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A search is initiated for new solvents for liquid–liquid extraction (LLE) chemistry of actinides for future separations. Of late, reports on deep eutectic solvents (DES), which resemble ionic liquids, are on the rise. Two hydrophobic DES based on tri–n-octylphosphine oxide (TOPO) and simple dicarboxylic acids, namely, oxalic acid and its higher homologue, malonic acid are prepared and characterized by FT-IR, UV–Vis, water content, density and viscosity measurements. The LLE chemistry of U(VI) and Am(III) is carried out using the above DES as a function of a few parameters and UV–Vis and IR spectra of the extracted phases were also recorded. The results are discussed with appropriate explanations in this report.

The production cross section of the medical isotope 68Ga in the 68Zn(p,n)68Ga reaction was measured with the proton energies of 8.6 ± 0.9, 12.1 ± 0.5, 15.1 ± 0.3 and 17.7 ± 0.2 MeV by using the method of stacked-foil activation and off-line γ-ray spectrometry. The proton beam intensity at the front position of each natZn was determined by using the natCu(p,x)62Zn monitor reaction with the recommended cross section from the IAEA data base library. The 68Zn(p,n)68Ga reaction cross-section as a function of proton energy was theoretically calculated by using the default parameters of the computer code TALYS 1.9 and are found to be in general agreement with the present results.

Two new deep eutectic solvents, different from hitherto known and based on common choline chloride, were prepared. 1-methyl-3-decylimidazolium bromide mixed with hydrogen bond donors, malonic acid and diglycolic acid to form DES. Dissolution of uranium oxides (UO3 and UO2) was explored in both of them and characterization of the resultant solutions was carried out by IR, TGA and UV–Vis spectroscopy. Redox speciation of dissolved uranium oxides was probed in these redox-active DES through cyclic voltammetry, differential pulse voltammetry and in situ spectroelectrochemical measurements. Interestingly, the formation of uranium oxo species was observed through the dissolution of UO3 in both the DES. The electrochemical characteristics viz. redox thermodynamics (peak potential and formal redox potential), transport property (diffusion coefficient D0), heterogeneous electron transfer kinetic parameters (αn and k0) and mechanistic electron transfer of the dissolved uranium species in two DES were investigated. The speciation of uranium was decoded through the electronic absorption spectra of uranium in its lower oxidation states [U(V) and U(IV)] acquired through in situ spectroelectrochemical electrolysis with varying cathodic potentials. Studies were also carried out using Molecular Dynamics (MD) and density functional theory (DFT) simulations to authenticate the electrochemical outcomes and to acquire the binding energy, optimized structure and molecular orbital diagram of dissolved uranium species. Further, the MD simulation sheds light on the probable equatorial coordinating atoms of dissolved uranium species. This is the first report, to the best of our knowledge, on imidazolium-based DES and actinide ions.

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.

Extraction of uranium with bis-(2-ethylhexyl) phosphonic acid (PC-88A) and bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex-272) was studied in several imidazolium-based room-temperature ionic liquids (RTILs), Cnmim·X (where n = 4, 6, 8 and X = PF6 and Tf2N). The extraction kinetics was slow and about 0.5–1 h equilibration time was required for most of the extraction systems, except in C8mim·PF6, where 2 h and 4 h were required to reach the equilibrium values for PC-88A and Cyanex-272, respectively. The extraction of UO22+ ion by the two ligands was significantly affected by the nature and the composition of the RTILs.

Extraction behaviour of trivalent americium and europium was investigated with 1-phenyl-3-methyl-4-acetyl-5-pyrazolone (HPMAP) and tri-n-octylphosphine oxide (TOPO) in a room-temperature ionic liquid, 1-methyl-3-octyl-imidazolium bis(trifluoromethylsulphonyl) imide (C8mim·Tf2N). In select cases, comparison was made using xylene, a molecular diluent. For binary extraction studies involving only PMAP, Eu3+ was marginally better extracted than Am3+ and the species extracted into C8mim·Tf2N conformed to species of the type M(PMAP)3 (where M = Am or Eu). On the other hand, cationic species were extracted for the ternary extraction systems involving HPMAP and TOPO. Luminescence spectroscopic studies suggested no inner-sphere water molecules in the extracted species. The luminescence decay lifetime showed mono-exponentials, suggesting the extraction of single species.

Extraction behaviour of trivalent actinides and lanthanides was studied using solutions of 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (HPMBP), a beta-diketone, in a room temperature ionic liquid, 1-methyl-3-octyl-imidazolium bis(trifluoromethylsulphonyl) imide (C 8 mim·Tf 2 N). The complex extracted into C 8 mim·Tf 2 N differs in its composition than those observed in molecular diluents such as benzene. Whereas, neutral ML 3 complex is predominant in molecular diluents, a positively charged complex, [ML 2 ·HL] + (where M = La 3 + , Eu 3 + , Lu 3 + and Am 3 + ; L = PMBP − ; HL = HPMBP), was identified to be extracted into the ionic liquid medium. Luminescence spectroscopic studies suggested presence of four inner-sphere water molecules in the extracted species. This paper reports for the first time the stability constant of a lanthanide (Nd 3 + ) complex with HPMBP in C 8 mim·Tf 2 N which are significantly larger than those reported in molecular diluents. Thermodynamic parameters were also determined to throw light on the nature of complexation.

The effect of tri-n-butyl phosphate (TBP) and iso-decanol as phase modifiers on the complexation of Eu3+ with octyl-phenyl N,N-diisobutyl carbamoyl methyl phosphine oxide (CMPO) was studied. On an increase of iso-decanol the extraction efficiency of Eu3+ decreases. The metal–ligand stoichiometry was found to be 1:3. The Eu complex of CMPO–TBP was more symmetric compared to CMPO–iso-decanol. The Eu3+ complex exhibited D3h and C3h symmetry for 30% and 5% iso-decanol, while that for TBP was C6v. The radiative, non-radiative life time, electric and magnetic dipole transition probabilities, branching ratio, quantum efficiency etc. were evaluated. The covalency between Eu3+ and CMPO is as follows: CMPO–TBP < CMPO-5% iso-decanol < CMPO-30% iso-decanol.

Selective separation of uranium using bis(2,4,4-trimethylpentyl)phosphinic acid in xylene and C8mimNTf2 was investigated. For ionic liquid based system, the extraction kinetics was found to be slower with the predominance of ion exchange mechanism through [UO2(NO3)·2L]+, while for xylene based system solvation mechanism. The nature of the extracted species was found to be different in both the media as observed in luminescence study. Ionic liquid based system was more radioresistant than that of molecular diluents. Na2CO3 was successfully used for stripping. The selectivity was investigated by processing simulated high level waste of pressurized heavy water reactor origin.

Keeping reprocessing of 233U–Th based fuel in perspective, solvent extraction of Th(IV), U(VI) and some relevant metal ions has been carried out from nitric acid media and simulated high-level waste (HLW) typical of a fast-breeder reactor using dihexyloctanamide (DHOA) in commercially available alternate diluents, viz. Solvesso 100 and ShellSol D70. Acid uptake constant (KH) and distribution ratios (D) of metal ions as a function of nitric acid, thorium ion and extractant concentrations are determined. Slope-analysis results showed various types of species extracted into the organic phase. For comparison, a similar set of experiments were carried out with tri-n-butyl phosphate (TBP) in both diluents. A few clear and interesting trends were observed in the variation of D values of metal ions. Interference of other relevant metal ions likely to get co-extracted along with Th(IV) and U(VI) was also studied by ICP-AES using a simulated HLW.

With an aim to understand the nature of species, cyclic voltammetry (CV) of Pu(IV) in dilute HBr and in a room temperature ionic liquid (RTIL), 1-octyl-3-methylimidazolium bromide (C8mimBr) was carried out. Shifts of cathodic and anodic peak potentials of Pu(IV) cyclic voltammograms were observed towards negative potentials in the extended electrochemical window for ionic liquid medium compared to 2 M HBr. The diffusion coefficient of the most likely species of Pu(IV) in aqueous medium was found to be greater than that of the corresponding species in ionic liquid while the activation energy showed reverse trend. The Pu(IV)/Pu(III) redox reaction was found to be exothermic in aqueous medium while it was endothermic in C8mimBr. The redox reaction was found to be quasi reversible for both the media while the extent of irreversibility was more in ionic liquid. UV-Vis spectroscopy of Pu in these media showed significant differences in the peak positions and their relative intensities, indicating the possible differences in the interactions of Pu(IV) with the solvent molecules resulting in speciation differences. A new prominent peak was observed in RTIL which could be for a new species of Pu(IV). Computational studies were also carried out to understand the solvation of Pu and the possibility of thermodynamic conversion from Pu(IV) to Pu(III).

An attempt to modify the TRUEX solvent has been initiated by replacing TBP with long-chain alcohols such as isodecanol. Solvent extraction experiments have been carried out determining distribution ratios for Am(III) as a function of concentrations of nitric acid and isodecanol. Acid uptake constant for the combined organic phase has also been arrived at which strongly suggests the interaction of CMPO and isodecanol. The suitability of the organic phase was tested for simulated high-level waste solutions.

0.2 M CMPO in isodecanol(10%)–dodecane system was taken for evaluating the extraction behavior of actinides in different oxidation states. The order of decrease in distribution ratio at fixed acidity was found to be M 4 + > MO 2 2 + > M 3 + (M = actinide ion). The metal–ligand stoichiometry was determined by slope analysis. Though, increasing isodecanol content decreases the distribution ratio, no perturbation was found on O U O moiety as revealed by UV–vis spectroscopy. Application of van't Hoff equation to the extraction data at different temperatures enabled the determination of thermodynamic parameters. The radiolytic stability of the solvent system was evaluated by dose dependent study (gamma exposure in the range of 0–500 kGy). Finally the solvent system was used for actinide partitioning from simulated high level waste (SHLW) of fast breeder reactor (FBR) fuel.

An attempt was made for the potentiostatic electrodeposition of 241Am using six different room temperature ionic liquids (RTILs). Effect of electrodeposition time on the % of electrodeposition of 241Am, pH change of the solution and the temperature change of the systems were investigated. It was observed that for water immiscible RTILs, the least viscous RTIL gave the best yield (when mixed with iso-propanol), while for water miscible RTILs, reverse trend was observed (when mixed with water). Out of all water immiscible RTILs under consideration for the present case, the octyl-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide (C8mpyNTf2) in isopropanol was found to yield almost quantitative (99.6 %) electrodeposition of 241Am within 45 min whereas the most effective system was found to be C8mimBr with ~90 % of 241Am deposited on the electrode for water miscible RTILs. To the best of our knowledge, this is the first approach ever been reported in the literature.

A systematic study was carried out to explore the electrochemical behavior of Ce in room temperature ionic liquid (CnmimBr, where n=6, 8, 10) and mixture of C6mimBr and ethanol by cyclic voltammetry. With increase in the number of carbon atoms on the alkyl substituent on methyl imidazolium cation, the electrochemical window of the ionic liquids was found to extend towards more negative potential value, as a result there was a possibility of reduction of Ce to lower oxidation states. The diffusion coefficient and activation energy for the diffusion were calculated in all the ionic liquids and one of their mixtures with ethanol. With increase in n value, the diffusion coefficient of Ce decreased due to increase in viscosity of the medium while the activation energy for the diffusion followed a reverse trend for C6mimBr, C8mimBr and C10mimBr, respectively. The observations indicated that the nature of species of Ce might be different in room temperature ionic liquids (RTILs) from that present in their mixtures with ethanol.

Activity Standards of 63Ni was used to benchmark our triple-to-double coincidence ratio (TDCR) primary standardization instrument Hidex 300SL TDCR device under different chemical and colour quench conditions. The results were compared with a secondary standardization instrument Tricarb 2910TR that employs transformed spectral index of external standard to assess the quench level of samples. Excellent agreement was observed (within 3 %) for a wide range of standard activity and quench conditions. The method was subsequently used for validating chemical separation procedure for estimation of 63Ni in neutron activated standard nickel and steel samples. Further the method was applied for estimation of 63Ni from decommissioning waste of a research reactor, APSARA.

On the growing awareness of the environmental impact associated with the use of volatile organic diluents, room temperature ionic liquid gained world-wild acceptance as environmentally benign diluents for actinide partitioning. The observed unusual behavior of less extraction efficiency of Eu with TODGA in RTIL in comparison with that of Am-TODGA was addressed in this paper. The stoichiometry of Am-TODGA complex was found to be 1:2 while that of Eu-TODGA was 1:1. More the ligand molecules associated in the metal ligand complex, the organophilicity of the complex will be more and the solubility of the metal–ligand complex in RTIL will be more which reflects in the higher distribution ratio for Am. In RTIL both Am and Eu showed slower kinetics of extraction with TODGA which can be attributed to the high viscosity coefficient of RTIL compared to the molecular diluents. The observed slower kinetics of extraction was quantified and found to follow first order kinetics with the rate constant of 5.5 × 10−4 s−1. The formation constant of Am-TODGA complex was found to be more (4.18 × 108 M−1) than Eu-TODGA complex (3.31 × 108 M−1) in RTIL. The parameters viz. diffusion coefficient, activation energy for Eu(III)/Eu(II) were determined and found to be 3.08 × 10−8/cm2 s−1 (at 303 K) and 39.34 kJ mol−1 respectively. The thermodynamic parameters ΔG, ΔH and ΔS for the reaction were evaluated using the linear regression of the plot of E 0* versus T. The redox reaction was found to be exothermic with decrease in entropy value.

Actinide partitioning is considered as one of the most challenging issues in nuclear waste remediation. Herein, we unravel a novel extraction mode pertinent to the competitive host–guest interactions for highly efficient actinide extraction. The host–guest recognition event involves binding of a room temperature ionic liquid (RTIL), 1-n-octyl-3 methylimidazolium bis(trifluoromethane)sulfonamide (C8mimNTf2), as both the guest and the solvent by the hosts pillar[5]arene-based diglycolamides (P5DGAs) and the subsequent displacement of the guest by a metal ion. This two-step process suggests a unique competitive ion-mediated displacement mechanism for the metal ion partitioning in the extraction process. The supramolecular extraction system is evaluated for its extraction abilities towards actinide ions such as UO22+, PuO22+, Pu4+, Am3+, and fission product elements such as Eu3+, Sr2+, Cs+. The results demonstrate the exceedingly high distribution ratios and favorable separation of Am3+ and Pu4+ in nitric acid media. All the three P5DGAs form 1 : 1 complexes with Am3+. Time resolved laser fluorescence spectroscopic (TRLFS) studies reveal a strong complexation involving no inner-sphere water molecules in the Eu3+–P5DGA complexes when C8mimNTf2 is used as the diluent. With high efficiency in the extraction of actinides and a quantitative back extraction outcome, the RTIL-based solvent systems containing pillar[5]arene-DGA ligands developed in this work hold potential as promising candidates for nuclear waste remediation in a more sustainable fashion.

A systematic study was carried out to understand the effect of structural modification of Cnmim+ moiety of CnmimBr (n = 6, 8 or 10) on the electrochemical behavior of uranium. The cyclic voltammetric study of the above room-temperature ionic liquids (RTIL) media revealed that with increase in the chain length the electrochemical window extended more towards the negative potential. This resulted in the possibility of conversion of U(VI) to U(III) or even possibly to, U metal via U(IV) (as UO2) when n ≥ 10. The diffusion coefficient of U(VI) was found to decrease from n = 6 to 8 to 10 due to the increasing order of viscosity of the RTIL. As a consequence, the activation energy was found to follow reverse order i.e. E act(C6mimBr)

The high level waste (HLW) generated from the reprocessing of the spent fuel of pressurized heavy water reactor has been characterized for the minor actinides. The radiation dose of the waste solution was reduced by radiochemical separation of cesium from HLW by solvent extraction with chlorinated cobalt dicarbollide dissolved in 20% nitrobenzene in xylene. Minor actinides (Np, Pu, Am, Cm) in the high level waste were assayed by alpha spectrometry following radiochemical separation. The gross alpha activity determined by liquid scintillation agrees well (within 10%) with the cumulative quantities of actinides determined by alpha spectrometry.

Efficacy of chlorinated cobaltdicarbollide in a modified diluent, 20% nitrobenzene in xylene was tested for the extraction and recovery of Cs from simulated high-level waste (HLW) solutions generated from PHWR-fuel reprocessing. Concentration of the reagent, composition of the diluent, numbers of contacts, the nature of stripping agents are some of the parameters optimized for the complete removal of Cs from such waste solutions. The above solvent extraction procedure can be applied to genuine HLW solutions for effective reduction of the dose due to Cs so that HLW can be handled in fume hoods for its characterization.

The extraction of uranyl nitrate by TBP in two room temperature ionic liquids (RTILS), viz. 1-alkyl-3 -methyl imidazolium (Cnmim, n = 4 and 8) cation with hexafluorophosphate anion and, for comparison purposes, in dodecane has been studied. The species extracted were determined by slope analysis, UV-VIS spectra and supported for the first time by two known soft ionization mass spectrometric techniques, viz. MALDI-MS and ESI-MS. The results show that the extraction mechanisms differ in the two RTILS, as cation exchange is more likely for a butyl substituted RTIL, C4mimPF6 as noted in literature, whereas the formation of a neutral adduct (i.e., UO2(NO3)22TBP) by a solvation mechanism is operative for octyl analogue, C8mimPF6.

Extraction behaviour of actinides, lanthanides, fission products and structural elements has been studied with the two diglycolamide extractants, namely N,N,N′,N′-tetra-2-ethylhexyl diglycolamide (T2EHDGA) and N,N,N′,N′-tetraoctyl diglycolamide (TODGA). The acid extraction studies suggested that T2EHDGA (KH: 1.8) is less basic as compared to its linear homologue, TODGA (KH: 4.1). The distribution ratio of Am(III) by 0.1 M diglycolamides followed the order: TODGA > T2EHDGA. The number of ligand molecules present in the stoichiometry of the extracted species of Am(III) was found to be three and four for T2EHDGA and TODGA, respectively. Thermodynamics studies suggested that the extraction of Am(III) by both the extractants is exothermic in nature. The radiolytic stability of TODGA and T2EHDGA solutions in n-dodecane has been investigated. Due to lower distribution ratio of Am by T2EHDGA, 0.2 M of its solution has been used as compared to 0.1 M solution of TODGA. The distribution behaviour of various metal ions, viz. Am, Nd, Fe, Mo, Cr, Sr and Cs has been studied from nitric acid as well as from simulated high level waste solution.

The thermodynamic parameters for the complexation reaction of Sr(II) and Ba(II) with 18 Crown 6 (18C6) were determined in the binary water–ethanol mixtures as solvent. The stability of both complexes was found to increase with increase in ethanol mole fraction ( X E ). The complexation reaction is exothermic with the Δ H value increasing with X E . The entropy of complexation was found to decrease for X E up to 0.1 above which it increased monotonically. The complexation process was enthalpically favored but entropically unfavorable. The data have been explained in terms of the solvent effects on metal ion, ligand and complex stabilization in binary mixture. The ab initio calculations were also carried out to investigate the stability of metal ion and ligand in water and ethanol medium.

A mixture of N,N,N′,N′-tetraoctyl diglycolamide (TODGA) and N,N-dihexyl octanamide (DHOA) dissolved in NPH has been evaluated for actinide partitioning from simulated high-level waste by cold tests in mixer–settler runs. The feed solution was a synthetic purex raffinate of pressurized heavy water reactor (PHWR) origin where lanthanides were taken as stand-in for trivalent actinides. Quantitative extraction (forward and backward) of trivalent lanthanides was observed in four stages each. Elements such as Fe, Mn, Ni, Ba and Cs were practically un-extracted. However, Cr and Mo were partially co-extracted. Reusability of the organic phase in five successive cycles suggested excellent hydrolytic stability of the reagent. Though the solvent system was susceptible to radiolytic degradation, negligible effects on the extraction as well as on the stripping of lanthanides were observed with solvent irradiated to 100 KGy radiation dose.

A novel, simple technique based on magnetically assisted chemical separation (MACS) has been developed for the uptake of lanthanides and actinides from pure nitric acid solutions as well as from Simulated Pressurized Heavy Water Reactor-High Level Waste (PHWR-SHLW). Uptake profiles of various metal ions, such as Pu(IV), U(VI), Th(IV), Am(III), Eu(III), Sr(II), Cs(I) and Fe(III) were investigated as a function of time and nitric acid concentrations usingN,N,N′,N′-tetraoctyl-3-oxapentane-1,5-diamide (TODGA) impregnated magnetic particles and compared withN,N′-dimethyl-N,N′-dibutyl tetradecyl malonamide (DMDBTDMA) and trialkyl phosphine oxide coated magnetic particles and also with TODGA coated extraction chromatographic resins. The uptake of various metal ions follows the order Eu(III) > Am(III) > Th(IV) > Pu(IV) > U(VI) > Sr(II) > Fe(III) > Cs(I) in pure nitric acid solutions. On the other hand, distinctly high distribution coefficient (Kd) value has been observed for Pu(IV) as compared to Eu(III) and Am(III) in SHLW. Further, no significant extraction of Cs(I) or Sr(II) was observed in SHLW. Also, at any acidity theKdvalue of a given metal ion is less in the SHLW as compared to that in pure HNO3, apparently due to the co-extraction of the other metal ions present in SHLW. The loading capacity of the TODGA impregnated magnetic particles with respect to Th(IV), U(VI) and Eu(III) was determined, along with the distribution isotherms to simulate multiple contacts. The adsorption models of Langmuir and Freundlich were fitted to the experimental data and best correlations was obtained for Langmuir model suggesting monolayer adsorption is the prevalent mechanism. The stability and reusability of the TODGA coated magnetic particles was also assessed.

A systematic study was carried out to understand the complexation of a diglycolamide functionalized task-specific ionic liquid (DGA-TSIL) and its molecular analogue, (tetraoctyldiglycolamide) TODGA with uranyl ion by cyclic voltammetry, solvent extraction and UV–Vis spectroscopy. Significant shifts of cathodic peak potential towards more positive values as compared to the uranyl ion in a room temperature ionic liquid-diluent, [C8mim][Br] were attributed to the complexation of it with the ligands. The order of diffusion coefficient values determined gave the idea of the bulkiness of the U bearing species. In the case of DGA-TSIL, the measurable, relatively slower kinetics in ionic liquid observed by both electrochemical and biphasic extraction techniques was attributed to high viscosity coefficient of the ionic liquid. The complexation reaction with U(VI) was found to follow the first order kinetics with a rate constant of 4.8 × 10−4 s−1. Titration data from cyclic voltammograms for a series of additions of the ligand to a fixed concentration of uranyl ion indicated that uranyl ion forms 1:1 complexed species with DGA-TSIL with the formation constant of 1.0 × 103 M−1 which agreed well with that obtained by slope analysis from biphasic extraction results. Difference in the UV–Vis spectra in terms of shifts of peak positions and relative peak intensities could possibly indicate the presence of different species of the uranyl ion in the RTIL with and without the ligand. It was also proposed that the bond (Odouble bond; length as m-dashUdouble bond; length as m-dashO) becomes weaker on complexation due to the approach of the ligand towards the metal ion, partially neutralizing the charge on the uranyl moiety. The symmetric stretching frequency calculated from UV–Vis spectra was in conformity of the above fact.

The radiolytic stability of TBP, DHOA, Cyanex 923 and Cyanex 272 in ionic liquid vis a vis molecular diluents have been evaluated for the extraction of thorium. The decrease in DTh value was found to follow the trend of irradiated (Xylene + ligand) > irradiated (ionic liquid + ligand). Ionic liquid was found to act as a sink to protect the ligand functionality from radiation damage. On gamma exposure, the other metal ions were also found to be co-extracted into organic phase from simulated high level waste solution of fast breeder reactor origin consequently reducing the selectivity. The reduction in selectivity on gamma exposure was found to be more in xylene than C8mimNTf2 based systems.

A cyclic voltammetric study on Np(IV) complexes with task-specific ionic liquid with 3-dodecylimidazolium cation appended with diphenylcarbamoylmethylphosphine oxide and bis(trifluoromethyl-sulfonyl)-imide anion dissolved in the room temperature ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)-imide has been carried out. The results are compared with its molecular entity, viz., octyl(phenyl)carbamoylmethylphosphine oxide dissolved in the same diluent. The diffusion coefficient values were determined using its variation with scan rate. The standard rate constant values were also computed. The activation energy for diffusion and thermodynamic parameters for the redox reactions of the Np complexes were determined and compared.

This paper reports a first-ever cyclic voltammetric study and the electrochemical characterization of Np(IV) complexes with task-specific ionic liquid with appended diglycolamide (DGA-TSIL) ligand dissolved in the room-temperature ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (C4mimNTf2). The results are compared with molecular entity, N,N,N′,N′-tetraoctyl diglycolamide (TODGA) dissolved in the same diluent. The diffusion coefficient (D) values were determined using the Randles–Sevcik equation. The standard rate constant (k s) values were also computed for the Np(IV)/Np(III) electrode redox reaction. The activation energy for diffusion (E a) and thermodynamic parameters for the redox reactions of the Np complexes were determined and compared.

Cyanex‐923 has been used as the stationary phase in the extraction chromatographic separation of actinide ions from simulated high‐level waste (SHLW). Chromosorb‐W was used as the solid inert support. The uptake behaviour of U(VI), Pu(IV), and Am(III) was studied by batch studies. Breakthrough capacity of the column for Am(III) in the presence of macro amount of Eu(III) has been determined in three successive cycles of loading and elution. The influence of interfering ions like Fe(III), Cr(VI), Al(III), and Ni(II), etc. has been investigated. Effect of column parameters like diameter and height on Am(III) elution profile has also been studied.

The efficiency of immobilized moss as a bio-sorbent for the removal of 137Cs and 90Sr radionuclides from actual low-level radioactive waste (LLW) solutions was investigated. Preliminary batch experiments with the moss (Funaria hygrometrica) for the sorption of Cs and Sr have shown a pH dependent binding trend from pH 1–13, with maximum binding between pH 5–10. Time dependence of the batch studies showed that a contact time of 30 minutes was sufficient to reach equilibrium. Column experiments for the sorption of Cs and Sr by moss after immobilizing in polymer silica matrix demonstrated that the sorbent is capable of removing considerable amounts of Cs and Sr from actual LLW solutions under constant flow conditions. The adsorption capacity was estimated to be 8.5 mg/g for Cs and 15 mg/g for Sr. These sorbed metal ions from the column could be leached out using 0.20M nitric acid. The regenerated sorbent exhibited relatively the same initial binding capacity of both Cs and Sr even after 3 cycles of reuse.

A method for the separation of Fe(III) from Co(II) in nitric acid medium has been developed using 30% Cyanex-923 in n-dodecane. Nitric acid extraction studies (0.5 to 6.0M) as a function of Cyanex-923 concentration (10-30%) suggest the probable extraction of more than one species of Cyanex-923. HNO3 complex. Third phase formation was observed at 8.0M HNO3. Extraction of Fe(III) increases monotonously with acidity (1.0-7.0M) whereas that of Co(II) is negligible at all acidities. Fe(III) was quantitatively loaded in the organic phase in two contacts at 7.0M HNO3

Extraction of Am(III) and Eu(III) from NO3 -, ClO4 -, SCN- and NO3 - + ClO4 - media with tri-n-octyl phosphine oxide (TOPO) in xylene has been carried out at 15, 25, 30 and 35°C. Under the extraction conditions the species M(NO3)3·3TOPO, M(SCN)3·4TOPO, M(ClO4)3·4TOPO and MNO3(ClO4)2·4TOPO are predominantly extracted at all the temperatures (M=Am or Eu). The two phase equilibrium constant (log K ex) follows an order SCN- > NO3 - + ClO4 - > ClO4 -> NO3 -. Extraction enthalpies have been calculated in each system from the temperature dependence of the K ex. The thermodynamic parameters ΔG, ΔH and ΔS have been discussed and compared with other mono- and bidentate organophosphorus extractants for Am(III) and Eu(III) from same aqueous medium. The -ΔH values for the two-phase reaction follow an order NO3 - + ClO4 - > ClO4 - > SCN- > NO3 - for both metal ions. This has been explained on the basis of heat energies involved with the formation of ML3 complex (L being the anion used), the transfer of ML3 to the organic phase and the attachment of TOPO molecules, and also on the limiting partial molal volume of the anions.

The sorption of 241Am, 233U and 137Cs from nitric acid solutions on a synthesized sodium potassium fluoro-phlogopite (SPFP) gel, structurally close to the fluorine mica mineral, has been studied. The synthesized gel was characterized by energy dispersive spectrometry, X-ray powder diffraction pattern, FTIR and thermogravimetric analysis and has a composition of Na0.5K0.5Mg3(Si3AlO10)F2.6H2O. Different parameters like contact time, acid concentration, amount of SPFP, metal ion concentrations, effect of competing cations, desorption of the nuclides from the loaded SPFP gel etc., were studied using batch technique. Also, the SPFP gel was loaded with Eu(III), U(VI) and Cs(I) and the amounts sorbed on the gel has been estimated by difference from the concentrations in the original solution and those remaining in the solution after loading. Na, K, Mg, Eu and U were estimated by ICP-AES and Cs by electrothermal atomization atomic absorption spectrometry. The exchange of Na, K and Mg with the loaded cations has been evaluated and discussed in the light of ion exchange and surface precipitate sorption mechanisms.

The extraction of UO2 2+ from nitrate and thiocyanate media at pH 2.0 has been carried out using N,N-methylbutyldecanamide (MBDA), N,N-dibutyldecanamide (DBDA), and N,N-dihexyldecanamide (DHDA) in dodecane, chlorobenzene, o-dichlorobenzene, and xylene. Thermodynamic parameters for the extraction of UO2 2+ in the system NO3 −/SCN−–DHDA in dodecane have been calculated from the temperature dependence of the log K ex values. UO2 2+–SCN–amide complexes have been synthesized, characterized, and compared with the species extracted in the organic phase from such systems.

Extraction, loading and stripping studies of Pu(IV) have been carried out using three phosphine oxides namely CyanexO-923 (cyn-923), CyanexO-925 (cyn-925) and TOPO in dodecane from nitric acid medium. All the three phosphine oxides have shown very high extraction of Pu. The order of extraction for Pu by these compounds is cyn-923 > TOPO - cyn-925. Loading of Pu (30.0 mg/l) in 3.0M HNO3 was carried out using 5% solution of each of the phosphine oxides in dodecane. It was found that even at an organic to aqueous phase ratio of 1:10, the loading of Pu is >96%. From the loaded organic phase, Pu could be almost quantitatively stripped using 0.1 or 0.5M oxalic acid. The extraction of Pu(IV) with cyn-925 has also been carried out from HCl, HNO3 or HClO4 (0.5 to 9.1M). The species extracted into the cyn-925/dodecane phase from 3.0M HNO3 or HCl media was found to be Pu(L)4.2 cyn-925 where L = NO3– or Cl–. Similar species were observed to be formed when dodecane was replaced by xylene, chlorobenzene or o-dichlorobenzene.

The ability of the back-fill and the host rock materials to take up radioisotopes like 241Am, 85,89Sr and 137Cs has been examined as a function of contact time, pH, amount of sorbent, sorbate concentration, and the presence of complementary cations. A batch technique using actual borehole water from the granite formation has been utilized. In general, the uptake of nuclides by bentonite is much higher than that with granite. The sorption order of nuclides on bentonite is Am>Cs>Sr. The presence of complementary cations, Na+, K+, Ca2+ and Mg2+ depresses the sorption of Cs and Sr on bentonite. The sorption data have been interpreted in terms of Freundlich and Langmuir isotherm equations. Utilizing the Langmuir isotherm equation, the monolayer capacity, Vm,and the binding constant, K, have been evaluated. The change in free energy for the sorption of nuclides on bentonite has also been calculated.

Reagents and methods that have been developed during the past 20 years for hydrometallurgical partitioning of actinides from different types of transuranium (TRU) wastes and dissolved fuels are reviewed. Emphasis is placed on the extraction performance of the fully-optimized reagents rather than on the structural iterations that were undertaken (and in some cases are still being conducted) to identify the optimum species. Particular attention is paid to separation processes that have been demonstrated in batch and counter-current solvent extraction, and batch and column mode extraction chromatography. The salient features of the various techniques and reagents for actinide recycle are compared. Sections of the review focus on neptunium behavior in hydrometallurgy and on characterization of those reagents best suited to the separation of trivalent actinides from fission product lanthanides. Selected flowsheets that have been reported for the separation and recovery of actinides from TRU wastes are presented.

The partitioning of long-lived alpha-emitting actinides, present in high-level radioactive waste (HLW) solutions from PUREX reprocessing of spent nuclear fuels, has been carried out using a commercially available, reasonably inexpensive, trialkylphosphine oxide (TRPO), Cyanex®-923 alone or its mixture with tri-n-butylphosphate (TBP) in dodecane. The studies have been carried out from nitric acid as well as from three types of synthetic HLW solutions. With 30% TRPO alone, third-phase formation was observed when HLW in 3.0 M HNO3 was taken as such. With the mixture of TRPO and TBP, it has been shown that the HLW need not be diluted 10 times, but only the acidity has to be reduced from ∼3 to ∼1 M (without substantial dilution) to achieve an efficient separation of the minor actinides. The results thus obtained using TRPO has been compared with those already reported while using dihexyl-N,N-diethylcarbamoylmethyl phosphonate, diisodecyl phosphoric acid, and octyl(phenyl)N,N-diisobutylcarbamoylmethylphosphine ...

The extraction of Am(III) and Eu(III) by octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) in xylene from aqueous media containing 1.0 M NH4NO3, NH4SCN, NH4ClO4 or a mixture of 0.3 M NH4NO3 + 0.7 M NH4ClO4 at pH 2.70 and at the temperatures of 15, 25, 35 and 45±0.1 °C has been studied. At all the temperatures, the species extracted were ML3 · 3CMPO (M = Am(III) or Eu(III), L = NO3 −, SCN− or ClO4 −) and M(NO3)(ClO4)2 · 3CMPO. The thermodynamic parameters of the extraction reactions have been evaluated using the temperature coefficient method. The −ΔG values follow the order SCN− > NO3 − + ClO4 − > NO3 − ≈ ClO4 −, whereas the −ΔH values an order NO3 − + ClO4 − > SCN− > NO3 − ≈ ClO4 −. The effect of these anions on the thermodynamic parameters have been discussed employing compensation effects and also on the basis of the energy associated with the transfer of these anions from aqueous to the extractant phase.

The extraction behaviour of neptunium from 3 M nitric acid as well as simulated pressurised heavy water reactor high level radioactive waste (PHWR-HLW) solution by 30% TBP/dodecane was studied using AKUFVE. Np(IV)/Np(V) was oxidised to Np(VI) using oxidising agents, such as K2Cr2O7, VO2 + and NaNO2. Stripping of neptunium from the loaded TBP phase was studied using reducing agents like hydrogen peroxide, ascorbic acid, hydroxyl-amine hydrochloride and hydrazine sulphate. Results of these extraction and stripping studies have been discussed in this paper.

A study on the separation of the long-lived heat generating fission products137Cs and90Sr from acidic solutions has been carried out using a specially fabricated electrodialytic cell equipped with a pair of cation and anion exchange membranes forming a catholyte and anolyte, respectively, and a radioactive feed chamber. The studies were done with feed solutions containing different concentrations of Na+, Cs+ and Sr2+ individually and with a mixture of these cations in 0.3 M HNO3. In all the cases, the transfer of Cs and Sr was found to be greater than 90%. To facilitate the separation of the above radionuclides from higher acidity (∼3.0M HNO3), diffusion dialysis was taken as a possible pretreatment step using a two compartment diffusion cell with an anion exchange membrane in between. All the experiments were done under non-stirring mode.

The extraction behavior of yttrium and trivalent lanthanoids has been investigated from thiocyanate solutions using bis(2,4,4-trimethylpentyl)octylphosphine oxide (CYANEX 925) in xylene as an extractant by tracer techniques. The results demonstrate that these trivalent metal ions are extracted as M(SCN)3•3CYANEX 925. The equalibrium constants of the extracted complexes have been deduced by non-linear regression analysis. The extraction behavior of trivalent lanthanoids and yttrium was found to be ambiguous since the distribution ratios of these metal ions are nonmonotinic function of atomic number (La

The present work deals with countercurrent extraction studies on the partitioning of uranium, neptunium, and plutonium using 30% tributyl phosphate (TBP) from simulated high level waste solution generated during reprocessing of spent uranium fuel from pressurized heavy water reactors. The oxidation states of neptunium and plutonium were adjusted either by 0.01 M potassium dichromate or 0.01 M dioxovanadium ion. Neptunium and plutonium, extracted in the TBP phase, were stripped together using a mixture containing 0.05 M ascorbic acid and 0.25 M hydrogen peroxide in 2.0 M nitric acid solution. Although dioxovanadium ion is more effective for proper adjustment of the oxidation states of plutonium and neptunium, subsequent recovery of these actinides from loaded TBP is better if potassium dichromate is used for the valency adjustment. Results of the stagewise analysis of extraction and stripping of actinides using mixer-settlers are presented.

The radiolytic degradation of the extractant mixture 0.2 M octylphenyl-N,N{prime}-diisobutylcarbamoylmethyl phosphine oxide (CMPO) + 1.2 M tributyl phosphate in n-dodecane [to be utilized for the partitioning of minor actinides from high level waste (HLW) solutions of PUREX origin] has been investigated in contact with 3 M HNO{sub 3} or synthetic pressurized heavy water reactors (PHWR)-HLW solution under dynamic conditions. The distribution ratios of Am, Zr, Fe and Ru with the irradiated extractant mixture at varying doses have been determined under various aqueous phase conditions and correlated with the formation of degradation products. Various cycles of loading the extractant mixture with Am from PHWR-HLW, irradiating at a fixed gamma dose, and then primary and secondary clean-up of the solvent has been carried out to illustrate its reusability during partitioning of minor actinides from actual HLW solutions. The degradation products of CMPO have been identified by employing GC and GC-MS techniques.

A novel CMPO (carbamoylmethylphosphine oxide) based task specific ionic liquid (TSIL) with an NTf(2)(-) counter anion was synthesized and evaluated for actinide/lanthanide extraction from acidic feed solutions using several room temperature ionic liquids (RTILs). The extraction data were compared with those obtained with CMPO in the same set of RTILs and also in the molecular diluent, n-dodecane. The extracted species were analyzed by the conventional slope analysis method and the extraction followed an ion-exchange mechanism. The nature of bonding in the extracted complexes was investigated by various spectroscopic techniques such as FT-IR and UV-visible spectroscopy.

The present work deals with the extraction of neptunium into the TBP/dodecane phase under conditions relevant to highly radioactive waste solutions, along with uranium and plutonium, by oxidizing it to the hexavalent state using 0.01 M K2Cr2O7 and subsequently recovering it by selective stripping. Three types of simulated HLW solutions, namely sulfate-bearing (SB, in ∼0.3 M HNO3) and non sulfate wastes originating from the reprocessing of fuels from pressurised heavy water reactors (PHWR) and fast breeder reactors (FBR) (both in 3.0 M HNO3), have been employed in this study. Very high extraction of U(VI), Np(VI), and Pu(VI) was obtained from PHWR and FBR-HLW solutions, whereas extraction was less but reasonably high from the SB-HLW solution. The uptake of cerium at tracer level concentrations in the millimolar range (encountered in HLW solutions) and from the simulated HLW solutions containing 0.01 M K2Cr2O7 by 30% TBP has shown that its extraction takes place only at tracer level concentrations ...

The extraction behaviour of selected trivalent lanthanides, actinides and yttrium was studied from thiocyanate and nitrate solutions using octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide(CMPO) in xylene as an extractant. It was found that these trivalent metal ions were extracted as MX3.3CMPO (where X - SCN - or N03-). The equilibrium constants(K) of the above species were determined by non-linear regression analysis. The K values of trivalent lanthanides in nitrate solutions do not increase monotonically with increasing atomic number(Z), but have a maximum at Eu. On the other hand, in thiocyanate solutions, the K values increase with increasing Z. In the extraction systems containing soft ligands like thiocyanate the distribution ratio (D) of Y is lower than that of La, whereas trivalent actinides Am and Cm have much higher D values than their corresponding counterparts in the lanthanide series. However, in the extraction systems containing a hard ligand such as nitrate, it is interes...