Ultrasonic decoating of solid oxide cell particles for raw material recycling

Abstract

With the expansion of hydrogen production capacities, solid oxide cells (SOCs) are becoming increasingly important. SOCs are multi-layer components which contain high concentrations of critical raw materials, including rare earth elements, making recycling crucial. Most published recycling approaches to date involve either manual labor or hydrometallurgical processes where harmful residues are produced. Ultrasonic decoating is a novel method that avoids these problems. A previous study showed that with ultrasonic decoating the perovskite layers on the air side of the SOCs can be selectively separated. However, this approach can be challenging due to the orientation dependence of the ultrasonic stress on the cells in combination with their mechanical fragility. To overcome this, this study investigates the ultrasonic decoating of SOC particles instead of whole cells. For this purpose, two cells with varying air sides are mechanically crushed and sieved, whereby the crushing behavior is investigated. The coarse particles are subsequently subjected to ultrasonic stress. Overall, the perovskites are selectively comminuted, enabling an initial concentrate to be obtained by crushing alone. Subsequent ultrasonic decoating improves the purity of both products, thereby increasing the recovery of the perovskites from the examined cells to 85% and 98%, respectively.