Volume 67, Nº 1 (2025)

The reaction of nitric acid with formic acid, including uranium-containing solutions, was studied. Empirical equations for the dependence of the induction period duration (τ) on the concentrations of reagents and temperature were determined. The dependence of τ on the concentration of formic acid is exponential. The effect of uranium concentration on τ in denitrated solutions becomes noticeable only at temperatures lower than 60°C. The main factor affecting the completeness of denitration is the molar ratio [formic acid] : [NO₃]¯. Starting with the molar ratio of ≥3, uranium-containing solutions are denitrated at 90°C in an hour almost quantitatively. The resulting uranyl formate is partially precipitated. The initial stage of the reaction is accompanied by violent gas evolution. At 90°C, ~80% of the gas volume is released at this stage (about 10 s), whereas at 40°C, only ~10%.

The reaction of nitric acid with formic acid, including uranium-containing solutions, was studied. Empirical equations for the dependence of the induction period duration (τ) on the concentrations of reagents and temperature were determined. The dependence of τ on the concentration of formic acid is exponential. The effect of uranium concentration on τ in denitrated solutions becomes noticeable only at temperatures lower than 60°C. The main factor affecting the completeness of denitration is the molar ratio [formic acid] : [NO₃]¯. Starting with the molar ratio of ≥3, uranium-containing solutions are denitrated at 90°C in an hour almost quantitatively. The resulting uranyl formate is partially precipitated. The initial stage of the reaction is accompanied by violent gas evolution. At 90°C, ~80% of the gas volume is released at this stage (about 10 s), whereas at 40°C, only ~10%.

The solubility of hexavalent plutonium and uranium nitrates in nitric acid solutions with the ratios in initial solutions Pu/(Pu + U) = 0.3 ± 0.015 (main data), Pu/(Pu + U) = 0.25 ± 0.025, and Pu/(Pu + U) = 0.5 ± 0.025 (single compositions) at +25, +15, and +5°C (±3) was determined by the method of isohydric crystallization. The calculated solubility isotherms of plutonyl and uranyl nitrates are presented in a wide range of nitric acid concentrations.

A process was developed for the extraction and separation of actinides and REEs from PUREX process raffinates using TODGA in meta-nitrobenzotrifluoride (F-3). The proposed flowsheet was tested under dynamic conditions using simulated raffinates of the PUREX process. The scheme includes joint extraction of actinides and REE, nitric acid stripping, actinide stripping, and REE stripping. The conditions of selective MA stripping by DTPA solution in the presence of a salting-out agent were determined.

Experimental data on the extraction of nitric acid, europium, and americium with 40% TBP in C13 in the presence of salting-out agents such as sodium, magnesium, iron, and aluminum nitrates were obtained. The nitric acid and nitrate ion concentrations ensuring efficient recovery of transplutonium and rare earth elements were chosen. Based on the data obtained, corrections to the existing program for mathematical modeling (Statics, Dynamics program complexes) were made. To check the adequacy of program operation, computations were made for the experimentally tested flowsheet of the high-level raffinate partitioning using the extraction system based on TBP in paraffin in the presence of a salting-out agent. Comparison of the calculation results with the results of cell-by-cell analysis of samples from the first block shows that the deviations are within the measurement uncertainty of the analytical equipment. The possibility of predicting the operation of the extraction cascade at varied parameters (phase flow rates, number of steps, salting-out agent concentration) was demonstrated.

The effect of cobalt(II) speciation on the parameters of its interphase distribution was studied for different types of sorbents. Inorganic sorbents based on the hydrolyzable elements have shown the highest selectivity for Co in neutral and alkaline media (pH 7–10). The experiments on the cobalt sorption onto KU-2 strong acid cation-exchange resin at pH 3–5 have shown the presence of Co²⁺, which shows a high affinity for all the sorbents studied. In the neutral and low alkaline media, the inorganic sorbents adsorbed Со(ОН)⁺ and $\mathrm{Со}{\left(\mathrm{ОН}\right)}_2^0$ hydroxo complexes due to heterogeneous ion-exchange reaction (surface complex formation). The appearance of the S–pH dependences for the inorganic sorbents suggests higher stability of cobalt hydroxo complexes at microconcentrations as compared to the literature data. In the whole pH range studied, cobalt(II) showed a behavior of an inert sorbate with all the inorganic sorbents studied.

It was demonstrated by the example of serotonin, 3-(N-pyrrolyl)propanoyl-L-histidine, sodium p-phenylbenzoate, and Pro–Gly–Pro that activation of isotope exchange with D₂O also occurred when a solution of an organic compound in D₂O was mixed with 5% Pd/Al₂O₃ or 5% Pd/С (after preliminary treatment of catalysts with deuterium gas on heating). When implementing this technique, 2–3 atoms of deuterium were incorporated in serotonin, 4–5 atoms, in Pro–Gly–Pro, 7–8 atoms, in 3-(N-pyrrolyl)propanoyl-L-histidine, and 3–4 atoms, in sodium p-phenylbenzoate. In the latter case, as judged from the composition of the reaction products, atomic deuterium takes part in the activation of isotope exchange with D₂O. The participation of atomic deuterium in these reactions follows from the intensification of the degradation of the compounds during deuteration. When using compounds that do not contain labile fragments, isotope exchange with D₂O can be activated by keeping the catalyst at room temperature and heating.