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Two solid phase extraction resins (SPER) were prepared by impregnating solutions of two diglycolamide-functionalized calix[4]arenes in 10% isodecanol in n-dodecane into Chromosorb W, as the stationary phase. While SPER-I contained n-propyl functionalized calix[4]arene, SPER-II contained the calix[4]arene with isopentyl groups at the carboxamide nitrogen atoms. The SPERs were characterized by SEM, TGA, FTIR, etc. and were used for the batch uptake of neptunium(IV) from nitric acid feed solutions. While the uptake of Np(IV) was extremely high with SPER-I (K d : 47,544 at 3 M nitric acid, ca. 8% extractant loading), SPER-II displayed a significantly lower extraction efficiency (K d : 13,724 under identical conditions) as indicated by the batch uptake studies. Sorption isotherm studies were carried out which indicated good fitting to the Langmuir model suggesting uptake conforming to monolayer sorption. Fitting to the D-R isotherm model conformed to a chemisorption model. Column studies were also carried out and the elution profiles, obtained with solutions of oxalic acid and nitric acid indicated very sharp peaks suggesting that the column can be used for the separation of Np(IV) from acidic radioactive feeds., Competing Interests: Declaration of Competing Interest The authors have no conflict of interest to declare., (Copyright © 2021. Published by Elsevier B.V.)

Low molecular weight diglycolamide (DGA) extractants were tested for the extraction of europium(III) and americium(III) from nitric acid solutions in n-dodecane, a molecular diluent and 1-butyl-3-methylimidazolium bis(trifluoromethanesulphonyl) imide (C 4 mim⋅NTf 2 ), a room temperature ionic liquid, as the diluents. N,N,N',N'-tetra-n-butyl diglycolamide (TBDGA) was selected for extraction chromatography (XC) studies involving Eu(III) and Am(III). While the TBDGA resin containing n-dodecane gave reasonably high K d values, that containing the ionic liquid showed higher Eu(III) uptake values. Compared to Eu(III), Am(III) was extracted by the resins to a lower extent. The loaded Eu(III) was back extracted from the resin using 0.05 M EDTA solutions in a buffered medium containing 1 M guanidine carbonate. Reusability studies indicated that, while the ionic liquid-based resin can be conveniently recycled five times with very marginal decrease in the percentage extraction values, there was a sharp decrease in the percent extraction after three cycles with the n-dodecane-based resin. The uptake data was fitted into different isotherm models and the results conformed to the Langmuir model. Based on the batch uptake studies, columns were prepared and the breakthrough as well as elution profiles were obtained. The elution profiles were found to be sharp without any significant tailing., Competing Interests: Declaration of Competing Interest The authors have no conflict of interest to declare., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Two diglycolamide (DGA) functionalized poly(propylene imine)diaminobutane dendrimers, first generation (Gen I) and second generation (Gen II), termed as LI and LII, were used for the extraction of the tetravalent actinide ions Np4+ and Pu4+ from nitric acid medium. The metal ion extraction followed a 'solvation' type mechanism showing increasing metal ion extraction with increasing nitric acid concentration with species of the type: M(NO3)4·L (M = Np or Pu) with some contribution of M(NO3)4·2L for Pu. Pu4+ formed much stronger complexes with both DGA-dendrimer ligands as compared with Np4+, as reflected in their two-phase extraction constants and higher ΔH values, attributed to its higher ionic potential. Binding of the metal ions was to one 'DGA pocket' in each of the dendrimers. The structure and bonding analysis was done on the basis of DFT studies. [ABSTRACT FROM AUTHOR]

Neptunium is one of the most important minor actinide elements with some of its isotopes having very long half-lives, therefore necessitating its separation from acidic radioactive wastes. Solvent extraction of Np4+ and NpO22+ was studied using three multiple diglycolamide (DGA) extractants with n-propyl, n-octyl and 3-pentyl substituents termed as LI, LII and LIII, respectively, in a mixed diluent of 5% isodecanol and 95% n-dodecane. For comparison purpose, the extraction of Pu4+ and UO22+ was carried out under identical conditions. The extraction efficiency of the ligands for the tetravalent ions followed the trend: LII > LI > LIII, which changed to LIII > LII > LI for the hexavalent ions. While the extraction of the tetravalent ions was reasonably good (ca. 90–98%) with an extremely low (5.0 × 10−5 M) ligand concentration, poor extraction (ca. 5–16%) of the hexavalent ions was seen even with a 20 times higher concentration of the ligand. In general, Pu4+ was better extracted than Np4+, while NpO22+ was marginally better extracted then UO22+. A 'solvation' type extraction mechanism was proposed based on the extraction profiles obtained as a function of the concentrations of the feed nitric acid, extractant as well as nitrate ion. The extracted species were found out to be M(NO3)4·mL and MO2(NO3)2·nL (M = Np or Pu, 1 < m < 2, n ≃ 1). [ABSTRACT FROM AUTHOR]

• Three tripodal diglycolamide extractants were evaluated for the extraction of Np(IV and Np(VI) • The studies using ionic liquids resulted in higher extraction as compared to those in molecular diluents. • The benzene based tripodal was the most efficient and extraction of Np(IV) was much higher than that of Np(VI) • The nature of the extracted species was determined by slope analysis and structural models are given. • The bonding in the extracted species was studied by Vis-NIR spectroscopy and cyclic voltammetry. Complexation of Np(IV) and Np(VI) ions was studied in a room temperature ionic liquid (C 4 mim.NTf 2) using three tripodal ligands with an 'N' atom, a 'C' atom and a benzene ring at the center, which are termed as L I , L II and L III , respectively. The studies include solvent extraction, visible-near infrared (vis-NIR) spectroscopy, and cyclic voltammetry. The trend of the extraction of Np4+ was L III > L II > L I , which resembled that reported before in a mixture of molecular diluents but with about 10 times higher ligand concentration. Np(VI) was extracted to a much lower extent than Np(IV). Slope analysis of Np(IV) extraction suggested formation of Np(NO 3) 4.L species for L II and L III , while a cationic species of the type [Np(NO 3) 2.L]2+ was seen for L I. On the other hand, for Np(VI), formation of NpO 2 (NO 3) 2. L species was proposed for L I and L III and [NpO 2 (NO 3). L ]+ for L II. All the extracted species conform to a 'solvation' type extraction except for Np(IV) with L I and Np(VI) with L II which point to a 'cation-exchange' mechanism. The complexation of the metal ions with the tripodal ligands was supported by peak shifts in the vis-NIR as well as the cyclic voltammetric studies. [ABSTRACT FROM AUTHOR]

• An extraction chromatographic resins containing TBDGA in C 4 mimNTf 2 was evaluated for Pu uptake. • The resin showed very high uptake efficiency for Pu and was tested for Pu recovery from acidic feeds. • The reusability of the resin was found to be quite satisfactory from data obtained in four cycles. • Column studies showed very encouraging results and only 8 mL was needed for >99% recovery. • Kinetic modeling and fitting of the uptake data to various sorption isotherms was also done. An extraction chromatography (XC) material containing N,N,N',N' -tetra- n -butyl diglycolamide (TBDGA) and 1-butyl-3-methylimidazolium bis(trifluoromethanesulphonyl) imide (C 4 mim∙NTf 2), a room temperature ionic liquid, was used for the uptake of the tetravalent actinide ions Th(IV), Np(IV), and Pu(IV) from nitric acid feed solutions. The uptake of the metal ions followed the trend: Th(IV) < Np(IV) < Pu(IV), which is the same as that of their ionic potential values. While a decrease in the Np(IV) and Pu(IV) uptake was seen with increasing HNO 3 concentration at lower acidities, an opposite trend was observed at higher acidities. Th(IV) uptake was not affected with the acid concentration. In view of the very high uptake and its importance in the nuclear fuel cycle, the major part of the studies was carried out with Pu(IV) ion. The loaded Pu(IV) was back extracted from the XC material using a mixture of 0.5 M oxalic acid and 0.5 M nitric acid. The Pu(IV) uptake by the XC material was fitted into different kinetic and isotherm models. The results conformed to the pseudo-second order kinetic model and the Langmuir monolayer sorption model. Column studies were carried out using a feed having 1.6 mg/L Pu solution in 3 M HNO 3. While the breakthrough was obtained after passing ca. nine bed volumes, a sharp elution peak was obtained with >99% recovery in about seven bed volumes. [ABSTRACT FROM AUTHOR]

• Two resins containing Chromosorb W and DGA-calix[4]arenes were prepared and characterized. • Batch uptake studies were carried out using Th-234 and U-233 radiotracers. • Column studies were done to obtain a breakthrough profile of Th-234, while U was not retained. • Th-234 was separated from bulk U with a decontamination factor of ca. 170. • Kinetic modeling and sorption isotherm studies were also carried out. Two novel extraction chromatography resins (ECRs) containing two diglycolamide (DGA) -functionalized calix[4]arenes with n -propyl and isopentyl substituents at the amide nitrogen atom, termed as ECR-1 and ECR-2, respectively, were evaluated for the uptake of Th(IV) from nitric acid feed solutions. While both the resins were having a quite high Th(IV) uptake ability (K d >3000 at 3 M HNO 3), the uptake was relatively lower with the resin containing the isopentyl DGA, which appeared magnified at lower nitric acid concentrations. Kinetic modeling of the sorption data suggested fitting to the pseudo-second order model pointing to a chemical reaction during the uptake of the metal ion. Sorption isotherm studies were carried out showing a good fitting to the Langmuir and D-R isotherm models, suggesting the uptake conforming to monolayer sorption and a chemisorption model. Glass columns with a bed volume of ca. 2.5 mL containing ca. 0.5 g lots of the ECRs were used for studies to assess the possibility of actual applications of the ECRs. Breakthrough profiles obtained with feed containing 0.7 g/L Th(NO 3) 3 solution resulted in breakthrough volumes of 8 and 5 mL, respectively, for the ECR-1 and ECR-2 resins. Near quantitative elution of the loaded metal ion was possible using a solution of oxalic acid and nitric acid. A method for the separation of Th-234 from natural uranium was demonstrated for the possible application of ECR-1. [ABSTRACT FROM AUTHOR]

• Three tripodal diglycolamide extractants were evaluated for the extraction of Np(IV and Pu(IV). • The tripodal ligand with a benzene center was considered as the most efficient. • Pu(IV) was extracted to a much higher extent than Np(IV) with all the three ligands. • The order of extraction for other metal ions was: Am3+ > UO 2 2+ ~ NpO 2 2+ > Sr2+ > Cs+. Studies on the liquid – liquid extraction of Np4+ and Pu4+ were carried out using three tripodal diglycolamide ligands with different centers viz. a carbon atom (termed as C-pivot tripodal DGA or T-DGA), a nitrogen atom (termed as N-pivot tripodal DGA or TREN-DGA) and a benzene centered tripodal diglycolamide (termed as TAETEB) in an aliphatic diluent mixture of n -dodecane (95%) and isodecanol (5%). The extraction efficiency of the ligands followed the trend: TAETEB > T-DGA > TREN-DGA, while Pu4+ was far more efficiently extracted than Np4+. A solvation type extraction mechanism was proposed based on the extraction profiles obtained as a function of the feed nitric acid concentration where the extracted species was found out to be M(NO 3) 4 · n L (where M = Np or Pu and n was in between 1 and 2). The extraction of other relevant metal ions was also investigated which followed the trend: Am3+ > UO 2 2+ ~ NpO 2 2+ > Sr2+ > Cs+. While Am3+ extraction was lower with TREN-DGA as compared to that of Np4+ and Pu4+, the trend being Am3+ < Np4+ < Pu4+, the relative extraction trend changed with the extractants to Np4+ < Am3+ < Pu4+ for T-DGA and to Np4+ < Pu4+ < Am3+ for TAETEB. The radiolytic stability of the extractants showed contrasting behavior with respect to the metal ion extraction. While the solvent containing 1 × 10−3 M solutions of the ligands showed decreased metal ion extraction for T-DGA and TAETEB when exposed to 200 kGy gamma radiation, an opposite trend was seen for TREN-DGA where the metal ion extraction was found to increase by over 2 times. The metal ions were efficiently stripped using a mixture of 0.5 M oxalic acid and 0.5 M nitric acid. Temperature variation studies were carried out to determine the thermodynamic parameters. [ABSTRACT FROM AUTHOR]

The extraction of Np4+ and NpO 2 2+ was investigated from nitric acid feeds using solutions of tri- n -butyl phosphate (TBP) in two room temperature ionic liquids viz. 1-butyl-3-methylimidazolium bis(trifluoromethane)sulfonamide (C 4 mim•NTf 2) and 1-methyl-3-octylimidazolium bis(trifluoromethane)sulfonamide (C 8 mim•NTf 2). For comparison purposes, the extraction of Pu4+ and UO 2 2+ were also studied in select cases in view of their similarity with the tetra- and hexavalent neptunium ions. The nature of the extracted species was ascertained by slope analysis and two-phase extraction constants were determined. While the Np4+ ion bearing species of the type Np(NO 3) 3 (TBP) 2 + and Np(NO 3) 3 (TBP)+ were extracted into C 4 mim•NTf 2 and C 8 mim•NTf 2 , respectively, species of the type NpO 2 (NO 3) 2 ∙TBP were obtained for NpO 2 2+ ion in both the ionic liquids. The extraction data were compared with those reported before in other solvent systems. Cyclic voltammetric studies were carried out using the Np(IV)-TBP extract in both the ionic liquid medium and the conversion to the penta-valent state (NpO 2 +) was confirmed by UV–visible spectrophotometric analysis of the extract. • The extraction of Np(IV) and Np(VI) from nitric acid was studied in ionic liquids containing TBP. • For comparison purposes, the extraction of Pu(IV) and U(VI) were studied under identical conditions. • The extracted species were determined by slope analysis. • Spectroelectrochemical studies were carried out to identify the Np(V) obtained by cyclic voltametry. [ABSTRACT FROM AUTHOR]