Applicability of the Electrochemical Oxygen Sensor for In-Situ Evaluation of MgO Solubility in the MgF2–LiF Molten Salt Electrolysis System

Abstract

<jats:p>The measurement and evaluation of MgO solubility in the molten fluoride system is of significant importance in the recently proposed magnesium electrolysis reduction process. In the present study, an in-situ quantitative method of evaluating the concentration of dissolved MgO in molten fluoride is proposed. The MgO solubility in the 32.8MgF2–67.2LiF system was measured at 1083 and 1123 K using a combustion analyzer. MgO saturation was achieved in under 2 h, and higher solubilities were observed as the temperature increased. Thermodynamic assessment was carried out in order to ascertain the applicability of the electrochemical oxygen sensor, which indicated that the logarithm of oxygen concentration in molten fluoride has a linear relationship with the measured electromotive force (EMF) potential. The EMF potential of the controlled MgO concentration was measured, and a straight calibration line was obtained, describing the relationship between the measured EMF and the logarithm of MgO concentration. From the obtained calibration line, MgO concentration in the 0.4 wt% MgO was calculated. The calculated value was 0.44 wt% that was in excellent accordance with the controlled MgO concentration of 0.4 wt%, verifying the practical applicability of electrochemical oxygen for the in-situ monitoring and evaluation of MgO solubility in the electrolysis magnesium reduction process.</jats:p>

Scale-Up Study of Molten Salt Electrolysis using Cu or Ag Cathode and Vacuum Distillation for the Production of High-Purity Mg Metal from MgO

“…The mass percentage of MgO used in the MgF 2 -LiF molten salt was 6.99-14.9 mass%, as shown in Table 1. The physicochemical properties of the MgO-MgF 2 -LiF system were investigated previously by the authors [22,23]. The solubility of MgO in MgF 2 -LiF molten salt at 1083 K was 0.56 mass% [22].…”

“…The physicochemical properties of the MgO-MgF 2 -LiF system were investigated previously by the authors [22,23]. The solubility of MgO in MgF 2 -LiF molten salt at 1083 K was 0.56 mass% [22]. As a result, the MgO feed used in the MgF 2 -LiF molten salt was saturated.…”

Magnesium production by molten salt electrolysis with liquid tin cathode and multiple effect distillation

“…There are three important challenges with this electrolyte and process. First, MgO solubility is low, around 0.5–0.8 wt% at the 1,083–1123 K operating temperature range ( Kim et al, 2020 ), compared with 8–15 wt% for alumina in cryolite ( Zhang et al, 2003 ), such that maximum current density is likely low. Second, Ca and other electropositive raw material impurities accumulate in the electrolyte bath with no proposal for removing them.…”