Enhancing Co, Mo and Al leaching from spent HDS catalysts during scale-up process based on fluid dynamic and leaching mechanism

Large amounts of Mo, Co and Al are contained in spent hydrodesulfurization (HDS) catalysts, and recovering these valuable metals from spent catalysts achieves sustainable utilization of resources and promotes environmental protection. However, the leaching efficiency of valuable metal often experiences a sharp decline during scale-up. In this study, leaching experiments and fluid dynamics were used to jointly investigate the major factors and regulation mechanisms affecting leaching efficiency during the scale-up process. Optimization of flow field conditions is guided by Computational Fluid Dynamics (CFD) simulation. including different paddle types, agitation speed and particle size. After controlling flow field assisted with CFD simulation, about 20% of the sulfuric acid solution was saved and 99.7% of Mo, 98.2% of Co and 83.7% of Al were successfully recovered. Additionally, the leaching mechanisms of these metals in H2SO4 were systematically studied. The findings indicated that the leaching kinetics of Co, Mo and Al are governed by diffusion-controlled model, consistent with the shrinking core model. Correlation coefficients and activation energy analyses further demonstrated that the leaching process is diffusion-controlled, highlighting the importance of flow field mixing in scaling up the acidmediated recovery of Mo, Co and Al from spent HDS catalysts. The fluid dynamic and leaching mechanism study provides valuable insights for large-scale recovery of valuable metals.