Electrochemical Iron Recovery from Biologically Produced Magnetite via Iron Oxide/Hydroxide Conversion: First Steps towards Terrestrial and Martian Applications

Abstract Ferrihydrite (Fe 10 O 14 (OH) 2 ), an iron oxide/hydroxide, is found in a variety of terrestrial and extraterrestrial environments. This study presents a novel approach that combines bio-mineralization and electrolysis for the efficient mining of low-grade iron resources. Iron-reducing Carboxydothermus ferrireducens bacteria converted an iron oxide/hydroxide Fe(III)-mixture to magnetite. This ferrimagnetic phase was magnetically extracted and subsequently electrolyzed at 363 K in an alkaline medium to produce metallic iron. Integrating a heat treatment step increased the iron yield to 67%. This resulted in a high current efficiency of 63% and an energy consumption of 19.1 MJ/kg, which is competitive with current pyrometallurgical practices. Heat-induced morphological and chemical changes facilitated iron reduction and suppressed parasitic hydrogen evolution. Furthermore, improved reducibility of the biomineralized material was observed. This method could facilitate the exploitation of marginal iron reserves, particularly in areas where no rich ores are available. The process also promises adaptation to extraterrestrial sources such as the Martian regolith.