Development of a novel electrolytic process for producing high-purity magnesium metal from magnesium oxide using a liquid tin cathode

Abstract

The current electrolytic processes for magnesium (Mg) metal have several disadvantages, such as anhydrous magnesium chloride (MgCl2) preparation and generation of harmful chlorine (Cl2) gas. To overcome these drawbacks, a novel Mg production process to produce high-purity Mg metal directly from magnesium oxide (MgO) was investigated in this study. The electrolysis of MgO was conducted using a liquid tin (Sn) cathode and a carbon (C) anode in the eutectic composition of a magnesium fluoride (MgF2) – lithium fluoride (LiF) molten salt under an applied voltage of 2.5 V at 1053 – 1113 K. Under certain conditions, the Mg – Sn alloys with Mg2Sn and Mg (Sn) phases were obtained with a current efficiency of 86.6 % at 1053 K. To produce high-purity Mg metal from the Mg – Sn alloy, vacuum distillation was conducted at 1200 – 1300 K for a duration of 5 – 10 h. Following the vacuum distillation, the concentration of Mg in the Mg – Sn alloy feed decreased from 34.1 to 0.17 mass%, and Mg metal with a purity of 99.999 % was obtained at 1200 K. Therefore, the electrolytic process developed here is feasible for the production of high-purity Mg metal from MgO using an efficient method.