Development of Numerical Analysis Model for New Magnesium Electrolysis Process Using COMSOL

Abstract

Magnesium (Mg) has good physical properties including light weight, excellent specific strength and high stiffness, and Mg is used in many fields. But current production methods of Mg have disadvantages, such as the generation of sulfur oxide and chlorine gas. In this situation, The Korea Institute of Geoscience and Mineral Resources (KIGAM) developed a Molten Salt Electrolysis Using Liquid Metal Cathode (MSELMC) method to produce high-purity magnesium. The MSE-LMC method can obtain 99.998-99.999% highpurity magnesium by the electrolysis of MgO dissolved in (MgF2)-LiF molten salt at 1053-1083 K, and by vacuum distilling an alloy generated by reacting with a metallic liquid cathode at 1200-1300 K. This study developed a numerical analysis model using COMSOL Multiphysics electrodeposition module to optimize the design of the electrolysis process. The model temperature was 1053K and molten salt was 54MgF2-46LiF with a 0.6wt% MgO system. 10A constant current was applied at the anode. This model uses the Butler-Volmer equation and the Nernst equation for the electric reaction. The Stokes-Einstein equation and Nernst-Einstein relation were used to calculate the diffusivity and electric mobility of salts. Unlike the experiment, in this model chlorine gas was generated. However, this model satisfied Faraday’s law. Therefore we define a new parameter using electric flux and voltage to conduct a quantitative evaluation according to the electrode shape, and compared that parameter by the changing angle of the anode.