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 (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 (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 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. (C) 2021 Chongqing University. Publishing services provided by Elsevier B.V. on behalf of KeAi Communications Co. Ltd.