Application of neutron techniques to separation processes

by Dr Cyril MICHEAU (Japan Atomic Energy Agency)

Monday 14 Jul 2025, 14:30 → 15:30 Europe/Berlin

PH HS 3 (Physics Department)

The growing demand of electricity and the development of high technology devices are ones of the main preoccupations of our modern societies, in parallel to a reduction of their impact on the environment. These imply the use of critical metal resources, such as platinoid group metals (PGM) and more specifically rare earth elements (REE), which are limited in their supply and due to their strategic importance required the exploration of new sources. Considering that many countries made the choice of recycling, urban mines became a major source of supply as they contain many wastes from electrical and electronic equipment (WEEE). Simultaneously, the recycling of spent nuclear fuel is also part of this global strategy for a sustainable future.

To support this strategy, the hydrometallurgy industry focused on the development of efficient metal separation processes, among them the liquid-liquid extraction (LLE). This process consists in the transfer of target metal ions from an aqueous phase to an immiscible organic phase containing an extractant molecule. While conventional approaches focused solely on the coordination properties of the extractant for the metal, they were unable to explain unexpected solvent effect on the selectivity and kinetics of the process. However, the recent use of scattering techniques in the LLE field has demonstrated that these unpredictable effects were due to the formation of supramolecular structures of extractant molecules, called aggregates.^[1]

From this observation, we decided to describe more precisely the impact of these aggregates on the process efficiency. In this way, using a combination of scattering techniques with neutron reflectivity (NR), we evidenced an aggregate size-recognition effect on the metal selectivity, and an interfacial organization effect on extraction rate.^[2] Based on these evidences, we investigate, by using small-angle neutron scattering (SANS), the potentiality to finely tune the size of the aggregates to ultimately control the selectivity of the extraction process.

In parallel, as LLE uses a lot of organic solvent, and in order to reduce the ecological impact of the hydrometallurgy industry, the flotation process has demonstrated a growing interest as an alternative process. This process allows to separate and concentrate ions or other charged entities in a foam phase formed by a surfactant molecule, and ultimately to decrease wastewater volume. Similarly to LLE, the focus is put on the surfactant-solute interaction while the impact of surfactant aggregates and foam structures on the process is usually disregarded. In this way, we successfully applied SANS to the flotation process using a pH-sensitive surfactant, focusing on the foam, and we were able to correlate the foam structure to the 3 different extraction regimes.^[3]

These two applications demonstrated the strong role of neutron techniques to develop separation processes and finally to contribute to the development of a more sustainable industry.

 

[1] R. Porot et. al., ChemPhysChem, 2016, 17, 2112-2117

[2] C. Micheau et. al., J. Mol. Liq., 2024, 401, 124372

[3] C. Micheau et. al., Langmuir, 2023, 39, 10965-10977