2025 Vols Leaching of Solid Oxide Electrolyzer Cells

Solid oxide electrolyzer cells (SOECs) contain many critical and/or strategic elements such as Co, Mn, Ni, Sr and rare earth elements (Ce, Gd, La). To achieve a circular economy, an efficient recycling process needs to be developed. For electrolyte-supported cells, no mechanical separation processes come into question because of their brittle construction. Hence, a hydro-metallurgical approach was chosen in this work, starting with a leaching process of grinded membrane electrode assemblies from spent SOECs. Different leaching reagents (H2SO4, HNO3, HCl, citric acid, ammonia solution) with and without additives (Na2SO3, H2O2), which potentially support the reduction and thus the dissolution of higher oxides present, were tested. The best conditions were further investigated, resulting in an optimal leaching process using 4.5 M hydrochloric acid without the addition of any reducing agent at 60 °C for 2.5 h. The elements of the electrolyte (Hf, Zr, Y) were not leached under these conditions. Leaching efficiencies over 89% could be reached for all leached elements except Gd (leaching efficiency of at least 81%). Hence, an electrolyte separation is possible through this leaching process and both material flows (electrolyte residue and leaching solution) can be handled separately in further recycling steps.