Mechanical pre-treatment of waste solid oxide cell stacks

Clean hydrogen is recognized as one of the key energy vectors for the future, with electrolysis including high-temperature solid oxide cells (SOC) being the most prominent technology to meet the anticipated demand. The unique composition of SOC stacks and the growing demand for clean hydrogen create a strong incentive for securing raw material supply. Recycling can help to alleviate this pressure. This study investigated robust pre-treatment processes, such as crushing and magnetic separation, on end-of-life (EOL) planar SOC stacks to separate larger steel components and sealing material from cell/electrode material. The characterization of produced fractions revealed that the process separated efficiently large steal particles, while electrode materials were enriched from the seal material. Magnetic separation purified the fine active material fraction composed of electrode material to a purity of above 90 % and sealing material to over 95 % purity. The main unwanted elements in the produced electrode fraction from other components were Ba, Fe, Mg and Si. Additionally, hydrometallurgical processing was considered on a concept level. Although the material contains nearly inert (Zr, Y, Gd, Ce) compounds as well as readily leachable ones (La, Co, Sr), it also contains compounds with reactivity differences (Ni, Fe). It is likely that Fe would be introduced into leachates alongside Ni during leaching. Further research should be pursued to gain a more comprehensive understanding on how minor components are leached as part of a comprehensive processing studies.