Study on the Influence of CaO on the Electrochemical Reduction of FeO in NaCl-CaCl Molten Salt.

The presence of calcium-containing molten salts in the electrolysis of oxides for metal production can lead to the formation of CaO and, subsequently, the generation of intermediate products, affecting the reduction of metals. To investigate the impact of CaO on the reduction process, experiments were conducted using a FeO-CaO cathode and a graphite anode in a NaCl-CaCl molten salt electrolyte at 800 °C. The electrochemical reduction kinetics of the intermediate product CaFeO were studied using cyclic voltammetry and - curve analysis. The phase composition and morphology of the electrolysis products were analyzed using XRD, SEM-EDS, and XPS. The experimental results demonstrate that upon addition of CaO to the FeO cathode, CaFeO is formed instantly in the molten salt upon the application of an electrical current. Research conducted at different voltages, combined with electrochemical analysis, indicates that the reduction steps of CaFeO in the NaCl-CaCl molten salt are as follows: CaFeO ⟶ FeO ⟶ FeO ⟶ Fe. The presence of CaO accelerates the electrochemical reduction rate, promoting the formation of Fe. At 0.6 V and after 600 min of electrolysis, all of the CaFeO is converted into Fe, coexisting with CaCO. With an increase in the electrolysis voltage, the electrolysis product Fe particles visibly grow larger, exhibiting pronounced agglomeration effects. Under the conditions of a 1 V voltage, a study was conducted to investigate the influence of time on the reduction process of CaFeO. Gradually, it resulted in the formation of CaFeO, CaFeO, FeO, and metallic Fe. With an increased driving force, one gram of FeO-CaO mixed oxide can completely turn into metal Fe by electrolysis for 300 min.