The combination of two neutral CHON reagents, a lipophilic phenanthroline dicarboxamide and a hydrophilic diglycolamide, resulted in a synergistic separation of adjacent light lanthanides in nitrate medium as the ligands present a reversed lanthanide selectivity. Separation factors higher than 7 were obtained for the pair Pr/Nd, which is one of the highest values reported in the literature.

Abstract This paper presents first investigations on a novel An(III), Ln(III), Cs(I) and Sr(II) co-extraction conceptual process using a CHON solvent composed of the calixarene crown-ether MAXCalix and the diglycolamide TODGA in a 1-octanol/kerosene diluent. The co-extraction is followed by a sequential stripping of (1) Cs(I) and Sr(II), (2) An(III) and (3) Ln(III).

Asse II salt mine, in Germany, contains low and intermediate-level radioactive waste that must be retrieved in the upcoming years. Potentially contaminated salts and brines will require treatment, with 137Cs being the main contaminant. Cs+ is problematic to selectively recover due to its chemical similarity with Na+ and K+ which are present in high quantities in a salt mine. This paper offers a novel solution for Cs+ separation from concentrated chloride salt media by solvent extraction with calixarene-crown-ether extractants in an alcoholic diluent. The proposed solvent extracts Cs+ at elevated chloride concentrations (3–4 M) while back-extraction is achieved by contacting the solvent with dilute (0.01 M) hydrochloric acid.

Precise separation and purification of f-block elements are important and challenging especially for the reduction of nuclear waste and the recycling of rare metals but are practically difficult mainly because of their chemical similarity. A promising way to overcome this difficulty is controlling their oxidation state by nonchemical processes. Here, we show resonance-enhanced multiphoton charge transfer in actinide complexes, which leads to element-specific control of their oxidation states owing to the distinct electronic spectra arising from resonant transitions between f orbitals. We observed oxidation of trivalent americium in nitric acid. In addition, we found that the coordination of nitrates is essential for promoting the oxidation reaction, which is the first finding ever relevant to the primary process of photoexcitation via resonant transitions of f-block elements. The resonance-enhanced photochemical process could be used in the nuclear waste management, as it would facilitate the mutual separation of actinides, such as americium and curium.

Phenanthroline carboxamide compounds are promising for lanthanide intra-series separation. This paper presents a study on the effect of structure modification of phenanthroline carboxamides on the extraction of the whole lanthanide series. The study consists of theoretical calculations, extraction experiments of the 14 stable lanthanides, and extended X-ray absorption fine structure (EXAFS) analyses of Nd and Dy complexes. Tridentate monocarboxamides and tetradentate dicarboxamides show different trends in series extraction, although both preferentially extract the light lanthanides. The amide substituents, although not directly coordinating the metal ions, were also found to impact the distribution ratio, most probably due to a modification in the internal polarity of the molecules. This latter effect, if extrapolated to other nitrogen-based ligands such as pyridines or triazines, can be used to further fine-tune extractants for a process improvement.

The demand for rare earths is expected to keep increasing throughout the following years. Separation of lanthanides in particular is especially challenging because of their chemical similarities. Therefore, improving the separation process is essential. In this work, we present the effect of the counterion nature on the lanthanide extraction by a 1,10-phenanthroline derivative, the N-octyl-N-tolyl-1,10-phenanthroline-2-carboxamide in chloroform. Modification of the counterion yields a drastic change in selectivity, with a shift in the maximum of extraction from the light lanthanides (Pr, Nd, Sm) in the nitrate system to the heavy lanthanides (Dy, Ho) in the perchlorate system. Other salts (NaCl, NaNO2) showed a gradual increase in extraction along the whole lanthanide series or no effect (Na2SO4). This selectivity shift was explained by possible different coordination in the organic phase. The reversed behavior depending on the anion is especially interesting because a cycling extraction/back-extraction of light lanthanides in nitrate/chloride media or a cycling extraction/back-extraction of heavy lanthanides in perchlorate/nitrate media can enhance the separation factors of Nd and Dy/Ho, respectively.

Cesium extraction from acidic media by seven dialkoxy-calix[4]arene-crown-6 compounds in several diluents was studied. 2-Nonanone was found to be a suitable diluent for cesium extraction. Nitric acid concentration variation reveals a maximum distribution ratio, whose position depends on extractant and diluent. This maximum was explained quantitatively by a competitive extraction of H+. An analytical mass-action extraction model accounting for activity effects is proposed that fits correctly the different datasets. The analysis showed a nitrate hyper-stoichiometry in alkyl ketone diluents. This effect yields efficient back-extraction at low acidity. Benzo substitution on the crown ether lowers nitric acid extraction, improves sodium separation, but also degrades potassium and rubidium separation.

This paper is an attempt to find out thorium oxide dissolution mechanism in HNO3 -HF mixture. In a previous paper, several parameters effects on thorium oxide dissolution have been described, with specific focus on hydrofluoric acid effect, which can lead to an increase of the dissolution rate if present in small amount, but precipitates as ThF4 at higher content. Based on this previous study, experimental data were fitted using several dissolution models in order to find out the best one. Finally, a revisited model based on literature and considering the ThF(4 )formation was proposed. It describes the main steps of dissolution and is able to fit the experimental data for a wide range of solution compositions. This point is crucial since it allows considering an extrapolation of the established model to not-yet-studied conditions.

Separation of cesium from nuclear waste can greatly decrease its decay heat.Calix-crown ethers are commonly used for liquid-liquid cesium extraction.However, their low lipophilicity makes them nearly insoluble in solvents like dodecane.In this study, experiments were conducted in different solvents with the final aim to find a way to predict solvent efficiency for cesium extraction.An extraction mechanism is proposed, and by fitting the data, this model provides empirical constants which can be related to solvent parameters, thus giving a basis for comparison and prediction.We finally discuss the best solvents for cesium extraction when using calix-crown ethers based on this study.

Abstract Thorium oxide is poorly soluble: unlike uranium oxide, concentrated nitric acid medium is not sufficient to get quantitative dissolution. Addition of small amounts of fluoride is required to achieve thorium oxide total dissolution. The effect of several parameters on thorium oxide dissolution in order to optimize the dissolution conditions is reported in this paper. Thus the influence of solid characteristics, dissolution method, temperature and composition of dissolution medium on ThO2 dissolution rate has been studied. No complexing agents tested other than fluoride allows total dissolution. Beyond a given HF concentration a decrease of the dissolution rate is observed due to the formation of a precipitate at the solid/solution interface. It was demonstrated by XPS measurements that this precipitate is constituted of thorium fluoride (ThF4) formed during the ThO2 dissolution. The low concentration of HF required to achieve a total dissolution and the activation energy value measured tends to show a catalytic effect of HF on the dissolution process.