In-Situ-Generated Fluoride-Assisted Rapid Dissolution of Uranium Oxides by Ionic Liquids.

A quantitative, rapid, endothermic dissolution of U3O8 in C4mim·PF6 (1-alkyl-3-methyl imidazolium hexafluorophosphate) has been achieved within 2 h at 65 °C by in situ generated fluoride ions by pre-equilibrating the ionic liquid with suitable concentrations of nitric acid. The efficiency of the dissolution followed the trend: UO3 > UO2 > U3O8. The fluoride generation was found to increase with the concentration of nitric acid being equilibrated, the water content of the ionic liquid, and also the time of equilibration. The rate of dissolution of U3O8 followed the trend: C4mim·PF6> C6mim·PF6 > C8mim·PF6. The maximum loading observed for the present case was 200 mg mL-1 which is considered to be quite high with an ionic liquid. The effects of different acid pre-equilibration (HClO4, HCl) on F- generation and subsequent dissolution characteristics have also been investigated. The in situ F- generation, as well as U3O8 dissolution, were found to predominantly follow a pseudo-second-order rate kinetics, while the rate constants for U3O8 dissolution were found to be higher than that of F- generation. The dissolved uranium was successfully electrodeposited on a Cu plate, as confirmed by EDXRF, while the formation of UO2 was revealed from the XRD pattern of the deposit.

Understanding the Interaction of Uranyl Cation with Two C-Pivot Tripodal Amides: Synthesis, Complexation, Microcalorimetry, and DFT Studies.

Complexation of uranyl ions with two structurally related C-pivotal tripodal amides with varying spacer lengths, synthesized for the first time, was studied by optical spectroscopy. In the tripodal amides, the coordination was through the carbonyl O atoms where the carbonyl groups were away from the central C-atom by three spacer atoms (LI) and four spacer atoms (LII), respectively. Increasing the spacer atoms going from LI to LII favors the complexation with the linear uranyl cations and results in stronger complex formation. The complexation heat between the uranyl cations and the two amide ligands was directly measured by microcalorimetric titrations. The complexation with both the ligands was driven by exothermic enthalpy and positive entropy changes. Formation of the complex proceeded by the replacement of water molecules from the primary coordination sphere of the uranyl cation. Both ligands formed bisolvated (ML2-type) complexes in which one unit of the ligand binds in a monodentate manner and the other in a bidentate mode. Density functional theory calculations further supported our experimental observations.

Experimental and Theoretical Insight into the Ionic Liquid-Mediated Complexation of Trivalent Lanthanides with ß-Diketone and Its Fluorinated Analogue.

A multitechnique approach with theoretical insights has been employed to understand the complexation of trivalent lanthanides with two ß-diketones, viz. 1-phenyl-1,3-butanedione (L1) and 4,4,4-trifluoro-1-phenyl-1,3-butanedione (L2), in an ionic liquid (C6mim·NTf2). UV-vis spectral analysis of complexation using Nd3+ revealed the predominance of ML2+ and ML4- species. The stability constants for the PB complexes were higher (ß2 ∼ 10.45 ± 0.05, ß4 ∼ 15.51 ± 0.05) than those for the TPB (ß2 ∼ 7.56 ± 0.05, ß4 ∼ 13.19 ± 0.06). The photoluminescence titration using Eu3+ corroborated the same observations with slightly higher stability constants, probably due to the higher ionic potential of Eu3+. The more asymmetric (AL2ML4 ∼ 5.2) Eu-L2 complex was found to contain one water molecule in the primary coordination sphere of Eu3+ with more covalency of the Eu3+-O bond (Ω2L1 = 8.5 × 10-20, Ω4L1 = 1.3 × 10-20) compared to the less asymmetric Eu-L1 complex (AL1ML4 ∼ 3.5) with two water molecules having less Eu-O covalency (Judd-Offelt parameters: Ω2L1 = 7.3 × 10-20, Ω4L1 = 1.0 × 10-20). Liquid-liquid extraction studies involving Nd3+ and Eu3+ revealed the formation of the ML4- complex following an 'anion exchange' mechanism. The shift of the enol peak from 1176 to 1138 cm-1 on the complexation of the ß-diketones with Eu3+ was confirmed from the FTIR spectra. 1H NMR titration of the ß-diketones with La(NTf2)3 evidenced the participation of α-H of the ß-diketones and protons at C2, C4, and C5 positions of the methylimidazolium ring. For the ML2 complex, 4 donor O atoms are suggested to coordinate to the trivalent lanthanides with bond distances of 2.3297-2.411 Å for La-O, 2.206-2.236 Å for Eu-O, and 2.217-2.268 Å for Nd-O, respectively, while for the ML4 complex, 8 donor O atoms were coordinated with bond lengths of 2.506-2.559 Å for La-O, 2.367-2.447 Å for Eu-O, and 2.408-2.476 Å for Nd-O. The Nd3+ ion was higher by 9.7 kcal·mol-1 than that of the La3+ ion for the 1:4 complex. The complexation energy with L1 was quite higher than that with L2 for both 1:2 and 1:4 complexes. Using cyclic voltammetry, the redox behavior of trivalent lanthanides Eu and Gd with ß-diketonate in ionic liquid medium was probed and their redox energetic and kinetic parameters were determined.

Understanding the Complexation of Alkyl-Substituted Nitrilotriacetamides with Uranium: A Study by Absorption Spectroscopy and Microcalorimetry.

Complexation thermodynamics of UO22+ ions with a series of alkyl-substituted nitrilotriacetamides (NTA) was investigated by absorption spectroscopy and microcalorimetry. The hexamethyl derivative of NTA (HMNTA) forms the weakest two successive complexes with UO22+ ions with stability constants of log ß11 = 3.5 ± 0.1 and log ß12 = 6.1 ± 0.1. The formation constant values increased linearly with increasing alkyl chain length of the substituents from hexamethyl NTA to hexabutyl NTA (HBNTA) and to hexahexyl NTA (HHNTA). The complexation with each ligand was both enthalpy and entropy driven with exothermic enthalpy changes of ΔH11 = -14.7 ± 1.0 kJ/mol, ΔH12 = -10.2 ± 0.8 kJ/mol for HMNTA, ΔH11 = -19.2 ± 1.2 kJ/mol, ΔH12 = -16.4 ± 1.1 kJ/mol for HBNTA, and ΔH11 = -21.3 ± 1.4 kJ/mol, ΔH12 = -19.4 ± 2.3 kJ/mol for HHNTA. Similarly, the positive entropy changes with each ligand were ΔS11 = 18.1 ± 2.7 J/mol/K, ΔS12 = 82.9 ± 3.8 J/mol/K for HMNTA, ΔS11 = 14.4 ± 1.2 J/mol/K, ΔS12 = 87.2 ± 4.2 J/mol/K for HBNTA, and ΔS11 = 16.1 ± 2.4 J/mol/K, ΔS12 = 92.6 ± 3.1 J/mol/K for HHNTA. Structural features of the complex suggest the participation of two ligands coordinating in a bidentate mode via the carbonyl oxygens. The [UO2L2]2+ complexes appear to be noncentrosymmetric with two ligands and one water molecule occupying the equatorial plane of the dioxo uranyl cation. The structure of the complex was confirmed by 1H NMR titration, EXAFS measurements, and DFT calculations.

Remarkable Improvement in Am3+ and Cm3+ Separation Using a Cooperative Counter Selectivity Strategy by a Combination of Branched Diglycolamides and Hydrophilic Polyaza-heterocycles.

Separation of Am3+ and Cm3+ is one of the most challenging problems in the back-end of the nuclear fuel cycle. In the present work, we exploited the cooperative effect of the opposite selectivity of hydrophobic branched DGA derivatives and hydrophobic N-donor heterocyclic ligands taken in two different phases to achieve improved separation behavior. A systematic study was performed using a series of DGA derivatives to understand the effect and the position of branching in the alkyl chains on the separation behavior of Am3+ and Cm3+. A separation factor (S.F.) value as high as 10 for Cm3+ over Am3+ was obtained in the case of TiBDGA (N,N,N',N'-tetra-iso-butyl diglycolamide) using SO3PhBTPhen ((phenanthroline-2,9-diyl)-1,2,4-triazine-5,5,6,6-tetrayltetrabenzenesulfonic acid) as the aqueous complexant, which is the highest reported value so far for the ligand-based separation of Am3+ and Cm3+ without involving any oxidation or reduction step. The high selectivity favoring Cm3+ ion extraction in the case of this DGA derivative is also explained with the help of computational studies.

Ionic Liquid Assisted Exothermic Complexation of Trivalent Lanthanides with Fluorinated ß Diketone: Multitechnique Approach with Theoretical Insight.

The complexation of the betadiketone,1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedione (HFOD) was studied with trivalent lanthanide ions, viz. Nd3+, La3+, and Eu3+ in several methylimidazolium-based ionic liquids (Cnmim•NTf2, where, n = 4,6,8). In C6mim•NTf2, predominant formation of ML2+ and ML4- species was evidenced from the UV-vis absorption (Nd3+) as well as luminescence (Eu3+) spectral studies with log ß2 ≈ 5.88 ± 0.04, log ß4 ≈ 10.95 ± 0.06. The formation constants followed the trend C4mim•NTf2 > C6mim•NTf2 > C8mim•NTf2. The asymmetry factors for the ML2+ and ML4- species were found to be 1.2 and 1.59, respectively. The ML4- complex was found to have one primary coordination sphere water molecule with enhanced covalency between Eu3+ and O from HFOD (Judd Offelt constants Ω2 and Ω4 ≈ 17.2 and 2.35) compared to Eu3+aq, yet comparable to other ß diketones. Complexation-induced temperature increase was confirmed by calorimetric measurements, indicating the exothermic complexation reaction (ΔHcomplexation ≈ -13.7 kJ mol-1), which is also spontaneous in nature (ΔG ≈ -68.1 kJ mol-1), with an enhancement in the entropy values. Due to complexation, the shifts in the peak positions (1686.66 cm-1, 1633.53 cm-1) associated with ß diketone/ketone functional groups were evidenced. Density functional theory (DFT) calculation was performed to optimize the structural parameters including bond distance, bond angles, and energetics associated with the complexation.

Aggregation Behavior of Nitrilotriacetamide (NTAmide) Ligands in Thorium(IV) Extraction from Acidic Medium: Small-Angle Neutron Scattering, Fourier Transform Infrared, and Theoretical Studies.

Two tripodal amides obtained from nitrilotriacetic acid with n-butyl and n-octyl alkyl chains (HBNTA(LI) and HONTA(LII), respectively) were studied for the extraction of Th(IV) ions from nitric acid medium. The effect of the diluent medium, i.e., n-dodecane alone and a mixture of n-dodecane and 1-decanol, onto aggregate formation were investigated using small angle neutron scattering (SANS) studies. In addition, the influence of the ligand structure, nitric acid, and Th(IV) loading onto ligand aggregation and third-phase formation tendency was discussed.The LI/LII exist as monomers (aggregarte radius for LI: 6.0 Å; LII:7.4 Å) in the presence of 1-decanol, whereas LII forms dimers (aggregarte radius for LII:9.3 Å; LI does not dissolve in n-dodecane) in the absence of 1-decanol. The aggregation number increases for both the ligands after HNO3 and Th(IV) loading. The maximum organic concentration (0.050 ± 0.004 M) of Th(IV) was reached without third-phase formation for 0.1 M LI/LII dissolved in 20% isodecanol +80% n-dodecane. The interaction of 1-decanol with LII and HNO3/Th(IV) with amidic oxygens of LI/LII results in shift of carbonyl stretching frequency, as shown by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) studies. The structural and bonding information of the Th-LI/LII complex were derived from the density functional theoretical (DFT) studies. The molecular dynamics (MD) simulations suggested that the aggregation behavior of the ligand in the present system is governed by the population of hydrogen bonds by phase modifier around the ligand molecules. Although the theoretical studies suggested higher Gibbs free energy of complexation for Th4+ ions with LI than LII, the extraction was found to be higher with the latter, possibly due to the higher lipophilicity and solubility of the Th-LII aggregate in the nonpolar media.

In Situ Preconcentration during the Di-(2-ethylhexyl) Phosphoric Acid-Assisted Dissolution of Uranium Trioxide in an Ionic Liquid: Spectroscopic, Electrochemical, and Theoretical Studies.

Dissolution of uranium oxide was carried out using a solution of HD2EHP in C8mim·NTf2, which was apparently facilitated by the in situ generation of water during the complex formation reaction. The dissolved complex in the ionic liquid phase led to splitting of the latter into a light phase and a heavy phase where the former contained predominantly the UO2(HL2)2 complex (HL = HD2EHP), while the latter contained the ionic liquid as supported by FTIR and UV-Visible spectral analyses. The complexation of the uranyl ion was suggested to take place in the equatorial plane where two dimeric units of the H-bonded HD2EHP molecules took part in complexation. An increase in temperature facilitated the dissolution rate with an activation energy of 31.0 ± 2.8 kJ/mol. The cyclic voltammetry studies indicated potential chances of recovery of the dissolved uranium by electrodeposition at the cathode. The proposed dimeric structure of HD2EHP in the complexation with U(VI) was supported by DFT studies also.

Highly Efficient N-Pivot Tripodal Diglycolamide Ligands for Trivalent f-Cations: Synthesis, Extraction, Spectroscopy, and Density Functional Theory Studies.

A series of four N-pivot tripodal diglycolamide (DGA) ligands, where three DGA moieties are attached to the central N atom via spacers of different lengths and with varying alkyl substituents on the amidic nitrogen of DGA (LI-LIV), were studied for their extraction and complexation ability toward trivalent lanthanide/actinide ions, including solvent extraction, complexation using spectrophotometric titrations, and luminescence spectroscopic studies. Introduction of a methyl group on the amidic nitrogen atom gives rise to a 400 fold increase of the Eu distribution ( D) value [LIII (NMe) vs LII (NH)] at 1 M HNO3. Enlargement of the spacer length between the pivotal N atom and the DGA moieties with one carbon atom results in a 14 times higher DEu value [LI (C3) vs LII (C2)]. Slope analyses showed that Eu3+ was extracted as a bis-solvated species with all four ligands. The compositions of the Eu3+/L complexes were further confirmed by spectroscopic measurements, its formation constants following the order: LIII > LIV > LI > LII. Luminescence spectroscopy and electrospray ionization mass spectrometry revealed that all four ligands form [Eu(L)2(NO3)3] complexes. Density functional theory and thermodynamic parameters corroborated the existence of [Eu(L)2(NO3)3] complexes.

Remarkable Enhancement in Extraction of Trivalent f-Block Elements Using a Macrocyclic Ligand with Four Diglycolamide Arms: Synthesis, Extraction, and Spectroscopic and Density Functional Theory Studies.

A multiple diglycolamide (DGA)-containing ligand having four DGA arms tethered to a tetraaza-12-crown-4 ring, viz. 2,2',2'',2'''-(((1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetrakis(2-oxoethane-2,1-diyl)) tetrakis (oxy)) tetrakis(N,N-dioctylacetamide) (T12C4ODGA), was synthesized and evaluated for the extraction of different actinide and lanthanide ions, viz. Am3+, Eu3+, Pu4+, Np4+, and UO22+. The extraction efficiency of the present ligand was found to be the highest reported so far, more specifically for the trivalent metal ions Am3+ and Eu3+, when one considers the very low ligand concentration used in the present study, compared to that of the various previously reported multiple DGA-based ligands. The nature of the complexes formed during the extraction of Eu3+ was investigated using time-resolved fluorescence (TRFS) and extended X-ray absorption fine structure (EXAFS) spectroscopy. Both the solvent extraction and TRFS studies indicated the presence of 1:1 and 1:2 complexes during the extraction of Am3+ and Eu3+ having three inner-sphere water molecules in the 1:1 complex. Density functional theoretical (DFT) studies were performed on the Am3+ and Eu3+ complexes of both T12C4ODGA and an analogous compound having methyl groups in place of the n-octyl groups, and the DFT results of the T12C4ODGA nicely explain the extraction behavior of Am3+ and Eu3+.

First Report on the Separation of Trivalent Lanthanides from Trivalent Actinides Using an Aqueous Soluble Multiple N-Donor Ligand, 2,6-bis(1 H-tetrazol-5-yl)pyridine: Extraction, Spectroscopic, Structural, and Computational Studies.

A terdentate multiple N donor ligand, 2,6-bis(1 H-tetrazol-5-yl)pyridine (H2BTzP), was synthesized, and its complexation with trivalent americium, neodymium, and europium was studied using single-crystal X-ray diffraction, attenuated total reflectance-fourrier transform infrared spectroscopy, time-resolved fluorescence spectroscopy, UV-vis absorption spectrophotometry. Higher complexation strength of BTzP toward trivalent actinide over lanthanides as observed from UV-vis spectrophotometric study resulted in an effective separation of Am3+ and Eu3+ in liquid-liquid extraction studies employing N,N, N',N'-tetra- n-octyl diglycolamide in the presence of BTzP as the aqueous complexant. The selectivity of BTzP toward Am3+ over Eu3+ was further investigated by DFT computations, which indicated higher metal-ligand overlap in the Am3+ complex as indicated from the metal-nitrogen bond order and frontier molecular orbital analysis of the BTzP complexes of Am3+ and Eu3+.

First Report on the Complexation of Actinides and Lanthanides Using 2,2',2''-(((1,4,7-Triazonane-1,4,7-triyl)tris(2-oxoethane-2,1-diyl)) tris(oxy)) tris( N, N-dioctylacetamide): Synthesis, Extraction, Luminescence, EXAFS, and DFT Studies.

A novel tripodal diglycolamide ligand containing a triazamacrocycle center (2,2',2''-(((1,4,7-triazonane-1,4,7-triyl)tris(2-oxoethane-2,1-diyl)) tris(oxy)) tris( N, N-dioctylacetamide), abbreviated as T9C3ODGA) was synthesized and characterized by conventional techniques. The ligand resulted in efficient extraction of actinide/lanthanide ions yielding the trend: Eu3+ > Pu4+ > Am3+ > NpO22+ > UO22+ > Sr2+ > Cs+. Similar to most of the other diglycolamide (DGA) ligands, Eu3+ was preferentially extracted as compared to Am3+; the separation factor ( DEu/ DAm) value at 3 M HNO3 was ca. 4.2. In contrast, separation from UO22+ ion was less effective as compared to that of other tripodal DGA ligands studied earlier. Solvent extraction studies indicated extraction of species of the ML2 (where L is T9C3ODGA) stoichiometry. The formation of an inclusion complex with no inner-sphere water molecule was confirmed from luminescence spectral studies. DFT computations predicted the presence of an inner-sphere nitrate ion in the most preferred complex, which was also supplemented by EXAFS and luminescence studies. The selectivity of T9C3ODGA could be explained on the basis of its more favorable interactions with Eu3+ as compared to those with Am3+ both in the gas and the solution phases.

A highly efficient in situ redox stabilization strategy for Am-Cm separation using AgBiO3.

AgBiO3 is reported for the exclusive oxidation of Am3+ → AmO2+ at near-neutral pH conditions. Literature methods of AmO2+ generation are generally two-step processes; i.e., Am3+ → AmO22+ oxidation followed by AmO22+ → AmO2+ reduction. These methods for Am3+ → AmO2+ oxidation use high temperatures (80-100 °C) and/or several reagents, causing the in situ presence of the AmO2+-complex rather than the AmO2+aq ions. This not only interferes with the much-needed Am-Cm selectivity but also limits the use of AmO2+aq in any other experimental study. The single-step Am3+ → AmO2+ oxidation in the present work using AgBiO3 is done at 25 °C in a non-complexing medium at pH ∼4, making it a first-of-its-kind report. Am-Eu and Am-Cm separation in a single contact, with a separation factor >104, was achieved using the present method, which is unprecedented among aqueous feed solutions. The AmO2+ generated using the present method under non-complexing pH conditions makes it also suitable for exploring the fundamental chemistry of the higher valent americyl ion. A complexation study using the thus-generated AmO2+ ion with acetate ion supports the concept.

Efficient actinide sequestration with ionic liquid-based extraction chromatography resins containing Aza-crown ether functionalized diglycolamides.

Two new extraction chromatographic resins (ECRs) were prepared by impregnating two exotic diglycolamide (DGA) ligands (having three or four DGA moieties tethered to aza-crown ether scaffolds) dissolved in an ionic liquid onto an inert solid support. A room temperature ionic liquid (RTIL) was used for enhancing the performance of the ECRs. The ECR containing triaza-9-crown-3 functionalized with three DGA moieties (TAM-3-DGA), and tetraaza-12-crown-4 tethered with four DGA arms (TAM-4-DGA) were evaluated for the separation of Am3+ and Pu4+from nitric acid solutions. The resin capacity for Eu3+ was 9.52 mg/g and 7.24 mg/g for TAM-3-DGA and TAM-4-DGA resins, respectively. Similarly, the resin capacity for Pu4+was 7.44 mg/g and 5.72 mg/g for TAM-3-DGA and TAM-4-DGA resins, respectively. These maximum loading values corresponded to the formation of a 1:1 metal/ligand complex for the Eu3+ ion and a 1:2 metal/ligand complex for the Pu4+ ion. The sorption of Eu3+and Pu4+on the resins followed a chemisorption phenomenon on both resins. The sorbed Eu3+and Pu4+ions from the resin phase could be efficiently desorbed with complexing ligands such as guanidine carbonate/HEDTA and oxalic acid, respectively.

Highly efficient diglycolamide-based task-specific ionic liquids: synthesis, unusual extraction behaviour, irradiation, and fluorescence studies.

Two new diglycolamide-based task-specific ionic liquids (DGA-TSILs) were evaluated for the extraction of actinides and lanthanides from acidic feed solutions. These DGA-TSILs were capable of exceptionally high extraction of trivalent actinide ions, such as Am(3+), and even higher extraction of the lanthanide ion, Eu(3+) (about 5-10 fold). Dilution of the DGA-TSILs in an ionic liquid, C(4)mim(+)·NTf(2)(-), afforded reasonably high extraction ability, faster mass transfer, and more efficient stripping of the metal ion. The nature of the extracted species was studied by slope analysis, which showed that the extracted species contained one NO(3)(-) anion, along with the participation of two DGA-TSIL molecules. Time-resolved laser fluorescence spectroscopy (TRLFS) analysis showed a strong complexation with no inner-sphere water molecule in the Eu(III)-DGA-TSIL complexes in the presence and absence of C(4)mim(+)·NTf(2)(-) as the diluent. The very high radiolytic stability of DGA-TSIL 6 makes it one of the most-efficient solvent systems for the extraction of actinides under acidic feed conditions.

Diglycolamide-functionalized calix[4]arenes showing unusual complexation of actinide ions in room temperature ionic liquids: role of ligand structure, radiolytic stability, emission spectroscopy, and thermodynamic studies.

Diglycolamide-functionalized calix[4]arenes (C4DGAs) with varying structural modifications were evaluated for actinide complexation from their extraction behavior toward actinide ions such as UO2(2+), Pu(4+), PuO2(2+), and Am(3+) in the room temperature ionic liquid (RTIL) 1-n-octyl-3-methylimidazolium bis(trifluoromethane)sulfonamide (C8mimNTf2). The formation constants were calculated for Am(3+) which showed a significant role of ligand structure, nature of substituents, and spacer length. Although the alkyl substituents on the amidic nitrogen increase the extraction efficiency of americium at lower acidity because of the inductive effect of the alkyl groups, at higher acidity the steric crowding around the ligating site determines the extraction efficiency. All C4DGAs formed 1:1 complexes with Am(3+) while for the analogous Eu(3+) complexes no inner sphere water molecules were detected and the asymmetry of the metal ligand complex differed from one another as proved by time-resolved laser induced fluorescence spectroscopy (TRLIFS). Thermodynamic studies indicated that the extraction process, predominant by the Am(3+)-C4DGA complexation reaction, is exothermic. The unique role of the medium on Am(3+) complexation with the C4DGA molecules with varying spacer length, L-IV and L-V, was noticed for the first time with a reversal in the trend observed in the RTIL compared to that seen in a nonpolar molecular diluent like n-dodecane. Various factors leading to a more preorganized structure were responsible for favorable metal ion complexation. The solvent systems show promise to be employed for nuclear waste remediation, and sustainability options were evaluated from radiolytic stability as well as stripping studies.

Highly efficient separation of Am(III) and Pu(IV) from lean feeds and soil using an extraction chromatographic resin containing a diglycolamide in an ionic liquid.

A TODGA based extraction chromatographic resin containing an ionic liquid was used for the separation of actinide ions such as Am3+ and Pu4+ from samples such as lean effluents emanating from laboratory waste, environmental water as well as soil samples adjacent to a nuclear plant site. The methodology involved feed adjustment to 3 M HNO3 followed by conditioning of the column, loading, washing (3 M HNO3), and elution of the actinide ions. The elution of Am3+ was done using EDTA in a buffered medium (1 M guanidine carbonate) while that of Pu4+ was carried out using a mixture of 0.5 M oxalic acid and 0.5 M HNO3. The elution peaks were sharp with almost no tailing suggesting the efficiency of the separation method. The results obtained were compared with the literature results which suggested the high efficiency of the present method.

A comparative study on the uptake of lanthanides from acidic feeds using extraction chromatography resins containing N,N,N',N'-tetra-n-alkyl diglycolamides with varying alkyl chain lengths in an ionic liquid.

A comparative study on the uptake of several rare earth element (REE) ions viz. La(III), Ce(III), Pr(III), Nd(III), Sm(III), Gd(III) and Dy(III) was carried out from nitric acid feeds using four extraction chromatography resins which contained the diglycolamide (DGA) ligands, N,N,N',N'-tetra-n-alkyldiglycolamide with n-pentyl (TPDGA), n-hexyl (THDGA), n-octyl (TODGA) and n-decyl (TDDGA) groups taken in a room temperature ionic liquid (C4mim·NTf2). The uptake of the lanthanides followed the trend: La(III) < Ce(III) < Pr(III) < Nd(III) < Sm(III) < Gd(III) < Dy(III), which is similar to their ionic potential values and the uptake trend of the resins was TPDGA > THDGA > TODGA > TDDGA. The uptake of the metal ions was very high (>104 g/mL) for all the lanthanide ions and was found to increase with increasing nitric acid concentrations. Based on the encouraging batch data, column studies were carried out with all the four extraction chromatography resins with the lanthanide ions used in this work. The column studies were carried out with both individual lanthanide ions and their mixtures. While the loading studies were carried out with 80 mg/L solutions of the metal ions (with respect to each of those) in the mixture of REEs, the elution studies were carried out using a solution of 0.05 M EDTA in 1 M guanidine carbonate. For the column studies involving individual REEs, 550 mg/L solutions were used. The elution profiles appeared to be sharp as >95% elution of the metal ions was accomplished in only 3 mL of the eluent which amounted to only 1.6 bed volumes which is highly impressive. When the studies were carried out with the mixture of the lanthanide ions, the breakthrough of Dy(III) was last while that of La(III) was seen at much lower volumes which was dependent on the nature of the extractant in the resins.

Stability of composite polymeric beads containing a calix[4]arene-mono-crown-6 ligand for radio-cesium separation.

Bis-octyloxy-calix[4]arene-mono-crown-6 (BOCMC) is a selective ligand for Cs(I) cation, and has been used in solvent extraction method for its separation from acidic feed. Looking at the various advantages and ease of extraction chromatography separation method, an attempt was made to prepare stable composite beads containing BOCMC entrapped in a suitable polymeric matrix. Therefore, an attempt was made to prepare a series of composite polymeric beads containing BOCMC in polysulfone (PS), polyether sulfone (PES) and sodium alginate polymeric matrix. Preparations of the beads were attempted by dissolving the solid BOCMC in the polymer solution, and also by using the ligand solution in isodecanol/dodecane and ionic liquids and then mixing in the polymeric solution. Every attempt failed to get the desired quality of beads in PES and sodium alginate matrix. However, very good quality and stable beads were obtained when 25 mM ligand solution dissolved in C8mim.Tf2N ionic liquid was used in PS matrix. Detail study for the extraction chromatography separation of Cs(I) was studied with BOCMC/C8mim.Tf2N/PS composite beads. Detail investigations on the preparation, characterization, reusability and radiation stability of these beads have been studied and reported in details.

Highly efficient Plutonium(IV) uptake from acidic feeds using four extraction chromatography resins containing diglycolamides and ionic liquid.

Quantitative recovery of plutonium from lean effluents is one of the most challenging tasks for separation scientists. Four extraction chromatography (XC) resins containing substituted diglycolamide ligands viz. N,N,N',N'-tetra-n-pentyl diglycolamide (TPDGA), N,N,N',N'-tetra-n-hexyl diglycolamide (THDGA), N,N,N',N'-tetra-n-octyl diglycolamide (TODGA) and N,N,N',N'-tetra-n-decyl diglycolamide (TDDGA) and a room temperature ionic liquid (RTIL) were tested for the extraction of plutonium (IV) from nitric acid feed solutions. The relative efficiency of uptake of the metal ion in the entire range of HNO3 studied was: TPDGA > THDGA > TODGA > TDDGA, which was opposite to the chain length of the attached alkyl groups. Also, for all the four XC resins the uptake of Pu(IV) was found to decrease with increasing nitric acid concentration in the lower acidity range followed by an increase thereafter. The uptake of Pu(IV) with all the four XC resins was fitted into different kinetic and isotherm models. It was found that all the four resins followed the pseudo-second order kinetic model and Langmuir monolayer adsorption model. Column studies with these XC resins using a loading solution containing 1.2 g/L Pu(IV) in 3 M HNO3 showed early breakthrough for the higher homolog DGA ligands as compared to the lower homologs. Effective elution of the loaded Pu(IV) from the column was done in about 5.5 column volumes using a solution containing 0.5 M oxalic acid in 0.5 M HNO3.