Reaction mechanism for direct electrodeposition of high-purity magnesium from NaCl-KCl-MgCl2 molten salt

To achieve green and efficient production of high-purity magnesium, this work investigates the electrochemical reduction and deposition mechanism of Mg(II) in a NaCl-KCl-MgCl 2 molten salt system at 953 K. A combination of thermodynamic analysis and electrochemical techniques, including cyclic voltammetry, square wave voltammetry, chronopotentiometry, and potentiostatic electrolysis, was employed on a tungsten electrode. The reduction of Mg(II) to Mg(0) was confirmed to be a single-step, two-electron transfer reversible process controlled by ion diffusion. The diffusion coefficient of Mg(II) was determined to be 1.19 × 10 −8 cm 2 /s to 1.25 × 10 −8 cm 2 /s. Potentiostatic electrolysis at -1.68 V (vs. Ag/AgCl) successfully produced high-purity liquid magnesium, which was collected and solidified. X-ray diffraction and scanning electron microscopy with energy-dispersive X-ray spectroscopy analyses unequivocally identified the deposits as metallic magnesium with a purity exceeding 99.9 wt.%. The key innovation lies in simultaneously establishing the fundamental electrochemistry of Mg(II) and demonstrating its direct electrodeposition in a low‑cost, industrially scalable NaCl-KCl‑based electrolyte, providing a critical foundation for a continuous, green magnesium electrolysis technology.