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

铂族金属(PGM)，如铂、钯和铑，是汽车、电子和医疗保健应用中必不可少的关键原材料。然而，PGM面临稀缺性、地缘政治供应风险以及采矿和加工带来的高环境影响。随着需求的上升，从废汽车催化剂等二次来源中回收PGM对供应的可持续性至关重要。废旧汽车催化转化器含有比原生矿石浓度更高的PGM，代表着关键的城市矿山。全球的回收利用率仍然很低，有很大的改善潜力。2020年，只有15%-20%的铂、钯和10%的铑被回收。PGM回收提供经济和战略价值，减少初级采矿对环境的影响，并符合循环经济原则。然而，传统的PGM回收方法存在缺陷。火法冶金涉及高能耗和高排放。湿法冶金使用腐蚀性化学物质并产生废物。需要更可持续的技术。生物电化学系统(BES)，如微生物燃料电池(MFC)，可以通过微生物还原金属的机制，以较低的能量和化学输入优势，潜在地回收PGMS。金属铜绿假单胞菌是一种耐金属细菌，它展示了PGMS的金属形式的生物矿化作用。虽然已经有研究探索使用金属假单胞菌回收金属，但有限的研究评估了它在MFC中的潜力。工程生物学方法，如在细菌表面过表达金属结合蛋白，可以进一步提高PGM的生物吸附和回收效率。该项目将研究在MFC中使用野生型和转基因金黄色葡萄球菌，以开发从废汽车催化剂中回收PGM的可持续工艺。评估生物催化和电化学性能以及生命周期的影响可以证明该方法的技术可行性、经济可行性和环境效益。本项目涉及设计和优化微生物燃料电池(MFC)，以使用金属还原细菌Cupriavidus metalliduans从废催化剂中回收PGMS。在选择合适的阳极材料(如碳布)和阳离子交换膜(如Nafion)以获得最佳的电化学性能后，将通过跟踪生长动力学和测量PGM浓度，分析野生型金属芽孢杆菌在有废催化剂的间歇培养中对PGM的耐受性和回收率。然后，该菌株将在MFC原型中进行测试，在不同的pH、温度、催化剂负载和电极电位条件下，找到最优水平，最大限度地提高阴极上的发电量和PGM回收率。详细的电化学分析将阐明其机理。为了进一步改善对PGM的生物吸附，将对金属芽孢杆菌进行基因工程，以过表达通过组学方法确定的内源金属结合蛋白或金属硫蛋白等异源蛋白。在MFC中，将在不同的操作条件下对性能最好的菌株进行优化。最后，将使用生命周期评估对排放、资源消耗和废物产生等影响类别进行生命周期评估，对照传统的火法和湿法冶金法评估基于MFC的技术在PGM回收方面的可持续性。

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.