Electrochemical Extraction of Fe–Si Alloy Form SiO2–CaO–CaF2–FeOx Slags by Molten Oxide Electrolysis

Abstract

Materials like metallic iron and its alloys are essential to daily living and industrial production. The benefits of using electrolysis technology to prepare iron and its alloys are great efficiency, controllability, and environmental protection. This study focuses on the feasibility of the electrochemical method for the direct preparation of metallic iron and Si–Fe alloys in iron ores with high fluoride content. The electrochemical behavior of Fe(II) and Fe(III) in molten SiO₂–CaO–CaF₂ slag on tungsten electrodes was investigated by using cyclic voltammetry and square wave voltammetry methods. It was determined that the reduction of Fe(II) ions follows a one-step two-electron transfer process: Fe(II) + 2e⁻ → Fe(0). The reduction of Fe(III) involves a two-step electron transfer process: Fe(III) + e⁻ → Fe(II) and Fe(II) + 2e⁻ → Fe(0), respectively. The Fe(II)/Fe(0) process is an irreversible reaction controlled by diffusion. The diffusion coefficient of Fe(II) is D_Fe(II) = 1.5 × 10⁻⁶ cm² s⁻¹. The cathodic deposits of iron were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS). The findings indicate that the production of Fe₂Si alloy through electrolysis is more favorable when Fe(II) is present in the slag, while the production of metallic iron is more favorable when Fe(III) is present in the slag. This work provides a basis for the electrochemical direct preparation of Fe–Si alloy and metallic iron in high fluorine iron ore.