Development of new ligands for the selective extraction of uranium and rare earths

L’offre en combustible nucléaire à base d’uranium est un enjeu clé de la stratégie française de production d’électricité, d’autant plus que la demande en uranium naturel continuera à augmenter dans un futur proche. Les terres rares sont aussi considérées comme des métaux stratégiques de par leurs propriétés remarquables qui les rendent indispensables dans de nombreuses applications liées aux nouvelles technologies.Il y a donc un intérêt à proposer de nouveaux procédés d’extraction de l’uranium et des terres rares plus efficaces que ceux utilisés actuellement. Le but est de répondre à un accroissement permanent de la demande en matières-premières, avec en toile de fond, le développement de procédés de recyclage, plus particulièrement pour les terres rares.Par le biais d’une étude multi-échelle, ce travail de thèse vise à développer de nouveaux ligands organiques ayant un fort pouvoir extractant pour l’uranyle (UO22+) ou pour les terres rares (TR3+), ainsi qu’une forte sélectivité vis-à-vis de diverses impuretés, notamment le fer (Fe3+). Ainsi, de nombreux ligands ont été imaginés, synthétisés et testés par extraction liquide-liquide dans plusieurs milieux synthétiques acides. Des molécules bifonctionnelles bi-, tri- et pentadentates ont été développés et leurs propriétés complexantes et leur spéciation en milieu organique évaluées avec l’UO22+ et le Fe3+ par différentes approches (DFT, UV-visible, IR, ESI-MS, EXAFS). Plusieurs nouveaux ligands ont été évalués dans le cadre de l’extraction sélective des terres rares et les résultats obtenus sont remarquables. Ces études ont permis, dans certains cas, d’aboutir au développement de nouveaux designs moléculaires ayant d’excellentes propriétés extractantes. Leur optimisation, couplée à différentes techniques analytiques, a permis d’atteindre les objectifs de cette thèse et servira dans le futur au développement de nouveaux extractants efficaces et sélectifs.The supply of uranium-based nuclear fuel is a key issue of the electricity production strategy in France, especially as demand for natural uranium will continue to increase in the near future. Rare earths are also considered as strategic metals due to their remarkable properties which make them essential in many applications related to new technologies.There is therefore an interest in developing new, more efficient processes for the extraction of uranium and rare earths than those currently used. The aim is to respond to a permanent increase in demand for raw materials, against the backdrop of the development of new recycling processes, especially for rare earths.Through a multi-scale approach, this PhD thesis sets to develop novel organic ligands with a strong extractant ability for uranyl (UO22+) or for rare earths (TR3+), as well as a high selectivity with respect to various impurities, in particular iron (Fe3+). Thus, many ligands have been designed, synthesized and tested by liquid-liquid extraction in several acidic synthetic media. Bifunctional bi , tri- and pentadentate molecules have been developed and their complexing properties and their speciation in organic medium have been evaluated in the presence of UO22+ and Fe3+ by different approaches (DFT, UV-visible, IR, ESI-MS, EXAFS). Furthermore, several new ligands have been evaluated for the selective extraction of rare earths and the results obtained are remarkable. Overall, these studies have led in some cases to the development of novel molecular designs with excellent extractant properties. Their optimization, coupled with different analytical techniques, fulfilled the objectives of this thesis and will serve in the future to the development of new efficient and selective extractants

Recherche de nouveaux ligands pour l'extraction sélective de l'uranium et des terres rares

The supply of uranium-based nuclear fuel is a key issue of the electricity production strategy in France, especially as demand for natural uranium will continue to increase in the near future. Rare earths are also considered as strategic metals due to their remarkable properties which make them essential in many applications related to new technologies.There is therefore an interest in developing new, more efficient processes for the extraction of uranium and rare earths than those currently used. The aim is to respond to a permanent increase in demand for raw materials, against the backdrop of the development of new recycling processes, especially for rare earths.Through a multi-scale approach, this PhD thesis sets to develop novel organic ligands with a strong extractant ability for uranyl (UO22+) or for rare earths (TR3+), as well as a high selectivity with respect to various impurities, in particular iron (Fe3+). Thus, many ligands have been designed, synthesized and tested by liquid-liquid extraction in several acidic synthetic media. Bifunctional bi , tri- and pentadentate molecules have been developed and their complexing properties and their speciation in organic medium have been evaluated in the presence of UO22+ and Fe3+ by different approaches (DFT, UV-visible, IR, ESI-MS, EXAFS). Furthermore, several new ligands have been evaluated for the selective extraction of rare earths and the results obtained are remarkable. Overall, these studies have led in some cases to the development of novel molecular designs with excellent extractant properties. Their optimization, coupled with different analytical techniques, fulfilled the objectives of this thesis and will serve in the future to the development of new efficient and selective extractants.L’offre en combustible nucléaire à base d’uranium est un enjeu clé de la stratégie française de production d’électricité, d’autant plus que la demande en uranium naturel continuera à augmenter dans un futur proche. Les terres rares sont aussi considérées comme des métaux stratégiques de par leurs propriétés remarquables qui les rendent indispensables dans de nombreuses applications liées aux nouvelles technologies.Il y a donc un intérêt à proposer de nouveaux procédés d’extraction de l’uranium et des terres rares plus efficaces que ceux utilisés actuellement. Le but est de répondre à un accroissement permanent de la demande en matières-premières, avec en toile de fond, le développement de procédés de recyclage, plus particulièrement pour les terres rares.Par le biais d’une étude multi-échelle, ce travail de thèse vise à développer de nouveaux ligands organiques ayant un fort pouvoir extractant pour l’uranyle (UO22+) ou pour les terres rares (TR3+), ainsi qu’une forte sélectivité vis-à-vis de diverses impuretés, notamment le fer (Fe3+). Ainsi, de nombreux ligands ont été imaginés, synthétisés et testés par extraction liquide-liquide dans plusieurs milieux synthétiques acides. Des molécules bifonctionnelles bi-, tri- et pentadentates ont été développés et leurs propriétés complexantes et leur spéciation en milieu organique évaluées avec l’UO22+ et le Fe3+ par différentes approches (DFT, UV-visible, IR, ESI-MS, EXAFS). Plusieurs nouveaux ligands ont été évalués dans le cadre de l’extraction sélective des terres rares et les résultats obtenus sont remarquables. Ces études ont permis, dans certains cas, d’aboutir au développement de nouveaux designs moléculaires ayant d’excellentes propriétés extractantes. Leur optimisation, couplée à différentes techniques analytiques, a permis d’atteindre les objectifs de cette thèse et servira dans le futur au développement de nouveaux extractants efficaces et sélectifs

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

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

Bis‐catecholamide‐based materials for uranium extraction

International audienceThis work reports the synthesis of formo‐phenolic resins containing four catecholamide (CAM) moieties with admixture of phenol, catechol or resorcinol. These chelating resins have been developed to selectively extract U(VI) from seawater. This media is a challenging environment due to a pH around 8.2 and a large excess of alkaline and earth‐alkaline cations. From the various sorption experiments investigated, the results indicate that the synthesized material exhibit good sorbent properties for U(VI) with uptake capacity about 50 mg/g for the more promising resins with a pronounced selectivity for uranium even under saline conditions. Thermodynamic and kinetic adsorption data were determined for the best resin (Langmuir adsorption model and pseudo‐second order model)

Les volcans de Colima (Mexique)

SIGLECNRS-CDST / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc