Bio-electrochemical Recovery of Platinum Group Metals from Spent Car Catalysts by Cupriavidus metallidurans.

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Platinum group metals (PGMs) like platinum, palladium, and rhodium are critical raw materials essential for automotive, electronics, and healthcare applications. However, PGMs face scarcity, geopolitical supply risks, and high environmental impacts from mining and processing. With rising demand, recovering PGMs from secondary sources like spent automotive catalysts is crucial for supply sustainability. Spent car catalytic converters contain PGMs at higher concentrations than primary ores and represent a critical urban mine. Global recycling rates are still low, with significant potential for improvement. In 2020, only 15-20% of platinum and palladium and 10% of rhodium were recycled. PGM recycling provides economic and strategic value, reduces the environmental impacts of primary mining, and aligns with circular economy principles. However, conventional PGM recovery methods have drawbacks. Pyrometallurgy involves high energy use and emissions. Hydrometallurgy utilizes corrosive chemicals and generates waste. There is a need for more sustainable techniques. Bio-electrochemical systems (BES) like microbial fuel cells (MFC) can potentially recover PGMs through microbial metal reduction mechanisms with lower energy and chemical input advantages. Cupriavidus metallidurans, a metal-resistant bacterium, demonstrates biomineralization of PGMs into their metallic forms. While studies have explored metal recovery using C. metallidurans, limited research has evaluated its potential in MFCs. Engineering biology approaches like overexpression of metal binding proteins on bacterial surfaces could further enhance PGM biosorption and recovery efficiency. This project will investigate the use of wild-type and genetically modified C. metallidurans in MFCs to develop a sustainable process for PGM recovery from spent automotive catalysts. Evaluating the biocatalytic and electrochemical performance along with life cycle impacts can demonstrate the method's technical feasibility, economic viability, and environmental benefits over conventional techniques.This project involves designing and optimizing a microbial fuel cell (MFC) to recover PGMs from spent catalysts using the metal-reducing bacterium Cupriavidus metallidurans. After selecting suitable anodic electrode materials like carbon cloth and cation exchange membranes like Nafion for optimal electrochemical performance, the wild-type C. metallidurans will be analyzed for PGM tolerance and recovery in batch cultures with spent catalysts by tracking growth kinetics and measuring PGM concentrations. The strain will then be tested in an MFC prototype under different conditions of pH, temperature, catalyst loading, and electrode potentials to find optimal levels that maximize electricity generation along with PGM recovery on the cathode. Detailed electrochemical analysis will elucidate the mechanisms. To further improve PGM biosorption, C. metallidurans will be genetically engineered to overexpress endogenous metal binding proteins identified through omics approaches or heterologous proteins like metallothioneins. The best-performing strain will be optimized under different operating conditions in the MFC. Finally, the sustainability of the MFC-based technique will be evaluated against conventional pyrometallurgy and hydrometallurgy for PGM recovery using life cycle assessment across impact categories like emissions, resource consumption, and waste generation.