Novel tools for recycling technology critical metals

<p dir="ltr">The demand for metal recycling and recovery technologies is constantly increasing due to the large amount of electronic waste generated in recent years. Metallic and semiconductor structures can be present in organic and inorganic phases and are crucial for sustainable energy. However, the primary processing methods for complete metal ,digestion, specifically hydro- and pyro-metallurgical routes, are not energy-efficient or ,environmentally friendly. In this thesis, ultrasound was used as a physical method, and selective oxidation as a chemical method, to investigate the recovery of technology-critical metals, including platinum group metals (PGMs), bismuth, tellurium, and antimony. These approaches were implemented using oxidising agents, such as copper(II) chloride and iodine, in combination with chloride-based deep eutectic solvents (DESs) and concentrated brines, enabling acid-free, selective dissolution. In addition, oxidising agents can be used in multiple cycles and may be regenerated by reacting with oxygen present in the solution. The electrochemistry and redox properties of copper were also studied, revealing that the solvent anion has a more significant impact on redox properties than the salt anion type. Changing the ionic liquid’s anion led to changes in speciation, based on coordinating ,strength, which in turn affected redox potentials. These differences were exploited to finetune redox behaviour and enhance selectivity in metal recovery. Copper was also investigated as a reversible redox catalyst and as a structural component in thermoelectric devices, where its selective removal is often necessary to isolate high-value materials. In systems with low chloride levels, oxidation was limited by surface passivation and the solubility of oxidised species. Conversely, high-chloride systems faced mass transport limitations due to viscosity. According to this study, forced convection or targeted ultrasound can effectively enhance mass transport in viscous media. Overall, this research shows that tuneable ionic systems can provide more efficient and selective alternatives compared to conventional methods for the recovery of technology critical metals from complex end-of-life materials.</p>