(575h) Selective Electrochemical PGM Recovery from Complex Feedstocks via Molecular Design of Redox-Copolymers

Platinum group metals (PGMs) are critical for various industrial and energy applications, but their recovery from complex feedstocks, such as mining ores and spent catalysts, presents significant challenges. PGMs are difficult to separate due to very similar physical and chemical properties and low concentrations and complex speciation depending on pH or type of electrolyte used. Conventional recovery methods such as hydrometallurgy and pyrometallurgy are often energy-intensive and environmentally harmful. Electrochemical separation, however, offers an environmentally benign alternatives with good modularity and scalability. In this study, a novel electrochemical recovery method using redox-copolymers for the selective separation of PGMs was introduced.

Redox electrodes have proven effective in optimizing the operational voltage range and enhancing Faradaic efficiency for ion binding while minimizing side reactions that could otherwise increase energy consumption. Additionally, polymer-functionalized electrodes have demonstrated the ability to support selective electrosorption and facile regeneration, offering a more energy-efficient method for metal recovery. Redox-copolymers, particularly those incorporating a ferrocene redox moiety and metal-affinity ligands, offer a promising method for the selective recovery of PGM chloroanions. These redox-copolymers enable efficient adsorption and release of PGMs through a dual mechanism involving electrochemical reduction of ferrocene and pH-induced ligand deprotonation. By adjusting the ratio of redox to ligand groups, a separation factor greater than 20 between palladium and platinum was achieved. The copolymer demonstrated excellent stability, maintaining over 90% of its capacity after 300 cycles of electrochemical testing and achieving up to 60% regeneration efficiency. Additionally, it maintained high PGM uptake even under harsh conditions, such as highly acidic leachates (pH ~1) with high concentrations of transition metals. Techno-economic analysis confirmed the cost-effectiveness of the method, with platinum recovery becoming economically viable after seven regeneration cycles. This work demonstrates the potential of redox-copolymers as a sustainable, efficient platform for PGM recovery.