It is a matter of strategic independence for Europe to urgently find processes taking into account environmental and economic issues, when recycling rare earth elements (REE). As of 2015, only 1% of used REE were recycled in the EU and 80% of the mining operations were performed in China. With SYNEXTRACT, we propose to leverage on discoveries made (and patented) within ERC-Advanced project REE-CYCLE combining experimental milli-fluidic devices to measure the chemical potential step associated to transfer of rare earth between fluids, and to predictively model those.
Most of efficient liquid-liquid extraction process currently investigated to bring at least one solution to large usage for recycling are based on “synergy:” efficient separation is only obtained by combining in a special manner -i.e. at a special pH and temperature-, at least two “extracting” molecules.
Hence, SYNEXTRACT will try to trigger for the first time synergic effects in a solid-liquid extraction process based on “Simulated Moving Bed Chromatography” technology. In classical simulated bed technology, the extractant is grafted on the surface. The hybrid technology to be developed is based on one extractant is grafted and the other one circulating in the liquid phase during extraction only.
The new hybrid technology proposed within SYNEXTRACT should provide a better implementation as in classical liquid-liquid in mixer-settlers or chromatography, where the active volume is very low. Moreover, since most fluid is circulating in a circular design, effluents are minimized.
Indeed, the SYNEXTRACT project is to bring of proof-of-concept TRL 3. Several research teams of the Institute for separation chemistry of Marcoule are involved in this project. The steps towards that goal are following: synthetize and purify water-soluble analogues of mimicking currently used extractants, then chemically graft via a flexible linker another extractant to a resin, and finally test at lab-scale the efficiency of surface co-micellisation in extracting as well as stripping steps needed for efficient separation and recycling. This would enable highly flexible purification processes for REEs containing waste streams, that can be adapted in real time to variable waste stream lixiviates. It should also be mentioned that SYNEXTRACT process would be all aqueous, therefore avoid the use of organic solvent and would drastically reduce process wastes and running costs of rare earth contained in electronic wastes.
In the present state of the project, predictive modelling of the synergy is submitted for publication. Three representatives of a new class of short-branched chain analogues to anionic extractant has been identified and their peculiar behaviour studied, opening unexpected possibilities at the border-line between hydrotropes and surfactants. The experimental proof of co-micellisation around rare earths at the surface has not been obtained yet. All the current static solid phases tested had 2 to 3 orders of magnitude too low grafting densities. Going beyond TRL3 requires the more advances in solid grafted phases that should combine low cost, high capacity, long-lasting and accessible recycling or reprocessing that could be implemented by industry within ten years.
