Electrochemical behavior of Fe(III) in Na₂SiO₃-SiO₂-Fe₂O₃ molten salt

Abstract

The high-temperature requirement for liquid iron smelting via molten oxide electrolysis presents significant challenges. This study investigates the electrochemical reduction of Fe(III) in a novel low-temperature electrolyte, Na₂SiO₃-SiO₂-Fe₂O₃, utilizing cyclic voltammetry and square wave voltammetry techniques. The results show that Fe(III) reduction occurs in two steps: Fe(III)+e⁻→Fe(II), Fe(II)+2e⁻→Fe, and that the redox process of Fe(III)/Fe(II) at the tungsten electrode is an irreversible reaction controlled by diffusion. The diffusion coefficients of Fe(III) in the molten Na₂SiO₃-SiO₂-Fe₂O₃ in the temperature range of 1248–1278 K are between 1.86×10⁻⁶ cm²/s and 1.58×10⁻⁴ cm²/s. The diffusion activation energy of Fe(III) in the molten salt is 1825.41 kJ/mol. As confirmed by XRD analysis, potentiostatic electrolysis at −0.857 V (vs. $\mathrm{O}_{2}/\mathrm{O}_{(\text{complex})}^{2-}$) for 6 h produces metallic iron on the cathode.

Keywords

molten oxide electrolysis (MOE) / electrochemical behavior / cyclic voltammetry / potentiostatic electrolysis / diffusion coefficients / Fe(III)

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