Spontaneous and applied potential driven indium recovery on carbon electrode and crystallization using a bioelectrochemical system

[Display omitted] •MFC-driven indium recovery was demonstrated for the first time.•More than 90% of In3+ was removed after 2 weeks of MFC operation.•The cathode induces the electrochemical reduction and precipitation of In3+ ions.•Amorphous and crystalline indium hydroxides form on the carbon electrode surface.•Alternate positive/negative potential induces the crystalline indium oxide. Indium removal and recovery on a carbon electrode under a microbial fuel cell (MFC)-based oxidation/reduction reaction were examined using synthetic wastewater. More than 90% of In3+ ions were removed after continuous operation of the MFC for 14 days with an average current generation of ∼50 μA. During operation, indium particulates formed on the cathode carbon electrode. Scanning electron microscopy equipped with X-ray energy dispersive spectroscopy showed that they were composed of amorphous and crystalline indium hydroxides (In(OH)3 and In(OH)·H2O). When the current flow was reversed to drive the oxidation of the particles to recover the indium from indium hydroxides, a few indium oxide (In2O3) nanocrystals with a rectangular platelet shape formed on the electrode, while the majority of the amorphous and crystalline indium hydroxides re-dissolved into the aqueous environment. Overall, these results demonstrate a feasible route towards the MFC-based recovery of indium with the simultaneous generation of bioelectricity.