Electrochemical evaluation of Fe2+ ions in MgCl2-NaCl-KCl melt
(1. National Engineering Research Center for Integrated Utilization of Salt Lake Resource, East China University of Science and Technology, Shanghai 200237, China;
2. Joint International Laboratory for Potassium and Lithium Strategic Resources, East China University of Science and Technology, Shanghai 200237, China)
2. Joint International Laboratory for Potassium and Lithium Strategic Resources, East China University of Science and Technology, Shanghai 200237, China)
Abstract: A comprehensive electrochemical assessment of Fe2+ behavior in a MgCl2-NaCl-KCl melt was reported, involving cyclic voltammetry (CV), square wave voltammetry (SWV), and chronoamperometry (CA) analyses. Reduction of Fe2+ in MgCl2-NaCl-KCl was observed to occur in a single step involving two electrons, exhibiting quasi-reversible behavior. The diffusion coefficient of Fe2+ (5.75×10-5 cm2/s) in this system was experimentally determined at 973 K, with an associated diffusion activation energy of 25.06 kJ/mol in the range of 973-1048 K, and an estimated standard rate constant for Fe2+/Fe of around 1×10-3 cm/s. The nucleation of Fe on the tungsten electrode in the MgCl2-NaCl-KCl molten salt is insensitive to temperature and overpotential. It is found that the nucleation mode is related to the concentration of Fe2+ surrounding the electrode and evolves from an instantaneous to a progressive process, accompanied by a deterioration of magnesium electrolysis due to Fe impurities.
Key words: Fe2+; MgCl2-NaCl-KCl melt; electrochemical reduction; kinetic properties; nucleation mechanism