Highly selective separation of tetravalent plutonium from complex system with novel phenylpyridine diamide ligands

In this study, three phenylpyridine diamide ligands, namely, 2,2'-((pyridine-2,6-diylbis(3,1-phenylene))bis(oxy))bis(N,N-diethylacetamide) (PPEA, L1), 2,2'-((pyridine-2,6-diylbis(3,1-phenylene))bis(oxy))bis(N-ethyl-N-phenylacetamide) (PEPA, L2), and 2,2'-(((4-phenylpyridine-2,6-diyl)bis(3,1-phenylene))bis(oxy))bis(N,N-dioctylacetamide) (PPOA, L3), were synthesized and explored for the solvent extraction of Pu(iv) in a HNO3 medium using 1-(trifluoromethyl)-3-nitrobenzene as the diluent. The effects of HNO3 concentration, extractant concentration, and temperature on the Pu(iv) extraction efficiency were studied. All three extractants displayed high selectivity for Pu(iv) over other metals such as U(vi), Np(v), Am(iii), and various fission elements. At 3 M HNO3, the distribution ratio for Pu(iv) reached 27.18, in contrast to 1.11, 0.3, and 0.03 for U(vi), Np(v), Am(iii), respectively. Slope analysis and UV titration revealed the formation of 1 : 1 Pu(NO3)4/ligand complexes during extraction. The extraction reactions had negative Gibbs free energies, indicating the spontaneous nature of Pu(iv) extraction at room temperature. Furthermore, the extractants demonstrated good stripping ability and reusability, and their radiolytic stability was reasonable up to an absorbed dose of 100 kGy, underscoring their potential for practical applications. Overall, this study broadens our understanding of actinide-diamide ligand coordination and actinide chemistry during coordination, paving the way for the design and synthesis of new extractants.

Solvent extraction of rare earths elements from nitrate media in DMDOHEMA/ionic liquid systems: performance and mechanism studies

Extraction of La(iii), Eu(iii) and Fe(iii) was compared in n-dodecane and two ionic liquids (ILs) (1-ethyl-1-butylpiperidinium bis (trifluoromethylsulfonyl)imide [EBPip⁺] [NTf₂⁻] and 1-ethyl-1-octylpiperidinium bis (trifluoromethylsulfonyl)imide [EOPip⁺] [NTf₂⁻]). Using the extractant N,N′-dimethyl-N,N′-dioctylhexylethoxymalonamide (DMDOHEMA), the effect of pH was investigated in detail to recover extraction mechanisms. The use of ILs as the organic solvent instead of n-dodecane, greatly enhances extraction efficiency, and an ionic liquid with a shorter alkyl chain [EBPip⁺] [NTf₂⁻] provides higher extraction than [EOPip⁺] [NTf₂⁻]. The mechanistic study points out that for low nitric acid concentrations ([HNO₃] ≤ 0.01 M), metal is extracted via a cation of the ionic liquids, while for higher nitric acid concentrations ([HNO₃] ≥ 1.0 M), extraction occurs through pure solvation mechanism of DMDOHEMA as in conventional diluents. This latter case is of high interest for applications, as higher extraction can be obtained without any loss of ILs by ion exchange mechanisms.

Extraction of La(iii), Eu(iii) and Fe(iii) was compared in n-dodecane and in two ionic liquids (ILs) [EBPip⁺] [NTf₂⁻] and [EOPip⁺] [NTf₂⁻]. Extraction mechanisms have been investigated as a function of pH.

Sequestration of tetravalent neptunium from acidic feeds using diglycolamide-functionalized dendrimers in a room temperature ionic liquid: extraction, spectroscopic and electrochemical studies

Extraction of Np(iv) was studied using RTIL containing two poly(propyleneimine) based dendrimer ligands from HNO3 solutions. Studies of the extracted complexes were also carried out by Vis-NIR and cyclic voltammetry.

Hydrophobic polymerized ionic liquids for trace metal solid phase extraction: thallium transfer from hydrochloric acid media

To our knowledge, there are a few articles on the application of polymerized ionic liquids for metal extraction from aqueous solutions.

Effect of an alkyl substituent and spacer length in benzene-centered tripodal diglycolamides on the sequestration of minor actinides

Three benzene-centered tripodal diglycolamide (Bz-T-DGA) ligands, where diglycolamide (DGA) moieties are tethered to the central benzene ring through a methylene spacer and having either a hydrogen atom (LI) or an isopentyl group (LII) attached to the N-atom, and DGA moieties attached via an ethylene spacer and having an isopentyl group attached to the N-atom (LIII), were studied for their complexation and extraction abilities towards trivalent actinides and lanthanides. The distribution ratio of Am(iii) and Eu(iii) with 1 mmol L-1 ligand in 5% iso-decanol/n-dodecane followed the order: LII > LIII > LI. The substitution of the H atom with the isopentyl group on the N-atom of the DGA moieties resulted in two orders of magnitude enhancement in the extraction ability of the ligand. On the other hand, increase in the spacer length between the benzene ring and the DGA moieties resulted in several fold reduction in the extraction ability of the ligand. Spectroscopic studies with Eu3+ ions in acetonitrile also confirmed the metal/ligand complex formation constant in the order: LII > LIII > LI. Luminescence decay lifetimes of Eu3+/ligand complexes confirmed the absence of water molecules and that all the primary coordination sites of the metal ion are occupied by the ligands.

Unique reversibility in extraction mechanism of U compared to solvent extraction for sorption of U(VI) and Pu(IV) by a novel solvent impregnated resin containing trialkyl phosphine oxide functionalized ionic liquid

Novel Solvent Impregnated Resin (SIR) material was prepared by impregnating a trialkyl phosphine oxide functionalized ionic liquid (IL) into an inert polymeric material XAD-7. A series of SIR materials were prepared by varying the IL quantity. Sorption of both U(VI) and Pu(IV) were found to increase with increasing IL concentration in SIR up to an optimum IL concentration of 435 mg g^-1 of SIR beyond which no effect of IL concentration was observed. A change of mechanism of sorption for U(VI) by SIR was observed in comparison to solvent extraction. The dependency of U(VI) sorption with nitric acid concentration showed a reverse trend compared to solvent extraction studies while for Pu(IV) the trend remained same as observed with solvent extraction. Sorption of both the radionuclides was found to follow pseudo second order mechanism and Langmuir adsorption isotherm. Distribution co-efficient measurements on IL impregnated SIR showed highly selective sorption of U(VI) and Pu(IV) over other trivalent f-elements and fission products from nitric acid medium.

Separation of neptunium (IV) from actinides by solid phase extraction using a resin containing Aliquat 336

An extraction chromatographic resin material containing Aliquat 336 as the liquid anion exchanger extractant and Chromosorb W as the solid support was prepared and tested for the uptake of UO₂²⁺, Np⁴⁺, Pu⁴⁺, and Pu³⁺ from nitric acid feed solutions. The resin beads were characterized by thermogravimetry/differential thermogravimetry (TG/DTG) and scanning electron microscopy (SEM) surface morphology analysis. The uptake trend for the metal ions from 3 M HNO₃ was found to be Pu⁴⁺ >> Np⁴⁺ >> UO₂²⁺ > Pu³⁺ which clearly followed the trend of their ionic potentials. In view of the significant difference in the uptake of Np⁴⁺ with respect to those of UO₂²⁺ and Pu³⁺, a separation scheme was developed for the selective separation of Np from feeds containing U, Np and Pu in nitric acid. The purity of the product was verified by alpha spectrometry.

Extraction of plutonium(IV) by diglycolamide extractants in room temperature ionic liquids

Extraction of Pu(IV) was investigated using solutions of two diglycolamide extractants viz., N,N,N′,N′-tetra-n-octyldiglycolamide (TODGA) and its branched homolog, N,N,N′,N′-tetra(2-ethylhexyl) diglycolamide (T2EHDGA), dissolved in two imidazolium based room temperature ionic liquids viz., 1-butyl-3-methylimidazolium bis(trifluoromethanesulphonyl) imide ([C4mim][NTf2]) and 1-octyl-3-methylimidazolium bis(trifluoromethanesulphonyl) imide ([C8mim][NTf2]) from aqueous nitric acid medium. The extraction kinetics was found to be extremely slow which is reported for the first time for analogous extraction systems and took as long as 30 h to attain equilibrium D Pu values. In general, TODGA based solvents showed better extraction of Pu(IV) than the T2EHDGA based solvents, one order of magnitude higher, and though both the ionic liquids ultimately yielded comparable D Pu values, attainment of equilibrium was slower with [C4mim][NTf2]. The extracted species conformed to 1:1 for TODGA in both the ionic liquids while a mixture of 1:1 and 1:2 species was observed for T2EHDGA at 1 M HNO3 which changed to 1:1 species at 4 M HNO3. The extracted species is proposed to be (Pu(L)x 4+)IL (where, L is the extractant and x=1 or 2) at lower acidities suggesting a cation exchange mechanism which changes over to (Pu(NO3)4⋅L)IL at 4 M HNO3 conforming to a solvation mechanism for all the systems except for T2EHDGA-[C8mim][NTf2]. UV-VIS spectroscopic studies were carried out to throw light on the nature of the extracted species.

Unusual extraction of trivalent f-cations using diglycolamide dendrimers in a room temperature ionic liquid: extraction, spectroscopic and DFT studies

The complexation of Am³⁺ and Eu³⁺ was studied with three generations of DGA-Den ligands in a room temperature ionic liquid.

Actinide ion extraction using room temperature ionic liquids: opportunities and challenges for nuclear fuel cycle applications

Studies on the extraction of actinide ions from radioactive wastes have great relevance in nuclear fuel cycle activities, mainly in the back end processes focused on reprocessing and waste management.

An ionic liquid-based extraction system using diglycolamide functionalized macrocyclic platforms for the extraction and recovery of lanthanides

Macrocyclic-DGA platforms are engaged in an ionic liquid-based extraction system. The system exhibits selectivity for middle and heavy lanthanides.

Role of Tf2N− anions in the ionic liquid–water distribution of europium(iii) chelates

The replacement of water molecules of [Eu(tta)₃(H₂O)₃] with Tf₂N⁻ was evidenced in water-saturated [C_nmim][Tf₂N] by time-resolved laser-induced fluorescence spectroscopy.

Thallium Transfer from Hydrochloric Acid Media into Pure Ionic Liquids

Pure hydrophobic ionic liquids are known to extract metallic species from aqueous solutions. In this work we have systematically investigated thallium (Tl) extraction from aqueous hydrochloric acid (HCl) solutions into six pure fluorinated ionic liquids, namely imidazolium- and pyrrolidinium-based ionic liquids with bis(trifluoromethanesulfonyl)imide and bis(fluorosulfonyl)-imide anions. The dependence of the Tl extraction efficiency on the structure and composition of the ionic liquid ions, metal oxidation state, and initial metal and aqueous acid concentrations have been studied. Tl concentrations were on the order of picomolar (analyzed using radioactive tracers) and millimolar (analyzed using inductively coupled plasma mass spectrometry). The extraction of the cationic thallium species Tl(+) is higher for ionic liquids with more hydrophilic cations, while for the TlX(z)(3-z) anionic species (where X = Cl(-) and/or Br(-)), the extraction efficiency is greater for ionic liquids with more hydrophobic cations. The highest distribution value of Tl(III) was approximately 2000. An improved mathematical model based on ion exchange and ion pair formation mechanisms has been developed to describe the coextraction of two different anionic species, and the relative contributions of each mechanism have been determined.

Mutual solubility of water and hydrophobic ionic liquids in the presence of hydrochloric acid

Possible mechanism for ionic liquid dissolution in HCl solution.