ species and the role played by nitric acid in the TBP phase.     

Chemistry of NOx and HNO3 Molecules with Gas-Phase Hydrated O.− and OH− Ions

The gas-phase reactions of O ^{. −}(H₂O)_n and OH⁻(H₂O)_n, n=20–38, with nitrogen-containing atmospherically relevant molecules, namely NO_x and HNO₃, are studied by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and theoretically with the use of DFT calculations. Hydrated O ^{. −} anions oxidize NO ^. and NO₂ ^. to NO₂⁻ and NO₃⁻ through a strongly exothermic reaction with enthalpy of −263±47 kJ mol⁻¹ and −286±42 kJ mol⁻¹, indicating a covalent bond formation. Comparison of the rate coefficients with collision models shows that the reactions are kinetically slow with 3.3 and 6.5 % collision efficiency. Reactions between hydrated OH⁻ anions and nitric oxides were not observed in the present experiment and are most likely thermodynamically hindered. In contrast, both hydrated anions are reactive toward HNO₃ through proton transfer from nitric acid, yielding hydrated NO₃⁻. Although HNO₃ is efficiently picked-up by the water clusters, forming (HNO₃)_0–2(H₂O)_mNO₃⁻ clusters, the overall kinetics of nitrate formation are slow and correspond to an efficiency below 10 %. Combination of the measured reaction thermochemistry with literature values in thermochemical cycles yields ΔH_f(O⁻(aq.))=48±42 kJ mol⁻¹ and ΔH_f(NO₂⁻(aq.))=−125±63 kJ mol⁻¹.     

L'extraction des lanthanides et des actinides par les oxydes d'alkylphosphine : L'extraction del'acide nitrique par quelques dioxydes de diphosphine

The distribution of nitric acid between an aqueous phase of constant or variable ionic strength and a benzene solution of diphosphine dioxide can be explained by the following reactions H⁺_a+ NO_3^-a+ DiPO₀ ? D1PO·HNO₃₀ H⁺_a+ NO_3^-a+ DiPO·HNO₃₀ ? DiPO·2 HNO₃₀ At constant ionic strength, the stability constants K₁″ were determined for the complexes 1,1-DiPO·HNO₃ (98 ± 01 (M)^-1), 1,4-DiPO·HNO₃(44±3 (M)_-1) and 1,5-DiPO·HNO₃ (51 ± 1 (M)^-1). The constants K₁₁″ for the complexes 1,1-DiPO·2 HNO₃ and 1,5-DiPO.2 HNO₃ are respectively 035±001 (M)^-1 and 62 ±0.05 (M)^-1 at 25°. With an aqueous phase of variable ionic strength, values of K₁'=54±7 (M)^-2 for 1,5-D1PO.HNO₃ and K_II'=65 ± 04 (M)^-2 for 1,5-DiPO·2 HN0₃ were obtained     

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.     

Study on the synergic extraction of uranium(VI) with petroleum sulfoxides (PSO) and tri-n-butyl phosphate (TBP) mixture

The synergic extraction of uranium(VI) from nitric acid solution with petroleum sulfoxides (PSO) and tri-n-butyl phosphate (TBP) mixture has been studied. It has been found that maximum synergic extraction effect occurs if the molar ratio of PSO to TBP is two to three. The composition of the complex of synergic extraction is UO₂(NO₃)₂·TBP·PSO. The formation constant of the complex isK _PT=8.19. The effect of extractant concentration, nitric acid concentration, salting-out agent concentration and temperature on the extraction equilibrium of uranium(VI) was also studied.     

Solvent extraction of hafnium(IV) by TBP and topo from acidic organic-aqueous solutions

Tracer concentrations of Hf(IV) were extracted by 60% TBP solution in benzene from 5M HClO₄, 5M HCl, 6M HNO₃ and 8M H₂SO₄ solutions, and by 1·10^?4 M TOPO solution in benzene from 2M HClO₄ and 2M HCl solutions in the presence of a variety of organic solvents miscible with the aqueous phase. Whereas for TBP these solvents caused an increase of HF(IV) extraction, an opposite effect was observed for TOPO. The results were discussed from the point of view of various solute-solvent and solvent-solvent interactions.     

Extraction liquide-liquide par des esters alkylphosphoriques. II. Extraction des nitrates de béryllium et des autres alcalino-terreux par le tri-n-butylphosphate

The solvent extraction systems Be(NO₃)₂? HNO₃? H₂O? TBP/kerosene and M(NO₃)₂? H₂O? TBP/kerosene (TBP = tri-n-butylphosphate, M = Be, Mg, Ca and Sr) have been studied. The alkaline earths elements are poorly extracted. Only very high acidities allow better extraction of beryllium. The sequence of extraction of the alkaline earths elements by the TBP depends on the concentration of the cations and is Ca > Be > Sr > Mg if the metal concentration is lower than 2 M.     

Radiation-induced decomposition of the tributyl phosphate-nitric acid system: Role of nitric acid

Radiation-induced decomposition of tributyl phosphate-nitric acid as a two-component system has been studied. Degradation products, dibutylphosphoric acid (DBP) and monobutylphosphoric acid (MBP), were determined by separation-extraction method. 0.59, 0.78 and 1.38 are the G (DBP) values and 0.15, 0.17 and 0.13 are the G (MBP) values obtained for pure TBP, TBP-3M HNO₃ extract and TBP-5M HNO₃ extract, respectively. G (–HNO₃) values are 5.19 and 6.15 for 3M HNO₃ and 5M HNO₃ extracts. It is shown that nitric acid plays a significant role in enhancing the decomposition of TBP.     

Direct dissolution of intact UO<Subscript>2</Subscript> pellet and in situ extraction by organic solutions of TBP-HNO<Subscript>3</Subscript> at atmospheric pressure: role of solvate composition

Recently authors demonstrated direct dissolution of g-level PHWR UO₂ fuel pellet fragments and in situ extraction by TBP-HNO₃ and TiAP-HNO₃ solutions at atmospheric pressures. Extending the work, similar studies were performed on intact unirradiated PHWR UO₂ fuel pellets (~15 g U) with varying compositions of organic solvate of tri-n-butyl phosphate (TBP). It was observed that extent of dissolution was a strong function of organic solution composition TBP·(HNO₃) _x (H₂O) _y . Complete dissolution of intact UO₂ pellet in a reasonable time was observed only in case of a particular solvate composition.     

Uptake of some lanthanides on γ-zirconium phosphate-phosphite and its 1,10-phenanthroline and 2,2-bipyridyl intercalated products

γ-Zirconium phosphate-phosphite, γ-Zr·PO₄·H₂PO₃·2H₂O, (γ-ZrPP), was prepared and characterized. Direct treatment of γ-zirconium phosphate-phosphite with an ethanol solution of 0.1M 1,10-phenanthrolin and 2,2'-bipyridyl gave the well defined composites, γ-Zr·PO₄·H₂PO₃(phen)_0.15·H₂O and γ-Zr·PO₄·H₂PO₃(bipy)_0.18·0.6H₂O respectively.K _d values of a mixture of lanthanide ions: La³⁺, Sm³⁺, Eu³⁺ and Yb³⁺ for the intercalated products and for γ-ZrPP in HNO₃ solution at room temperature and at pH 2 and 4 were determined by a radiotracer technique.¹⁴⁰La,^152mEu,¹⁵³Sm and¹⁷⁵Yb radioisotopes were used for the equilibration experiment using 500 μl (4.0·10⁻⁵ mmole) each of the solutions of the tracers as a mixture in 7.5 M HNO₃ solution at the desired pH with 0.1 g of γ-ZrPP and of the intercalated products. The selectivity order was found to be dependent on the nature of the ligand and on the pH. The 2,2'-bipyridyl product posseses, at pH 2 in general, a highK _d value, specially for Sm³⁺ (9815.9) compared to that of the 1,10-phenanthrolin product (3375.5) and to γ-ZrPP (419.8). This could be attributed to partial deintercalation of the 2,2'-bipyridyl at pH 2 and increasing of ionogenic groups.