Improving metal extraction using microwave-assisted leaching
VITO has continued to develop valuable metal extraction processes for a range of different types of waste materials as part of the PEACOC project. Hereby, VITO applies microwave (MW) heating as the core technology to improve the extraction efficiency and to lower the energy and chemicals demand in the applied hydrometallurgical process.
VITO has now fully optimised the MW-assisted leaching process for platinum group metals (PGMs) from spent automotive ceramic catalysts. The researchers have achieved significant reduction in the use of hydrochloric acid without a need to add an oxidation agent. Through this rapid process, lasting only 5 to 10 minutes, final extraction yields for palladium (Pd), platinum (Pt) and rhodium (Rh) of at least 90% were reached.
Subsequently, VITO tested the integration of the MW-assisted leaching step with the Gas Diffusion Electrocrystallisation (GDEx) technique, which recovers the PGMs from the obtained leaching solution. This enables the reuse of the leaching solution and further reduction in chemical usage. It has been thus demonstrated that this approach allows for even more selective extraction of PGMs (compared to other elements present in spent catalysts) during the leaching step. As a result, the process is now fully prepared to be tested at pilot scale.
VITO also further developed MW-assisted leaching methods to extract gold (Au) and silver (Ag) from end-of-life products, such as printed circuit board assemblies (PCBAs) and photovoltaic (PV) scraps. The hydrometallurgical extraction of the valuable metals from these materials in a one-pot system is challenging, as many different metals are present alongside the low concentrations of, for instance, Au and Ag. Consequently, a step-by-step approach was adopted and leaching processes were developed and optimised to extract base metals first, such as iron (Fe), zinc (Zn), copper (Cu), tin (Sn), etc. These processes were optimised to work at low temperatures and under conditions that are reasonably mild so that noble metals are not extracted. This enables the selective removal of base metals and concentration of noble metals. Currently, VITO is optimising the final MW-assisted leaching step to extract Ag and Au from such concentrates. The first results are promising, as complete extraction of Ag and Au can be reached.
More information about Microwave-assisted leaching in the scientific publication: Microwave-assisted leaching approaches to recover Platinum Group Metals from waste and intermediate streams