Cesium separation from radioactive waste by extraction and adsorption based on crown ethers and calixarenes

Soft-hard-donor-combined ligands are a type of promising extractant for actinide and lanthanide separation. In this work, the effects of counteranions (Cl-, NO3-, and ClO4-) on the extraction and complexation behaviors of a recently reported tetradentate phenanthroline-derived phosphonate (POPhen) ligand toward lanthanides were thoroughly investigated using solvent extraction, NMR titration, UV-vis titration, and single-crystal X-ray diffraction measurements. It is found that C4-POPhen showed excellent extraction and selectivity toward heavy lanthanides [Lu(III)] compared to light lanthanides, particularly with the counterion of ClO4- and at low acidity. NMR titration studies demonstrated that both 1:1 and 1:2 Lu(III)/C4-POPhen complexes were formed in a CD3OD solution with all three counteranions and the 1:2 species was easier to form in a complexation of C4-POPhen with Lu(ClO4)3 under the same conditions. Furthermore, the stability constants of Nd(III) complexation with C4-POPhen in the counteranions of Cl-, NO3-, and ClO4- systems were determined through UV-vis titration, and a much larger value of log β of complexes was found in the ClO4- system, which was in good agreement with the results of solvent extraction. In addition, the structures of C2-POPhen complexation with Ln(NO3)3/Ln(ClO4)3 in the solid state were clearly unraveled by the single-crystal X-ray diffraction technique. This work demonstrated that the solvent extraction and complexation mechanisms of POPhen ligands with Ln(III) were significantly affected by the counteranions from both the solution and solid-state aspects, which might shed light on the lanthanide/actinide separation.

Effect of Counteranions on the Extraction and Complexation of Trivalent Lanthanides with Tetradentate Phenanthroline-Derived Phosphonate Ligands.

N,O-hybrid diamide ligands with N-heterocyclic skeletons are one of the promising extractants for the selective separation of actinides over lanthanides in a highly acidic HNO3 solution In this work, three hard-soft donor mixed diamide ligands, pyridine-2,6-diylbis(pyrrolidin-1-ylmethanone) (Pyr-PyDA), 2,2'-bipyridine-6,6'-diylbis(pyr-rolidine-1-ylmethanone) (Pyr-BPyDA), and (1,10-phenanthroline-2,9-diyl)bis(pyrrolidin-1-ylmethanone) (Pyr-DAPhen), were synthesized and used to probe the influence of N-heterocyclic cores on the complexation and extraction behaviors with trivalent lanthanides and actinides 1H NMR titration experiments demonstrated that 1:1 metal-to-ligand complexes were mainly formed between the three ligands and lanthanides, but 1:2 type complexes were also formed between tridentate Pyr-PyDA and Lu(III) The stability constants (log β) of these three ligands with two typical lanthanides, Nd(III) and Eu(III), were determined through spectrophotometric titration It is found that Pyr-DAPhen formed the most stable complexes, while Pyr-PyDA formed the most unstable complexes with lanthanides, which coincided well with the following solvent extraction results The solid-state structures of 1:1 type complexes of these three ligands with La(III), Nd(III), and Er(III) in nitrate media were identified by a single-crystal X-ray diffraction technique Nd(III) and Er(III) were 10-coordinated with Pyr-PyDA, Pyr-BPyDA, and Pyr-DAPhen via one ligand molecule and three nitrate ions La(III), because of its larger ionic radius, was 11-coordinated with Pyr-DAPhen through one ligand molecule, three nitrate ions, and one methanol molecule Solvent extraction experiments showed that the preorganized phenanthroline-derived Pyr-DAPhen had the best extraction performance for trivalent actinide among the three ligands tested This work provides some experimental insights into the design of more efficient ligands for trivalent actinide separation by adjusting the N-heterocyclic cores

Influence of a N-Heterocyclic Core on the Binding Capability of N,O-Hybrid Diamide Ligands toward Trivalent Lanthanides and Actinides.

The chemical separation of minor actinides (MAs) over lanthanides from high-level waste (HLW) is one of the hottest and most difficult topics in international separation science. N, O-hybrid phenanthroline-derived extractants have shown good potential in the separation of minor actinides over lanthanides from highly acidic HNO3 solution by liquid–liquid solvent or solid extraction method. The 1,10-phenanthroline skeleton can serve as a platform to design various extractants for the separation of actinides. In this review, the recent progress made in the hard-soft donors combined 1,10-phenanthroline type extractants for separation and complexation with f-block elements is summarized. The structure–activity relationships between the extractants and their separation performances are discussed, which can provide practical strategies to design more efficient extractants for actinides separation. Finally, the future perspectives and trends in those phenanthroline-derived extractants for actinides separation are proposed. 

Separation and complexation of f-block elements using hard-soft donors combined phenanthroline extractants

In this work, a tetradentate N,O-hybrid 2,9-bis(diphenylphosphine oxide)-1,10-phenanthroline (Ph2-BPPhen) ligand was studied for the coextraction of trivalent f-block elements from nitric acid media. The extraction as well as the complexation behaviors of Ph2-BPPhen with f-block elements were thoroughly investigated using 31P and 1H NMR spectrometry, UV-vis spectrophotometry, single crystal X-ray diffraction, and density functional theoretical (DFT) calculation. Ph2-BPPhen exhibits remarkably extraction ability for both Am(III) and Eu(III) and more than 99.5% of Am(III) and Eu(III) were extracted from 1.0 M HNO3 solution. Slope analysis suggests that both 2:1 and 1:1 ligand/metal complexes were probably formed during the extraction. The 1:1 and 2:1 Ln(III) complexes with Ph2-BPPhen were also identified in CH3OH solution by NMR spectrometry, and the stability constants were determined via UV-vis spectrophotometry. Structures of the 1:1 Eu(Ph2-BPPhen)(NO3)3 and Am(Ph2-BPPhen)(NO3)3 complexes were further elucidated by single X-ray crystallography and DFT calculations. The higher extractability of Ph2-BPPhen toward trivalent Am(III) and Eu(III) compared with the previously reported phenanthroline-derived amide and phosphonate ligands was attributed to the stronger affinity of the -P═O(R)2 group to metal ions. The results from this work indicate that the N,O-hybrid 1,10-phenanthroline derived phosphine oxide ligand can serve as a new and promising candidate for coextraction of trivalent f-block elements in the treatment of nuclear waste.

Unfolding the Extraction and Complexation Behaviors of Trivalent f-Block Elements by a Tetradentate N,O-Hybrid Phenanthroline Derived Phosphine Oxide Ligand.

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.

Study on Phenanthroline Carboxamide for Lanthanide Separation: Influence of Amide Substituents.

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 ac...

Quantitative Analysis of Cs Extraction by Some Dialkoxycalix[4]Arene-Crown-6 Extractants

/pdf/cesium-liquid-liquid-extraction-by-calix-crown-ethers-33u3d575ij.pdf

Cesium liquid-liquid extraction by calix-crown ethers: solvent effect

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. T...

Lanthanide Intra-series Separation by a 1,10-Phenanthroline Derivative: Counterion Effect

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Study on Phenanthroline Carboxamide for Lanthanide Separation: Influence of Amide Substituents.

Quantitative Analysis of Cs Extraction by Some Dialkoxycalix[4]Arene-Crown-6 Extractants

Cesium liquid-liquid extraction by calix-crown ethers: solvent effect

Lanthanide Intra-series Separation by a 1,10-Phenanthroline Derivative: Counterion Effect