Study on Pretreatment and Leaching Behaviors of Spent Fluid Catalytic Cracking Catalysts

The reclamation of exhausted Fluid Catalytic Cracking (FCC) catalysts has attracted considerable interest. However, the leaching rates of valuable metals in waste can be influenced by the pretreatment and calcination process. This study focuses on investigating the impact of pretreatment temperature on the metal-leaching process of spent FCC catalysts. After calcination at 1200 °C, the Al₂O₃ carrier transformed from γ-Al₂O₃ to α-Al₂O₃ with a denser structure. Subsequently, the valuable metals react with the carrier to form regular acid salts, which are averse to the leaching process. While the pretreatment roasting of spent FCC catalysts at 600 °C could not only remove the surface impurities effectively but also keep the original γ-Al₂O₃ structure, promoting the leaching process. Finally, the kinetic model is studied with the aim of achieving the high-efficiency leaching of Ni in spent FCC catalysts. The leaching kinetics model of Ni accords with the ash diffusion model, and the reaction activation energy is 53.05 kJ/mol, in the temperature range of 60–90 °C, sulfuric acid concentration of 2 mol/L, particle size of less than 200 mesh (75μm). Specifically, for spent FCC catalysts, pretreatment at high temperatures is not conducive to subsequent leaching, while pretreatment at low temperatures is conducive to subsequent leaching of valuable metals.