Bring precious metal back: recovery of recovery of trace platinum from waste source Linfan Cui 1,2 , Kirsi Yliniemi 1,2 , Jaana Vapaavuori 2 , Mari Lundström 1 1 Department of Chemical and Metallurgical Engineering, School of Chemical Engineering, Aalto University, Espoo 02105, Finland, 2 Department of Chemistry and Materials Science, School of Chemical Engineering, Aalto University, Espoo 02105, Finland Innovative methods for metal recovery are required due to the depletion of the world’s natural resources and increasing demand. Exposit of lower-grade raw materials-waste sources is also beneficial to relieve raw material supply risks. For example, there are still minor quantities (ppm or ppb level) of precious metals (Au, Pt, Ag, etc.) contained as impurities in the hydrometallurgical process solution. Efficient recovery of precious metals from waste sources not only prevents material loss to generate additional revenues but also reduces environmental impact and carbon footprint significantly. Electrochemical metal recovery has become more prevalent due to the sustainable route through the utilization of renewable electricity. Recently, the electrodeposition and redox replacement (EDRR) - technique has been developed to selectively recover precious metals (Te, Pt, Au, and Ag) and create high-value-added functional surfaces (photocatalyst, corrosion resistant) directly from industrial process solutions [1] . During EDRR, a sacrificial metal with less nobility is first deposited through electrodeposition, then the precious metal is recovered onto the electrode surface through RR reaction, driven by the reduction potential difference between the two metals. The RR reaction can also be achieved by reduction between dissolved sacrificial metal and precious metal species [2] , indicating a metal recovery process with lower energy consumption and an end-product with higher purity. In the current study of the electrochemically aqueous reduction (EAR) method, multivalent iron was selected as reductive species to recover platinum - a critical element as the catalyst for the hydrogen economy. Specifically, dissolved Fe(III) in chloride-based media is reduced to a lower oxidation state Fe(II), which then serves as a reductant to trigger the RR reaction with dissolved Pt in the solution. Consequently, platinum was successfully recovered onto the electrode through the EAR method. The influence of EAR process parameters (e.g., the applied potential and time to reduce Fe(III), or RR time), the concentration of the input components and pH in the solution on the recovery efficiency and structure of final deposits were fundamentally studied, further paving the way to apply EAR method into other metal recovery or recycling system. Acknowledgements This work was supported by the Academy of Finland project EARMetal (LC, KY, ML: 339979 and LC, KY, JV: 342080) and the RawMatTERS Finland Infrastructure (RAMI) funded by the Academy of Finland and based at Aalto University. References 1. L. Cui, K. Yliniemi, J. Vapaavuori, M. Lundström, Recent developments of electrodeposition-redox replacement in metal recovery and functional materials: A review, Chem Eng J. (2023). https://doi.org/10.1016/j.cej.2023.142737 2. I. Korolev, S. Spathariotis, K. Yliniemi, B.P. Wilson, A.P. Abbott, M. Lundström, Mechanism of selective gold extraction from multi-metal chloride solutions by electrodeposition-redox replacement, Green Chem. 22 (2020) 3615–3625. https://doi. org/10.1039/D0GC00985G
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