Urban Biomining of Rare Earth Elements: Current Status and Future Opportunities.

Rare earth elements (REEs) are critical to modern technologies and national security, playing essential roles in electronics, electric vehicles, and defense systems. Although they are not truly rare, their widespread but low-concentration presence in the Earth's crust, combined with their chemical similarity, makes conventional mining both technically difficult and environmentally taxing. As a result, recycling REEs from electronic waste (e-waste), a practice often referred to as urban mining, has emerged as a promising alternative. However, current recycling methods face major challenges, including high energy demands, extensive use of harsh chemicals, generation of large volumes of solvent waste, and poor selectivity for REEs. These limitations significantly hinder the sustainability and scalability of REE recovery from e-waste, underscoring the urgent need for innovative, environmentally friendly strategies to extract and recover REEs. Recently, microorganism-based bioleaching and biosorption techniques have emerged as promising green alternatives to reduce the environmental burden caused by conventional recycling methods and further enhance the recovery efficiency and specificity of REEs from e-waste. Bioderived substances emerged as sustainable alternatives to upgrade the efficiency and specificity of REE exploitation and recovery from various resources. This review highlights three key areas essential for advancing REE biorecovery technologies, particularly in the context of urban biomining: (i) the use of bacteria-derived organic compounds as leaching agents for REE bioleaching from e-waste; (ii) the application of recombinant biomolecules, such as proteins, peptides, nucleic acids, and other engineered compounds, for selective biosorption and bioprecipitation of REEs; and (iii) the development and utilization of advanced microbial chassis and alternative nonchassis systems to enhance biorecovery efficiency. Key insights and future perspectives are provided to guide future design and advancement of integrated bioleaching-bioseparation systems for efficient and robust REE recovery from e-waste.