Metal partitioning in coccolith-based calcite and biotechnological applications of metal-doped coccolith materials
Despite established cultures of coccolithophore microalgae and attainable large-scale production of coccolith biominerals (gram quantities of calcite mineral from litres of culture), the coccolith as an advanced functional material has made little progress in bionanotechnologies. This project will quantitatively describe metal doping into and on the surface of coccolith-based calcite for several transition metals, main group elements and lanthanides. Elucidating the potential of coccolithophore to incorporate metal ions into/onto biogenic calcite production will not only reveal the biotechnological possibilities for coccolith materials but will offer insights on the role of metals in the biomineralization process and the biological screening effect. Metal-doped coccolith materials will be subjected to physical and chemical characterization (focus placed on strategic metals that have enchanced incorporation into biogenic calcite or can be replaced/deposited on coccoltih surface). Select metal-doped coccolith candidates will be pursued for biotechnological application accordingly based on their physical and optical properties (e.g., catalytic activity for transition metals and photoluminescence for lanthanides).
Study of the CHON-UNEX process for the removal of high heat-emitters from spent fuel
The removal of high heat emitters from spent fuels allows to reduce the volume necessary for a safe storage in deep repository. Some of these isotopes can also be recycled, for instance 241Am as fuel for fast-breeder reactors and 137Cs as a gamma source (radiotherapy, sterilization). A new process called CHON-UNEX has been recently proposed, whose ligands and diluents are composed of only C, H, O and N elements so that the effluents can be eventually vaporized and do not form secondary wastes. It consists in a co-extraction of all high heat emitters followed by successive stripping steps to enable the recycling of these elements. The Sr, Am and Ln extractant is a diglycolamide (DGA) that also serves as modifier for the Cs extractant, a calixarene crown-ether (CC) insoluble in kerosene.
At first, the Ph.D. student will study several commercially available DGAs in combination with 2 CCs to assess their extraction efficiency and selectivity, followed by the determination of the speciation and the supramolecular assemblies of these systems by various analytical tools. Then, the student will perform the selective stripping of Am by phenanthroline-based hydrosoluble ligands previously tested on Lns by an other student.
The student will eventually gain knowledge on the nuclear fuel cycle, hydrometallurgy and analytical tools that can lead to pursue academic work or to a job in the hydrometallurgy industry.
The candidate is M.Sc. with chemistry as major. A solid basis in analytical chemistry is recommended.
New cyclic extractant molecules for uranium/plutonium separation
This thesis subject is dedicated to the optimization of the uranium/plutonium separation process (PUREX) for spent nuclear fuels reprocessing. New extractant molecules will be studied for targeted elements separation by liquid-liquid extraction from nitric acid medium. They should be soluble in industrial aliphatic diluents, adaptable to extraction technologies actually used in terms of density, viscosity, solubility and extraction kinetics. In order to help in the target molecules selection, theoretical DFT calculations (Density Functional Theory) will be investigated to make a comparative estimate of their affinity towards U and Pu elements. Then the student will have to determine the feasibility of organic synthesis and to optimize synthesis pathways. Once the molecules will be purified and their structures and purity characterized, their separation performances will be assessed by liquid-liquid batch extraction tests involving radioelements. Finally, the structures of metallic complexes formed in organic phases with those new extractant molecules will be studied to better understand extraction mechanisms.