Bioleaching for Cobalt Recovery from Mining Tailings: A Circular Economy Approach for Critical Metal Supply Patricio Martínez-Bellange1, Natalia Zuñiga-Prohaska1, Camilo Sánchez1, Roberto Collao1, Brian Townley2, Pilar Parada1. 1 Centro de Biotecnología de Sistemas, Universidad Andrés Bello (CSB UNAB), Chile 2 Advanced Mining Technology Center (AMTC) and Departamento de Geología, Universidad de Chile, Chile ABSTRACT Chile hosts one of the world's largest inventories of mine tailing’s deposits, with 836 facilities recorded as of December 2025. These deposits represent critical environmental liabilities due to the potential mobilization of toxic elements such as arsenic, copper, zinc, and heavy metals through acid mine drainage (AMD). Within the framework of circular economy principles, mine tailings are increasingly recognized as secondary sources of strategic metals, particularly cobalt, which plays a crucial role in the global energy transition. However, conventional recovery processes remain economically and environmentally constrained by high operational costs and energy demands. Microbial bioleaching emerges as a sustainable alternative, leveraging acidophilic chemolithotrophic microorganisms to solubilize metals under low pH conditions with reduced energy consumption and carbon emissions. This study evaluates different microbial inoculation strategies for enhancing cobalt recovery from sulfidic tailings through column bioleaching experiments. The results demonstrate that the thermotolerant Kobold B (S) consortium (DSM 35389), combined with optimized acid curing, achieved over 90% cobalt recovery. These findings contribute to the development of optimized biotechnological strategies for tailings valorization, supporting sustainable mining practices aligned with circular economy principles and long-term environmental stewardship. KEYWORDS Bioleaching, microbial inoculation, cobalt recovery, mining tailings, circular economy, critical metals, sustainable mining 1. Introduction Chile currently ranks third globally in the number of mine tailing’s facilities, with 836 deposits identified as of December 2025 [1]. The operational status of these deposits is a significant environmental concern; only 129 are active, while 223 are inactive, 455 are abandoned and the rest are under construction or under review [1,2]. This vast accumulation represents a major environmental liability, necessitating urgent cross-sectoral action for long-term remediation and valorization [3,4]. Although not intrinsically hazardous, tailings often contain toxic elements like arsenic, copper, and lead [3]. Exposure to atmospheric oxygen and water triggers sulfide oxidation
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