The recovery of elements of interest (uranium, plutonium, minor actinides, and platinum-group metals) generated by fission reactions involves a cascade of hydrometallurgical processes based on liquid–liquid extraction (LLE). Following dismantling, shearing, and leaching of spent nuclear fuel in concentrated nitric acid, the various elements are sequentially and selectively transferred into an immiscible phase, typically consisting of a lipophilic ligand dissolved in an organic diluent. Within the framework of the CEA’s accelerated research programme dedicated to downstream scientific and technological developments for nuclear energy, this PhD project will focus on a grouped actinide separation strategy following the preliminary extraction of uranium with a monoamide (PUMAS process). The objective is to develop an alternative to the GANEX process, enabling the selective partitioning of elements between the leachate and the solvent through competition between an organic phase containing a lipophilic diglycolamide (DGA)-type extractant or related diamide analogues and a water-soluble DGA dissolved in the aqueous leachate. The affinity and selectivity of these ligands will be controlled and tuned by modifying the topology and stereochemistry of their substituents, using lipophilic substituents for ligands in the organic phase and hydrophilic substituents for those in the acidic aqueous phase. Depending on the position of these substituents, either on the nitrogen atoms and/or on the methylene bridges of the DGA backbone, different stereogenic centres will be introduced. These structural modifications are expected to enhance both affinity and selectivity, as previously demonstrated.¹,2 In the first stage of the project, the PhD candidate will synthesise a series of chiral DGA derivatives in both unresolved and diastereomerically pure forms. Their ability to discriminate between actinides (thorium, the latter being used as a surrogate for plutonium), lanthanides, and other competing metals, including platinum-group metals, will then be evaluated. Elemental concentrations will be determined by ICP analysis of the aqueous phases and X-ray fluorescence (XRF) analysis of the organic phases. The molecular and supramolecular mechanisms associated with each diastereomer, including coordination and aggregation phenomena, will subsequently be investigated using both established and advanced characterisation techniques, including UV spectroscopy, IR spectroscopy, multinuclear NMR, density functional theory (DFT) calculations, X-ray scattering, neutron scattering, and extended X-ray absorption fine structure (EXAFS) spectroscopy.
The doctoral training provided through this project will equip the PhD candidate with a broad range of skills relevant to both academic and industrial careers, particularly in the fields of the nuclear fuel cycle and separation chemistry. The research will be carried out within the LISA laboratory at ICSM, which is recognised for its expertise in the chemistry and physical chemistry of extractants for hydrometallurgical applications. The PhD candidate will benefit from high-quality scientific supervision and a collaborative working environment alongside fellow PhD candidates, postdoctoral researchers, and research engineers, within a supportive and stimulating research setting.