Recovery of Ytterbium from End-of-Life Yb-Silicate Environmental Barrier Coatings—A Conceptual Study

The enormously increasing demand for rare earth elements (REE), due to their wide high tech-application areas and their limited and unproportioned reserves across the globe, induced the utilization of secondary resources to provide more robust REE supply chains. In several studies, hydrometallurgical/pyrometallurgical routes have been employed to recover REE’s from secondary resources such as industrial residues, end-of-life magnets, batteries, and catalysts. In this pioneer study, we investigate the feasibility to use end-of-life RE-silicate environmental barrier coatings (EBCs) of turbine engine components as a secondary Yb resource. For this purpose, state-of-the-art EBC materials, ytterbium monosilicate (Yb2SiO5), and ytterbium disilicate (Yb2Si2O7), were exposed to a fictional aeroengine scenario involving in service contamination by airborne mineral dusts, commonly referred to as CMAS corrosion. CMAS-corroded Yb-silicate pellets were exposed to sulfuric acid leaching. Phase and microstructural analyses were conducted on starting materials and leaching residues, in a comparative manner, to explain the leaching mechanism. Leaching solutions were analyzed by ICP-OES indicating a very promising preliminary leaching efficiency and selectivity for Yb2SiO5, whereas Yb2Si2O7 displayed a very low leachability. Further prospects were suggested to enhance process efficiency and implications on repair/overhaul end-of-life Yb-silicate EBCs are discussed.