Sustainable recovery of critical metals from printed circuit boards via integrated bioleaching

Abstract Electronic waste (e-waste), particularly waste printed circuit boards (PCBs), represents a rapidly growing secondary resource of critical and precious metals. However, conventional pyrometallurgical and hydrometallurgical recovery processes are energy intensive and generate significant environmental pollution. Sustainable bioleaching offers a promising alternative, yet comparative studies integrating strain-specific bioleaching performance with environmental life cycle assessment (LCA) remain limited. In this study, three indigenous bacterial strains, Exiguobacterium himgiriensis , Enterobacter quasihormaechei and Arthrobacter gandavensis , were evaluated for the recovery of valuable metals from waste PCBs under laboratory-scale bioleaching conditions (37 °C, 150 rpm, 5 g L − 1 PCBs loading, 5 days). Metal recovery efficiencies were quantified using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), while bioleaching-induced physicochemical changes were characterized by Field-Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive Spectroscopy (EDS), Fourier Transform Infrared Spectroscopy (FT-IR), and X-ray diffraction (XRD) analyses. Environmental sustainability was assessed through cradle-to-gate LCA using openLCA v2.4.1 and the ecoinvent 3.11 database. E. himgiriensis achieved the highest copper recovery (95.55%), A. gandavensis exhibited the greatest silver (96.77%), iron (86.75%), and manganese (95.63%) recovery, whereas E. quasihormaechei demonstrated the highest zinc recovery (61.07%), highlighting strain-dependent metal selectivity. Physicochemical characterization confirmed substantial surface deterioration and elemental depletion of PCB particles following bioleaching. The LCA identified downstream metal refining and electricity consumption as the principal environmental hotspots, while overall results demonstrated the environmental potential of heterotrophic bioleaching compared with conventional recovery routes. Overall, this study provides an integrated experimental and environmental evaluation of heterotrophic bioleaching, demonstrating the potential of indigenous bacterial strains for sustainable recovery of critical metals from waste PCBs.