Electrochemical Investigation of Molten Lanthanum-Yttrium Oxide for Selective Liquid Rare-Earth Metal Extraction

The electrochemical separation of lanthanum from yttrium as liquid metal is investigated starting from their molten mixture as sesquioxides, La2O3 and Y2O3, at temperature in excess of 2500K. Using iridium electrodes, a combination of dc and ac electrochemical methods and a thermal imaging furnace, the selectivity for liquid rare-earth metal recovery is evaluated for 6 compositions across the pseudo-binary La2O3 - Y2O3. Departure from the thermodynamic predictions based on ideal mixture for the molten rare-earth oxides and their alloy is experimentally demonstrated, with selectivity several order of magnitude different than the standard state predictions. A critical assessment of a possible model for the thermodynamic of mixing is presented to describe the non-ideal mixing behavior for the pseudo-binary La2O3 - Y2O3. The selective enrichment observed using molten rare-earth electrolysis suggests a possible new approach for direct, selective, REE separation and recovery. (C) The Author(s) 2019. Published by ECS.