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

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.