Scale-Up Study of Molten Salt Electrolysis using Cu or Ag Cathode and Vacuum Distillation for the Production of High-Purity Mg Metal from MgO

To produce high-purity Mg metal directly from MgO, the scale-up of a novel electrolytic process using a metal cathode and vacuum distillation was investigated. The electrolysis of MgO was conducted in MgF2-LiF molten salt using Cu or Ag cathode and graphite anode at 1053 K. The influence of the cathode metal and the concentration of Mg in the Mg alloy on the current efficiency was investigated. In addition, the interaction of Al2O3 in contact with the electrolyte and cathode was studied. When electrolysis was carried out with an applied current of 8.81-9.59 A for 75-95 h, Mg alloys such as Mg2Cu and MgAg were produced with a current efficiency of 82.2-88.0%. In addition, owing to the reaction between the Mg alloy and Al2O3, a dense layer of magnesium aluminum oxide was produced. Afterward, when the vacuum distillation of the Mg alloys was conducted at 1300 K, 99.9997% Mg metal was obtained.