Electrowinning magnesium from its oxide in a melt containing neodymium chloride

A new process for the electrolytic production of magnesium from its oxide is described, based on the reaction MgO + NdCl3-->MgCl2 + NdOCl. This is followed by electrolysis of the resulting MgCl2/NdCl3/NdOCl melt using a carbon anode, the proposed electrolysis reaction being 2MgCl(2)+C+ 2NdOCl-->2Mg + CO2 + 2NdCl(3). XRD studies confirm the formation of NdOCl when MgO is fused with NdCl3. Electrolysis of the melt, using a molten tin cathode and a graphite anode, produced a gas containing chlorine, suggesting some direct electrolysis of chlorides. At 700 degrees C only chlorine was found, but at 750 degrees C and above chlorine and carbon dioxide were evolved, the chlorine:carbon dioxide ratio decreasing markedly as the current density was decreased from 3600 to 890 A m(-2). This was consistent with the measured cell voltages, which at 750 degrees C and above fell below the calculated decomposition voltage of MgCl2 at current densities of less than 1000 A m(-2). There is extensive codeposition of neodymium with the magnesium with the molten tin cathode, but when magnesium metal was equilibrated with the MgCl2/NdCl3/NdOCl melt only 0.5 wt % of neodymium entered the metal.