Extraction Behavior of Ln(III) Ions by T2EHDGA/<i>n</i>-Dodecane from Nitric Acid and Sodium Nitrate Solutions

Campbell, Emily L.; Holfeltz, Vanessa E.; Hall, Gabriel B.; Nash, Kenneth L.; Lumetta, Gregg J.; Levitskaia, Tatiana G.

doi:10.1080/07366299.2018.1447261

Cited by 29 publications

(39 citation statements)

References 36 publications

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“…Table 1 shows the asymmetric factor (A 2 /A 1 ) in the case of 0.1 M T2EHDGA/n-DD and it varies from 2 to 2.9 in the studied feed acidity of 0.5 M-3 M. This trend could be attributed to the fact that the extraction of Eu(III) in 0.1 M T2EHDGA/n-DD follows a neutral solvation mechanism and the extraction factor of Eu(III) is improved with raise in the feed acidity. [20,21] However, the values of A 2 /A 1 refers that there is already stable complex formed between Eu(III) and T2EHDGA at 0.5 M nitric acid concentration (A 2 /A 1 = 2) and the gradual enhancement in A2/A1 at high acidity is only due to the increase in the abundance of metal-solvate species (table 1). Table 1 also highlights the lifetimes (τ) of Eu (III) in Eu-T2EHDGA complex at each acidity.…”

Section: Luminescence Spectra Of Eu(iii) In Aqueous and N-dd Phasementioning

confidence: 99%

Europium(III) Coordination in a Combined Ligand System: A Luminescence Spectroscopy Study

2020

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The coordination of europium(III) in a combined ligand system has been probed by luminescence spectroscopy by extracting it from nitric acid medium. The ligands used in the study are N,N,N′,N′‐tetra‐bis(2‐ethylhexyl)diglycolamide (T2EHDGA) and bis(2‐ethylhexyl)phosphoric acid (D2EHPA). Europium(III) complex with these ligands present in n‐Dodecane (n‐DD) medium and its detailed investigation by luminescence spectroscopy is emphasized in this paper. Various experimental parameters such as aqueous phase acidity, concentration of ligand and initial metal ion, radiation dose, etc. were tuned to find the luminescence behavior of Eu(III) in the extracted phase. The emission intensity of Eu(III) was extremely high in the organic phase after extraction at all nitric acid phases (0.5 M to 3 M HNO3) for T2EHDGA/n‐DD and from 0.01 M to 1 M for D2EHPA/n‐DD) as compared to that of the aqueous phase. The principal driving force for the complexation mechanism of Eu(III) at each nitric acid was ascertained by varying the concentration of D2EHPA in the solution of 0.1 M T2EHDGA/n‐DD. The decay profile of the Eu(III) complex was remarkably high (>1.2 millisecond (ms)) indicating theformation of inner‐sphere complex of Eu(III) with the ligands. The emission profile of Eu(III) was recorded in the irradiated solvent compositions and was compared with respect to unirradiated condition.

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Section: Luminescence Spectra Of Eu(iii) In Aqueous and N-dd Phasementioning

confidence: 99%

Europium(III) Coordination in a Combined Ligand System: A Luminescence Spectroscopy Study

2020

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“…Acid extraction breaks the dimeric form of T2EHDGA to form (HNO 3 )·T2EHDGA and (HNO 3 ) 2 ·T2EHDGA. When Ln 3+ ions are present in the aqueous phase, it was shown that not only do DGA and coextracted NO 3 – play a role in the coordination sphere but HNO 3 does as well . The stoichiometries of the organic complex were determined; however, the exact structure remained elusive.…”

Section: Introductionmentioning

confidence: 99%

Evolution of Acid-Dependent Am³⁺ and Eu³⁺ Organic Coordination Environment: Effects on the Extraction Efficiency

et al. 2020

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Coordination of trivalent lanthanide and actinide metal ions by lipophilic diglycolamides and phosphonic acids has been proposed for their separation through extraction from aqueous nitric acid solutions. However, the nature of M3+ coordination complexes in these combined solvent systems is not well understood, resulting in low predictability of their behavior. This work demonstrates that a combination of N,N,N′,N′-tetrakis(2-ethylhexyl)diglycolamide (T2EHDGA) and weakly acidic 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) in n-dodecane exhibits a complicated extraction mechanism for Eu3+ and Am3+, which continuously evolves as a function of the aqueous phase acidity. At low aqueous phase nitric acid concentrations, M3+ ions are primarily extracted via exchange of the phosphonic acid proton and coordination with HEH[EHP]. At high aqueous phase nitric acid concentrations, HEH[EHP] remains protonated, and M3+ ions are transported to the organic phase by the coextraction of nitrate anions from the aqueous phase, thus forming complex species with T2EHDGA. At moderate acid regimes, both ligands participate in the coordination of M3+ ions and show a synergistic relationship resulting in considerable enhancement of M3+ transport into the combined solvent system over the simple sum of the individual extractants. The observed synergism is caused by differences in organic phase M3+ speciation and has a significant impact on the performance of the organic solvent. Distribution studies with Eu3+ indicate that nominally two or three T2EHDGA ligands participate in metal extraction in the presence of phosphonic acid, while nominally three diglycolamide ligands participate in the presence or absence of phosphonic acid. While synergistic behavior has been observed in many solvent-extraction processes, this system demonstrates a clear correlation between the continuously changing organic speciation of M3+ and its transport into the organic solvent. This paper reports the spectroscopic characterization of the organic phase M3+ species by IR, X-ray absorption, and visible spectroscopies. Spectroscopic evidence indicates a mixed-ligand complex, i.e., a ternary complex at the moderate acid regime, where the greatest degree of synergism is observed. Differences in synergistic extraction of Am3+ and Eu3+ at the low acid regime were observed, indicating their dissimilar extraction behavior.

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“…This prediction hinted that metal/ligand complexation alone is not a sole contributor to the aggregation. In fact, any enthalpic contribution, such as protonation of the extractant polar headgroups or the water association to extractant headgroups, helps to fight the global entropy loss of confining extractant molecules to the crowded extractant film (expressed by MAL). Indeed, the prediction was backed by the tailored set of experiments with the aim of deciphering the synergistic peak, along with antagonistic and linear extraction regimes in DMDOHEMA and di(2-ethylhexyl) phosphoric acid (HDEHP) mixtures. , A full system speciation was predicted to provide for a complex phase diagram of metal extraction and aggregation as a function of the extractant mole fraction and the acid concentration in the aqueous phase.…”

Section: Introductionmentioning

confidence: 99%

Molecular Forces in Liquid–Liquid Extraction

et al. 2021

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The phase transfer of ions is driven by gradients of chemical potentials rather than concentrations alone (i.e., by both the molecular forces and entropy). Extraction is a combination of high-energy interactions that correspond to short-range forces in the first solvation shell such as ion pairing or complexation forces, with supramolecular and nanoscale organization. While the latter are similar to the long-range solvent-averaged interactions in the colloidal world, in solvent extraction they are associated with lower characteristic lengths of the nanometric domain. Modeling of such complex systems is especially complicated because the two domains are coupled, whereas the resulting free energy of extraction is around k B T to guarantee the reversibility of the practical process. Nevertheless, quantification is possible by considering a partitioning of space among the polar cores, interfacial film, and solvent. The resulting free energy of transfer can be rationalized by utilizing a combination of terms which represent strong complexation energies, counterbalanced by various entropic effects and the confinement of polar solutes in nanodomains dispersed in the diluent, together with interfacial extractant terms. We describe here this ienaics approach in the context of solvent extraction systems; it can also be applied to further complex ionic systems, such as membranes and biological interfaces.

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Extraction Behavior of Ln(III) Ions by T2EHDGA/n-Dodecane from Nitric Acid and Sodium Nitrate Solutions

Cited by 29 publications

References 36 publications

Europium(III) Coordination in a Combined Ligand System: A Luminescence Spectroscopy Study

Europium(III) Coordination in a Combined Ligand System: A Luminescence Spectroscopy Study

Evolution of Acid-Dependent Am³⁺ and Eu³⁺ Organic Coordination Environment: Effects on the Extraction Efficiency

Molecular Forces in Liquid–Liquid Extraction

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Extraction Behavior of Ln(III) Ions by T2EHDGA/n-Dodecane from Nitric Acid and Sodium Nitrate Solutions

Cited by 29 publications

References 36 publications

Europium(III) Coordination in a Combined Ligand System: A Luminescence Spectroscopy Study

Europium(III) Coordination in a Combined Ligand System: A Luminescence Spectroscopy Study

Evolution of Acid-Dependent Am3+ and Eu3+ Organic Coordination Environment: Effects on the Extraction Efficiency

Molecular Forces in Liquid–Liquid Extraction

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Product

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Evolution of Acid-Dependent Am³⁺ and Eu³⁺ Organic Coordination Environment: Effects on the Extraction Efficiency