Solar-assisted bioelectrochemical removal and solid-phase capture of critical group-13 metals: indium and gallium

Gallium (Ga) and indium (In) are essential for optoelectronic and photovoltaic (PV) applications.However, primary sources are limited, while recoverable metals exist in industrial effluents and end-of-life modules.In this study, a solar-assisted bioelectrochemical system (BES) is evaluated, in which a photovoltaic (PV) module directly biases a bioanode-based, two-chamber reactor.This setup facilitated the anodic half reaction and supplementary driving force under mild aqueous conditions.During seven-day batch operations on a real Ga-bearing semiconductor effluent and a synthetic In solution, a PV-assisted BES at ~1.25 V removed 88 % of Ga, reducing concentrations from 1016 4 to 127 1 mg/L.In contrast, a self-biased microbial fuel cell (MFC) and an open-circuit (OC) control removed only 17 % and 15 % of Ga, respectively.Initial In concentrations (1005 1 mg/L) declined by 31 %, 29 %, and 26 % in MFC, PV-assisted BES, and OC modes, respectively.Scanning electron microscopy (SEM)energy-dispersive X-ray (EDX) analysis revealed In-rich precipitates (~58 wt% In).The contrasting responses of Ga and In derive from their reduction potentials and interfacial chemistry: Ga reduction requires stronger polarization, whereas In can deposit under milder bias.Accordingly, PV assistance is essential for Ga removal but less critical for In stabilization.This BES can reduce energy and chemical inputs compared with conventional pyro-and hydrometallurgical routes and highlight these divergent recovery behaviors as a foundation for sustainable valorization of metal-bearing effluents.