Reduction mechanism and carbon content investigation for electrolytic production of iron from solid Fe2O3 in molten K2CO3–Na2CO3 using an inert anode

Iron and oxygen was recently electrochemically prepared in molten Na2CO3–K2CO3 eutectic melt at 750 °C using a solid iron oxide pellet cathode and a cheap Ni10Cu11Fe alloy inert anode. This paper focuses to reveal the detailed reduction kinetics of solid Fe2O3 in the melt and also the effect of reduction potential on the carbon content in the iron product. The reduction mechanism was systematically investigated by cyclic voltammetric measurements, potentiostatic electrolysis combining with the composition and morphology analysis of the products obtained at different potentials. It was found that the reduction of Fe2O3 involves three steps, with the formation of intermediate products, viz., NaFe2O3 and NaFeO2. The influence of electrolysis voltage/potential on the carbon content in the products was investigated by using both constant voltage and potentiostatic electrolysis under different conditions. The carbon content was found to be in the range of 0.035–0.76 wt.%, depending on the applied cathodic potential. The iron-based products with higher carbon content can be obtained upon electrolysis at a higher cell voltage or a more negative potential. The present results also demonstrated a controllable extraction of Fe–C steels with desired carbon content through an environmental friendly way.

► Reduction mechanism of solid Fe2O3 in molten carbonates was specified.
► NaFe2O3 and NaFeO2, formed through electrochemical inclusion of Na+ at different potential.
► The carbon content in iron was in a range of 0.035–0.76 wt.% by controlling cathodic potential.
► Low C content iron can be prepared with high current efficiency at cell voltage lower than 2.0 V.