Reactivity of suspended iron oxide particles in low temperature alkaline electrolysis

Abstract

Electrolysis of iron ore is a promising CO2-free iron production route based on the electrolytic reduction of solid iron oxide particles suspended in 110 °C concentrated alkaline electrolyte. The reactivities of different iron compounds during their reduction into iron through this process have been compared using a model laboratory cell. Chronoamperometry experiments were performed on suspensions containing hematite (α-Fe2O3), magnetite (Fe3O4) or goethite (α-FeOOH) at a cell voltage of 1.66 V. Current density response, anode and cathode electrochemical potentials, faradaic efficiency and iron deposit morphology were compared. Hematite reduces to iron at 1100 A/m2 with current yield near 85%. For goethite, the current density response was 33% lower and current efficiency dropped by 20% compared to hematite. Magnetite reactivity proved to be extremely low with eight-time lower current density and tenfold lower current efficiency than hematite. The weaker reactivity of goethite and magnetite particles could be ascribed to their more difficult adsorption on the cathode surface partly covered with metal iron, the far higher viscosity of goethite suspensions, although at the same solid concentrations as the other oxide particles and the occurrence of opposite electrode reactions with dissolved Fe(OH)3 − and Fe(OH)4 − ions.