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Neptunium, with a half life of 2.14 million years is one of the most notorious activation products in the nuclear fuel cycle. It has been more than 5 decades in the reprocessing of nuclear fuels by the well documented PUREX process, but the fate of Np in the PUREX cycle is still not well controlled. Although Np being stable in its pentavalent state in low acid media, its starts to undergo disproportionation at higher acidities. This disproportionation along with the oxidizing conditions of the HNO3 medium makes Np to exits as Np(IV), Np(V) and Np(VI) in the dissolver solution. The overall extractability of Np in the co-decontamination step of the PUREX cycle is dependent on its oxidation state in the medium as Np(VI) and Np(IV) being extractable while Np(V) being least extractable. The present review article discusses about the speciation of Np in HNO3 and its disproportionation. The variety of redox reagents are discussed for their effectiveness towards controlling Np redox behavior in the HNO3 media. The extraction of Np with the different class of extractant has also been discussed and the results are compared for better understanding. Solid phase extraction of Np using both commercially available resin and lab based synthesized resins were discussed. The anion exchange resins with the different cationic centers were shown to behave differently towards the uptake of Np form the acidic medium. The present review also highlight the chemical conditions required for controlling or minimizing the fate of Np in different process streams of the nuclear fuel cycle.

Cardiovascular disease (CVD) makes our heart and blood vessels dysfunctional and often leads to death or physical paralysis. Therefore, early and automatic detection of CVD can save many human lives. Multiple investigations have been carried out to achieve this objective, but there is still room for improvement in performance and reliability. This study is yet another step in this direction. In this study, two reliable machine learning techniques, multi-layer perceptron (MLP), and K-nearest neighbour (K-NN) have been employed for CVD detection using publicly available University of California Irvine repository data. The performances of the models are optimally increased by removing outliers and attributes having null values. Experimental-based results demonstrate that a higher accuracy in detection of 82.47% and an area-under-the-curve value of 86.41% are obtained using the MLP model, unlike the K-NN model. Therefore, the proposed MLP model was recommended for automatic CVD detection. The proposed methodology can also be employed in detecting other diseases. In addition, the performance of the proposed model can be assessed via other standard data sets.

A novel series of mixed-ligand complexes of the type, [M(L1)(L2)Cl]·2H2O [L1 = 2-(α-methyl salicylidene hydrazine) benzimidazole (primary ligand), L2 = 2,2′-bipyridine (bipy; secondary ligand), M = Co(ii), Ni(ii), Cu(ii) and Zn(ii)], were based on the physicoanalytical studies. The spectroscopic findings revealed tridentate nature of the Schiff base ligand (L1) and its coordination to the metal ions via azomethine nitrogen, ring nitrogen and the deprotonated phenolic oxygen atoms. Furthermore, the synthesized compounds were evaluated for antimicrobial activity against Bacillus subtilis, Escherichia coli and Salmonella typhi microorganisms. In addition, molecular docking studies were carried out against Middle East respiratory syndrome coronavirus (PDB ID: 4ZS6) and severe acute respiratory syndrome coronavirus 2 main protease (PDB ID: 6W63).

In the present study, the nature of Eu(III) complexes (Eu(III) was used as a surrogate for Am(III)) formed in kaolinite–humic acid (HA)/citric acid (CA) system was investigated by luminescence spectroscopy. In addition to the ternary system (kaolinite + Eu + L(CA/HA)), the binary system (Eu-L) was also looked at for a better understanding of the complexes formed at the kaolinite surface. The lifetime and emission spectra of Eu-L complexes on the kaolinite surface differ considerably as compared to the same in the aqueous phase. The Eu-HA aqueous complexation shows differences in the excitation spectra with similar decay lifetimes with increasing aqueous HA concentrations. The ligand-to-metal charger transfer (LMCT) in the Eu-HA excitation spectra suggests the complexation of Eu(III) with HA at pH ∼ 4. Although the mode of Eu(III) binding to the kaolinite surface in the presence of CA/HA was the same i.e. metal-bridged ternary complex formation, the local surroundings around the sorbed Eu(III) differ in the two cases. The loading of HA in the Eu-HA-kaolinite system does not have a large effect on the local structure around the sorbed Eu(III) ion, but enhances the percentage of Eu(III) uptake onto the kaolinite surface. The number of H2O molecules in the primary hydration sphere of sorbed Eu(III) differs in the Eu-HA-kaolinite and Eu-CA-kaolinite systems. In addition, Eu(III) assisted precipitation of HA was also seen using a radiometric method.

Ruthenium recovery from the alkaline media was attempted using solid phase extraction. UV-Vis and X-ray absorption studies were performed to understand the ruthenium speciation under different conditions relevant to its extraction from alkaline medium. Since Ru forms anionic complex in the alkaline solution, an anion exchange resin (Dowex 1x8) was selected for its recovery from alkaline media. The precipitation of black RuO2 at the resin surface hinders its back exaction. Experimental conditions were optimized for the quantitative uptake of Ru from alkaline feed and its subsequent back extraction by a series of batch studies. About 90 % of the Ruthenium was back extracted from the resin using alkaline hypochlorite solution and nitric acid solution at different stages in the Ru back extraction cycle. The column studies were done under the optimized condition and showed ~80 % Ru recovery with 5 mL of the eluent (8 M HNO3) and ~90 % recovery in 10 mL including the tailing. The mechanism for the ruthenium extraction from alkaline medium and its back extraction from the resin was proposed.

The extraction behaviour of U(VI), Th(IV) and Nd(III) was investigated as a function of nitric acid concentration for diamide based extractants, namely, N,N,N′,N′-tetraoctyl-3-carbonylpentanediamide (TOCPDA) and 4-carbonyl-heptanedioic acid bis-dioctylamide (CHADA). In addition, the distribution ratio was also measured for Pu(IV) and Sr(II) with 1.1 M CHADA in n-dodecane. These extractants were synthesized by adopting simple acid, amine coupling reaction with DCC (dicyclohexylcarbodiimide) and DMAP (N,N′-dimethylaminopyridine) as the coupling agent. The newly synthesized extractants were characterized by FT-IR, NMR, Mass, CHNS and HPLC. The extraction results indicated that CHADA shown has better extraction behavior for U(VI) compared to TOCPDA. In addition, CHADA coated HPLC column was examined for the retention behaviour of U(VI), Th(IV), and Nd(III). Computation studies based on density functional theory (DFT) were carried out to understand the complexing behaviour of U(VI), Pu(IV) and Sr(II) with CHADMA and TMCPDA.

Separation of trivalent actinide (An) and lanthanide (Ln) elements is one of the burning topics in the back end of the nuclear fuel cycle due to the similarity in their chemical behaviour. A significant amount of research is being carried out worldwide to develop suitable ligands for the separation of the trivalent actinides and lanthanides. Some of the research groups are engaged in continuous improvement of the di-ethylene-triamine-penta acetic acid (DTPA) based Ln/An separation method, whereas extensive research is going on for the development of the lipophilic and hydrophilic ‘N’ donor heteropolycyclic ligands as the actinide selective ligand. A number of ‘S’ donor ligands are also explored for the Ln/An separation. In the present review, we made an attempt to highlight various separation processes based on soft donor ligands developed for Ln/An separations. Beside the conventional solvent extraction processes, separation possibilities membrane based and solid phase extraction techniques are evaluated for the Ln/An separation and are compiled in the present review.

Ruthenium (106Ru), a notorious fission product in nuclear reprocessing cycle, which gets partitioned at each step needs to be recovered. The recovery of Ru from acidic high level waste (HLW) is of great importance to the nuclear fuel cycle. Quantitative recovery of Ru was achieved from acidic feeds using oxidative trapping mechanism strategy where NaIO4 was used as an oxidant to convert different species of Ru in acidic phase to RuO4 while n-dodecane was used as trapping agent for RuO4. Stripping was attempted using NaOH and NaClO mixture. Attempt was made to optimize various parameters for 103Ru extraction and stripping. 103Ru tracer spiked simulated high level waste was used to understand the 103Ru behaviour in actual waste. The composition of stripping solution (alkaline hypochlorite) was also optimized to have >95% Ru into the aqueous phase in ca. 180 min.

Making use of a meromorphic analogue of the Cho-Kwon-Srivastava operator for normalized analytic functions, we introduce below a new class of meromorphic multivalent function in the punctured unit disk and obtain certain sufficient conditions for functions to belong to this class. Some consequences of the main result are also mentioned.

The present paper describes the selective extraction of tetravalent plutonium employing several diamide ligands containing aromatic spacer groups. The ligands containing two amide functional groups attached to a 2,4,6-tri-phenyl pyridine moiety with different substituents viz.; L I (iso-butyl), L II (n-butyl), L III (n-octyl), L IV (2-ethylhexyl) at the amidic nitrogen atom were evaluated for the extraction of Pu(IV) using their nitrobenzene solutions. The distribution ratio values of Pu(IV) with the diamide ligands followed the order: LII >LI >LIII >LIV and were significantly higher than those of metal ions such as Cs(I), Sr(II), Am(III) and Eu(III). The distribution ratio values of U(VI) were about 2–3 orders magnitude lower than those of Pu(IV). The extraction and stripping kinetics were found to be moderately fast and it took less than 30 min (less than 5 min for L I and L IV ) to obtain equilibrium D values. The extraction was found to be increasing with the aqueous phase nitric acid concentration conforming to a solvation mechanism of extraction. The extracted species contained two ligand molecules for L I and L II while monosolvates were observed for the other two extractants. The ligands showed good radiation stability up to an absorbed dose of 630 kGy.

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.

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).

This review article gives a comprehensive account of the extraction of actinide ions using room temperature ionic liquid-based solvent systems containing diglycolamide (DGA) or functionalized DGA extractants. These extractants include multiple DGA-functionalized ligands such as tripodal DGA (T-DGA) and DGA-functionalized calix [4]arenes (C4DGA). Apart from metal ion extraction behaviour, other important features of the ionic liquid-based solvent systems such as separation behaviour, luminescence spectroscopic results, thermodynamics of extraction and radiolytic stability of the ionic liquid-based solvents are also reviewed. Results from studies on DGA-functionalized task-specific ionic liquids (TSIL) are also included in this review article.

Polymer inclusion membranes (PIM) containing N,N,N′,N′-tetra(2-ethylhexyl) diglycolamide (T2EHDGA) were evaluated for the separation of actinide ions such as Am3+, Pu4+, UO2 2+ and Th4+ from acidic feeds. The PIMs were prepared using cellulose triacetate (CTA) as the polymer matrix, 2-nitrophenyloctyl ether (NPOE) as the plasticizer and T2EHDGA as the carrier extractant and the optimized membrane composition was found to be 68.4% T2EHDGA, 17.9% NPOE and 13.7% CTA which resulted in 74% Am3+ uptake at 1 M HNO3 in 2 h. The uptake studies were carried out using feed solutions containing varying concentrations of nitric acid (0.5–3.0 M) and showed the trend: Pu4+ > Am3+ > Th4+ > UO2 2+. Quantitative stripping (> 99%) of the sorbed Am3+ was possible using a solution containing 0.01 M EDTA at pH 3.0. Reusability studies indicated deterioration of the PIM on continuous use.

The radiolytic stability of different substituted diglycolamides such as N,N,N′,N′-tetrapentyl diglycolamides(TPDGA), N,N,N′,N′-tetrahexyl diglycolamide (THDGA), N,N,N′,N′-tetraoctyl diglycolamide (TODGA), N,N,N′,N′-tetradecyl diglycolamide (TDDGA) and N,N,N′,N′-tetra-2-ethyl hexyl diglycolamide (T2EHDGA) was investigated in solvent systems containing 30% iso-decanol as a phase modifier in n-dodecane kept in contact with a 3 M HNO3 aqueous solution while irradiating in a gamma ray chamber up to 1000 kGy. The degradation of the solvent systems was qualitatively ascertained from measuring the distribution ratio values at 3 M and 0.2 M HNO3 which gave a direct indication of the reusability of the solvent for long term reuse in separation processes such as `actinide partitioning'. The effect of irradiation on distribution values of Sr, Pu, U was also investigated with diglycolamide extractants both under extraction and stripping conditions. Stoichiometry of the extracted species was determined for Am(III) extraction using the fresh as well as the irradiated solvent systems involving all the five substituted diglycolamides at 3 M HNO3 and the results indicated only marginal changes. GC-MS analysis was done for fresh and irradiated solvent systems of all the diglycolamides and attempts were made to identify the degradation products.

Two novel diglycolamide-grafted silica-based resins (DGSRs) were used for the sorption of trivalent actinides and lanthanides from 3 M nitric acid solutions. The sorption of Am(III) onto the resin containing one diglycolamide (DGA) moiety (DGSR-I) was less efficient than the resin containing two DGA moieties (DGSR-II) with Lagergren first order rate constants of (1.20 ± 0.03) × 10 –3 s –1 and (2.01 ± 0.05) × 10 –3 s –1, respectively. The maximum sorption of Eu(III) (used as a representative of the trivalent lanthanide/actinide ions in radioactive wastes) was 10.4 ± 1.1 mg g –1 and 13.9 ± 1.3 mg g –1 by the DGSR-I and DGSR-II, respectively. The sorption of Eu(III) on the grafted silica resins followed the Langmuir monolayer sorption phenomenon with sorption energies of 16.5 ± 2.05 and 17.8 ± 1.6 kJ mol –1 for DGSR-I and DGSR-II, respectively. Column experiments revealed that the breakthrough capacity of Eu(III) on the DGSR-II column was higher than that on the DGSR-I column. Efficient elution could be achieved with a 0.01 M EDTA solution. The radiolytic stability of the resins was ascertained by exposing the resins to a gamma ray dose up to 1030 kGy resulting in a decrease of the K d values with about 50%; at doses K d values remained unaffected.

A novel solvent system containing chlorinated cobalt dicarbollide (CCD) in a diluent mixture containing 2-nitrophenyloctyl ether (NPOE) and n-dodecane was found to be highly efficient for the extraction of radio-cesium from acidic feed conditions. When PEG-400 (polyethylene glycol with average molecular weight of 400) was added to the solvent system, it was found to extract radio-strontium as well similar to that reported with the UNEX (Universal Extractant) solvent. The solvent system was found to be superior as compared to analogous solvent systems reported previously using CCD in either nitrobenzene or PTMS (phenyltrifluoromethyl sulphone, a fluorinated diluent). The present work deals with less toxic solvent formulation which can be used as an alternative to these hazardous/toxic chemicals for simultaneous recovery of Cs(I) and Sr(II) from acidic solutions. Batch co-current extraction data are also presented for the simultaneous recovery of Cs and Sr which indicated near quantitative extraction (>99.5%) of the metal ions in 4 and 3 stages, respectively. The reusability and radiolytic stability studies were also carried out which suggested highly encouraging results.

Extraction chromatographic resin prepared by impregnating CMPO-RTIL (C8mim+·NTf2 −) on Chromosrob-W for the removal of trivalent actinides and lanthanides from aqueous solutions showed a significant improvement over the previously reported CMPO-n-dodecane resin. The resin was characterized by thermal analysis, for surface area by BET and for surface morphology by SEM. The K d value of Am(III) by CMPO-RTIL resin was found to be 5805 and 3.8E4 with 3 M and 0.01 M HNO3, respectively. The high K d values at lower acidity suggested metal ion uptake following a cation exchange mechanism usually seen with ionic liquid based solvents and use of 0.01 M EDTA resulted in a K d value of 0.11 which was subsequently used as the strippant. Uptake of other actinide ions such as UO2 2+, Pu4+, Np4+ and fission product element ions such as Eu3+, Sr2+ and Cs+ was also studied. Column studies using a feed containing 1 g/L Eu(III) in 3 M HNO3 suggested complete uptake of the metal ion up to passing 7 mL of the feed solution which corresponded to a column capacity of 7 mg of Eu. The loaded Eu(III) from the columns could be efficiently eluted with 0.01 M EDTA. The column capacity for Eu(III) was measured in the successive cycles of loading and elution and was found to be stable up to 60 d. The results suggested the possible application of the resins in the treatment of dilute laboratory radioactive waste.

Solvent extraction studies of several actinide ions such as Am(III), U(VI), Np(IV), Np(VI), Pu(IV) were carried out from nitric acid medium using a synergistic mixture of N, N′-diethyl-N, N′-di(para)fluorophenyl-2,6-dipicolinamide, (DEtD(p)FPhDPA, DPA), and hydrogen dicarbollylcobaltate (H+CCD−) dissolved in phenyltrifluoromethylsulphone (PTMS). The effects of different parameters such as aqueous phase acidity (0.01 – 3 M HNO3), oxidation states of metal ions, ligand concentration, nature of diluent and temperature on the extraction behavior of metal ions were studied. The extracted Am(III) species was determined as H+[Am(DPA)2(CCD)4]−. With increasing aqueous phase acidities, the extractability of both Am(III) and Eu(III) was found to decrease. The synergistic mixture showed better extraction in mM concentrations as compared to previously studied dipicolinamides. The thermodynamic studies were performed to calculate heat of extraction reaction and the extraction constants. The proposed synergistic mixture showed good extraction for all the metal ions, though lanthanide actinide separation results are not encouraging.

Batch sorption experiments have been carried out to understand the interaction of different metal cations such as Am(III), Eu(III), Sr(II), and Cs(I) with bentonite clay at varying pH (1–9). The effects of other experimental parameters such as ionic strength (0.01–1 M (NaClO4)), clay to metal ion concentration ratio, and the presence of complexing anions such as oxalic acid (ox), carbonate (CO3 2−), ethylenediaminetetraacetic acid (EDTA), and humic acid (HA) on Eu(III) sorption have also been investigated. The sorption of Eu(III) has been found to be invariant with the change in ionic strength suggesting inner-sphere complexation on the bentonite surface. Near quantitative sorption of Eu(III) and Am(III) has been observed in the entire pH range and there is marginal influence of the presence of 1 · 10 –4 M of ox and CO3 2− on the sorption profile. However, the presence of 1 · 10 –4 M EDTA suppresses the sorption of Eu(III) ion onto bentonite. Desorption studies of Eu(III) loaded onto bentonite using varying concentrations of HClO4 (0.01–1.0 M) solutions reveal that higher acidity favors the process. The sorption of Eu(III) on bentonite followed the Langmuir isotherm suggesting monolayer sorption process. The data fitting to D-R isotherm suggested that the Eu(III) sorption on bentonite follows ion exchange mechanism. The sorption capacity of bentonite clay was determined to be 3.8(± 0.1) × 10−4 moles/g using Langmuir and D-R isotherms.

Extraction behavior of Np4+ and Pu4+ was investigated using several tetraalkylsubstituted diglycolamide (DGA) extractants such as N,N,N′,N′-tetrapentyl-diglycolamide (TPDGA), N,N,N′,N′-tetrahexyl diglycolamide (THDGA), N,N,N′,N′-tetraoctyl diglycolamide (TODGA), and N,N,N′,N′-tetradecyl diglycolamide (TDDGA). The organic phases used were 0.1 M solutions of the diglycolamide extractants in n-dodecane modified with 30% iso-decanol for avoiding third phase formation while the aqueous phases contained dilute nitric acid solutions spikes with the radiotracers. The stoichiometry of the extracted species was ascertained by ligand concentration variation experiments and was found to be M(NO3)4 · 2L, where M was Np and Pu and L was the substituted DGA ligand. In general, the extraction equilibrium constant (log K ex) values for both Np4+ and Pu4+ showed an increasing trend with increasing alkyl group chain length and the log K ex values were higher for Pu4+ as compared to those for Np4+. While for Np4+, the K ex values were 7.03 ± 0.04 for TPDGA which increased steadily up to 7.98 ± 0.05 for TDDGA, for Pu4+, the respective value for TPDGA was 7.32 ± 0.05 which increased to 7.78 ± 0.03 for TDDGA. Thermodynamic parameters were also determined for the two-phase extraction equilibrium reaction.

A novel extraction chromatographic resin was prepared by impregnating CMPO-RTIL (C8mim+·NTf2 −) on Chromosrob-W for the removal of trivalent actinides from aqueous solution and its behaviour was compared with previously reported CMPO-n-dodecane resin. Under identical condition, the K d value of Am(III) by CMPO-RTIL resin (K d at 3 M HNO3 = 5805 ± 525) was one order magnitude higher than that obtained with CMPO-n-dodecane resin (K d at 3 M HNO3 = 610 ± 55). The sorption reaction of Am(III) followed a first-order rate law with both the resins. The metal sorption capacities for Eu(III) at 3 M HNO3 were found to be 18.95 ± 1.13 mg and 20.52 ± 1.25 mg/g of CMPO-RTIL and CMPO-n-dodecane resins, respectively. The analysis of the sorption data by different models supported the hypothesis that the sorption of Eu(III) on the resins was actually limited by the saturation of the CMPO complexing sites on the resin. The free energy for the sorption of Eu(III) obtained from D–R isotherm was 17.67 ± 1.63 kJ/mol and 16.51 ± 2.05 kJ/Mol for CMPO-RTIL and CMPO-n-dodecane resins, respectively. The sorption free energy is an indication of chemisorption monolayer mechanism. The monolayer sorption mechanism was also confirmed by the theoretical approach calculated based on the sorption kinetics.

N,N´-dimethyl-N,N´-dioctyl-2,(2´-hexyloxyethyl) malonamide (DMDOHEMA) has been synthesized by a relatively simpler route with a better yield than the conventional procedures for the synthesis of pentaalkyl substituted diamides. The proposed route replaces the use of acid chlorides and brominating agents (corrosive in nature) by acid diester and p-toluene sulphonyl (tosyl) chloride, respectively. The later easily replaces hydrogen from primary OH group of the 3-oxanonyl side chain and relatively less corrosive. The synthesized product has been tested for the extraction behavior of 241Am, Np, Pu as pure tracers as well as under Pressurized Heavy Water Reactor (PHWR) Simulated High-Level Waste (SHLW) conditions. The stoichiometries of extracted species of Np(IV), Pu(IV), and Am(III) from 3 M HNO3 using varying concentrations of DMDOHEMA in n-dodecane has been determined. The effect of the nature of mineral acid (viz. HCl, HNO3, and HClO4) on the extraction of Am(III) has also been investigated employing DMDOHEMA and N,N´-dimethyl-N,N´-dibutyl-tetradecyl malonamide (DMDBTDMA) as extractants and explained in terms of the aggregation behavior of diamides. The performance of DMDOHEMA has been evaluated vis-à-vis other proposed extractants for actinide partitioning under PHWR-SHLW conditions.

‘Actinide partitioning’ studies were attempted by hollow fibre supported liquid membrane (HFSLM) technique using pressurized heavy water reactor simulated high level waste (PHWR-SHLW) as the feed. Two diglycolamide extractants for actinide partitioning, viz. 0.1 M TODGA (N,N,N´,N´-tetraoctyl diglycolamide) + 0.5 M DHOA (N,N-dihexyl octanamide) and 0.2 M T2EHDGA (N,N,N´,N´-tetra-2-ethylhexyl diglycolamide) + 30% iso-decanol in n-dodecane were used as the carrier solvent. Quantitative recovery of all trivalent actinides and lanthanides from PHWR-SHLW was achieved with both the carriers within 30 min when the feed volume was 0.5 L. On the other hand, about 18 h were necessary for a similar study carried out using a feed volume of 20 L. None of the other elements present in the PHWR-SHLW were transported, except small quantities of Sr and Mo. The product could be concentrated to two and four times by maintaining the feed to receiver phase volume ratio of 2:1 and 4:1, respectively. The transport behaviour of trivalent actinides and lanthanides by the two diglycolamide extractants were remarkably similar. The present studies revealed that diglycolamide-HFSLM system offers a promising alternative approach for ‘actinide partitioning’, where the use of organic solvent inventory could be drastically reduced. A mathematical model was developed and there was good agreement between the predicted and experimentally obtained data.

Studies on the extraction of Cs(I) from nitric acid medium were carried out using three commercial calix-crown ligands, viz. calix[4]arene-bis-crown-6, calix[4]arene-bis-1,2-benzocrown-6 and calix[4]arene-bis-2,3-naphthocrown-6 dissolved in different room temperature ionic liquids (RTILs), viz. 1-butyl-3-methyl-imidazolium hexafluorophosphate (C4mim·PF6), 1-hexyl-3-methyl-imidazolium hexafluorophosphate (C6mim·PF6) and 1-octyl-3-methyl-imidazolium hexafluorophosphate (C8mim·PF6). The distribution ratio of Cs(I) decreased with increased alkyl chain length of RTILs. The effect of nitric acid concentration on distribution behaviour of Cs(I) by calix[4]arene-bis-1,2-benzocrown-6 was investigated. The extraction of Cs(I) from HNO3 was found to be exothermic and extraction was found to be enthalpy driven. Selective extraction of Cs(I) could be achieved from a mixt ure of various fission product elements like Tc, Mo, Zr, Ce, Ru, La, Ba, and Sr.

Polypropylene hollow fibre-based supported liquid membrane (HFSLM) containing calix[4]-bis-2,3-naphtho-crown-6 in 20% (v/v) n-dodecane+80% (v/v) 2-nitrophenyl octyl ether (NPOE) as the carrier solvent was employed for the first time to investigate the transport behaviour of radio-caesium. The carrier solution was 1 mM calix[4]-bis-2,3-naphtho-crown-6 in 20% (v/v) dodecane+80% (v/v) NPOE+0.4% alamine 336 and the feed was 3 M HNO3 while distilled water was used as the receiver phase. In spite of high viscosity of the carrier solvent, quantitative (>99%) transport was possible in about 6 h. Significant amount of acid transport was also noticed which was ascribed to a co-transport mechanism involving encapsulated hydronium ion. Selectivity studies were carried out by taking a mixture of radiotracers, viz. 51Cr, 59Fe, 85,89Sr, 137Cs, 152,154Eu and 241Am, which represent some of the elements present in the high level waste, in the feed solution. The decontamination factors for various metal ions were found to be in the range 540–890. High decontamination factors as well as possibility of working over several days without deterioration of the liquid membrane suggested possible application of the system for the recovery of radio-caesium from high level waste. Studies on the membrane stability indicated reproducible transport data over 40 h.

Hollow fibre supported liquid membrane (HFSLM) studies were carried out for the selective recovery of uranium from THOREX feed solution (0.2 g/L U+200 g/L Th+0.03 M HF+0.1 M Al(NO3)3 at 4 M HNO3) using di(2-ethylhexyl) isobutyramide (D2EHIBA) as the carrier and distilled water as the strippant. About 85% of uranium was selectively transported into the receiver phase in 30 min with n-butyl phosphate) was used as the carrier, but a relatively large amount of thorium (>10%) was also co-transported to the product side. Strip phase acidity analysis revealed significant amount of acid co-transport with both the carriers. Acid transport was found to increase with the total salt content of the feed solution. The transport of metal ions was explained with the help of a theoretical model. Stability of the liquid membrane was also studied over about 5 d for long term reusability.

Summary Membrane based non-dispersive solvent extraction (NDSX) of U(VI) from aqueous nitric acid medium was carried out using a commercial hollow fibre module containing microporous hydrophobic polypropylene capillaries. The NDSX operation was carried out by pumping U(VI) solutions at varying concentrations of nitric acid (1-5 M) through the tube side and organic solvent (di-n-hexyl octanamide (DHOA) in normal paraffin hydrocarbon (NPH)) through the shell side of the hollow fibre capillaries. Extraction studies were performed under different hydrodynamic conditions and the overall mass transfer was evaluated under counter-current flow conditions. Counter-current mode was found to be better as compared to the co-current mode. The U(VI) mass transfer rates were positively influenced by the nitric acid as well as DHOA concentrations.

Summary The extraction behaviour of Np(IV) by 3-phenyl-4-acetyl-5-isoxazolone (HPAI) was investigated from nitric acid medium in the presence of tri-n-octyl phosphine oxide (TOPO). Speciation studies, carried out by the slope analysis method, yielded binary species of the type Np(PAI)4 when only HPAI was used as the extractant and ternary and quaternary species of the type Np(PAI)4·TOPO and Np(PAI)3·(NO3)·TOPO, respectively when both HPAI and TOPO were used together as the extractants. The two-phase extraction constant for the binary species (log k ex) was calculated to be 8.44±0.05 while those for the ternary and quaternary species were found to be 12.84±0.22 and 11.26±0.07, respectively.

Summary We have determined K d values for Mo and W in batch experiments on various anion-exchange resins in HCl and HNO3 as well as in mixed HCl-HF and HNO3-HF solutions in order to create a data base and to select optimum conditions for the determination of K d values of Sg (element 106) in a future on-line experiment using continuous chromatography with the multi-column technique (MCT). Their influence by hydrolysis and fluoride complexation is discussed and the average charge of the complexes is determined from slope analyses. It is shown that the selectivity of anion exchangers for the Mo- and W complexes and, thus, the separation factors between them, depend strongly on the choice of the functional group of the anion-exchange resin.

Summary The fluoride complexation of the group-4 elements Zr, Hf, and Rf, and of the pseudo-homolog Th, was previously investigated in mixed HNO3/HF solutions by studying K d values on both cation-exchange resins (CIX) and anion-exchange resins (AIX) using the automated rapid chemistry apparatus ARCA. On the CIX, the fluoride complexation of Rf was found to be weaker than that of Zr and Hf but stronger than that of Th. On the AIX, the competition for the binding sites by the counter ion NO3 - was found to be stronger for the fluoride complexes of Rf than for those of Zr and Hf. The aim of the present work is to add independent evidence to the latter result by measuring K d values for Rf on the AIX in 0.1 M HNO3/0.5 M HF and in 0.01 M HF without any HNO3. The results are obtained via an activity ratio of the long-lived α-decay descendant of 261mRf, 20-d 253Es, using the multi-column technique (MCT). These experiments corroborate the seemingly much more pronounced competition of NO3 - for the exchanging sites of the AIX with respect to [RfF x ]( x -4)- than with [ZrF x ]( x -4)- and [HfF x ]( x -4)-.

SummaryThe extraction behaviour of Np(IV) by 3-phenyl-4-benzoyl-5-isoxazolone (HPBI) in the presence of tri-n-octyl phosphine oxide (TOPO) was investigated from nitric acid medium. The speciation studies, carried out by the slope analysis method, yielded binary species of the type Np(PBI)4when only HPBI was used as the extractant and ternary species of the type Np(PBI)4·TOPO when both HPBI and TOPO were used as the extractants. The two-phase extraction constant for the binary species (logkex) was calculated to be 10.11±0.03, while that for the ternary species was found to be 17.24±0.05. Thermodynamic parameters for the binary and ternary extraction systems were also determined. Both the binary and ternary extraction systems were found to be highly spontaneous processes with predominant enthalpy stabilization. The very high negative entropy factor suggested contribution of unfavourable steric factors.

The extraction behaviour of Uranium (VI) from aqueous nitric acid medium employing 3-phenyl-4-benzoyl-5-isoxazolone (HPBI) has been studied in the presence of various amides, e.g , di-2-ethylhexylacetamide (D2EHAA), di-2-ethylhexylpropanamide (D2EHPrA), di-2-ethylhexylisobutylamide (D2EHiBA) and di-2-ethylhexylpivylamide (D2EHPvA) in toluene medium. The extraction constant (log k ex) for the binary species UO2(PBI)2·nH2O was found to be 1.42±0.14 which is by far the largest amongst the corresponding values known for the other β-diketones. The overall equilibrium constant (log K) for the ternary species UO2(PBI)2·D2EHAA, UO2(PBI)2·D2EHPrA, UO2(PBI)2·D2EHiBA and UO2(PBI)2·D2EHPvA were estimated to be 6.51, 6.21, 6.11 and 5.77 respectively. This trend in equilibrium constants was in accordance with the substitution of the amides as sterically crowded amides show relatively lower equilibrium constant values. The extraction constants follow an inverse correlation with the pK a values of the β-diketonates while the equilibrium constants vary linearly with the size of the amides. The steric factors have been found to play a significant role in the co-ordination of the amides to the uranyl β-diketones when the carbonyl group is a part of the heterocyclic ring. The distribution ratios of the metal were measured in the temperature range 15 to 52 °C using each of the amide donors in combination with HPBI. Calculation of enthalpy and entropy therefrom indicated that the extraction was thermodynamically favoured process and maximum extraction resulted in the case of UO2(PBI)2·D2EHAA.

The extraction behaviour of plutonium (IV) was investigated from nitric acid and perchloric acid using 3-phenyl-4-benzoyl-5-isoxazolone (HPBI) as well as a mixture of HPBI and tri-n-octyl phosphine oxide (TOPO) in xylene. Studies on the binary extraction system Pu(IV)-HPBI indicated extraction of species of the type Pu(PBI)4. In the presence of TOPO, while species of the type Pu(PBI)3(ClO4)·(TOPO) and Pu(PBI)4·TOPO were co-extracted from perchloric acid medium, a mixture of Pu(PBI)2(NO3)2·2TOPO, Pu(PBI)3(NO3)·(TOPO) and Pu(PBI)4·TOPO were co-extracted from nitric acid medium. In addition to the electronic factors, steric factors were found to play a significant role during the formation of binary/ternary/quaternary complexes. The steric hindrance due to the unusual conformation of the isoxazolone led to lowering of the equilibrium constants for both the binary and ternary extraction systems. Possible steric factor influences are explained with the help of molecular modelling.

Summary An attempt has been made to explore the use of di(2-ethylhexyl)isobutyramide (D2EHIBA) as an extractant for the recovery of Pu from the (proposed) AHWR fuel fabrication scrap solution. The extraction of Pu in the hexavalent state has been found to be distinctly more efficient than that in the tetravalent state. Distribution studies have been carried out by maintaining Pu as Pu(VI) employing AgO as the oxidant. Scrubbing at 5M HNO3 has been proposed to reduce the interference due to the co-extracted Th(IV). Quantitative stripping of the extracted Pu was achieved using Hydroxyl Ammonium-Nitrate (HAN) as reductant. Ion exchange studies have been carried out for the final purification of Pu. It is proposed to employ the cation exchanger, Biorad AG 50X8 for the final purification of Pu from the stripped solution, keeping Pu as Pu(III).

Summary The extraction behaviour of plutonium (IV) and neptunium (IV) was studied from nitric as well as hydrochloric acid employing 3-phenyl-4-benzoyl-5-isoxazolone (PBI) in toluene as the extractant. The forward extraction in hydrochloric acid medium was carried out in presence of several holding oxidants out of which ammonium meta vanadate was found to give the best results. The stripping behaviour of Np and Pu was studied employing a variety of reagents out of which 0.1 M hydroquinione in 1:1 HCl was the most promising. The separation of Np from Pu under simulated conditions was attempted from hydrochloric acid medium giving a decontamination factor value of >104 and ∼60% Pu recovery.

The extraction of Sr(II) from 4 M nitric acid was carried out employing two substituted crown ethers, viz. dicyclohexano 18crown6 (DCH18C6) and di-t-butyl cyclohexano 18crown6 (DTBuCH18C6) in n-octanol and n-butanol-n-octanol mixtures. The extracted species conformed to SrL2+ · 2(NO3 -) · xH2O where L = DCH18C6/DTBuCH18C6 and x = no. of water molecules associated with the extracted complex. The log DSr vs. log[L] plots yielded straight lines with unity slope for DTBuCH18C6 as well as DCH18C6. Thermodynamics of Sr(II) extraction for the mixed diluent system employing these crown ethers has been investigated (in the temperature range of 10° to 50°C). The negative enthalpy as well as negative entropy values suggest ion-association type species getting extracted into the organic phase which are stabilised by solvation in the water rich alcohol phase.

Studies on the effect of temperature on the liquid-liquid extraction behaviour of a trivalent actinide ion, Am 3+ and a trivalent lanthanide ion, Eu 3+ using a "S"-donor soft ligand, bis (2,4,4-trimethylpentyl) dithiophosphinic acid (Cyanex ® -301) were carried out. The temperature effect on the enhancement in extraction as well as the selectivity which occurred in the presence of neutral soft donor auxiliary ligands with "N" donor atoms viz., bipyridyl (bipy) and 1,10-phenanthroline (phen) was also investigated. Thermodynamic parameters like the changes in the extraction enthalpy (ΔH°), entropy (ΔS°) and free energies (ΔG°) for both the binary as well as ternary extraction systems were obtained. These thermodynamic parameters could explain the nature of the species extracted with both Am(III) and Eu(III).

Solvent extraction and flat sheet liquid membrane (FSSLM) transport studies for radiostrontium separation from nitric acid medium were carried out using 4,4'(5')-di-tert-butyl-dicyclohexano-18-crown-6 (DTBCH18C6) as the extractant. Role of diluent on the extraction and transport of Sr(II) was investigated. Encouraging results were obtained during the solvent extraction investigations using 0.1 M DTBCH18C6 in a diluent mixture comprising 80% toluene-20% 1-octanol as the solvent which displayed significantly lower nitric acid extraction as compared to pure 1-octanol as the diluent. However, a saturation transport value for Sr(II) was reported at about 60% which was primarily linked to acid transport. The influence of the composition of feed and receiver phase on the transport efficiency was also investigated.