Limited knowledge of the thermodynamic and transport properties of refractory materials in the liquid state remains a key challenge limiting their application. Using alternating current (AC) and direct current (DC) techniques, the electrochemical kinetics of oxygen evolution and metal deposition was investigated in a pendant droplet of molten alumina (Al 2 O 3 ) with three iridium (Ir) electrodes in a thermal imaging furnace. For the first time, the direct electrolytic decomposition of molten Al 2 O 3 to oxygen gas and aluminum ( Structural materials developed for lasers, nuclear, aerospace or materials processing are required to sustain high temperature, and therefore often rely on solid refractory materials, e.g. iridium-based superalloys exhibiting exceptional corrosion and creep resistance.

The electrochemical separation of lanthanum from yttrium as liquid metal is investigated starting from their molten mixture as sesquioxides, La 2 O 3 and Y 2 O 3 , 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 La 2 O 3-Y 2 O 3. Departure from the thermodynamic predictions based on ideal mixture for the molten rareearth 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 La 2 O 3-Y 2 O 3. The selective enrichment observed using molten rare-earth electrolysis suggests a possible new approach for direct, selective, REE separation and recovery.

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Current industrial methods used for rare earth element (REE) extraction involve: 1) ore enrichment, 2) separation of rare earth oxides (REOs), 3) chlorination or hydrofluorination, and 4) individual electrowining of REEs from a molten halide electrolyte. The complexity of REE extraction is inherited from their electronic configuration. Recently, molten oxide electrolysis (MOE) has been used to produce reactive metals directly from their oxides, e.g. titanium. As a single-step alternative to processes 3) and 4), or laboratory has investigated rare earth extraction by MOE. A key challenge is to find a molten electrolyte more stable than REOs. One possibility is to use binaries of REOs directly as a solvent. We have, therefore, developed two experimental approaches for studying molten REOs at temperatures exceeding 2200 o C. The present work reports the most recent experimental results obtained with La 2 O 3-Y 2 O 3. Those promising results demonstrate potential for operating with molten REOs and refine the underlying materials challenge for electrodes to enable metal recovery.