[en] Kinetics of Pu⁵⁺ disproportionation in nitric acid solutions of oxalic acid is studied spectrophotometrically at 10-30 deg C and ionic strength of 2.0 mol/l (KNO₃+HNO₃). It is shown that at concentrations of HNO₃ and H₂C₂O₄ equal to 1.0-2.0 and (0.5-5.0)·10^-2 mol/l respectively the rate of the reaction in specified by disproportionation of PuO₂⁺ ions, uncombined in complexes. Disproportionation is catalyzed by H⁺ ions. The reaction of Pu³⁺ accumulation in this case is excluded at the expense of Pu⁴⁺ binding in a monooxalate complex. The value of the true constant of Pu⁴⁺ disproportionation rate found at 25 deg C is equal to 0.142±0.004 l²/mol².min

[en] The kinetics of the isotopic exchange between Pu(III) and PU(IV) in 7.5 M HNO₃ solutions, as well as in the presence of the macroporous anion exchanger VP-1AP and TBP have been studied by α-spectrometry. It is shown that in the system containing VP-1AP the rate of isotopic exchange is first-order with respect to Pu(III) and Pu(IV) concentrations and is independent of the particle size of the resin. The rate constant k for isotopic exchange in the system at 25⁰C is 4.5 +/- 0.4 liter/mole x sec (ΔH = 40 +/- 5 kJ/mole x deg; ΔS = -97 +/- 32 kJ/mole x deg). The values of k in the homogeneous solutions and in the system containing TBP are 4.3 +/- 0.7 and 4.4 +/- 0.5 liter/mole x sec respectively. It is postulated that the limiting stage of the reaction in the heterogeneous systems containing the anion exchanger and TBP is isotopic exchange in solution

[en] Kinetic isotope effects of ²⁴³Am/²⁴¹Am isotope pair in reaction of ligand exchange (LE) between AmX₂^17-complex, where x=P₂W₁₇O₆₁, and ethylenediaminetetraacetic acid (H₄A) were investigated by spectrophotometric method at 25 deg C. LE kinetics in CeX₂^17- - H₄A system was studied as model reaction. It is shown that Am³⁺ complexes enter LE reaction in half the time, than Ce³⁺, and ²⁴³Am³⁺ complexes exchange quicker, than ²⁴¹Am³⁺ at that

No abstract available

[en] By the method of α-spectrometry kinetics of isotopic exchange between Pu⁴⁺ and Pu³⁺ in nitric acid solutions in the presence of tributylphosphate, dicyclohexyl-18-crown-6 and tenoyltrifluoroacetone, applied on hydrophobizated silica gel, as well as TBP solid extractant, has been studied. It is shown that in the presence of extractants applied on silica gel isotopic exchange in solution is the threshold stage, and in system with solid extractant-diffusion inside polymeric matrix. Kinetic parameters of isotopic exchange are calculated

[en] Spectrophotometry at 25 deg C and ionic force μ=1.0 mol/l (KNO₃+HNO₃) was used to show that at HNO₃ concentration 0.1-1.0 mol/l H₂C₂O₄ introduction to nitric acid solutions of Np⁵⁺ in the presence of nitrite-ion resulted in the shift of equilibrium between Np⁵⁺ and Np⁶⁺ to the side of Np⁶⁺ accumulation. The presence of H₂C₂O₄ at HNO₃ concentration > 1.0 mol/l doesn't affect the equilibrium position. The values of nominal equilibrium constant at different HNO₃ and H₂C₂O₄ concentrations were calculated. It was found that isotope exchange (²³⁹Np/²³⁷Np) between Np⁵⁺ and Np⁶⁺ in oxalate solutions proceeded more slowly than in oxalate absence. Rate constants of isotope exchange calculated at 9 deg C, μ=1.0 mol/l (KNO₃), H₂C₂O₄ concentration 0.01 mol/l and pH=2.2 and 3.5 are equal to 0.49x10³ and 0.67x10² l/mol·min respectively. Mechanism of isotope exchange including electron transport between Np⁵⁺ and Np⁶⁺ oxalate complexes is suggested

[en] Kinetics of uranium (4) oxidation with nitrous acid in the presence of oxalate-ions are studied spectrometrically. It is shown that even at small oxalate concentrations a notable effect of tetravalent uranium stabilization is observed relatively to the oxidation with nitrous acid. In case of a significant excess of oxalate-ions the oxidation rate will be considerably slower as a result of the formation of U(4) bisoxalate complex

[en] Short note

[en] Kinetics of isotope exchange (²³⁹Pu/²⁴²Pu) between Pu⁴⁺ and Pu³⁺ in hydrochloric acid and sulfate solutions was studied using α-spectrometry for the purpose of investigating the mechanism of electron transfer reaction in Pu⁴⁺-Pu³⁺ system in the presence of chloride- and sulfate-ions. It is shown that the rate of isotope exchange decreases with increase of Cl^- concentration and the dependence of exchange rate on sulfate concentration is described by the curve with maximum at Li₂SO₄ concentration equal to 0.2-0.4 mol/l. It is assumed that exchange in hydrochloric acid media is proceeds between aquacomplexes of Pu³⁺ and Pu⁴⁺. Sulfate complexes of Pu³⁺ and Pu⁴⁺ participate in exchange along with aquacomplexes in sulfate solutions. Rate constants and activation parameters of corresponding processes were calculated. The model describing kinetics of isotope exchange in studied systems is suggested

[en] Kinetic isotope effect for ^242/238Pu and ^240/238Pu isotopes was studied in the reaction of Pu⁵⁺ disproportionation in the presence of HDEHP or triisoamylphosphinoxide, applied on hydrophobizated silica gel or polysorb. It is shown that the value of elementary coefficient of isotope separation does not depend on the nature of extractant and carrier, and for ^242/238Pu and ^240/238Pu it is 1.023-1.029 and 1.008-1.011 respectively