A new method for extraction kinetics studying in a biphasic system using time-lapse recording of IR absorption spectra in the attenuated total internal reflection (ATR IR) geometry is developed. The method is examined by studying the extraction process of europium, yttrium and cesium ions with various extractants both from acidic and carbonate media. The mechanism of step-wise coordination with functional groups of the ligand is proposed. The extraction kinetics constants are calculated for the extraction systems with europium. The main advantages of the new method are miniaturization and rapidity, compared to classical methods.

The article presents the results of studies on composition optimization, properties, and laboratory dynamic tests of extraction mixtures based on p-isononylcalix[6]arene for the alkaline HLW purification to remove 137Cs. The distribution of 137Cs among the products of the technological scheme is presented and the coefficients of raffinate purification to remove 137Cs are determined. It was revealed that, in the case of using nitric acid as a stripping solution, nitrosation of p-isononylcalix[6]arene is possible in the technological process. The composition of the resulting product was determined. To prevent nitrosation of p-isononylcalix[6]arene, formic acid was used in the stripping stage, which ensured stable operation of the extraction stand for 48 h with 137Cs extraction from model alkaline HLW at a level of 99.7%.

A new method of yttrium recovery with a mixture of hydroxyaromatic compound (8-hydroxyquinoline, 2,3-dihydroxynaphthalene) and methyltrioctylammonium carbonate separation from strontium in carbonate media has been proposed. Yttrium extraction from carbonate media has been studied. The structures of yttrium solvates with ligands formed during extraction have been proposed. The suggested method for yttrium recovery from soil by sample calcination followed by carbonate leaching and extraction with the specified mixture allows the efficient separation of yttrium-strontium pair and yttrium recovery.

Изучена жидкостная экстракция пары 90 Y/ 90 Sr из карбонатных сред смесями ароматических дигидроксисоединений и четвертичной аммониевой соли - карбоната метилтриоктиламмония (МТОАК) - в толуоле и бутилацетате. Установлено, что МТОАК повышает коэффициенты распределения и самого экстрагента, и его сольвата с иттрием за счет образования смешанного комплекса иттрия и дигидроксиароматического лиганда с МТОАК. При экстракции из щелочно-карбонатных сред в интервале рН 12-13.5 смесями 0.01 M 2,3-дигидроксинафталина и 0.015 M MTOAК в бутилацетате или толуоле коэффициенты распределения иттрия превышают 80; коэффициенты разделения пары 90 Y/ 90 Sr в этих условиях более 10 5 . Для полной реэкстракции иттрия могут быть использованы разбавленные растворы соляной, азотной и серной кислот. Изученные смеси химически устойчивы и не изменяют экстракционных свойств при многократном повторении циклов экстракции-реэкстракции. Модельные эксперименты по выщелачиванию иттрия из природных образцов показали, что процент извлечения стабильного иттрия из песка составляет 70-80%, в то время как процент извлечения иттрия из почвы - 50-60%.

The solvent extraction of the 90Y/90Sr pair from carbonate media with mixtures of aromatic dihydroxy compounds and a quaternary ammonium salt—methyltrioctylammonium carbonate (MTOAC)—in toluene and butyl acetate was studied. It was found that MTOAC increases the distribution coefficients of both the extractant itself and its solvate with yttrium due to the formation of a mixed complex of yttrium and a dihydroxyaromatic ligand with MTOAC. During extraction from alkaline carbonate media in the pH range of 12–13.5 with mixtures of 0.01 M 2,3-dihydroxynaphthalene and 0.015 M MTOAC in butyl acetate or toluene, the distribution coefficients of yttrium exceed 80; the separation factors of the 90Y/90Sr pair under these conditions are more than 105. Dilute solutions of hydrochloric, nitric, and sulfuric acids can be used for the complete stripping of yttrium. The studied mixtures are chemically stable and do not change the extraction properties upon multiple extraction/stripping cycles. Model experiments on the leaching of yttrium from natural samples showed that the percentage of stable yttrium extraction from sand is 70–80

The extraction ability and selectivity of nonmacrocyclic (8-quinolinol and 2,3-dihydroxynaphthelene) and macrocyclic (sulfur-containing calixarene derivatives) ligands toward rare earth and transplutonium elements in carbonate media was studied. Both macrocyclic and nonmacrocyclic derivatives showed moderate selectivity to americium in the Am/Eu pair (separation factor SF from 1.6 to 14 at pH > 12), and sulfur-containing calixarenes showed also high selectivity to Am in the Am/Cm pair (SF 3–8 at pH > 13). The compounds studied show promise as extractants for group recovery and separation of actinides, and also for separation of rare earth and transplutonium elements in carbonate media.

The extraction of cesium, strontium, and a number of stable components of simulated high-level waste solutions from nitric acid media with solutions of crown ether derivatives in new fluorinated diluents was studied. Based on the data on the solubility of the extractants into the aqueous phase and the physicochemical properties of the diluents used, the most promising extraction systems were chosen: crown ethers 4,4'(5')-di-tert-butyldibenzo-18-crown-6 (L1) and 4,4'(5')-di-tert-butyldicyclohexyl-18-crown-6 (L2) in bis(2,2,3,3-tetrafluoropropyl) carbonate (BK-1) and bis(2,2,3,3-tetrafluoropropoxy)methane (FN-1). For these systems, the extraction of a number of stable components and their subsequent stripping with water and solutions of chelating agents were studied. Lead was found to be co-extracted to the greatest extent. To a lesser extent, barium and calcium cations are co-extracted with strontium, and rubidium and potassium cations with cesium. Lead, barium, and silver are the most difficult to strip; however, the problem of lead stripping can be solved by using DTPA or citric acid solutions neutralized with ammonia to weakly alkaline (pH 8) media.

The possibilities of 90Y/90Sr separation from carbonate media are investigated as a green alternative method. Solvent extraction of yttrium and strontium from carbonate solution is studied using several extractants in different organic diluents. 8-hydroxyquinioline and 2,3-dihydroxynaphtalene possess a promising Y/Sr separation. Yttrium and strontium distribution ratios D and separation factors SF are evaluated. pH interval 13 13.5 is regarded as the optimum for separation. Yttrium is extracted much better in 2-nitrotoluene (DY=3.9), maximum separation is observed in 2-nitrotoluene SF = 195 at pH 13.5.

Several extraction systems based on functionalized calixarenes in mixed fluorinated diluents were examined. Technological flowsheets for radioactive waste processing with these extraction systems were developed and tested. It is shown that under the selected conditions one can achieve decontamination factors from cesium isotopes and alpha-emitters, sufficient for converting high-level waste of the “Mayak” Production Association into the low-level category with the subsequent possibility of their disposal at near-surface sites.

The effect of γ-radiation on the extraction properties of two functionalized calixarenes (p-tert-butyl-thiacalix[4]arene and p-tert-butylcalix[8]arene) is studied. The most characteristic products of the irradiated extractants interaction with diluent are identified by mass spectrometry. Extraction ability of studied calixarenes towards cesium and americium before and after irradiation is evaluated. Quantitative analysis of chloride and sulfate ions after irradiation is performed to estimate the radiological degradation degree of components. Irradiation has different effect on p-tert-butyl-thiacalix[4]arene and p-tert-butylcalix[8]arene extraction ability towards americium, which may be due to the nature and extraction ability of radiolysis products, and practically does not affect cesium extraction.

The review substantiates the desirability of developing spent nuclear fuel reprocessing technologies alternative to the Purex process. The practical use of radiochemical technologies based on alkaline and carbonate media, such as extraction of radiocesium from alkaline high-level waste and CARBEX process, is considered. Extraction of actinides with aliphatic amines, β-diketones, phenol derivatives (alkylpyrocatechols, aminomethylphenols, alkylphenol oligomers, calixarenes), and carboxylic acids, as well as extraction in two-phase aqueous systems based on water-soluble polymers, is discussed. The extraction of technetium is considered separately.

Extraction efficiency of uranium and transuranium elements (Np, Pu, Am and Cm) with tert-butylthiacalix[4]arene TCA from carbonate-alkaline solutions is studied and compared with that of europium (III). Plutonium (III, IV) extraction efficiency with TCA is found to be lower comparing with that of trivalent americium and europium. Extraction efficiency of studied radionuclides decreases as following: Am ≫ Eu ≫ Pu (III), U(VI), Np (V) > Pu (IV) at pH 12. Carbonate concentration increase in aqueous phase suppresses significantly extraction of all studied radionuclides, except americium. This condition can be used for americium individual recovery from complex radioactive carbonate-alkaline solutions.

Trends of cesium-137 and americium-241 extraction from carbonate–alkaline media with p-tert-butylcalix[n]arenes with macrocycles of different size (n = 4, 6, 8), including monofunctional derivatives with lipophilic substituents for increasing their solubility in organic media, were studied. It was demonstrated that O-n-octyl ethers of p-tert-butylcalix[6]arene appeared to be the most efficient extractants for Cs(I) cations, while it was p-tert-butylthiacalix[4]arene for and americium(III) cations.

Volatile complexes of fluorinated β-diketonates of neodymium(III) (hexafluoroacetylacetonates with glyme and diglyme and decafluoroacetylacetonate with glyme) were studied for applicability in lowbackground Nd-containing organic liquid scintillators. The complexes were prepared in one step and purified by vacuum sublimation. The composition of complexes was determined by 1 H, 19 F, and 13 C NMR and IR spectroscopy and confirmed by elemental and functional analysis. It was shown that these adducts are suitable for the design of Nd-containing organic liquid scintillators with neodymium concentration of ~1–2 g/L.

Kinetics of 152 Eu and 241 Am extraction by nitrogen-bearing alkyl amino phenol oligomer YaRB and tert -butylthiacalix[4]arene TCA from carbonate-alkaline media was studied. Both extractants efficiently extract americium and europium in pH interval 12–14. The maximum of americium extraction is located at the lower values of pH, compared with europium. YaRB extracts americium and europium faster than TCA, and at the same time, americium is extracted faster than europium by both extractants. In general, thiacalixarene TCA is regarded as more efficient extractant than alkyl amino phenol oligomer YaRB.

152Eu and 241Am recovery from HNO3 by conventional and micelle mediated extraction are studied. It is stated that radionuclides distribution ratios D (K D) in micelle mediated extraction are significantly higher than those of conventional extraction, with 241Am is slightly less extracted than 152Eu. Distribution ratios dependence on medium acidity is similar for both processes, with extraction maximum at C (HNO3) = 0.2–1 mol L−1. Microscopic research and dynamic light scattering prove micellar nature of calixarene solutions. Nano-scale of particles, which accumulate radionuclides, is confirmed by ultramicrofiltration. This method is also applied for studies of radionuclides re-extraction and electrochemical deposition.