Fundamental Study of Electrolysis of MgO in MgF2 - LiF - KCl Molten Salt Using Cu Cathode

Abstract

For the commercial production of magnesium (Mg) metal using the electrolytic method, anhydrous magnesium chloride (MgCl2) is used as a feedstock. However, preparation of anhydrous MgCl2 is energy-intensive and toxic chlorine (Cl2) gas is generated during electrolysis. In order to resolve these problems, a novel molten salt electrolysis of magnesium oxide (MgO) using copper (Cu) cathode was investigated in this study. The effect of the electrolysis temperature, the size of the Cu metal pellets used for the cathode, the concentration of Mg in the Mg – Cu alloy, and the cathodic current density on the current efficiency were investigated. In addition, the reaction between the Mg – Cu alloy cathode and the alumina (Al2O3) crucible containing the Mg alloy during the electrolysis was analyzed. In the experiments, the electrolysis of MgO was conducted in a magnesium fluoride (MgF2) – lithium fluoride (LiF) – potassium chloride (KCl) molten salt using Cu cathode and carbon (C) anode by applying current in the range of 1.42 – 2.15 A at 1043 – 1173 K for 9.50 – 27.5 h in an argon gas atmosphere. After the electrolysis, the Mg – Cu alloys with a mixture of Cu2Mg and Cu (Mg) were obtained with 87.8 – 92.0 % current efficiency under certain conditions. Therefore, it was demonstrated that the green and effective electrolytic Mg production method using MgO, developed in this study, is feasible.