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The radiolytic stability of aqueous solutions containing two different bis-1,2,4-triazines was studied under static gamma irradiation. Sulphophenyl derivatives of bis-1,2,4- triazinyl pyridine (SO3-Ph-BTP) and bis-1,2,4-triazinylbipyridine (SO3-Ph-BTBP) were dissolved in 0.1 M and 1 M HNO3 solutions and the impact of gamma irradiation was assessed by the measurement of distribution ratios of Am(III) and Eu(III) using irradiated samples. The results were compared for two different organic solvents containing N,N,N’,N’-tetraoctyldiglycolamide (TODGA) or N,N-didodecyl-N’,N’-dioctyldiglycolamide (D3DODGA). The separation efficiency of all the systems remained unchanged when the absorbed dose was 100 kGy, and gradually decreased at 200 kGy and 500 kGy. The radiolytic degradation was more apparent for SO3-Ph-BTBP in comparison to SO3-Ph-BTP at higher acidity. The degradation of sulphonate groups in the molecules was evidenced in ATR-FTIR spectral studies.

The organic phase containing tetra(2-ethylhexy)diglycolamide (TEHDGA) and n-dodecane (n-DD) was irradiated to various absorbed dose levels in a 60Co gamma irradiation chamber. The organic phase subjected to irradiation was classified in to four different categories. The extraction behavior of Nd(III) from nitric acid was studied in the degraded solution of 0.2 M TEHDGA/n-DD and the reverse micellar aggregation behavior of the extracted phase was probed by dynamic light scattering technique and ATR-FTIR spectroscopy. The results revealed that the concentration of TEHDGA decreased upon irradiation and minimized the aggregation in organic phase. The presence of n-DD along with TEHDGA during irradiation enhanced the degradation of TEHDGA, due to sensitization effect. In contrast to the assumption of deteriorating effect of gamma radiation on organic phases, the study showed that the radiolytic degradation of TEHDGA/n-dodecane minimized the aggregation and threw the third phase formation limit of Nd(III) in aqueous phase to higher values.

A customized single-stage cylindrical combined air lift mixer-settler (C-CALMIX) device has been developed and its performance was evaluated by studying the extraction behavior of U(VI) in a solution of 1.1 M tri-n-butyl phosphate (TBP) in n–dodecane (n-DD) from 4 M nitric acid medium, at 298 K. The extraction of U(VI) was studied as a function of process parameters of the C-CALMIX such as flow-rate of organic and aqueous phases, ratio of organic to aqueous flow-rates, air flow-rate etc., that are amenable for variation. The distribution ratio of U(VI) obtained under dynamic conditions in a C-CALMIX was compared with those obtained in a batch equilibrium mode. The process parameters were optimized to obtain high distribution ratio of U(VI) in C-CALMIX, comparable to that obtained at batch equilibrium mode without compromising the throughput of C-CALMIX. The stripping behavior of U(VI) from the loaded organic phase was studied using 0.01 M nitric acid. The results are reported in this paper.

Long chain monoamide extractants, N,N-di-decyloctanamide(DDOA), N,N-di-hexyldecanamide(DHDA), N,N-di-2-ethylhexyloctanamide(D2EHOA) and N,N-dihexyl-2-ethylhexanamide(DH2EHA) were synthesized and studied for the recovery of U(VI), Pu(IV) and Zr(IV) from a simulated dissolver solution of un-irradiated U–Zr metallic fuel. The results were compared with the results of N,N-dihexyloctanamide(DHOA) and tri-n-butylphosphate(TBP) under similar conditions. Solvent extraction studies were carried out for comparing the extraction behavior of U(VI), Pu(IV) and Zr(IV) in monoamide extractants with TBP system. The influence of length and branching of alkyl chains on either side of the amidic group on the extraction efficiency, third phase behaviour and metal ion selectivity in long chain monoamides has been discussed based on the results of above studies.

Zirconium was identified as a troublesome fission product interfering with the separation of trivalent actinides from high-level liquid waste (HLLW) solution. Since zirconium was used as a fuel component in metallic fuels, the amount of Zr(IV) present in HLLW arising from reprocessing of metallic fuel was nearly ten times higher than the conventional HLLW solutions. In the present study, the diglycolamide extractants proposed for the separation of trivalent actinides from HLLW were employed for the extraction of metal ions from nitric acid medium and fast reactor simulated high level liquid waste (FR-SHLLW) having the Zr(IV) concentrations varied from 0.006 M to 0.09 M. Dynamic light scattering study was performed on the organic phase obtained after extraction of zirconium to analyze the aggregation of extractants. The solvent system consisting of 0.1 M TODGA (N,N,N’,N’-tetraoctyldiglycolamide) along with 0.25 M HDEHP (bis(-2-ethylhexyl)phosphoric acid) in n-dodecane showed minimal aggregation tendency and higher loading capacity of Zr(IV) and was selected for further extraction of trivalent metal ions from FR-SHLLW. To minimize the extraction of Zr(IV) in organic phase, the effect of aqueous soluble complexing agent namely trans-1,2-diaminocyclo-hexane-N,N,N’N’-tetraaceticacid (CyDTA) was also studied during the extraction of trivalent lanthanides.

The imidazolium bis(2-ethylhexyl) phosphate moiety was chemically attached on silica gel by chemical modification. The resulting product ([SG-Im]+ [DEHP]−) was characterized by FT-IR spectroscopy, thermogravimetry and elemental analysis. The sorption behavior of Am(III) and Eu(III) on [SG-Im]+ [DEHP]− was studied from dilute nitric acid medium for the separation of Am(III) and Eu(III) from aqueous waste. The effect of time, concentrations of nitric acid and europium in aqueous phase on the distribution coefficient (K d) was studied. The study indicated the possibility of using modified silica for the separation of Eu(III) from Am(III) with high separation factors (>50 at 0.1 M HNO3).

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) (DAm(III)) and also by the measurement of hydrodynamic properties such as density, viscosity and phase disengagement time.

The limit of reverse micellar aggregation of amphiphilic ligands in n-dodecane medium, known as the third phase formation, is an undesirable event during the course of solvent extraction. The tetraalkyl diglycolamide (DGA) in n-dodecane (n-DD) is a promising solvent medium for the extraction of trivalent actinides from high-level nuclear waste, but it is susceptible to third phase formation. The DGAs in n-dodecane medium undergo a number of chemical transformations in organic phase, known as the radiolytic degradation products, when it was contacted with nuclear waste. While the effect of radiolytic degradation products on the solvent extraction behaviour of actinides was reasonably understood, the third phase formation and reverse micellar aggregation behaviour of the radiolytically degraded DGAs/n-DD has been not explored so far and unfamiliar to the solvent extraction community. To unravel the effect of radiolytic degradation on the aggregation behaviour(third phase formation) of DGAs in n-DD, the following categories of liquids comprising of (1) 0.2 M solution of tetra(2-ethylhexyl)diglycolamide (TEHDGA) present in n-DD, (2) TEHDGA alone, (3) n-dodecane alone, and (4) 0.2 M TEHDGA/n-DD in the presence of extracted nitric acid, were irradiated to a specified absorbed dose levels (10 kGy to 500 kGy) in a 60Co gamma irradiator. The irradiated liquids were made to a solution of 0.2 M TEHDGA in n-dodecane, if required, and the extraction behaviour of nitric acid in the irradiated organic phase was studied. The organic phase obtained after extraction was subjected to dynamic light scattering studies to explore the aggregation behaviour of TEHDGA in organic phase and compared with those obtained before extraction and irradiation. The results revealed that the formation of polar degradation products upon irradiation minimized the aggregation, and the production of higher homologs of n-paraffins enhanced aggregation. In reality, the formation of nitration and other polar radiolytic degradation products in organic phase, confirmed by FTIR spectroscopy, minimized the aggregation and therefore prevented the third phase formation to a significant extent in the present system.

The process methods developed for partitioning of trivalent actinides from high-level liquid waste (HLLW) are being focussed on single-cycle processing approaches. This method involves the separation of trivalent actinides and chemically similar lanthanides, as a group, from HLLW followed by the mutual separation of lanthanides and actinides from the loaded organic phase using aqueous soluble complexing agents. The potential solvents identified for the group separation of trivalents from HLLW are 1) 0.2 M TODGA (N,N,N’N′-tetraoctyldiglycolamide) + 5% octanol / n-DD, 2) 0.2 M TODGA + 0.5 M TBP (tri-n-butylphosphate) / n-DD, 3) 0.1 M TODGA + 0.25 M HDEHP (di-(2-ethylhexyl)phosphoric acid) / n-DD, 4) 0.2 M TDDGA (N,N,N’N′-tetradecyldiglycolamide) / n-DD, 5) 0.2 M D3DODGA (N,N-didodecyl-N’N′-dioctyldiglycolamide) / n-DD, 6) 0.4 M DOHyA (N,N-dioctyl-2-hydroxyacetamide) / n-DD. The extraction behaviour of Am(III) and Eu(III) from dilute nitric acid solution (0.1 M to 1 M) containing aqueous soluble nitrogen-donor derivative, SO3-Ph-BTP, was studied in the above solvents. The separation factor (SF) of Eu(III) over Am(III) was determined. Among the different solvents investigated, the SF achieved in TDDGA and D3DODGA was quite higher than other solvents, and recommended for the single-cycle separation of trivalent actinides from HLLW.

The radiolytic degradation of N,N-di-dodecyl-N′,N′-di-2-ethylhexyl-3-oxapentane-1,5-diamide (D3DEHDGA) was studied at various absorbed doses of γ-radiation. The degradation was assessed by measuring the variation in the extraction behavior of Am(III) in irradiated solvent systems composed of neat D3DEHDGA or 0.1 M D3DEHDGA/n-dodecane in the presence and absence of nitric acid. The distribution ratio of americium (D Am(III)) decreased with increase of absorbed dose. The presence of n-dodecane and nitric acid enhanced the radiolytic degradation of the solvent. The third phase formation behavior of Nd(III) decreased with increase of absorbed dose and the third phase was not observed at absorbed doses above 100 kGy. The recovery of Am(III) from the irradiated system was near quantitative in five contacts. The study revealed that the extraction and stripping behavior of the irradiated solvent was quite satisfactory for partitioning of minor actinides from real wastes.

The radiation stability of N,N-di-dodecyl-N′,N′-di-octyl-3-oxapentane-1,5-diamide (D3DODGA) was studied by γ-irradiation of the solvent up to a absorbed dose of 1,000 kGy. The effect of γ-irradiation on the radiolytic degradation of D3DODGA was assessed by measuring the distribution ratio of Am(III) (D Am(III)) as well as the third phase formation in the irradiated D3DODGA-n-dodecane solution. The D Am(III) in the irradiated solution decreased with increase of absorbed dose. The critical aqueous concentration of Nd(III) above which the third phase forms, increased with increase of absorbed dose. However, the limiting organic concentration of Nd(III) remained at ~25 mM irrespective of the absorbed dose. Recovery of Am(III) from the radiolytically degraded organic phase showed that back extraction of Am(III) was quantitative in a few contacts using dilute nitric acid. Our studies clearly indicated that radiolytic degradation of D3DODGA in n-dodecane is marginal even at the absorbed dose of 1,000 kGy, and therefore D3DODGA is a potential candidate for minor actinide partitioning.

Commercially available polystyrene-divinylbenzene (PS-DVB) resins functionalized with isothiouronium (Tulsion CH-95), phosphinic acid (Tulsion CH-96) and methylene thiol (Tulsion CH-97) moieties have been used for separating palladium from nitric acid medium. Extraction of palladium has been studied as a function of time, concentration of nitric acid and palladium. The distribution coefficients (Kd, ml/g) of palladium on sulfur based resins (Tulsion CH-95 and Tulsion CH-97) are higher (5000-104ml/g in 0.1M nitric acid) than on Tulsion CH-96 resin and decrease with increasing concentration of nitric acid. The initial rate of extraction of palladium by Tulsion CH-95 and Tulsion CH-97 resins was very rapid and the time required for the establishment of equilibrium was a function of palladium concentration in the aqueous phase. The rate data could be fitted by a second order rate equation and the magnitude of rate constant for the extraction of palladium by these resins (~102M-1. min-1) decreased in the order of: Tulsion CH-95 > Tulsion CH-97 > Tulsion CH-96. The extraction isotherms of Tulsion CH-95 were fitted by Langmuir adsorption model and the coefficients were obtained by regression. The extraction capacity of palladium on Tulsion CH-95 was found to be ~20 mg/g at 3M nitric acid. Column experiments have been conducted and the data were fitted using Thomas model. A column utilization of 75% was achieved for the extraction of palladium by Tulsion CH-95 resin.