Comprehensive recovery of metals in spent Ni–Mo/γ–Al2O3 hydrofining catalyst

This study proposes a technical route toward the comprehensive recovery of valuable metals from spent Ni–Mo/γ–Al2O3 hydrofining catalysts, which were employed to remove S, N, and O elements and metal–organic compounds from crude oil and petroleum products. Additionally, the process conditions are optimized, thereby providing good economic and environmental benefits. Sodium carbonate-assisted roasting of the spent catalyst effectively improves the secondary pollution and leaching effect. After Al, Mo, and Ni elements in the spent catalyst were converted into NaAlO2, Na2MoO4, and NiO, more than 99.8% of the metal ions entered the leaching solution, minimizing the loss. A synergistic extraction system using the di-(2-ethylhexyl)phosphoric acid (P204) and tri-n-octylamine (TOA) extractants were employed to extract molybdenum from the clarified acid leaching solution, and more than 97.5% of Mo was separated from Al and Ni. The MoO3 product was obtained by stripping with ammonia, followed by evaporating, and roasting. Furthermore, by adding ammonia to adjust the pH value of the molybdenum extraction solution to 4, 98.0% of the Al was extracted by P204. Subsequently, a Na2S precipitation agent was employed to convert Ni2+ into Ni(OH)S with a precipitation efficiency of 97.9%. Ultimately, the comprehensive recovery efficiencies of Al, Mo and Ni were 97.5%, 95.5%, and 90.9%, respectively, thereby realizing the comprehensive recovery of metals in the spent catalyst.