Green Biohydrometallurgy for Gold Recovery from Electronic Wastewater: Advances, Challenges, and Future Directions

The rapid growth of electronic waste (e-waste) creates both environmental risks and untapped resource recovery opportunities, particularly for gold present at trace levels in complex electronic wastewater streams. Traditional methods—cyanidation and aqua regia leaching—achieve high recovery but entail high energy consumption, toxic reagents, and substantial secondary waste, conflicting with circular economy and decarbonization goals. Green biohydrometallurgy—encompassing bioleaching, biosorption, and bioreduction—offers a promising alternative under milder conditions with lower environmental impacts, especially when integrated with advanced solvents (IL/DES) and sorbents (COFs). This review critically examines recent advancements in gold recovery from e-waste-derived electronic wastewater using bio-based and bio-enabled technologies. Key topics include: (i) metabolism-dependent bioleaching using bio-lixiviants; (ii) biosorption and bioreduction of Au from polymetallic solutions; and (iii) integration with ionic liquids/deep eutectic solvents (IL/DES) and molecularly designed sorbents (e.g., covalent organic frameworks, COFs). Synthesized performance data reveal gold leaching efficiencies up to 98% in optimized thiourea-based bioleaching and adsorption capacities reaching 3108 mg g-¹ for CS-MoS2 composites, demonstrating the exceptional potential of sulfur-rich biosorbents. Critical challenges—slow kinetics, selectivity, biocatalyst stability, and scaling in real wastewater matrices—are examined. Future priorities include low-carbon hybrid flowsheets, life cycle assessment (LCA), techno-economic analysis (TEA), and safe-and-sustainable-by-design approaches to establish green biohydrometallurgy as a cornerstone of sustainable urban mining for precious metals recovery from electronic wastewater.