Reduction of Solid Al 2 O 3 with Electrolysis of CaCl 2 -Based Melt

Abstract

Cyclic and square-wave voltammetry methods are used to investigate the mechanism of the cathode process on molybdenum in a CaCl2-CaF2 melt at 750°C. It is shown that calcium reduces on an inert cathode in the form of its solution in catholyte at potentials more positive than are required for metallic calcium formation. The presence of Al2O3 in the catholyte increases currents of calcium reduction on the forward cathodic wave at potentials more positive than are required for metallic calcium formation. A decrease in the ohmic resistance between the anode and cathode is observed to have been caused by the appearance of electronic conduction during the calcium cathodic reduction in the studied melt. A mechanism for the reduction of Al2O3 in the catholyte during electrolysis of the CaCl2-CaF2 melt, including Ca+ subions and calcium cathode formation and the secondary reduction of Al2O3, is proposed. In order to demonstrate the supposed mechanism for the Al2O3 reduction, the electrolysis tests were performed in two laboratory-scale electrolyzers with different separation type of anolyte and catholyte. The necessity of separating the anolyte and catholyte for providing stable continual electrolysis in the CaCl2-based melt is demonstrated.