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

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

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

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

Radiation stability of two extraction chromatography resin materials containing substituted diglycolamide ligands in an ionic liquid.

The radiation stability of two extraction chromatography resins containing diglycolamide ligands viz. TPDGA (N,N,N',N'-tetra-n-pentyl diglycolamide) and TODGA (N,N,N',N'-tetra-n-octyl diglycolamide) in a room temperature ionic liquid (C4mim.NTf2) was studied by exposing to gamma rays from a 60Co source. The resins were irradiated to varying gamma ray dose up to 1000 kGy where both the dry resins and wet resins (containing a fixed amount nitric acid in contact) were used. The performance assessment of the resins was done by physicochemical characterization as well as uptake studies; both by batch as well as column methods. The physicochemical characterization of the resins was done using FTIR analysis while the surface morphology of the resins was carried out by scanning electron microscopy. The uptake of the metal ions, typically that of Am(III) and Eu(III), representing the trivalent actinides and lanthanides was studied by batch method. The dry resins and those in contact with nitric acid yielded nearly identical results suggesting minimal effect of the radiolytic products of nitric acid on the resin performance. There was negligible change in the Kd values up to an absorbed dose of 300 kGy beyond which there was sharp decrease. However, the Kd values were still quite large even after an absorbed dose of 1000 kGy. The column performance of the irradiated resins was also assessed by the uptake and elution of Eu(III) ion and though loading was affected, the elution behavior was found to have insignificant effect.

Highly efficient uptake of Europium (III) and Americium (III) from acidic feeds using extraction chromatography resins containing N,N,N',N'-tetra alkyl diglycolamides with varying alkyl chain length in an ionic liquid.

A comparative study on the uptake of Eu(III) and Am(III) was carried out using four extraction chromatography (XC) resins impregnated with constant weight of the tetra-n-pentyl diglycolamide (TPDGA) ligands, viz. tetra-n-hexyl diglycolamide (THDGA), tetra-n-octyl diglycolamide (TODGA) and tetra-n-decyl diglycolamide (TDDGA) along with C4mim·NTf2, a room temperature ionic liquid (RTIL), from nitric acid feed solutions. The uptake of Eu(III) was higher than that of Am(III) while the uptake trend with the four XC resins followed the order: TPDGA > THDGA > TODGA > TDDGA, which was opposite to the alkyl chain length attached to the DGA extractant. When constant moles of the extractants were used, the observed trend was TODGA > THDGA > TDDGA > TPDGA. Also, for all the four XC resins, the uptake of both Eu(III) and Am(III) ions increased with increasing nitric acid concentration. The uptake data with all the four resins were fitted into different kinetic and isotherm models which conformed to a pseudo-second order kinetics and Langmuir monolayer sorption isotherm. Furthermore, columns were prepared with these XC resins and were used to obtain breakthrough profiles using a feed solution containing 0.55 g/L Eu(III) in 3 M HNO3. Subsequently, the elution of the loaded metal ion from the column was accomplished with a strippant solution containing 1 M guanidine carbonate + 0.05 M EDTA in distilled water. Elution profiles for all the four resins showed sharp peaks with almost no tailing.

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

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

Highly efficient uptake of tetravalent actinide ions from nitric acid feeds using an extraction chromatography material containing tetra-n-butyl diglycolamide and a room temperature ionic liquid.

An extraction chromatography (XC) material containing N,N,N',N'-tetra-n-butyl diglycolamide (TBDGA) and 1-butyl-3-methylimidazolium bis(trifluoromethanesulphonyl) imide (C4mim∙NTf2), a room temperature ionic liquid, was used for the uptake of the tetravalent actinide ions Th(IV), Np(IV), and Pu(IV) from nitric acid feed solutions. The uptake of the metal ions followed the trend: Th(IV) < Np(IV) < Pu(IV), which is the same as that of their ionic potential values. While a decrease in the Np(IV) and Pu(IV) uptake was seen with increasing HNO3 concentration at lower acidities, an opposite trend was observed at higher acidities. Th(IV) uptake was not affected with the acid concentration. In view of the very high uptake and its importance in the nuclear fuel cycle, the major part of the studies was carried out with Pu(IV) ion. The loaded Pu(IV) was back extracted from the XC material using a mixture of 0.5 M oxalic acid and 0.5 M nitric acid. The Pu(IV) uptake by the XC material was fitted into different kinetic and isotherm models. The results conformed to the pseudo-second order kinetic model and the Langmuir monolayer sorption model. Column studies were carried out using a feed having 1.6 mg/L Pu solution in 3 M HNO3. While the breakthrough was obtained after passing ca. nine bed volumes, a sharp elution peak was obtained with >99% recovery in about seven bed volumes.

Highly efficient plutonium scavenging by an extraction chromatography resin containing a tetraaza-12-crown-4 ligand tethered with four diglycolamide pendent arms.

An efficient extraction chromatography resin, containing tetraaza-12-crown-4 functionalized with four diglycolamide moieties, was evaluated for the separation of plutonium. This chromatography resin yielded very large distribution coefficients for Pu4+ (>105) in 0.5 - 6 M HNO3 feed solutions. Various physicochemical properties such as sorption kinetics, Pu4+ sorption mechanism, and its sorption capacity were investigated. The sorption kinetics, following a pseudo-second-order model, showed that about 10 minutes of equilibration was sufficient for >99.9% sorption of Pu4+. The sorption of Pu4+ on the resin followed the Langmuir monolayer model, which was confirmed by a theoretical calculation based on the kinetic model. The Pu4+ sorption on the resin was driven by a large exothermic enthalpy change (ΔH = -31.4±2.2 kJ/mol) and a positive entropy change (ΔS = 224±15 J/mol/L). The resin could sorb a maximum of 12.1±0.8 mg of Pu per gram of resin, which is equivalent to 1:2 metal/ligand complex on the resin. The Pu4+ from the resin phase was completely stripped with 0.5 M oxalic acid. A possible application of this resin for the separation / pre-concentration of Pu4+ was successfully demonstrated in the column mode.

Comparative uptake studies on trivalent f-cations from acidic feeds using two extraction chromatography resins containing a diglycolamide in molecular diluent and ionic liquid.

Low molecular weight diglycolamide (DGA) extractants were tested for the extraction of europium(III) and americium(III) from nitric acid solutions in n-dodecane, a molecular diluent and 1-butyl-3-methylimidazolium bis(trifluoromethanesulphonyl) imide (C4mim⋅NTf2), a room temperature ionic liquid, as the diluents. N,N,N',N'-tetra-n-butyl diglycolamide (TBDGA) was selected for extraction chromatography (XC) studies involving Eu(III) and Am(III). While the TBDGA resin containing n-dodecane gave reasonably high Kd values, that containing the ionic liquid showed higher Eu(III) uptake values. Compared to Eu(III), Am(III) was extracted by the resins to a lower extent. The loaded Eu(III) was back extracted from the resin using 0.05 M EDTA solutions in a buffered medium containing 1 M guanidine carbonate. Reusability studies indicated that, while the ionic liquid-based resin can be conveniently recycled five times with very marginal decrease in the percentage extraction values, there was a sharp decrease in the percent extraction after three cycles with the n-dodecane-based resin. The uptake data was fitted into different isotherm models and the results conformed to the Langmuir model. Based on the batch uptake studies, columns were prepared and the breakthrough as well as elution profiles were obtained. The elution profiles were found to be sharp without any significant tailing.