Direct electrolytic reduction of solid alumina using molten calcium chloride-alkali chloride electrolytes

Abstract

Solid alumina was reduced by electro-deoxidation to aluminium metal containing 1.8 and 5.4 at% Ca in molten CaCl2–NaCl and CaCl2–LiCl electrolytes at 900 °C, respectively. The potential-pO2− diagrams for the Al–O–M–Cl (M = Na or Li, or/and Ca) system were constructed to predict equilibrium phase relationships in the electrolytes at 700 and 900 °C. It was found that calcium aluminates were formed as the main intermediate reaction products and were subsequently reduced to form the Al-rich Al–Ca alloys during electro-deoxidation. Calcium and/or lithium, at reduced activities, were created at the cathode especially at 700 °C at the same time as the ionization of the oxygen from the cathode, which resulted in Al2Ca formation. The experimental results were consistent with the thermodynamic predictions.