Radiation-Chemical Resistance of Anion Exchangers and Safety of Sorption Processes in Nitric Acid Solutions: IV. Thermal Gravimetric Study of VP-1AP Anion Exchanger in Nitrate Form

Thermal gravimetric analysis of the samples of VP-1AP anion exchanger in sulfate and nitrate forms was carried out. In the derivatograms of the anion exchanger in the nitrate form there are one endothermic and two exothermic peaks (100, 160-180, and 200-220°C). Heating of dry samples of VP-1AP anion exchanger in the nitrate form at 130-230°C induces oxidative degradation of the sorbent matrix with participation of nitrate ions. In the presence of products of anion exchanger degradation and sorbed HNO₃ in the anion exchanger phase, the weight loss of the samples abruptly increases at temperatures of approximately 180-190°C. The action of ionizing radiation strongly affects the heat resistance of the anion exchanger. At absorpbed dose of 5 MGy the first exothermic peak is shifted by 15-20°C; in this case, both exothermic peaks coalesce and the oxidation can be considered as single-stage process starting at 110°C.     

Radiation-Chemical Resistance of Anion Exchangers and Safety of Sorption Processes in Nitric Acid Media: V. Thermochemical Degradation Dynamics of VP-1AP Anion Exchanger

Thermal degradation of VP-1AP anion exchanger and its mixtures with HNO₃ was studied in open vessels at 40 to 260°C. The anion exchanger ignites only after drying and heating to 220-260°C. Heating VP-1AP mixtures with 3-12 M HNO₃ to 100°C is accompanied by gas evolution at a rate of 0.6 l min^-1 (lsorb)^-1. Removal of the aqueous phase from the mixtures at 130-170°C initiates intensive oxidation. It is accompanied by a temperature jump in the sorbent phase and by gas evolution acceleration and can be regarded as thermal explosion. Mixture preheating and irradiation reduce the thermal explosion "onset" temperatures.     

Radiation-Chemical Resistance of Anion Exchangers and Safety of Sorption Processes in Nitric Acid Solutions: II. Study of Gas Liberation in Systems Ion Exchanger-HNO3

Gas liberation in systems ion exchanger-nitric acid solution in open and closed vessels under the action of elevated temperature and ionizing radiation is studied. Preliminary data on the detonation properties of VP-1AP anion-exchange resin are given. No considerable gas liberation is observed in the system in the presence of the liquid phase, but explosive thermochemical degradation of the sorbent can occur as a result of drying of the sorbent phase. Elevated temperature and ionizing radiation increase the probability of this process.     

Recovery of Pd from Spent Fuel: 2. Sorption Recovery of Pd from Nitric Acid Solutions on Anion-Exchange Resins

Recovery of Pd from nitric acid solutions on various anion-exchange resins is studied. The effects of the HNO₃ concentration, temperature, and aminoacetic acid on the desorption of Pd are examined. Results of the experiments on Pd recovery from actual solutions from spent fuel reprocessing are reported.__________Translated from Radiokhimiya, Vol. 47, No. 4, 2005, pp. 339–342.Original Russian Text Copyright © 2005 by Korolev, Pokhitonov, Gelis, Milyutin.     

Recovery of Pd from Spent Fuel: 1. Electrochemical Recovery of Palladium from Nitric Acid Solutions

The rate of cathodic deposition of palladium from nitrate solutions at a platinum electrode and the current efficiency of the process were studied as influenced by the concentrations of nitric acid, NaNO₃, U, and other admixtures. In the range of potential E from +0.5 to +0.25 V, the rate of Pd deposition from 1 M HNO₃ solution was 0.7–0.9 mg cm⁻² at current efficiency of about 70%. The degree of palladium recovery by cathodic deposition is more than 99% with the coefficient of separation from α- and β-emitting nuclides of 10²–10³.__________Translated from Radiokhimiya, Vol. 47, No. 4, 2005, pp. 334–338.Original Russian Text Copyright © 2005 by Kirshin, Pokhitonov.     

Extraction of Am(III) and Rare-Earth Elements from Nitric Acid Solutions with (Diphenylphosphinylmethyl)phenylphosphinic Acid

Extraction of microamounts of Am, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu nitrates from aqueous HNO₃ with solutions of (diphenylphosphinylmethyl)phenylphosphinic acid in dichloroethane was studied. The stoichiometry of the extractable complexes was determined. Synergistic enhancement of the extraction of rare-earth elements in the presence of tetraphenylmethylenediphosphine dioxide was revealed.     

Redox Reactions of Platinum Elements: XV. Kinetics of Rhodium(III) Oxidation with Xenon Difluoride in Nitric Acid Solutions

The rate of the reaction 2Rh(H₂O)₆ ^{3 +} + XeF₂ = 2Rh(OH)₃ ⁺ + Xe + 2HF + 4H⁺ + 6H₂O is described by the second-order equation -d[Rh(III)]/dt = k ₁[Rh(III)][XeF₂], where k ₁ = 15.4±0.8 l mol^-1 min^-1 at 17.8°C and the solution ionic strength = 2. The activation energy of the reaction is E ₁ = 60.6±1.0 kJ mol^-1. This reaction is complicated by the parallel hydrolysis reaction 2XeF₂ + 2H₂O = 2Xe + O₂ + 4HF. The reaction mechanism includes a slow stage of H atom transfer from Rh(H₂O)₆ ³⁺ to XeF₂ molecule with formation of XeF^. radical as an intermediate. The subsequent stages of Rh(H₂O)₅(OH)³⁺ hydrolysis and reduction of XeF^· radical to Xe proceed rapidly.     

Extraction of Am(III) and Lanthanides from Nitric Acid Solutions with Polyfunctional Organophosphorus Acids

Extraction of microamounts of Am, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu nitrates from aqueous HNO₃ with solutions of (diphenylphosphinylmethyl)phenylphosphinic, (di-p-tolylphosphinylmethyl)phenylphosphinic, (di-p-anisylphosphinylmethyl)phenylphosphinic, and (dioctylphosphinylmethyl)phenylphosphinic acids and of butyl hydrogen (diphenylphosphinylmethyl)phosphonate in toluene was studied. The metal : extractant ratio in the extractable species was determined.     

Extraction of Am(III) and Rare-Earth Elements from Nitric Acid Solutions with Dibutyl Diphenylphosphinylmethylphosphonate

Extraction of HNO₃ and trace amounts of Am, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu nitrates from aqueous HNO₃ with solutions of dibutyl diphenylphosphinylmethylphosphonate in dichloroethane was studied. The stoichiometry of the extractable solvates was determined, and the apparent extraction constants were calculated.     

Extraction of Am(III) and Eu(III) from Nitric Acid Solutions with Bidentate Neutral Organophosphorus Compounds

Extraction of HNO₃ and microamounts of Am and Eu from nitric acid solutions with solutions of bidentate butyl (phosphorylmethyl)phenylphosphinates R₂P(O)CH₂P(O)Ph(OBu) [R = octyl (I), phenyl (II), p-tolyl (III), p-anisyl (IV)] in 1,2-dichloroethane was studied. The stoichiometry of the extractable complexes was determined, and the apparent extraction constants were calculated. The extractive power of the reagents studied toward HNO₃ increases in the order II < III < IV < I, and toward Am(III), in the order I < II < III < IV.     

Specific Features of Electrochemical Oxidation of Pu(III) in a Diaphragmless Cell in Hydrazine-Containing Nitric Acid Solutions

Oxidation of Pu(III) in a diaphragmless cell with a Ti cathode and a Pt anode in 1.0–3.9 M HNO₃ solutions containing 4.5 × 10^?2–1.8 × 10^?1 M hydrazine was studied. The final solutions contain, along with Pu(IV), also a small amount of Pu(VI), increasing with an increase in the current density. Methods allowing minimization of the Pu(VI) amount in the solutions after the electrolysis were suggested. The possible process mechanism involving reactions of Pu ions at the electrodes and in the bulk of the solution with HNO₂ was considered.

     

Features of Electrolysis of Nitric Acid Solutions of Silver: I. Behavior of Ag(II) in HNO3 Solutions

The current efficiency of Ag(II) formation in the course of electrochemical oxidative dissolution of PuO₂ was determined. It approaches 72% at the anodic potentials from 1.9 to 2.1 V (vs. SHE) and the anodic current densities of 0.006-0.013 A cm^{- 2}. The behavior of Ag(II) in 4 M HNO₃ at 8, 25, and 40°C was studied. The reaction of Ag(II) with water can be described by the equation d[Ag(II)]/dt = kapp[Ag(II)] ⁿ , where n 2 at 8-25°C and 2-1.5 at 39-41°C. The apparent rate constants of the reaction are 1.5 and 3.8 l mol^{- 1} min^{- 1} at 8.5°C and 25°C, respectively. At 39-41°C, the reaction order with respect to Ag(II) ranges from 2 to 1.5, and the rate constant is about 1.2 l^{1 / 2} mol^{- 1 / 2} min^{- 1}.     

Modeling of the Activities of Uranyl Nitrate and Nitric Acid in Mixed Solutions

Molal activity coefficients of uranyl nitrate and nitric acid in mixed solutions were calculated on the basis of Mikulin’s equations. Analytical equations for calculating these quantities at different concentrations were obtained. These equations are compatible with published activity coefficients for binary solutions, which allows their use for calculating the equilibria in uranium extraction from nitric acid solutions.     

Extraction of Scandium from Various Media with Triisoamyl Phosphate: 1. Extraction of Sc and Impurity Metals from Aqueous Nitric Acid Solutions

The main features of extraction of Sc from aqueous nitric acid solutions with triisoamyl phosphate (TIAP) were studied. It was shown that Sc passes into the organic phase in the form of Sc(NO₃)₃·3TIAP. The extraction isotherms of Sc from its aqueous HNO₃ solutions and from those containing salting-out agents (LiNO₃, NH₄NO₃) with TIAP in dodecane were obtained. The distribution factor of Sc was studied in relation to the concentrations of TIAP, salting-out agent, and HNO₃. The extraction of Sc and impurity metals (Zr, Th, REE) with TIAP was studied at widely varied HNO₃ concentration in the aqueous phase. The separation factors of Sc from impurity metals were determined.     

Separation of REE(III) and Am(III) by Extraction with Compounds of Zirconium and Dibutyl Phosphoric Acid from Solutions of Nitric and Hydrochloric Acids

Radiochemistry - The behavior of rare-earth elements (REE) and americium during their extraction with compounds of zirconium and dibutyl phosphoric acid (DBPA) in various solvents from solutions of...     

Extraction of REE(III), U(VI), and Th(IV) from Nitric Acid Solutions with Carbamoylmethylphosphine Oxides in the Presence of Dinonylnaphthalenesulfonic Acid

The extraction of REE(III), U(VI), and Th(IV) from nitric acid solutions with solutions of carbamoylmethylphosphine oxides (CMPOs) considerably increases in the presence of dinonylnaphthalenesulfonic acid. The stoichiometry of the extractable complexes was determined, and the influence of the aqueous phase composition, kind of organic diluent, and CMPO structure on the efficiency of the extraction of the metal ions was analyzed.     

Recovery of Pd from Spent Fuel: 4. Precipitation of Pd from Nitric Acid Solutions with Hydrazine and CO

Precipitation of palladium with hydrazine and CO from nitric acid solutions simulating process solutions formed in regeneration of spent nuclear fuel was studied. The influence of various factors on the degree of palladium recovery was studied. From 1.0–4.0 M HNO₃ solutions, 50–90 and 70–98% of Pd is precipitated with hydrazine and CO, respectively. Palladium recovery from simulated and real solutions formed in processing of spent nuclear fuel was studied. The decontamination factor of palladium with respect to most of elements including radionuclides was 10²–10³.__________Translated from Radiokhimiya, Vol. 47, No. 4, 2005, pp. 347–350.Original Russian Text Copyright © 2005 by Gevirts, Zelentsova, Kozlov, Kolobov, and Pokhitonov.     

Thermochemical Oxidation of Components of Extraction Solutions and Threshold Conditions of Thermal Explosion: 4. Kinetics of Reaction of TBP Solutions in Dodecane with Nitric Acid

The reaction of 30% solutions of TBP in dodecane with HNO₃ at the initial concentration of the acid of 1.4 M was studied in the temperature range 75-150°C. The kinetic parameters of acid consumption, gas evolution, and accumulation of liquid-phase products were determined. The effect of -preirradiation on the kinetics of oxidation processes was studied. From the kinetic data the threshold temperature conditions for transformation of oxidation processes into the thermal explosion were estimated and the presumable mechanism of initiation and development of oxidation reactions was discussed.     

Extractive Properties of P,P'-Di(2-ethylhexyl) Dihydrogen 1-Hydroxyethane-1,1-diphosphonate in Nitric Acid Solutions

Extraction of microamounts of U(VI), Th(IV), Am(III), and rare-earth elements from aqueous HNO₃ solutions with solutions of P,P'-di(2-ethylhexyl) dihydrogen 1-hydroxyethane-1,1-diphosphonate in organic diluents was studied. The stoichiometries of the extractable complexes were determined, and the effect of organic diluent on the extraction was considered. P,P'-Di(2-ethylhexyl) dihydrogen 1-hydroxyethane-1,1-diphosphonate extracts Am(III) more efficiently than does P,P'-di(2-ethylhexyl) dihydrogen methanediphosphonate.     

Recovery of Pd from Spent Fuel: 3. Recovery of Pd from Nitric Acid Solutions Using Carbamoyl Phosphine Oxides

Extraction and sorption recovery of Pd from nitric acid solutions with extractants containing carbamoyl phosphine oxides (CMPO) was studied. The Pd distribution coefficients under different extraction conditions were determined. The possibility of Pd recovery in the course of spent nuclear fuel processing was demonstrated. A number of solid extractants composed of carbamoyl phosphine oxides and inert matrices (styrene-divinylbenzene polymer and silica gel) were tested. The Pd distribution coefficients in the course of sorption and desorption under the static and dynamic conditions were measured.__________Translated from Radiokhimiya, Vol. 47, No. 4, 2005, pp. 343–346.Original Russian Text Copyright © 2005 by Zaitsev, Kvasnitskii, Korolev, Babain, Pokhitonov.