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 (MgCl 2 ) preparation and generation of harmful chlorine (Cl 2 ) 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 (MgF 2 ) – 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 Mg 2 Sn 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.