Strategic metal recycling in Ionic Liquids by EXtraction and Electrodeposition process – SILEXE

The SILEXE project brings the expertise of three academic laboratories and one industrial partner internationally recognized in the field of ion separation (ICSM-UMR 5257), ionic liquids (LCME-EA 1651), electrochemistry (IJL-UMR 7198) and metal recycling from e-cards (TerraNova). SILEXE will investigate Room Temperature Ionic Liquids (RTILs) as unusual media for strategic metal recycling, especially indium, tantalum and gold, through the use of a selective extraction (or back-extraction)/electrodeposition process starting from lipophilic or hydrophilic ligands and Task Specific Ionic Liquids (TSILs) as extractants. A successful recycling of the assessed critical metals is very important regarding increase of resource efficiency, avoidance of possible scarcities and reduction of the overall environmental impacts linked with the life cycles of the strategic metals. Furthermore the positive contribution of the recycling sector to employment and to adding value should be taken into account. Excepted from rare earths contained in the low-energy lamps for which an industrial process has recently emerged (Solvay process), until today for some metals like tantalum in dissipative applications (cell phones), lithium (batteries), gallium, indium and germanium (up-to-date just very small and dissipative amounts in post-consumer materials), there are no running recycling technologies at commercial scales and only first steps in small (pilot) plants are initiated. However, the supply of strategic metals has a clear impact on industrial defense and security of countries that would lack them. In this context, we propose to develop an efficient process for the extraction and purification of the strategic metal In, Ta and Au. RTILs containing chelating ligands or TSILs having strong affinity with the targeted metal will be used as extracting media. The pure metal will be recovered using selective electrodeposition process. Several studies on metal separation by liquid/liquid extraction techniques involving chelating agents in Ioni Liquids, or in Task Specific Ionic Liquids are already described in the literature. It appeared thus interesting to extend the study of metal recovering by extraction and electrodeposition in ionic liquids with potentially more selective synthesized ligands and/or new task specific ionic liquids binding chelating sites. Because they play a crucial role in the ligand-metal binding, the experimental conditions of temperature, acidity, concentrations in solution combined with the ionic liquid properties, especially the nature of the anionic species (hard/soft, BF4-, NTf2-, …) will be as many of parameters which will have to be considered in order to optimise the liquid/liquid separation. Extraction from aqueous phase to hydrophobic ionic liquid containing the ligand (or a mixture of ligands for a potential synergistic effect) or the TSILs or extraction from aqueous phase directly performed in TSILs will particularly be considered. Another strategy will be envisaged, based on a preliminary extraction step from aqueous phase in conventional alcane type solvent followed by a de-extraction process from the organic phase containing the metal-ligand complex to a hydrophilic ionic liquid or task specific ionic liquid. Based on the preliminary results obtained in SILEXE, modulated techniques (selective extraction/electrodeposition and/or de-extraction/electrodeposition ligand/TSIL, lipophilic/hydrophilic ionic liquid, initial aqueous phase containing the targeted metal, ionic strength…), could be extend to the purification of other strategic metals (Ga, Nb…).