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

Abstract

Ferrihydrite (Fe₁₀O₁₄(OH)₂), an iron oxide/hydroxide, is found in a variety of terrestrial and interplanetary environments. This study presents a novel combination of bio-mineralization and electrolysis to address the need for efficient mining of low-grade iron resources. Iron-reducing bacteria biologically convert iron oxide/hydroxide to magnetite. This could then be magnetically extracted and electrolyzed at 363 K using an alkaline medium into metallic iron. The innovation 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.

In our research, Carboxydothermus ferrireducens converted superparamagnetic iron oxide/hydroxide (Fe(III)) into a ferrimagnetic (Fe(II)/Fe(III)) phase. After 20 hours of alkaline deoxidation electrolysis, this ‘bio-magnetite’ could be electrochemically reduced to 25 wt.% of Fe(0). The iron yield was increased to 67 % by integrating a heat treatment step. This resulted in a high current efficiency of 63 % and an energy consumption of 17.9 MJ/kg, competitive with current industrial practices. The morphological and chemical changes induced by heat treatment facilitated iron reduction and minimized parasitic hydrogen evolution. Improved reducibility of bio-mineralized materials was also observed. These findings suggest the potential of biotechnological approaches in metallurgy.