Production of Iron from Iron Oxide Powder by Suspension Electrolysis in Alkaline Electrolyte

Iron was electrodeposited from suspensions of iron oxide powders (Fe2O3 or Fe3O4) by suspension electrolysis in highly concentrated alkaline electrolytes (25 mol·kg–1 NaOH–H2O or KOH–H2O) at 110 °C. The effects of current density, electrolyte composition, and oxide phase on faradaic efficiency, deposit morphology, and polarization behavior were investigated. Increasing the current density above 300 mA·cm–2 led to decreased faradaic efficiency due to enhanced hydrogen evolution, accompanied by dendritic iron growth induced by gas bubble coverage at the cathode surface. The measured steady-state cell voltage was analyzed as an apparent operating cell voltage, reflecting the combined contributions of electrochemical polarization, ohmic resistance, and side reactions inherent to the suspension electrolysis system. Gibbs energy changes derived from this voltage were therefore treated as apparent operating energy descriptors. The magnitude and temperature dependence of these values were found to be consistent with the electrochemical reduction of α-Fe2O3 at the cathode under the present conditions rather than being dominated by hydrogen-mediated pathways. Comparison between Fe2O3 and Fe3O4 suspensions show the roles of oxide conductivity and particle aggregation in governing polarization losses and the faradaic efficiency.