Progress Towards the Development of a New GANEX Process

We report first results on the development of a new system for a GANEX 2^nd cycle developed by the “ACSEPT” project. A solvent system consisting of 0.2 M N,N,N’,N’-tetra-n-octyl-diglycolamide (TODGA) + 0.5 M N,N’-dimethyl-N,N’-dioctyl-2(2-hexyloxyethyl)malonamide (DMDOHEMA) in kerosene was formulated which co-extracts TRU elements and lanthanides with high distribution ratios and allows for Pu(IV) loading up to ∼40 gáL^–1 at 3 M HNO3. Neptunium redox chemistry and extraction in the TODGA/DMDOHEMA phase has been studied in order to identify optimum conditions for Np extraction. Further, the behaviour of non-lanthanide fission products was investigated to identify a substitute for oxalic acid (used as a Zr masking agent in DIAMEX processes where there is no Pu in the feed). 1,2-cyclohexanediaminetetraacetic acid (CDTA) efficiently suppresses the extraction of Zr and also masks Pd which would otherwise be co-extracted.     

Flow-Sheet Design for an Innovative SANEX Process Using TODGA and SO3-Ph-BTP

An innovative SANEX process was designed using an organic phase comprising TODGA in TPH + 5% 1-octanol and an aqueous phase containing SO3-Ph-BTP for the selective strip. The flow-sheet was optimized using batch data, single stage data and data from previously run TODGA processes. Recoveries for some key elements were calculated for selective strip section of the process using the SX Process program. According to the calculations, the An(III) are recovered from the PUREX raffinate with insignificant amounts of impurities. The presented flow-sheet will be used for a centrifugal contactor demonstration process which is expected to be successful.     

Development of normal phase-high performance liquid chromatography-atmospherical pressure chemical ionization-mass spectrometry method for the study of 6,6'-bis-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo[1,2,4]-triazin-3-yl)-[2,2']-bipyridine hydrolytic degradation

In the field of nuclear waste management, the 6,6'-bis-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo[1,2,4]-triazin-3-yl)-[2,2']-bipyridine (CyMe(4)BTBP) is a polycyclic N-based molecule eligible to remove actinides from spent nuclear fuel by liquid-liquid extraction processes. In such processes, the organic phase containing the extracting molecules will undergo hydrolysis and radiolysis, involving degradation products. The purpose of this work was to develop a normal phase chromatography (NP-HPLC) coupled to atmospherical pressure chemical ionisation-mass spectrometry (APCI-MS) method to separate and identify degradation products of CyMe(4)BTBP dissolved in octanol, submitted to HNO(3) hydrolysis. 1 mol L(-1) HNO(3) hydrolysis conditions were used regarding the selective actinides extraction (SANEX) process, while 3 mol L(-1) HNO(3) conditions were applied for the group actinide extraction (GANEX) process. The first step consisted in optimizing the chromatographic separation conditions using a diode array detection (DAD). Retention behavior of a non hydrolyzed mixture of N,N'-dimethyl-N,N'-dioctyl-hexyloxyethyl-malonamide (DMDOHEMA), a malonamide used in the SANEX process to increase the kinetic of extraction, and CyMe(4)BTBP were investigated on diol-, cyano-, and amino-bonded stationary phases using different mobile phase compositions. These latter were hexane with different polar modifiers, i.e. dioxane, isopropanol, ethanol and methylene chloride/methanol. The different retention processes in NP-HPLC were highlighted when using various stationary and mobile phases. The second step was the setting-up of the NP-HPLC-APCI-MS coupling and the use of the low-energy collision dissociation tandem mass spectrometry (CID-MS/MS) of the precursor protonated molecules that allowed the separation and the characterization of the main hydrolytic CyMe(4)BTBP degradation product under a 3 mol L(-1) HNO(3) concentration. Investigation of the CID-MS/MS fragmentation pattern was used to suggest the potential ways leading to this hydrolysis degradation product. This NP-HPLC-APCI-MS method development is described for the first time for the CyMe(4)BTBP and should provide separation methods regarding the analysis of polycyclic N-based extracting molecules and more generally for the investigation of the organic phase coming from liquid-liquid extraction processes used in nuclear fuel reprocessing.     

Solvent extraction of Zr(IV) and Hf(IV) with <Emphasis Type="Italic">N,N,N′,N′</Emphasis>-tetraoctyldiglycolamide

N,N,N′,N′-tetraoctyldiglycolamide (TODGA) was synthesized and characterized with elemental analysis, infrared spectrometry and nuclear magnetic resonance spectrometry. The synthesized TODGA was applied for the extraction and separation of Zr(IV) and Hf(IV) from nitric acid solutions. The performed studies include the effects of TODGA, nitric acid, nitrate ion, hydrogen ion, and metal ion concentrations as well as time and temperature. TODGA shows effective extraction of Zr(IV) and Hf(IV) from HNO₃ ≥ 3 M. However, the maximum separation factor (D _Zr/D _Hf) obtained using TODGA is 2.8.     

Reverse-micelle formation in the partitioning of trivalent F-element cations by biphasic systems containing a tetraalkyldiglycolamide

The conditions for reverse-micelle formation were studied for solutions of tetra-n-octyldiglycolamide (TODGA) in alkane diluents equilibrated with aqueous solutions of nitric or hydrochloric acids in the presence and absence of Nd3+. Small-angle neutron scattering, vapor-pressure osmometry, and tensiometry are all consistent with the partial formation of TODGA dimers at the lowest acidities, transitioning to a polydisperse mixture containing TODGA monomers, dimers, and small reverse-micelles of TODGA tetramers at aqueous nitric acid acidities of 0.7 M or higher in the absence of Nd. Application of the Baxter model to the samples containing 0.005-0.015 M Nd reveals the persistence of tetrameric TODGA reverse-micelles with significant interparticle attraction between the polar cores of the micelles that increases with increasing organic phase concentrations of acid or Nd. Our experimental findings suggest that the peculiar behavior of TODGA with respect to the extraction of trivalent lanthanide and actinide cations arises from the affinity of these metal cations for the preformed TODGA reverse-micelle tetramers.     

UxTh1-x(C2O4)2 Solid Characterisation Studies

Many advanced reprocessing schemes under development are aimed at co-processing and co-conversion of actinides, unlike current reprocessing plants that produce separate uranium and plutonium products. The most well developed option for the co-conversion stage is probably oxalate co-precipitation, followed by the thermal co-conversion to a mixed oxide product. It is thus envisaged that future processes will avoid separation of plutonium from uranium and instead allow part of the uranium to flow with the plutonium, resulting in co-precipitation as the oxalate, and finally co-conversion to a mixed uranium-plutonium oxide (MOX), which can be fabricated into recycled nuclear fuel for further energy generation.The co-crystallisation of uranium (IV) and plutonium (III) into a single oxalate structure ensures the homogenous distribution of the two actinides at the molecular scale. The joint conversion of uranium and plutonium to the oxide form makes it possible to remove the complicated step of blending and grinding the two distinct oxide powders, as currently employed for the purposes of MOX fuel fabrication. This concept can also be extended to other actinides, including minor actinides from partitioning processes such as SANEX (Selective Actinide Extraction) and GANEX (Grouped Actinide Extraction) processes or even a thorium containing product from recycle of thorium based fuels.A selection of U_xTh_1-x(C₂O₄)₂ solids at varying concentrations of uranium and thorium were prepared by oxalate co-precipitation. Uranium (VI) was conditioned electrochemically at -0.7 V to uranium (IV), in the presence of hydrazine. The reduced uranium (IV) in nitric acid was mixed with thorium nitrate solutions at different concentration ratios with oxalic acid. The mixed tetravalent uranium-thorium oxalate solid products have been characterised by Raman and IR spectroscopies. The influence of thorium substituted into the uranium oxalate structure was evaluated. Several vibrational modes were found to be affected by the variation in ionic radius appearing to be metal sensitive and therefore, provide the initial indication in the evaluation of the chemical composition.     

Distribution coefficients of 60 elements on TODGA resin: Application to Ca, Lu, Hf, U and Th isotope geochemistry

Batch equilibration experiments are conducted to measure the distribution coefficients (K_d) of a large number of elements in nitric, nitric plus hydrofluoric, and hydrochloric acids on Eichrom TODGA extraction chromatography resin. The K_ds are used to devise a multi-element extraction scheme for high-precision elemental and isotopic analyses of Ca, Hf, Lu, Th and U in geological materials, using high-purity lithium metaborate (LiBO₂) flux fusion that allows rapid digestion of even the most refractory materials. The fusion melt, dissolved in nitric acid, is directly loaded to a TODGA cartridge on a vacuum chamber for elemental separation. An Ln-Spec cartridge is used in tandem with TODGA for Lu purification. The entire procedure, from flux digestion to preparation for isotopic analysis, can be completed in a day. The accuracy of the proposed technique is tested by measuring the concentrations of Ca (standard bracketing), Hf, Lu, Th and U (isotope dilution), and the isotopic composition of Hf in geostandards (USNM3529, BCR-2, BHVO-1, AGV-1 and AGV-2). All measurements are in excellent agreement with recommended literature values, demonstrating the effectiveness of the proposed analytical procedure and the versatility of TODGA resin.     

Comparative evaluation of two substituted diglycolamide extractants for ‘actinide partitioning’

Extraction behaviour of actinides, lanthanides, fission products and structural elements has been studied with the two diglycolamide extractants, namely N,N,N′,N′-tetra-2-ethylhexyl diglycolamide (T2EHDGA) and N,N,N′,N′-tetraoctyl diglycolamide (TODGA). The acid extraction studies suggested that T2EHDGA (K_H: 1.8) is less basic as compared to its linear homologue, TODGA (K_H: 4.1). The distribution ratio of Am(III) by 0.1 M diglycolamides followed the order: TODGA > T2EHDGA. The number of ligand molecules present in the stoichiometry of the extracted species of Am(III) was found to be three and four for T2EHDGA and TODGA, respectively. Thermodynamics studies suggested that the extraction of Am(III) by both the extractants is exothermic in nature. The radiolytic stability of TODGA and T2EHDGA solutions in n-dodecane has been investigated. Due to lower distribution ratio of Am by T2EHDGA, 0.2 M of its solution has been used as compared to 0.1 M solution of TODGA. The distribution behaviour of various metal ions, viz. Am, Nd, Fe, Mo, Cr, Sr and Cs has been studied from nitric acid as well as from simulated high level waste solution.     

Technetium chemistry in a novel group actinide extraction process

A newly developed method for advanced reprocessing of used nuclear fuel is the Group ActiNide EXtraction (GANEX) process. It is a liquid–liquid extraction process that aims at extracting all the actinides as a group from dissolved used nuclear fuel. This extraction can either be performed after a removal of the bulk uranium or directly on the dissolution liquor. At Chalmers University of Technology in Sweden a solvent that utilizes tributyl-phosphate (TBP) and a molecule from the bis-triazine bipyridine (BTBP) class of ligands dissolved in cyclohexanone has been developed for the use in a GANEX process. Previously the system has not been tested with the presence of technetium that is one of the major fission products. Technetium is often considered a problem within reprocessing since it has a chemical behaviour that differs from most other elements in the spent fuel. Therefore, a special emphasis was put on the investigation of technetium in the selected GANEX system. It was shown that technetium is readily extracted by the GANEX solvent and that cyclohexanone is the main extractant when no other metals were present in the system. It was also found that the presence of uranium decreased the overall technetium extraction despite a slight co-extraction with TBP, while irradiation of the GANEX solvent to large doses (>1 MGy) increased its technetium extraction capability. It was also discovered that an increased nitrate concentration in the aqueous phase and an addition of other fission products both inhibited the technetium extraction even though fission product loading most likely changed the extraction mechanism to co-extraction by BTBP.     

Solvent extraction of Pu(IV) with TODGA in C6mimTf2N

Studies on the solvent extraction of Plutonium(Pu(IV)) from aqueous nitric acid by N,N,N′,N′-tetraoctyl-diglycolamide (TODGA) in 1-hexyl-3-methylimidazolium-bis(trifluoromethylsulfonyl) imide (C₆mimTf₂N) room temperature ionic liquid (RTIL) were carried out. It was found that Pu(IV) is extracted into RTIL phase as [Pu(NO₃)(TODGA)]³⁺ through cation exchange mechanism. Extraction reaction equation is obtained by the influence of acidity and extractant concentration, and the parameters of thermodynamic equilibrium constant was calculated.     

Distribution behavior of U(VI), Am(III) and Eu(III) on diglycolamide based extraction chromatographic resin in perchloric acid medium

An attempt has been made in the present work to investigate the role of anion for the uptake of Am(III)/Eu(III)/U(VI) by extraction chromatography (EXC) resin incorporating tetra-n-octyl-3-oxapentanediamide, commonly referred to as tetra-octyl diglycolamide (TODGA). In contrast to the nitric acid, perchloric acid medium favors extraction of trivalent metal ions even at low acidity (pH 2) and is almost insensitive to the acidity up to 5 M. Exceptionally large distribution coefficients (10⁵–10⁶) in the wide range of perchlorate concentration (10^?2–5 M) is quite unusual and is by far the largest reported in the literature for Am(III)/Eu(III). Thermodynamic data suggests the possibility of inner sphere/cation exchange mechanism involving TODGA aggregates at higher acidity but outer sphere/cation exchange mechanism at low acidity for Eu(III). There is a possibility of employing TODGA based EXC resin for the remediation of liquid waste (contaminated with long lived transuranics like ^241/243Am and ²⁴⁵Cm) in the wide range of acidity.     

Extraction behavior of lanthanides using a diglycolamide derivative TODGA in ionic liquids

Liquid-liquid extraction of lanthanides from aqueous solutions into ionic liquids (ILs) has been investigated using N,N,N',N'-tetra(n-octyl)diglycolamide (TODGA) as an extractant, and compared with that in the isooctane system. Application of ILs as the extracting phase provided unprecedented enhancement of the extraction performance of TODGA for lanthanides compared with that of the isooctane system. Slope analysis confirmed that TODGA in ILs formed a 1 : 3 complex with La(3+), Eu(3+), or Lu(3+). On the other hand, the molar ratios of species extracted into isooctane were 1 : 3 for La(3+) or 1 : 4 for Eu(3+) and Lu(3+), depending on the atomic number of the lanthanide. The transfer of lanthanides with TODGA into ILs proceeded via a cation-exchange mechanism, in contrast to ion pair extraction in the isooctane system. Furthermore, we clarified that TODGA provided selectivity for the middle lanthanides in the ILs systems, but heavier lanthanides in the isooctane system.     

Extraction behavior of cerium by tetraoctyldiglycolamide from nitric acid solutions

The diamide N,N,N′,N′-tetraoctyldiglycolamide (TODGA) was synthesized and characterized. The prepared TODGA was applied for extraction of Ce(III) from nitric acid solutions. The equilibrium studies included the dependencies of cerium distribution ratio on nitric acid, TODGA, nitrate ion, hydrogen ion and cerous ion concentrations. Analysis of the results indicates that the main extracted species is Ce(TODGA)₂(NO₃)₃HNO₃. The capacity of Ce loading is approximately 45 mmol/L for 0.1 M solution of TODGA in n-hexane. Finally, the thermodynamic parameters were calculated: K (25 °C) = 3.8 × 10³, ΔH = −36.7 ± 1.0 kJ/mol, ΔS = −54.6 ± 3.0 J/K mol, and ΔG = −20.4 ± 0.1 kJ/mol.     

Hexanoic acid as an alternative diluent in a GANEX process: feasibility study

Used nuclear fuel is radiotoxic for mankind and its environment for a long time. However, if it can be transmuted, the radiotoxicity as well as its heat load are reduced. Before a transmutation the actinides within the used fuel need to be separated from the fission, corrosion and activation products. This separation can be achieved by using the liquid–liquid extraction technique. One extraction process that can be used for such a separation is the Group ActiNide EXtraction (GANEX) process. One GANEX process that can successfully accomplish the separation utilizes the diluent cyclohexanone in combination with the extractant tributylphosphate (TBP) (30 % vol) and a second extractant, CyMe₄-BTBP (10 mM). However, there are some issues when using cyclohexanone as diluent. In this work an alternative diluent has therefore been tried in order to determine if it can replace cyclohexanone. The diluent used was hexanoic acid. In a system containing 10–12 mM CyMe₄-BTBP and 30 % vol TBP in hexanoic acid with the aqueous phase 4 M HNO₃, the distribution ratios for americium and curium are unfortunately low (D _Am = 1.1 ± 0.27, D _Cm = 1.6 ± 1.81). The concentration of CyMe₄-BTBP ligand, the extractant of curium and americium, could unfortunately not be increased, because of limited solubility in hexanoic acid. The distribution ratios for fission, corrosion and activation products were low for most metals; however, cadmium, palladium and molybdenum all unfortunately have distributions ratios above 1. To conclude, low americium and curium extractions indicate that hexanoic acid is not a suitable diluent which could replace cyclohexanone in a GANEX process.     

Adsorption and desorption behavior of tetravalent zirconium onto a silica-based macroporous TODGA adsorbent in HNO3 solution

To understand the separation behavior of Zr(IV) in the partitioning process for high level liquid waste, a silica-based macroporous adsorbent (TODGA/SiO₂-P) was prepared by impregnating N,N,N′,N′-tetraoctyl-3-oxapentane-1,5-diamide (TODGA) into a macroporous silica/polymer composite particles support (SiO₂-P). Adsorption and desorption behavior of Zr(IV) from nitric acid solution onto silica-based TODGA/SiO₂-P adsorbent were investigated by batch experiment. It was found that TODGA/SiO₂-P showed strong adsorption affinity to Zr(IV) and this adsorption process reached equilibrium state around 6 h at 298 K. Meanwhile, HNO₃ concentration had no significant effect on the adsorption of Zr(IV) above 1 M. From calculated thermodynamic parameters, this adsorption process could occur spontaneously at the given temperature and was confirmed to be an exothermic reaction. This adsorption process could be expressed by Langmuir monomolecular layer adsorption mode and the maximum adsorption capacity were determined to be 0.283 and 0.512 mmol/g for Zr(IV) at 298 and 323 K, respectively. In addition, more than 90 % of Zr(IV) adsorbed onto adsorbent could be desorbed with 0.01 M diethylenetriamine pentaacetic acid solution within 24 h at 298 K.     

Studies on the separation of 90Y from 90Sr by solvent extraction and supported liquid membrane using TODGA: role of organic diluent

Solvent extraction and supported liquid membrane transport studies on Y(III) and Sr(II) were carried out using both nitric as well as hydrochloric acid feed conditions using N,N,N′,N′-tetra-octyldiglycolamide (TODGA) in several organic diluents. The solvent extraction studies indicated extremely large separation factor (SF) values with chloroform, carbon tetrachloride, 1-decanol and hexone when 6 M HNO₃ was used as the feed. On the other hand, the SF values were 1–2 orders of magnitude lower when the nitric acid concentration was 3 M HNO₃. Significantly large SF values were also obtained from 6 M HCl when xylene, carbon tetrachloride, n-dodecane and hexone were used as the diluent. Though mass transfer was not very promising in the supported liquid membrane studies with most of the diluent systems, quantitative Y(III) transport was observed with 0.1 M TODGA in xylene with negligible Sr(II) transport suggesting possibility of obtaining carrier free ⁹⁰Y. The purity of the radiotracer was checked by half-life method.     

Application of hollow fiber supported liquid membrane for the separation of americium from the analytical waste

Americium from analytical solid waste containing U and metallic impurities was separated using hollow fiber supported liquid membrane (HFSLM) technique impregnated with DHOA–TODGA from nitric acid medium. An aliquot of 5 g of the solid waste containing Am (19.95 mg) as minor actinide and of U (2,588 mg), Fe (1,360 mg), Ca (1,810 mg) and Na (3,130 mg) as major impurities was processed. The feed solution obtained after the dissolution of the residue in ~4 M HNO₃ was passed through HFSLM module. In the first stage using 1 M DHOA–dodecane U was recovered while Am and other impurities were left in the raffinate. In the second stage, 0.5 M DHOA + 0.1 M TODGA/dodecane was used for the separation of Am from other impurities. Though, majority of the elements were separated in this cycle, Ca was co extracted along with the americium. CMPO extraction chromatographic technique was used for further separation of americium from Ca. Significant decontamination factors were achieved in this three step separation process with respect to U, Fe, Na and Ca with ~77 % recovery of americium.     

Efficient extraction of Rh(III) from nitric acid medium using a hydrophobic ionic liquid

Rhodium(III) has been successfully extracted from an aqueous nitric acid solution using a hydrophobic ammonium based ionic liquid and CMPO or TODGA as extractant. This result has significant potential for the recovery of rhodium from spent nuclear fuel and thereby increasing the worldwide supply of this rare metal.     

Resistance properties of a macroporous silica-based N,N,N′,N′-tetraoctyl-3-oxapentane-1,5-diamide-impregnated polymeric adsorption material against nitric acid, temperature and γ-irradiation

The resistance of a novel silica-based N,N,N′,N′-tetraoctyl-3-oxapentane-1,5-diamide (TODGA) polymeric adsorption material (TODGA/SiO₂-P) against nitric acid, temperature and γ-irradiation had been investigated. The adsorption property of the treated TODGA/SiO₂-P was evaluated by a 3 M HNO₃ solution containing 0.01 M Nd(III). It was found that both 3 and 0.01 M HNO₃ concentrations did not decrease the stability of TODGA/SiO₂-P at 25°C. The quantity of TODGA leaked from TODGA/SiO₂-P was equivalent to its solubility in the corresponding HNO₃ aqueous solution. The effect of 3 M HNO₃ on the leakage of TODGA at 80°C was significantly higher than that in 0.01 M HNO₃ as well as in all cases at 25°C. The amount of Nd(III) adsorbed towards the treated TODGA/SiO₂-P was determined in the range of 0.143–0.148 mmol/g for the HNO₃ concentration effect and 0.142–0.0506 mmol/g for the temperature effect. γ-Irradiation showed a more noticeable destruction effect on TODGA/SiO₂-P. The content of TODGA leaked increased with an increase in the γ-irradiation dose (ID) from 1.06 to 3.72 MGy in terms of the linear equation [TODGA]=794.5ID+84.0. The amount of Nd(III) adsorbed onto the irradiated TODGA/SiO₂-P decreased rapidly from 0.134 to 0.0438 mmol/g, which was lower than 0.153 mmol/g, the adsorption of fresh TODGA/SiO₂-P for Nd(III), according to the equation Q_Nd(III)=−0.0301ID+0.160, showing that a large quantity of TODGA leaked from TODGA/SiO₂-P. The adsorbed amount of Nd(III) decreased obviously in this order: the HNO₃ concentration effect, temperature effect and γ-irradiation.     

Separation of curium from americium using composite sorbents and complexing agent solutions: part 2

TODGA–PAN composite sorbent and (PhSO₃H)₂–BTPhen in nitric acid solution were employed as a system for separation of curium from americium. The influence of aqueous phase composition (complexing agent and nitric acid concentrations) on weight distribution coefficients and Cm/Am separation factor was studied in batch experiments with trace amounts of ²⁴¹Am and ²⁴⁴Cm. Based on the results obtained, column experiment was designed and conducted. The Cm/Am separation factor of 3.8 ± 0.1 found in batch experiments with TODGA–PAN could be reproduced also in column experiment resulting in good separation of Cm from Am. The efficiency of Cm separation from Am in the TODGA–PAN system was compared with the analogous system with DGA resin (Triskem International). After separation on a 0.5 mL column (φ4.7 × 29 mm) the Cm fraction containing 93% of Cm(III) contained only 3% of Am(III) in optimum conditions.