Homogenous recycling of transuranium elements from irradiated fast reactor fuel by the EURO-GANEX solvent extraction process

The EURO-GANEX process was developed forco-separating transuranium elements from irradiatednuclear fuels. A hot flow-sheet trial was performed in acounter-current centrifugal contactor setup, using a genuinehigh active feed solution. Irradiated mixed (carbide,nitride) U80Pu20 fast reactor fuel containing 20 % Pu wasthermally treated to oxidise it to the oxide form which wasthen dissolved in HNO3. From this solution uranium wasseparated to >99.9 % in a primary solvent extraction cycleusing 1.0 mol/L DEHiBA (N,N-di(2-ethylhexyl)isobutyramidein TPH (hydrogenated tetrapropene) as the organicphase. The raffinate solution from this process, containing10 g/L Pu, was further processed in a second cycle of solventextraction. In this EURO-GANEX flow-sheet, TRU andfission product lanthanides were firstly co-extracted intoa solvent composed of 0.2 mol/L TODGA (N,N,N′,N′-tetran-octyl diglycolamide) and 0.5 mol/L DMDOHEMA (N,N′-dimethyl-N,N′-dioctyl-2-(2-hexyloxy-ethyl) malonamide)dissolved in Exxsol D80, separating them from most otherfission and corrosion products. Subsequently, the TRUwere selectively stripped from the collected loaded solventusing a solution containing 0.055 mol/L SO3-Ph-BTP(2,6-bis(5,6-di(3-sulphophenyl)-1,2,4-triazin-3-yl)pyridinetetrasodium salt) and 1 mol/L AHA (acetohydroxamicacid) in 0.5 mol/L HNO3; lanthanides were finally strippedusing 0.01 mol/L HNO3. Approximately 99.9 % of the TRUand less than 0.1 % of the lanthanides were found in theproduct solution, which also contained the major fractionsof Zr and Mo

An overview of solvent extraction processes developed in Europe for advanced nuclear fuel recycling, Part 2 — homogeneous recycling

The hydrometallurgical separation concepts for the recycling of irradiated nuclear fuels developed in Europe are presented and discussed. Whilst Part 1 of the review focused on concepts for heterogeneous recycling of minor actinides, this article focuses on group recycling of transuranic actinides, which would support homogeneous recycling scenarios. Most of these concepts were developed within European collaborative projects and involve solvent extraction processes separating all the actinides (U-Cm) in two cycles. The first cycle uses a monoamide extractant to recover uranium leaving all the transuranic actinides in the aqueous raffinate with the fission products. The second cycle aims for a group recovery of the transuranium elements and several strategies have been proposed for this stage. In this review article, the various solvent extraction processes are summarised and the key features of the process schemes are compared

Kinetics extraction of uranium(vi) and plutonium(iv)by n,n-dialkylamides using different experimental techniques

International audienceMass transfer coefficients of uranium(VI) and plutonium(IV) between nitric acid and a monoamide-based solvent upon extraction were determined to support the development of a liquid-liquid extraction process for the multirecycling of plutonium from the future spent nuclear fuels. The kinetics data were obtained by using three different techniques the single drop technique, the Nitsch cell and the rotating membrane cell (RMC). Beyond the comparison of the influence on the kinetics of the different technics, the main objective of this study was to determine whether the transfer is controlled by diffusion or chemistry. The results obtained by the single drop technique showed that U(VI) and Pu(IV) mass transfer constants are quite similar for the extraction step. The global results point out that the resistance to the transfer is essentially located in the organic phase and the diffusion process would mainly control the kinetics

Experimental and modeling study of fission products and minor actinides extraction with N,N-dialkylamides

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Development of the pyrochemical DOS process for the recovery of actinides and its application for reprocessing of transmutation fuel targets

International audiencePyrochemical technology using high-temperature molten salts and molten metal media presents a potential interest for an overall separation and transmutation strategy for long-lived radionuclides. Within the frame of the two French acts on radioactive waste management, a pyrochemical RandD program was launched at the CEA Marcoule in the late 90's. The developed so called DOS (Direct Oxide Solubilisation) process, based on a two- step liquid-liquid (molten salt/liquid metal) extraction, aims to demonstrate the feasibility of a group separation of actinides with sufficient decontamination from fission products.The first step consists of a selective reductive extraction of actinides coming from direct dissolution of oxide fuel in the molten fluoride salt, into liquid aluminium metal. The second step is the actinides back-extraction, which consists of a liquid/liquid oxidative stripping of the An from aluminium matrix into molten chloride media. The DOS process has been successfully demonstrated for treatment of oxide type fuels within the last years the core of the process has been already assessed and the studies have shown high selectivity and a quantitative recovery of actinides. Within the framework of the SACSESS European research program, the present work focuses on a potential application of the DOS process for the reprocessing of MgO based CERCER transmutation targets. The behaviour of Mg was investigated regarding the solubility of MgO in the fluoride salt and then regarding Mg reductive extraction in metallic Al. The impact of Mg on the efficiency of An reductive extraction was also studied using U3O8 simulating the behaviour of MA oxides. Eventually, the validity of the DOS process was demonstrated on a Pu0.5Am0.5O2-et61540;-MgO FUTURIX CERCER pellet synthesized at the ATALANTE facility within the framework of Eurotrans program. Substantial amount of Nd2O3 was added during the demonstration experiment in order to simulate fission products behaviour. Quantitative recovery of purified Pu and Am was achieved in a single batch experiment

Rare earth recovery and separation using diglycolamides

International audienceRare earth elements (REE) have become essential for our modern economy, in relation to the development of new energy and communication technologies. Depending on their technical-economic efficiency and environmental footprint, hydrometallurgical processes enabling the recovery of separated elements could be of particular interest.Typically these processes include a first pre-treatment (crushing, milling and sieving) and an acidic leaching step (with eventual selective precipitation sub-steps), followed by a solvent extraction (SX) step aimed at the separation and purification of REE. Recently, diglycolamides (DGA) appeared as a very interesting group of extractants for the selective recovery of trivalent REE from nitric acid solutions, particularly in the presence of transition metal ions commonly found in various waste products. In this work, the TODGA extractant was successfully used for designing an efficient REE recovery process. The process integrates the mechanical and physico-chemical treatment of waste, followed by a solvent extraction step for the recovery and intra-separation of REE. Based on the experimental batch data, a phenomenological model has been elaborated taking into account the various distribution equilibria. The model has been implemented in our simulation code and used for calculation of various flowsheets, which have been tested at our pilot facility using compact continuous counter-current mixer-settlers. Experimental SX and modeling data allowing the recovery of >99.95% pure Dysprosium solution will be discussed in this paper. Preliminary technical-economic assessment and life-cycle analysis have also been conducted. Following this first successful demonstration, several novel dissymmetrical DGA have been developed and their solvent extraction behaviour in different acid media has been studied. Indeed, most processes use symmetrical DGA such as TODGA. The present work improves upon the classic design and demonstrates that novel dissymmetrical extractants display a remarkable improvement on REE extraction efficiency compared to reference TODGA in various acid media. Furthermore, the REE separation factors towards major impurities such as Fe3+ are substantially enhanced.The development of novel DGA with increased efficiency paves the way for the recovery and separation of high value REE from different streams. This opens new market opportunities since the effluent treatment has often an important impact either in the CAPEX or the OPEX of a solvent extraction plant. With some DGA extractants adapted to sulfuric acid media, the resulting effluent treatment plant could be cheaper than it would be using nitric acid media. Furthermore, their enhanced performance at low concentration should reduce the price of reagents in the OPEX

Determination of U(VI) and Pu(IV) mass transfer constants with N,N-dialkylamides in liquid-liquid extraction

International audienceIn the frame of the development of Generation IV reactors, CEA is developing a new liquid-liquid extraction process for the multirecycling of plutonium from the future spent nuclear fuels. Thermodynamic data have already been acquired for the modelling of the extraction equilibriums in this process, however, a full phenomenological model requires kinetic data too. Thus, this paper summarizes the acquisition of mass transfer coefficients of uranium(VI) and plutonium(IV) between nitric acid and a monoamide-based solvent upon extraction with three different techniques using a constant interfacial area the single drop technique. They are compared to results obtained with Nitsch cell and rotating membrane cell (RMC) methods.The influence of temperature, nitric acidity, viscosity of the organic phase and, in the case of the moving drop technique, the drop size and the nature of the continuous phase (aqueous or organic) on the mass transfer coefficient of uranium and plutonium during the extraction step was studied

Optimization of novel bifunctional ligand design for uranium extraction

International audienceUranium is recovered from natural primary and secondary resources by hydrometallurgical processes including ore leaching and purification. Different processes are available for uranium extraction and separation from the associated elements, but the most widely used remains the liquid-liquid extraction. Improving the performance of current processes through the design of more efficient, selective and robust extractants is particularly important. To optimize the liquid-liquid extraction of uranyl (UO$_2$$^{2+}$) from highly complexing sulfuric or phosphoric acid solutions, an approach based on the design of bifunctional extractants combining in the same molecular architecture both cation exchanger and neutral-donor functionalities has led to the development of a new family of ligand molecules containing a pyridine $N$-oxide ring and an acidic phosphonate function. Several novel molecules have been synthesized using an optimized strategy. The affinity and selectivity of the extractants were evaluated by batch liquid-liquid extraction tests and very high distribution ratios of uranium(VI) were measured (D$_U$ > 4200) in the presence of large concentrations of complexing anions such as sulfates. However, the separation factor of U(VI) versus Fe(III) is low.To establish structure-activity correlations and understand the lack of selectivity of this family towards Fe(III), the molecular environment around U(VI) and Fe(III) cations has been investigated using a combination of experimental (UV-vis and FT-IR spectroscopy, ESI-MS spectrometry) and theoretical approaches. Density functional theory (DFT) calculations coupled to infrared spectroscopy have been performed in order to identify the chemical functions contributing to the uranyl (UO$_2$$^{2+}$) coordination environment. The acidity (p$K_a$) and the complexation constants (log$\beta$) of these new ligands were measured using UV spectroscopy. The influence of the molecular design on the efficiency of the molecules to selectively extract U(VI) versus Fe(III) from sulfuric and phosphoric acid solutions was thus established. The present studies will contribute to a better understanding of the factors influencing the extraction properties and will lead on the longer term to the development of improved uranium extraction processes by organic ligands

Enhanced extraction of rare earth elements by novel tuned diglycolamides

International audienceRare earth elements (REE) are essential for our modern economy, in relation to the development of new energy and communication technologies, however their recycling from electronic waste and end-of-life products (such as permanent NdFeB magnets, Ni-MH batteries, etc.) is still not sufficiently developped.1 Although substitution of these materials by less critical ones is growing faster and faster especially in Japan efficient and eco-designed recycling processes will be of great importance in a near middle term. Depending on their technoeconomics efficiency and environmental footprint, hydrometallurgical processes enabling the recovery of separated elements could be of particular interest.Typically these processes include a first pretreatment (crushing, milling, sieving,) followed by an acidic leaching step (with possibly selective precipitation substeps) and a solvent extraction step (SX) in order to separate and purify the REE.2 Recently, diglycolamides (DGAs) appeared as a very interesting group of extractants for the recovery of trivalent lanthanides from nitric acid solutions, particularly in the presence of metal ions commonly found in waste products.3 The TODGA extractant (N,N,N',N'-tetraoctyl diglycolamide) was successfully used for designing a full REE recycling SX process from used permanent magnets.4 Nevertheless its performances have not yet been validated against upscaling tests.Most works concerning the group of DGAs dealt with symmetrical extractants exhibiting different separation efficiencies for REE in nitric acid media. The chain length modification on one side of the DGA (asymmetrical DGAs) can lead to important variation in selectivity during the Eu/Am separation.5 Recently, new dissymmetrical DGAs with very short chains were reported for REE extraction, such as for instance MODGA (N,N'-dimethyl-N,N'dioctyl-diglycolamide),6 however their solubility in industrial diluents is rather limited.The present work describes the organic synthesis of several novel DGAs and their solvent extraction behaviour towards REE in several aqueous acid media which could increase the industrial interest of such SX process. These new ligands displayed a remarkable improvement of REE extraction efficiency compared to reference TODGA in acid media, while presenting a good solubility in industrial aliphatic diluents. Furthermore, the separation factors of REE towards major impurities such as Fe3+ are substantially improved. Figure Distribution ratio of a novel DGA compared to TODGA in an acid solutionNevertheless it will be of primary importance to check whether the REE can be quantitatively de-extracted from the organic phase without any impurity. These promising results will also contribute to the design of an optimized SX process for the separation of REE

Extraction performance of monoamide extractants in pulsed columns

International audienceProcess development approach adopted in CEA, based on modelling studies, includes the determination of mass transfer efficiency of the contactors used to perform the different process operations. For monoamide based solvents, tests of several process operations as uranium extraction and back extraction, nitric acid stripping from a uranium loaded solvent were performed in laboratory scale pulsed columns of different heights. The recorded concentration profiles of the species of interest (uranium, nitric acid, ..) were simulated using the PAREX code. Mass transfer kinetics of the species of interest realized with that extractant system permit a very good simulation of the concentration profiles. These results will permit to give the ground data to design the process operation in industrial scale contactors, and will be a guide for further development to enhance if necessary the transfer efficiency of the contactor