Journal of Alloys and Compounds 465 (2008) 255–260 Electrolytic magnesium production and its hydrodynamics by using an Mg–Pb alloy cathode G¨ okhan Demirci, ˙ Ishak Karakaya ∗ Department of Metallurgical and Materials Engineering, Middle East Technical University, ˙ In¨ on¨ u Bulvari, 06531 Ankara, Turkey Received 21 March 2007; received in revised form 10 October 2007; accepted 13 October 2007 Available online 24 October 2007 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. © 2007 Elsevier B.V. All rights reserved. Keywords: Magnesium; Magnesium alloy; Molten salt; Magnesium chloride; Hydrodynamics 1. Introduction The main reason of current losses in electrolytic magnesium production is the reaction between chlorine and magnesium pro- duced at the anode and the cathode, respectively. The interaction between the electrode products in their elemental state is highly dependent on cell geometry and could be decreased by increas- ing inter-electrode distance or employing a separation wall as in early cell designs [1]. Larger inter-electrode distance, on the other hand, increases the cell voltage and energy consumption. The residence time of the magnesium metal and chlorine gas in the inter-electrode region was shortened by increased electrolyte velocity due to lifting action of chlorine gas at smaller inter- electrode distances in recent industrial magnesium cell designs [2,3]. However the drastic decrease in energy consumption that ∗ Corresponding author. Tel.: +90 312 210 2533; fax: +90 312 210 1330. E-mail address: kkaya@metu.edu.tr ( ˙ I. Karakaya). has to be achieved to have a considerable decrease in produc- tion costs has not been experienced with newer cell designs yet. The recombination reaction still remains as the main reason for current inefficiency. It was reported that the dissolution of magnesium into the melt was the decisive factor that controls the back reaction [4,5] as a result of the calculations based on systems that might involve fine magnesium particles. This assumption is not quite in accord with higher current efficiencies obtained from cell designs involving fast removal of chlorine from electrolysis cells [6,7]. More accurate results could be obtained with a cell design where the fine magnesium particle formation was elim- inated. Moreover the bubble characteristics that were obtained for the actual cell design and electrolysis conditions, as in the case of present study, could help to increase the viability of the assessments. The physical interaction between the chlorine gas and mag- nesium metal was minimized with the present cell design [8,9]. Magnesium was collected as an Mg–Pb alloy at the bottom of 0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.10.070