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N,N-Dialkyl diglycolamic acid (HDRDGA) derivatives with alkyl groups varying from n-hexyl to n-dodecyl were synthesized, and the promising ligands such as N,N-dioctyl diglycolamic acid (HDODGA) and N,N-didecyl diglycolamic acid (HD2DGA) were investigated for the mutual separation of trivalent lanthanides and actinides from dilute nitric acid solution. Since diglycolamic acid is strongly polar, it was dissolved in a traditional diluent, n-dodecane, with the help of an isodecyl alcohol (IDA) phase modifier. Nevertheless, the hexyl and didodecyl derivatives were sparingly soluble even in the presence of 30% (v/v) IDA in n-dodecane, and therefore, the extraction behavior of the lanthanide and actinide representatives, Eu(III) and Am(III), respectively, was studied only in a solution of HDODGA or HD2DGA present in 30% (v/v) IDA/n-dodecane. The cation-exchange mechanism of extraction and the stoichiometry of trivalent metal to HDRDGA were elucidated from the slope analysis of the extraction data. Since the stoichiometry of the metal to ligand complex in the organic phase was unusually varied from 1 : 3 to 1 : 6 depending upon the Nd(III) loading into the organic phase, the reverse micellar aggregation behavior and the coordination chemistry of Nd(III) in the organic phase were probed by dynamic light scattering and visible spectroscopy, respectively. The results revealed that three molecules of anionic DRDGA were coordinated to Nd(III) in the inner-sphere at lower metal concentrations, and also three more molecules of HDRDGA in the outer-sphere at higher metal concentrations. The good separation factor achieved with the use of these ligands showed their potential ability to separate lanthanides from actinides in nitric acid medium. [ABSTRACT FROM AUTHOR]

Third phase formation is an undesirable event in a solvent extraction procedure. It is the splitting of the organic phase into two phases during the course of solvent extraction at a particular concentration of metal ions in the organic phase characterised by the limiting organic phase concentration (LOC). The occurrence of the third phase is due to the extensive aggregation of strongly polar reverse micelles formed beyond the LOC, leading to the de-mixing of polar aggregates from a non-polar diluent present in the solvent phase. In this work, the extraction behaviour of nitric acid and Nd(III) was studied in a solution of tetra-2-ethylhexyl diglycolamide (TEHDGA) in n-dodecane (n-DD) and was probed by dynamic light scattering, ATR-FTIR and NMR spectroscopy to understand the fate of the organic phase beyond the LOC. The studies revealed that the aggregation of reverse micelles in the organic phase increased gradually with an increase in the extraction of Nd(III) and nitric acid before the LOC, and remarkably increased in the third phase beyond the LOC. A significant increase in the aggregate size of the third phase beyond the LOC was due to the high loading of nitric acid and Nd(III) in the third phase, eventually leading to polydispersion of reverse micelles in third phase. Before poly-dispersion, the TEHDGA molecules present in the organic phase were completely transferred to the third phase beyond the LOC, facilitating a mode of recovery of the diluent, n-dodecane, from the solvent phase, even though the third phase formation was regarded as an undesirable event. [ABSTRACT FROM AUTHOR]

Diglycolamides (DGAs) are susceptible to organic phase splitting, known as third phase formation, during the course of solvent extraction of trivalent metal ions from high-level liquid waste (HLLW). Third phase formation was due to the extensive reverse micellar aggregation of the strongly polar extracted species of diglycolamide in the non-polar n-dodecane (n-DD) medium, which was conventionally employed as a diluent in a solvent extraction procedure. Since DGA/n-DD can undergo hydrolytic and radiolytic degradation during the course of solvent extraction from nuclear waste, the fate of aggregation and third phase formation behaviour of degraded DGA/n-DD is unknown. To unravel this feature, N,N,N′,N′-tetraoctyldiglycolamide (TODGA) in n-dodecane was irradiated to various absorbed gamma dose levels (up to 500 kGy) and the irradiated organic phase was subjected to dynamic light scattering and FTIR spectroscopic investigations. The organic phase composed of 0.1 M TODGA/n-DD was contacted either with nitric acid or Nd(III) solution in nitric acid to simulate the actual feed condition before subjecting the organic phase to irradiation. The DLS studies showed that the aggregate size and its distribution in the organic phase decreased with an increase of absorbed gamma dose, due to the decrease in the concentration of TODGA upon irradiation and also due to the formation of polar degradation products, which disperses the aggregates in the organic phase. Since the aggregation was significantly lowered in the irradiated TODGA/n-DD solution, the third phase formation, characterised by the limiting organic phase concentration (LOC) of nitric acid and Nd(III), as well as the limiting aggregate size (LAS) for third phase formation were shifted to much higher concentration levels in the feed solution. In view of this, the study pre-empted the widely conceived notion of early third phase formation in the irradiated solvent systems containing diglycolamide in n-DD. [ABSTRACT FROM AUTHOR]

The selective partitioning of trivalent actinides (An(III)) from high-level liquid waste (HLLW) is considered as an essential step in the management of spent nuclear fuel. The i-SANEX process for the separation of An(III) from the co-existing lanthanides (Ln(III)) in 4 M nitric acid solution and simulated HLLW was studied using a couple of symmetrical diglycolamides (TODGA and TDDGA) and an unsymmetrical diglycolamide (D3DODGA) in n-dodecane as the extraction phase. The selective stripping of Am(III) from the loaded organic phase containing trivalent Ln(III) was investigated using aqueous soluble bis-1,2,4-triazine derivatives such as SO3-Ph-BTP, SO3-Ph-BTBP and SO3-Ph-BTPhen in dilute nitric acid solution. The results revealed that the SF of Eu(III) over Am(III) decreased with increase in the concentration of nitric acid in all cases and SF decreased in the order SO3-Ph-BTP > SO3-Ph-BTBP > SO3-Ph-BTPhen. The co-stripping of lighter lanthanides (La, Ce, Pr, Nd) was also observed during the recovery of Am(III). [ABSTRACT FROM AUTHOR]

Diglycolamides have been proposed for partitioning of trivalent actinides from high-level liquid waste (HLLW). Third-phase formation is an undesirable event during the course of solvent extraction of trivalent actinides from HLLW into the solution of N,N,N',N'-tetra(2-ethylhexyl)diglycolamide (TEHDGA) in n-dodecane (n-DD). Polar reagents such as tri-n-butyl phosphate (TBP), and N,N-dihexyloctanamide (DHOA) have been added to the TEHDGA phase, as phase modifiers in significant concentration, to overcome the third-phase formation. To understand the role of these phase modifiers in controlling the third-phase formation, the extraction behaviour of nitric acid and the trivalent representative metal ion Nd(III) was studied in a binary solution containing TEHDGA and phase modifier in n-dodecane. The organic phase obtained after extraction was subjected to dynamic light-scattering studies to examine the aggregation behaviour of the reverse micelles formed upon extraction and to unravel the unique role of TBP and DHOA in controlling the third-phase formation. The study revealed that the addition of these modifiers brought down the average size of aggregates and their distribution in organic phase below the limiting aggregate size for third-phase formation and increased the dispersion of aggregates in the n-dodecane phase. Among the two phase modifiers proposed for trivalent actinide separation from HLLW, TBP has been identified as a promising reagent for minimizing the third-phase formation. [ABSTRACT FROM AUTHOR]

A combination of neutral and acidic extractant has been proposed for the single-cycle separation of trivalent actinides from high-level liquid waste (HLLW). The nature of acidic extractant in the combined solvent formulation plays a profound role in deciding the extraction and stripping of trivalent actinides. Therefore, the extraction behavior of Am(III) in a solution of tetra-bis(2-ethylhexyl)-diglycolamide (TEHDGA) and acidic extractant (HA) was studied from nitric acid medium. The acidic extractants chosen were bis(2-ethylhexyl)phosphoric acid (HDEHP), bis(2-ethylhexyl)phosphonic acid (PC88A) and bis(2,4,4-trimethylpentyl)phosphinic acid (CYANEX-272) whose pKa values were 3.24, 4.51 and 6.37, respectively. The distribution ratio of Am(III) was measured as a function of various parameters such as concentration of nitric acid, TEHDGA, HA etc. The data were compared with those obtained in individual solvent systems namely 0.1 M TEHDGA/n-DD and HA/n-DD. Slope analysis of the extraction data indicated the synergic participation of both TEHDGA and HDEHP in the extraction of Am(III) at all acidities. However, antagonistic effect was observed at lower acidity when TEHDGA was mixed to PC88A or CYANEX-272 present in n-DD. Accordingly, a suitable mechanism has been proposed for the extraction of Am(III) at all acidities using these combined solvent formulation. Studies with fast reactor simulated high level liquid waste indicated that extraction of Am(III) was accompanied by coextraction of lanthanides and unwanted metal ions such as Zr(IV), Mo(VI), Y(III) and Pd(II). However, addition of trans-1,2-diaminocyclohexane-N,N,N,N'-tetraaceticacid (CyDTA) reduced the extraction of unwanted metal ions. Batch extraction and stripping studies indicated the possibility of using 0.1 M TEHDGA + 0.25 M HDEHP in n-dodecane for the single cycle separation of Am(III) from FR-SHLLW. [ABSTRACT FROM AUTHOR]

Tri-n-butylphosphate (TBP) in an ionic liquid (IL) has been proposed as a suitable alternative for the solvent extraction of actinides from nitric acid solutions. This paper reports the detailed investigations on the physicochemical and hydrodynamic properties of the solvent system containing TBP in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide ([C4mim][NTf2]) IL. The properties such as density, viscosity, phase separation time (PST), etc., were measured for irradiated and unirradiated solvent phases composed of TBP, [C4mim][NTf2] and 1.1 mol.L-1 TBP in [C4mim][NTf2]. The results are compared with the values obtained in acid-equilibrated IL phases. ATR- FTIR spectroscopy and dynamic light scattering measurement of the IL phase were employed to characterize the interactions among the IL, TBP and nitric acid medium, and the aggregate size of the adduct formed in the IL phase. [ABSTRACT FROM AUTHOR]

The homologs of N,N-di-alkyl-2-methoxyacetamides (DAMeOA) having three different alkyl chains varying from hexyl to decyl (C6, C8 and C10) were synthesized and characterized by NMR and IR spectral analyses. Extraction behavior of U(VI) and Pu(IV) from nitric acid medium in a solution of 0.5 M of DAMeOA in n-dodecane (n-DD) was studied and the results were compared with those obtained using N,N-di-hexyloctanamide (DHOA) in n-dodecane. The effect of various parameters on the distribution ratio of U(VI) and Pu(IV) in DAMeOA was studied. The extraction of nitric acid increased with decrease in chain length of alkyl group attached to amidic nitrogen atom of DAMeOA and the conditional nitric acid extraction constant was determined. The extraction of nitric acid in DAMeOA/n-DD resulted in the formation of third phase in organic phase and the third phase occurred early with DAMeOA having smaller alkyl chain length. In contrast to this, the distribution ratio (D) of U(VI) and Pu(IV) in DAMeOA/n-DD increased with increase in the concentration of nitric acid and with increase in the chain length of alkyl group attached to amidic nitrogen atom of DAMeOA. The stoichiometry of the metal - solvate was determined from the slope of extraction data. Quantitative recovery of uranium and plutonium from the loaded organic phase was achieved using dilute nitric acid. [ABSTRACT FROM AUTHOR]

The radiation stability of N, N-di-alkyl-2-hydroxyacetamide derivatives having alkyl side chain varying from hexyl to decyl was studied as a function of absorbed dose of gamma irradiation up to 700 kGy. The samples were irradiated as neat, and as 0.2 M solutions in n-dodecane in the presence and absence of 4 M nitric acid. The radiolytic degradation of the compounds were assessed by the measurement of distribution ratio of Am(III) (D) and also by the measurement of hydrodynamic properties such as density, viscosity and phase disengagement time. [ABSTRACT FROM AUTHOR]

Higher homologs of trialkyl phosphates (TAlP) are proposed for reprocessing of fast reactor fuels. Solvent extraction behavior of U(VI) from nitric acid medium was studied in some TAlP present in 1-octyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C8mim] [NTf2]) ionic liquid. The extractants investigated were tri-n-propylphosphate (TPP), tri-n-butylphosphate (TBP), tri-n-amylphosphate (TAP), tri-n-octylphosphate (TOP), tri-iso-amylphosphate (TIAP) and tri-iso-butylphosphate (TIBP). The extraction of uranium (VI) was investigated as a function of various parameters, such as the equilibration time, [HNO3], [TAlP], temperature and nature of ionic liquid cation. The distribution ratios of U(VI) increased with an increase in the concentration of nitric acid and decreases in the order TOP > TAP  TIAP > TBP  TIBP > TPP. The stoichiometry of the extraction was determined by slope analysis of the extraction data. Distribution ratios of U (VI) were determined at various temperatures and the thermodynamic parameters were derived. Quantitative stripping of uranium from the loaded ionic liquid phase was achieved using dilute nitric acid. [ABSTRACT FROM AUTHOR]

Various diglycolamides (DGAs),N,N,N’,N’-tetraoctyl diglycolamide (TODGA),N,N-di-2-ethylhexyl-N’,N’-di-octyl diglycolamide (DEHDODGA),N,N,N’,N’-tetra-2-ethylhexyl diglycolamide (TEHDGA),N,N-di-decyl-N’,N’-di-hexyl diglycolamide (D2DHDGA),N,N-di-butyl-N’,N’-di-dodecyl diglycolamide (DBD3DGA),N,N,N’,N’-tetra-hexyl diglycolamide (THDGA), andN,N,N’,N’-tetradecyl diglycolamide (TDDGA) have been synthesized and studied for the extraction of Am(III) and Eu(III) from nitric acid medium. An attempt was made to understand the extraction and third phase formation behavior of trivalent metal ions in these DGAs. Our results revealed that despite having the same carbon to oxygen ratio in these DGAs, the third phase formation behavior and extractions achieved in these DGAs are significantly different. [ABSTRACT FROM AUTHOR]

The unsymmetrical diglycolamide, di-dodecyl-di-octyl diglycolamide (D3DODGA) is a modifier-free extractant proposed for partitioning of trivalent actinides from nitric acid medium. D3DODGA has been evaluated for the feasibility of using it in the absence of a phase modifier, for the partitioning of minor actinides from fast reactor high-level liquid waste (FR-HLLW). The extraction behavior of various metal ions present in the simulated FR-HLLW was studied in a solution of 0.1 M D3DODGA/n-dodecane from nitric acid medium. The distribution ratio of about 20 metal ions was measured as a function of concentration of nitric acid and other interfering ion. The extraction was found to be strongly dependent on the oxidation state of the metal ion. The extraction of Am(III) from 3–4 M nitric acid medium was quantitative in a single contact. However, it was accompanied by the quantitative extraction of fission products such as trivalent lanthanides (Ln(III)), Y(III), and Zr(IV). The extraction of Sr(II), Pd(II), and Ru(III) in 0.1 M D3DODGA/n-dodecane was not insignificant, but quite low. The extraction of Ba(II), Ni(II), Mo(VI), and Fe(III) was marginal and the extraction of Co(II), Sb(III), Mn(II), and Cs(I) in 0.1 M D3DODGA/n-dodecane was negligible. Our results indicated that 0.1 M D3DODGA/n-dodecane is a promising candidate for the separation of trivalent actinides from fast reactor high-level liquid waste containing significant quantities of trivalent lanthanides and actinides. [ABSTRACT FROM PUBLISHER]

The extraction behavior of Am(III) and Eu(III) in a solution of tetra-octyldiglycolamide (TODGA), bis(2-ethylhexyl)phosphoric acid (HDEHP), andn-dodecane (n-DD) was studied to understand the role of TODGA and HDEHP in the combined solvent system. The extraction behavior of these metal ions was compared with those observed in TODGA/n-DD and HDEHP/n-DD. The effect of various parameters such as concentrations of HNO3, TODGA, and HDEHP on the distribution ratio of Am(III) and Eu(III) was studied. Synergistic extraction of both the metal ions observed at lower acidities (<2.0 M) was attributed to the involvement of TODGA and HDEHP for extraction. However, the extraction of Am(III) and Eu(III) in the combined solvent was comparable with that observed in TODGA at higher acidities. The slope analysis of the extraction data confirmed the involvement of both the extractants at all acidities investigated in the present study. [ABSTRACT FROM AUTHOR]

An Aliquat-336 based ionic liquid, namely, tri-n-octylmethylammonium bis(2-ethylhexyl)phosphate ([A3636]+[DEHP]−) was prepared and studied for the extraction of U(VI), Pu(IV), and Am(III) from nitric acid medium. Since the ionic liquid, [A336]+[DEHP]−was miscible in n-dodecane (n-DD), the extraction of these actinides in the PUREX solvent, 1.1 M tri-n-butylphosphate (TBP) in n-dodecane (n-DD), was investigated in the presence of small concentrations of ionic liquid. The distribution ratio of U(VI) and Am(III) in 0.03 M [A336]+[DEHP]−/n-DD decreased with increase in the concentration of nitric acid; whereas the extraction of Pu(IV) initially increased, it reached a maximum at 4 M nitric acid followed by the decrease. The extraction of actinides in ionic liquid medium decreased in the order Pu(IV) > U(VI) >> Am(III), indicating the feasibility of modifying the extractive properties of TBP/n-DD to favor Pu(IV) extraction. Therefore, the extraction of Pu(IV) in a solution of TBP – [A336]+[DEHP]−in n-DD was also studied. The distribution ratio of Pu(IV) increased with increase in the concentration of ionic liquid and decrease in the concentration of TBP in organic phase. The distribution ratio of Pu(IV) determined in the presence of small concentration of ionic liquid in 1.1 M TBP/n-DD was always much higher than that observed in 1.1 M TBP/n-DD. In contrast to this, the distribution ratio of U(VI) decreased by the addition of ionic liquid and Am(III) was inextractable even in the presence of ionic liquid. [ABSTRACT FROM AUTHOR]

The extraction behavior of Am(III) and Eu(III) in a solution of tetra-bis(2-ethylhexyl)diglycolamide (TEHDGA) and bis(2-ethylhexyl)phosphoric acid (HDEHP) in n-dodecane (n-DD) was studied from nitric acid medium. The distribution ratio of Am(III) and Eu(III) in TEHDGA-HDEHP/n-DD was measured as a function of various parameters such as concentrations of nitric acid, TEHDGA, HDEHP, and nitrate ion. The data were compared with those obtained in individual solvents namely 0.1 M TEHDGA/n-DD and 0.25 M HDEHP/n-DD. The synergistic extraction of Am(III) and Eu(III) observed in a solution of 0.1 M TEHDGA – 0.25 M HDEHP/n-DD was attributed to the involvement of both TEHDGA and HDEHP for extraction. Slope analysis of the extraction data indicated the predominant participation of HDEHP for extraction at low acidities and TEHDGA and nitrate ion at higher acidity. The stripping behavior of Am(III) and Eu(III) from the extracted organic phase was investigated using citric acid (CA) and diethylenetriaminepentaacetic acid (DTPA). A suitable aqueous formulation was developed to separate Am(III) alone from chemically similar Eu(III) present in loaded organic phase, to facilitate a single-step separation of trivalent actinides from the high-level liquid waste (HLLW). [ABSTRACT FROM AUTHOR]

Room temperature ionic liquids (RTILs) are receiving increased attention for possible applications in nuclear fuel cycle. RTILs are being investigated as possible substitutes to molecular diluents in solvent extraction, and as an alternative to high temperature molten salts in non-aqueous reprocessing applications. It is well recognized that ionic liquids often display unique extraction behavior. Unusual extraction of various metal ions has been reported in literature when RTILs are used as solvent medium. These aspects make the subject of RTILs fascinating and challenging. This review provides the current status of room temperature ionic liquid research related to the extraction of actinides and fission products (cesium and strontium) from nitric acid medium, with special emphasis on the studies carried out in our laboratory. [ABSTRACT FROM AUTHOR]