Electrowinning magnesium metal from MgCl2-NdOCl melt using solid-oxide oxygen-ion-conducting membrane technology

Abstract

An electrolytic process for extraction of magnesium metal from its oxide is demonstrated. The process is based on the chemical system MgCl2-NdCl3-MgO. Since it has previously been shown that NdCl3 and MgO react to form NdOCl, this study has employed a MgCl2-NdOCl melt. Two experiments are described in detail. In the first, liquid magnesium metal is produced from a MgCl2-NdOCl melt at 700°C with a graphite cathode and graphite anode. In the second, liquid magnesium metal is produced from melt of the same composition at 690°C with a graphite cathode and porous nickel-yttriastabilized-zirconia cermet anode. The cermet anode is separated from the melt by an oxygen-ion-conducting yttria-stabilized zirconia membrane, which should ensure that water vapor is produced at the anode, rather than CO, CO2, or Cl2. Magnesium metal globules are observed in the frozen melt in the vicinity of the cathode after completion of each experiment, and the metal composition is determined using electron probe microanalysis to be greater than 99 weight percent magnesium.