The review is devoted to overview of the current status on some radiochemical studies and their technological applications in Russian Federation. Multiple view on the problem is given including achievements of recent years in this field. The collected data reflect importance of studies connected with spent nuclear fuel and explain how complicated is this problem.

Abstract—Radiation loads on the sorbent and eluent upon extraction of Cm and Am by displacement complexation chromatography from complex-composition solutions using an eluent containing DTPA and citric acid are calculated. The destruction of the eluent and sorbent in the columns is estimated. Good agreement is obtained between the calculation and experimental data on the concentrations and rate of curium band motion through the column.

Radiation loads and compositions of solid phases are calculated during the separation of TPE and REE from solutions generated in the course of SNF reprocessing. Sorption from weakly concentrated solutions under the action of high radiation loads in the upper part of the sorption column leads to the sorbent decomposition, up to 30% of its original capacity. The hydroxide forms of iron, chromium, aluminum and nickel pass from the solid to the liquid phase and generate gel-like precipitates under the action of high radiation loads, which block the sorption column. During elution, aluminum is washed out in the TPE region and forms a protonated complex with diethylenetriaminepentaacetic acid (DTPA), which precipitates at room temperature. This precipitate in the unheated connecting lines of the plant can bring about blocking of the separation columns.

A chromatographic method is proposed for recovery of macroconcentrations of irradiated targets and microconcentrations of target irradiation products using intercalators, nonferrous metal ions, such as Zn 2+ or Cd 2+ ions. A change in the ion exchange selectivity of ions of elements with variable valency when buffer additives are introduced into eluents, underlies the operating principle of intercalators. Intercalators at a certain composition of the eluent insert between the zones of the macrocomponent and the target microcomponent, ensuring its complete separation and high purity. The practical application of this method is summarized and analyzed on the 153 Gd and 163 Ho separation from irradiated europium and erbium targets, respectively, and also on 249 Bk, 249 Cf separation from irradiated 244 Cm targets. The separation and recovery of these radionuclides were carried out using ethylenediaminetetra- and diethylenetriaminepentaacetate-based eluents with the addition of citric acid.

Предложен хроматографический метод разделения макроконцентраций облученных мишеней и микроконцентраций продуктов облучения мишеней c использованием интеркаляторов - ионов цветных металлов, в качестве которых могут выступать ионы Zn 2+ или Cd 2+ . Принцип действия интеркаляторов основан на изменении селективности ионного обмена ионов разновалентных элементов при введении в элюенты буферных добавок. Интеркаляторы при определенном составе элюента вклиниваются между зонами макрокомпонента и целевого микрокомпонента, обеспечивая его полное выделение и высокую чистоту. Обобщается и анализируется практическое применение данного метода при выделении 153 Gd из облученных европиевых мишеней, 163 Ho из облученных мишеней эрбия, 249 Bk, 249 Cf из облученных мишеней 244 Cm. Разделение и выделение указанных радионуклидов проводили с помощью элюентов на основе этилендиаминтетра- и диэтилентриаминпентаацетата с добавками лимонной кислоты.

The effect of Fe, Cr, and Al impurities on the separation of REEs and TPEs was studied by displacement chelating chromatography using various eluents. The mutual position of impurity elements and separable REEs and TPEs on the output elution curves was studied. This position is unstable and depends on the type of eluent and the number of separation bands. The positive and negative aspects of the presence of impurity elements in the original concentrate are noted. The conditions for the complete leaching of impurity elements from the cation exchange resin were determined using 3–4 M nitric or 0.2–0.5 M citric acids.

The sorption parameters of a sorbent based on tetraoctyldiglycolamide (TODGA) and hypercrosslinked polystyrene AXIONIT MND 50 produced by the Russian company Axion-RDM relative to REE ions were studied. It is shown that the sorption parameters of the sorbent relative to REE (neodymium) in nitric acid media rise with an increase in the acidity and temperature of the solution and with a decrease in the filtration rate. Complete desorption of REEs occurs when 15 column volumes (c.v.) of a 0.01 M HNO3 solution are passed through, which allows using the AXIONIT MND 50 sorbent in a multicyclic sorption–desorption mode. In the sorption of REE (152Eu) from solutions prepared by dissolving sulfonic cation resin in nitric acid solutions in the presence of hydrogen peroxide and ferric ions, almost complete extraction of 152Eu is achieved at passing 550 c.v. solution. During the second sorption cycle, the volume of the purified solution is reduced by almost 10 times, which excludes the feasibility of its repeated use. A method is proposed for the disposal of spent ion resins containing residual amounts of REE and TPE radionuclides by their complete chemical dissolution with subsequent sorption extraction of radionuclides from the resulting solution using a TODGA-based sorbent AXIONIT MND 50.

A review is presented of the work performed from the early 1950s to the present at the Laboratory of Radioelement Chromatography of the USSR Academy of Sciences’ Institute of Physical Chemistry (the Russian Academy of Sciences’ Frumkin Institute of Physical Chemistry and Electrochemistry). The works in the field of studying the patterns of sorption and dynamics of chromatography for systems of chelate displacement chromatography (CDC), the chromatographic separation of elements under conditions of ionizing radiation, and the chromatographic separation of radionuclides with the use of separating ions are described. The separation of 137Cs radionuclide from irradiated nuclear fuel (INF) reprocessing solutions using ferrocyanide sorbents, the use of ion-exchange resins for the recovery of rare-earth elements (REEs) and actinides from solutions of different composition, and advances in the field of the sorption purification of liquid radioactive wastes of different chemical and radionuclide composition are also considered. The means developed at the Laboratory provided the basis for the technologies of the separation of radioactive elements from INF reprocessing solutions and the purification of liquid radioactive wastes. These technologies are used today at enterprises of the Rosatom State Atomic Energy Corporation, nuclear power stations, and other facilities of the nuclear industry.

This paper reported creating the all-chromatographic technique for the recovery of americium radionuclides from solutions of the complex composition generated in the radiochemical industry. The technique was based entirely on the displacement complexing chromatography; neither additional precipitation nor extraction stages were necessary. The technology used the elution with DTPA and NTA-based solutions containing the citric acid additives and the sequential elution with these eluents, emphasizing the separation of americium from the heavy rare earth elements, lead, and cadmium. The complete separation of americium from lead and cadmium was a peculiar exercise; the elution order of lead and cadmium changed in the presence of the citric acid additives. The recovery and separation of americium from actual radioactive waste solutions of different origins demonstrated 96 and 99% chemical purity of the final product.

In this work, the chemical digestion conditions for spent KU-2 × 8 sulfocationites manufactured in Russia were investigated. It was shown that the complete oxidative digestion of the ionites could be performed in solutions of H2O2 and HNO3 in the presence of Fe3+ ions adsorbed on the resin as an oxidation catalyst. The total digestion time of the resin was studied as a function of the presence of the digestion catalysts, solid-to-liquid phase ratio, process temperature, Fe3+ ion content in the solid sulfocationite phase, and the divinylbenzene (DVB) cross-linking agent content of the ionite. A possibility for the removal of rare earth element (REE) and transplutonium element (TPE) radionuclides from the solution of the digested sulfocationite was shown by the sorption technique using the tetra-n-octyldiglycolamide (TODGA)-based sorbent.

The ion exchange selectivity of complex displacement chromatography (CDC) is analyzed. It is found that the separation factors determined by other means of complex chromatography, frontal and elution, are not always interchangeable with CDC. A way of determining the separation factors applied to CDC is proposed. A technique for constructing isotherms for the ion exchange of components to be separated with the simultaneous presence of displacer ions, hydrogen ions, and a sorbed complexone in the system is proposed as well. The change in the selectivity towards different valence elements is considered. For protonated complexes, the complete inversion of selectivity corresponds to the transition of the S -shaped separation isotherm from convex to concave. When protonated and binuclear М 2 А complexes are simultaneously present in a system, the inversion of selectivity is accompanied by mixed isotherms of variable type with two intersection points with a diagonal. The spreading of the displacement fronts is determined using the McCabe–Thiele approach. The lower part of the displacement front of the second component is spread in the case of a convex isotherm with an S -shaped pattern. For complex isotherms with two maxima, the center of the front is spread, while the lower and upper parts of the front are quite sharp.

Isolation of Pu from a TPE/REE mixture by displacement complexing chromatography on KU-2 cation-exchange resin was studied. To stabilize Pu in the trivalent state, the sorption of the mixture components from the initial solutions was performed in the presence of hydrazine nitrate. To convert Pu to the tetravalent state, H2O2 was added to the DTPA solution used as an eluent. The influence of temperature and H2O2 concentration on the chromatographic isolation of Pu was studied. Optimum conditions were found for separating Pu from TPE and REE.

The process of curium and americium separation from solutions after spent fuel reprocessing by displacement complexing chromatography on sulfonic cation exchange resins was reported. Separation runs were performed using a 2-stage chromatographic process sequence. Stage 1 constituted the primary purification and produced the enriched trans-plutonium elements (TPE) concentrate by means of removing the principal quantity of light rare earth elements, namely, La, Ce, Nd, and Pr. Deep refining of the TPE concentrate from the residual chemical and radiochemical impurities was performed at Stage 2. The paper reports the results of three experimental cycles of americium and curium separation. The best results were obtained in Cycle 3, where the key factor was the application of the monodispersed Tokem-308 cationite. The purity of curium in the fraction containing 50% of the feed curium-244 was 99% relative to americium. About 60% of the enriched americium-241,243 fraction contained <0.1% of Eu-154,155 by radioactivity and <0.8% of Cm-244 by mass.

A mathematical description is developed for complex displacement chromatography (CDC) systems. It consists of mathematical models of the stationary state of each forming zone. It is noted that the theoretical analysis of elution systems is based on the principle of successively considering equilibria and calculating the concentrations of all varieties of ions in both phases. Numerical experiments are performed on eluting rare earth elements (REEs) on sulpho cation exchangers using eluents based on diethylenetriaminepentaacetic acid (DTPA). It is shown that increasing the pH and concentration of the eluent and the buffering species introduced into the eluent sharpen the displacement fronts. It is concluded that in the zone of a sorbed complexone, its concentration is many times greater than in the initial eluent. It is shown that raising the concentration of the displacing agent raises the pH and concentration of the eluted component, due to an increase in the amount of introduced alkali and the introduction of additional complexing or buffering species. A maximum is found on the curve of the REE content in the solid phase, which corresponds to the HETP minimum.

Separation of rare earth elements (REE) as a model system for transplutonium elements (TPE) partitioning via displacement complexing chromatography technique was investigated using sulfocationites commercially available from Purolite (UK), Dow Chemical (USA), Rohm and Haas (USA), and LLC SPA ‘Tokem’ (Russia). The specific volume, total mass and volume capacity of the sorbents were determined. Effects of the dispersity (monodispersed and polydispersed), grain size and cross-linking degree on the REE and TPE separation performance were discussed. Materials and conditions for the highest REE and TPE separation process efficiency were selected.

Приведен обзор результатов исследований по выделению америция методом вытеснительной комплексообразовательной хроматографии (ВКХ), проведенных в лаборатории хроматографии радиоактивных элементов ИФХЭ РАН. Разработаны способы выделения высокочистых препаратов америция из растворов различного сложного состава, в том числе из растворов, образующихся при переработке отработавшего ядерного топлива (ОЯТ).

В работе приведены результаты сравнительного изучения разделения РЗЭ с использованием сорбентов «Chromalite СGС» фирмы «Purolite» (Великобритания) и Российской компании «Токем», (г. Кемерово) методом вытеснительной комплексообразовательной хроматографии. Полученные результаты позволили рекомендовать данные сульфокатиониты для выделения и разделения РЗЭ и ТПЭ из растворов, полученных после переработки ОЯТ.