Effect of oxide and fluoride addition on electrolytic preparation of Mg-La alloy in chloride molten salt

Mg-La alloys were prepared by constant voltage electrolysis in the molten salt system of MgCl2-LaCl3-KCl at 750 °C, with a graphite crucible as the anode and a tungsten rod as the cathode. The effect of oxide and fluoride addition on the electrolysis was investigated comprehensively. X-ray diffraction (XRD) was used to characterize some of the Mg-La alloy products and the sludges. As the content of MgO or La2O3 in the electrolyte increased, both the current efficiency and the mass of alloy product decreased, indicating that both MgO and La2O3 may take part in the reactions in the electrolyte. When the same mass of the oxide was added, compared with La2O3, MgO had a more pronounced effect on both the current efficiency and the mass of alloy product. XRD studies confirmed the formation of LaOCl when MgO or La2O3 was added into the electrolyte. The formation of LaOCl sludge would be the main reason for the negative effect of the oxide addition on both the current efficiency and the mass of alloy. In the electrolytic system, the addition of CaF2 was not helpful to suppress the negative effect of MgO on the electrolysis, probably due to the complex reactions of the La compounds in the electrolyte.