Reduction of magnetite to metallic iron in strong alkaline medium

Abstract

This work focuses on assessing the feasibility of cathodic iron extraction from the magnetite basedprecursors. For this, electrochemical processes at Fe3O4/alkaline electrolyte interface were screened bycycling voltammetry. Based on these results, one obtained guidelines for selecting the conditions (i.e.,potential and temperature) where efficient direct electrochemical reduction of magnetite ceramics tometallic iron occurs. Electrochemical conversion of relatively dense magnetite samples yields apolycrystalline Fe scale, formed at the surface of the magnetite pellet in direct contact with the bulkelectrolyte. Still, the onset of slightly open porosity results in formation of intermediate layers withcoexisting magnetite and metallic Fe; this is ascribed to gradual development of additional porosity,which promotes sample impregnation with the electrolyte, extends the effective electrochemically activearea, and facilitates dissolution of soluble species in the inner pores. This is clearly demonstrated bytransient response behavior, with remarkable increase in the current density. The key roles of porosityand effective Fe3O4/electrolyte area are also emphasized by the enhanced kinetics of electrochemicalreduction observed for highly porous magnetite samples, with nearly homogeneous distribution ofreactant (Fe3O4) and product (metallic Fe), without a clear surface scale of metallic iron. In this case, thefinal productis very porous and fragile. The conversion of highly porous magnetite samples also proceedswith much higher Faradaic efficiency compared to nearly dense ceramics.