R. B. Gujar

Demonstration of T2EHDGA Based Process for Actinide Partitioning Part II: Counter-Current Extraction Studies

Abstract Counter-current mixer-settler studies for actinide partitioning were carried using N,N,N′,N′-tetra-2-ethylhexyl diglycolamide (T2EHDGA) as the extractant. The feed solution was Simulated High Level Waste of Pressurized Heavy Water Reactor (PHWR-SHLW) origin spiked with 241Am, 244Cm, 152Eu, 137Cs, 85,89Sr, 59Fe, 106Ru, 109Pd, 95Zr, and 99Mo tracers. The organic stream was 0.1 M T2EHDGA + 5% isodecanol in n-dodecane. Extraction, scrubbing, and stripping experiments were performed by maintaining an organic to aqueous phase ratio of 1. More than 99.9% of the trivalent actinides and lanthanides were extracted in four stages, and the decontamination factors (D.F.) values were >103 obtained for most fission products. The co-extraction of Zr and Pd was prevented by the addition of oxalic acid and N-(2-hydroxyethyl)-ethylenediamine-triacetic acid (HEDTA) into the feed solution. However, ∼20% Ru and 10% Mo was extracted into the organic phase, which was successfully scrubbed using a mixture of 0.2 M oxalic acid and 0.1 M HEDTA in 5 M HNO3. Finally, the extracted actinides and lanthanides were quantitatively stripped with 0.2 M HNO3. Raffinate of the extraction cycle was found to be free from any alpha activity.

Development of T2EHDGA Based Process for Actinide Partitioning. Part I: Batch Studies for Process Optimization

Abstract N,N,N′,N′-tetra-2-ethylhexyl diglycolamide (T2EHDGA) has been used for the extraction of actinides, lanthanides, fission products, and structural elements from Pressurized Heavy Water Reactor High Level Waste (PHWR-HLW). In view of third-phase formation under loading conditions, iso-decanol, tri-n-butyl phosphate (TBP), and N,N-di-n-hexyl octanamide (DHOA) were evaluated as the phase modifiers along with T2EHDGA. The loading of lanthanides (e.g. Nd(III), used as surrogate for trivalent minor actinides, Am(III) and Cm(III) and rare earth elements) in the organic phase sharply increased with the addition of iso-decanol as compared to other modifiers (TBP and DHOA). A minimum concentration of phase modifiers needed to avoid third-phase formation for 0.1 M T2EHDGA was 5% iso-decanol, 20% TBP or 20% DHOA. The most promising system, viz. 0.1 M T2EHDGA and 5% (v/v) iso-decanol was evaluated as extractant for actinide partitioning. The distribution behavior of various metal ions, viz. Am, Pu, U, Eu, Sr, Pd, Cs, Tc, Fe, and Mo has been studied from nitric acid as well as from synthetic PHWR-HLW using the optimized organic phase. Extraction of Am (tracer) from synthetic PHWR-HLW suggested a quantitative recovery of minor actinides in four contacts, while stripping (with 0.01 M HNO3) was quantitative in two contacts at O/A = 1. The testing of the optimized extraction system in mixer-settlers with simulated HLW is in progress.

Polymeric beads containing Cyanex 923 for actinide uptake from nitric acid medium: Studies with uranium and plutonium.

Conventional phase inversion technique has been successfully applied for the preparation of the solid phase extractant (SPE), Cyanex 923 loaded polymer beads. Two types of polymer beads prepared by blending Polyetherether ketone with card (PEEKWC)/DMF with 5% Cyanex 923 (SPE-I, av bead size: 900μm) and 10% Cyanex 923(SPE-II, av. bead size: 1100μm) were evaluated for the uptake of actinide ions. The polymer beads were characterized by various physical methods such as thermal analysis, surface morphology analysis by SEM, EDAX techniques, etc. The polymer beads were used for the experiments involving the uptake of both U(VI) and Pu(IV) at tracer scale and U(VI) at milli molar concentrations from nitric acid feeds. The actinide ion uptake studies involved kinetics of metal ion sorption, adsorption isotherms, and column studies. The metal sorption capacities for U(VI) at 3M HNO3 were found to be 38.8±1.9mg and 54.5±1.7mg per g of SPE-I and SPE-II, respectively. The sorption isotherm analysis with Langmuir, D-R and Freundlisch isotherms indicated chemisorption monolayer mechanism. Column studies were also carried out using 4.5mL bed volume columns containing about 0.4 and 0.45g of SPE-I and SPE-II, respectively. The breakthrough profiles were obtained for U(VI) and the elution profiles were obtained using 1M Na2CO3 as the eluent.

Multi-podant diglycolamides and room temperature ionic liquid impregnated resins: an excellent combination for extraction chromatography of actinides

Extraction chromatography resins, prepared by impregnating two multi-podant diglycolamide ligands, viz. diglycolamide-functionalized calix[4]arene (C4DGA) and tripodal diglycolamide (T-DGA) dissolved in the room temperature ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide (RTIL: C4mimTf2N) on Chromosorb-W (an inert solid support), gave excellent results for the removal of trivalent actinides from acidic waste solutions. Distribution coefficient measurements on several metal ions showed selective sorption of Am(III) over hexavalent uranyl ions and other fission product elements such as strontium and cesium. The sorbed metal ions could be efficiently desorbed with a complexing solution containing guanidine carbonate and EDTA buffer. The sorption of Am(III) on both resins followed pseudo-second order rate kinetics with rate constants of 1.37×10(-6) and 6.88×10(-7)g/cpmmin for T-DGA and C4DGA resins, respectively. The metal sorption on both resins indicated the Langmuir monolayer chemisorption phenomenon with Eu(III) sorption capacities of 4.83±0.21 and 0.52±0.05mg per g of T-DGA and C4DGA resins, respectively. The results of column studies show that these resins are of interest for a possible application for the recovery of hazardous trivalent actinides from dilute aqueous solutions.

Amazing selectivity for Am(III) uptake by composite graphene oxide-PES polymeric beads prepared by phase inversion

Novel polyethersulphone (PES) based polymeric beads containing graphene oxide (GO), prepared by a phase inversion technique for the first time, were evaluated for actinide ion uptake from acidic feed solutions. The actinide ions studied were Am3+, Pu4+, Th4+, UO22+ while Eu3+ was taken as a representative trivalent lanthanide ion. The feeds used for the uptake studies were unbuffered aqueous pH solutions and the observed trend was: Am3+ ∼ Eu3+ ≫ UO22+ ∼ Th4+ > Pu4+. The results were highly encouraging as Am3+ uptake was very high at pH ∼ 5 suggesting that the GO beads can be used for the remediation of low acidic radioactive effluents containing Am3+ ions. The metal sorption capacity for Am(III) at pH 4.0 was found to be 1.22 ± 0.07 mg g−1 of the GO resin whereas the qmax (the maximum predicted sorption capacity) obtained from the Langmuir isotherm was 1.72 ± 0.07 mg g−1 of the GO resin. The sorption isotherm analysis was done by fitting the batch uptake data to the Langmuir, D–R and Freundlisch models. Column studies carried out with the GO-PES beads showed a breakthrough of Am(III) beyond 4 mL. Elution profiles were obtained using 0.1 M HNO3 and about 20 mL was required for quantitative elution.

Extraction of some Hexavalent Actinide Ions from Nitric Acid Medium using Several Substituted Diglycolamides

Several substituted diglycolamides, namely TPDGA, THDGA, TODGA, and TDDGA, were evaluated in a comparative study on the extraction of hexavalent actinide ions such as UO22+, NpO22+, and PuO22+ from nitric acid medium. The acid extraction constants (KH) for the diglycolamides were determined to be 3.8 ± 0.6, 1.6 ± 0.1, 4.1 ± 0.4, and 1.4 ± 0.2 for TPDGA, THDGA, TODGA, and TDDGA, respectively. Though metal ion extraction generally increased with increasing the feed acid concentration, the nature of the extracted species changed with aqueous-phase acidity. While complexes of the type MO2(NO3)2·nL (where L is the diglycolamide extractant and n is 1 and 2) were found to be extracted at 1 M HNO3, the average number of ligand molecules associated with the complex decreased to ˜1 when the nitric acid concentration increased to 3 M. These results have great significance from the actinide separation point of view, as the actinides ions can be made virtually inextractable by adjusting their oxidation state. The thermodynamic parameters were also calculated, which indicated spontaneous reactions with large exothermicities.

Comparative Evaluation of CMPO and Diglycolamide Based Solvent Systems for Actinide Partitioning in Mixer-Settler Runs Using Tracer-Spiked PHWR Simulated High Level Waste

The TRUEX solvent (0.2 M CMPO + 1.2 M TBP) was employed for countercurrent extraction studies with radiotracers spiked pressurized heavy water reactor simulated high level waste (PHWR-SHLW) employing a 12-stage of mixer-settler. The results of the mixer-settler runs with CMPO were compared with those obtained under identical conditions employing TODGA (N,N,N’,N’-tetraoctyl diglycolamide) and T2EHDGA (N,N,N’,N’-tetra-2-ethylhexyl diglycolamide) as the extractants. Even though the TRUEX solvent revealed quantitative extraction of trivalent actinides and lanthanides in 5 stages at O/A = 1, stripping of the extracted metal ions from the loaded organic phase was poor with dilute HNO3 solution (0.2 M HNO3). Quantitative stripping could not be achieved in 12 stages even when a complexing solution (0.1 M citric acid + 0.1 M HNO3) was employed as the strippant. In contrast, the stripping from loaded TODGA and T2EHDGA solvents was possible in < 6 stages with 0.2 M HNO3. The experimental results suggested that the performance of TRUEX solvent was inferior to the diglycolamide based extractants such as TODGA and T2EHDGA.

Extraction of Eu(III) and Am(III) by 1-phenyl-3-methyl-4-acetylpyrazol-5-one (HPMAP) and tri-n-octylphosphine oxide (TOPO) in a room-temperature ionic liquid

ABSTRACT 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.

Superparamagnetic graphene oxide–magnetite nanoparticle composites for uptake of actinide ions from mildly acidic feeds

Super paramagnetic graphene oxide (GO) - Fe3O4 nanoparticle composites were prepared and characterized by conventional techniques such as XRD, SEM, EDX, FT-IR, Raman, XPS, DLS and zeta potential, etc. TEM studies have confirmed nanoparticle nature of the composites. The GO-magnetic nanoparticle composites can be dispersed in mildly acidic aqueous solutions and get concentrated in a small volume under application of an external magnetic field. The composites were evaluated for the uptake of actinide ions such as Am3+, UO22+, Th4+ and Pu4+ from mildly acidic aqueous solutions. Am3+ sorption sharply increased with pH as the Kd values increased from about 10 at pH 1 to 105 at pH 3 beyond which a plateau in the Kd values was seen. Eu3+ displayed nearly comparable uptake behaviour to that of Am3+ while the uptake of other metal ions followed the trend: Pu(IV)>Th(IV)>>UO22+. The adsorption behaviour of Am3+ onto the graphene oxide - Fe3O4 nanoparticle composites fitted very well to the Langmuir as well as Temkin isotherm models. The desorption rate (using 1M HNO3) was fast and reusability study results were highly encouraging. The very high uptake values suggest possible application of the magnetic nanoparticles in radioactive waste remediation in natural ground water.

Liquid–liquid extraction of Np4+ and Pu4+ using several tetra-alkyl substituted diglycolamides

Abstract 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 Kex) values for both Np4+ and Pu4+ showed an increasing trend with increasing alkyl group chain length and the log Kex values were higher for Pu4+ as compared to those for Np4+. While for Np4+, the Kex 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.