Closed-loop bioleaching for mobile phones from the bioregeneration of the leaching agent to the recovery of metal: A review

The rapid accumulation of electronic waste (e-waste) poses a pressing environmental challenge because of the toxic substances it contains, and the growing demand for metals required to sustain manufacturing. This review explores the potential of closed-loop bioleaching as a sustainable and eco-friendly solution for metal recovery, focusing on end-of-life mobile phones. The process is structured into four interconnected stages: (1) bioproduction of the leaching agent, leveraging microorganisms such as Acidithiobacillus ferrooxidans to oxidize Fe²⁺ to Fe³⁺; (2) pre-treatment of e-waste, which employs mechanical processes to optimize materials for leaching; (3) leaching, where Fe³⁺ solubilizes valuable metals from pre-treated e-waste; and (4) metal recovery, using methods such as solvent extraction, ion exchange, and electrodeposition. This review examined the critical parameters that influence these stages, including culture medium composition, pH, aeration rates, and the heterogeneous nature of e-waste. Compared to traditional pyrometallurgical and hydrometallurgical approaches, bioleaching offers advantages such as reduced energy consumption and a lower environmental impact. However, challenges remain such as improving the reaction kinetics, mitigating the inhibitory effects of metal accumulation, and scaling up the process for industrial applications. Therefore, this study identifies the key priorities for advancing closed-loop bioleaching: optimizing bioprocess efficiency, integrating automation and real-time monitoring systems, and addressing regulatory and economic barriers to large-scale implementation. By providing a comprehensive analysis of the bioleaching process and its applications, this review highlights its transformative potential in driving a circular economy and fostering the sustainable valorization of e-waste.