Radiochemistry

The physicochemical and extraction properties of calixarene crown ethers: 1,3-alt-bis(octyloxy)calix[4]arene-crown-6 (II) and its derivatives with o-phenylene (I), methylenepropoxy (IV) and methylene(2,2,3,3-tetrafluoropropoxy) (III) substituents in the crown ether ring, were studied. Solutions of compound II in bis(2,2,3,3-tetrafluoropropyl) carbonate (BK-1) effectively extract cesium from 3 mol/L nitric acid already at a concentration of 0.001 mol/L. The introduction of substituents into the crown ether ring significantly reduces the efficiency of cesium extraction, but increases the solubility of calixarene crown ethers in bis(2,2,3,3-tetrafluoropropyl) carbonate. The data on the solubility of calixarene crown ethers in water and 3 mol/L nitric acid, the distribution between the organic and aqueous phases, and the rate of interaction with nitric acid were obtained. Calixarene crown ether I with an o-phenylene substituent reacts with 3 mol/L nitric acid approximately 2 times faster than dibenzo-21-crown-7. The other calixarene crown ethers studied do not react with nitric acid under the similar conditions. Quantum chemical modeling, including optimization of the structure geometry and calculation of vibrational frequencies, was performed for the molecules of calixarene crown ethers, DB21C7 and their complexes with the cesium cation. The calculated ΔG⁰ values for the complexation of ligands with the cesium cation correlate well with the experimental lgD_Cs (except for compound III with a fluorinated substituent). Solutions of calixarene crown ethers in bis(2,2,3,3-tetrafluoropropyl) carbonate exhibit selectivity for cesium and do not extract ¹⁵²Eu and ²⁴¹Am from nitric acid media.

The interference of Sr(II) and Y(III) cations with cationic, anionic, and nonionic surfactants during competitive adsorption on lignin-produced activated carbon was studied. Dodecyltrimethylammonium bromide, sodium dodecylsulfate, and decaethylene glycol monododecyl ether (Brij-35) were used as surfactants. The radiotracers ⁹⁰Sr/⁹⁰Y and tritium were used to trace the equilibrium concentration of metal cations and the surface concentrations of the surfactants, respectively. Tritium-labeled surfactants were obtained using the tritium thermal activation technique. Liquid scintillation spectrometry was used to determine the concentration of all substances. The SpectraDec software was used for joint measurement of ⁹⁰Sr/⁹⁰Y and tritium radioactivity. It was shown that the presence of a surfactant affects the adsorption of strontium and yttrium onto activated carbon produced by thermochemical activation with orthophosphoric acid. The formation of a low-solubility precipitate with an anionic surfactant increased the adsorption of both cations, reduced their desorption, and promoted the sorption of the anionic surfactant itself. The nonionic surfactant (containing oxyethyl groups) did not affect the adsorption of strontium and yttrium cations but helped retain them on the carbon surface, preventing desorption. The cationic surfactant competed with strontium and yttrium cations for active sites on the activated carbon surface: adsorption of all components decreased, while desorption of cations increased.

The kinetics of 1,2-diformylhydrazine (reagent suggested for the reductive stripping of plutonium in the Purex process) oxidation with nitric acid was studied. The rate equation is first-order with respect to the reductant and third-order with respect to nitric acid in the interval [HNO₃] = 5.5–9.0 mol/L. It is postulated that reaction between diformylhydrazine and nitric acid involves their molecular undissociated forms. The activation energy of the reaction is 116 kJ/mol in temperature range 70–90°С.

The migration of ¹³⁷Cs from the upper reaches of the Vuoksa River, Lake Saimaa, to Lake Ladoga was studied to determine the role of the river in the contamination of Lake Ladoga with ¹³⁷Cs from the Chernobyl accident. During the migration period from 1988 to 2024, the concentration of ¹³⁷Cs in the river water decreased from 113 to approximately 4.0 Bq/m³. By 2015, the ¹³⁷Cs content in the Vuoksa River had approached the pre-accident level of 4–5 Bq/m³, which was due to global ¹³⁷Cs contamination of river waters. The decrease in “Chernobyl” ¹³⁷Cs in the Vuoksa River was approximated by a two-component exponential dependence with the water purification half-lives of T₁ = 5 and T₂ = 25 years, respectively. The discharge of “Chernobyl” ¹³⁷Cs with Vuoksa’s waters from Finnish Lake Saimaa in 1986–2023 amounted to 22.5 TBq – a value roughly comparable to the deposition of “Chernobyl” ¹³⁷Cs (74.1 TBq) on Lake Ladoga in 1986. During 1986–1988, the discharge of “Chernobyl” ¹³⁷Cs from Lake Saimaa amounted to approximately 30% of the total for 1986–2024. The long-term transit of ¹³⁷Cs from Lake Saimaa has led to increased accumulation of ¹³⁷Cs (≈300 Bq/kg) in the sediment profile of the Vuoksa River and the lakes within its basin.