Production of high-purity Mg metal from dolomite through novel molten salt electrolysis and vacuum distillation

Abstract

In this study, a novel Mg production process for producing high-purity Mg metal from dolomite was developed. When the electrolysis of calcined dolomite was conducted using Cu cathode and C anode in MgF2 – LiF molten salt at 1083–1173 K by applying an average current of 1.42–1.46 A for 9.50–21.0 h, the current efficiency of 66.4–88.6% was obtained. The produced Mg alloys consisted of MgCu2 and Cu (Mg) or MgCu2 and CuMg2 phases, depending on the Mg concentration in the Mg alloy. When the electrolysis of calcined dolomite was conducted in MgF2 – LiF – CaF2 molten salt at 1083 K, the current efficiency was 40.9–71.4%, owing to undesired reactions such as electroreduction of Ca2+ or/and CO32− ions. Meanwhile, the current efficiency increased from 40.9% to 63.2% by utilizing a Pt anode, because the occurrence of CO32− ions in the molten salt was prevented. After vacuum distillation of the obtained Mg alloys at 1300 K for 10 h, Mg metal with a purity of 99.9996–99.9998% was produced. Therefore, the feasibility of this novel process for the production of high-purity Mg metal from dolomite was demonstrated.

Keywords

• High-purity magnesium
• Dolomite
• Magnesium oxide
• Electrolytic process
• Copper metal cathode
• Vacuum distillation