Electrolytic magnesium production and its hydrodynamics by using an Mg–Pb alloy cathode

Abstract

Physical interaction of magnesium and chlorine was minimized by collecting magnesium in a molten Pb cathode at the bottom of the electrolyte and placing anode at the top where the chlorine gas was evolved. Thus the magnesium losses associated with the formation of suspending droplets and fine magnesium particles were eliminated and current losses were mainly due to the recombination reaction of dissolved magnesium and chlorine. Current yield changed by changing the tip angle of the conical anode. It was due to the fact that the amount of chlorine diffused into the melt was proportional to the chlorine bubble area in contact with the electrolyte per unit time. Therefore, correlation of experimentally measured electrolysis data requires the knowledge of the size and the total residence time of the chlorine bubbles in inter-electrode region. Average diameter and total residence time of the bubbles were determined for anode tip angles that were used in electrolysis experiments by a room temperature hydrodynamic model. Amount of magnesium that was lost as a result of reaction with the dissolved chlorine was calculated by assuming the dissolution of chlorine gas as the rate determining step. Theoretical magnesium losses calculated by using the data from the room temperature hydrodynamic model were in good agreement with the electrolysis experiments. Furthermore, calculated cell voltages that use the sum of theoretical decomposition potential and IR drop obtained from the composite resistance due to the electrolyte and chlorine bubbles were also in agreement with the experimental data.