Highly efficient recovery of total components from spent hydroprocessing catalysts (HPCs) with minimal CO & SO emissions.

It is imperative to recover the valuable components of spent HPCs. We have proposed a hydrometallurgical process and recovered 99.9% of V, 99.9% of Mo, and 95% of Al in our previous work. In this study, we focused on the Co and Ni recovery from the alkaline leaching residue of spent HPCs. We characterized the leaching residue by SEM-EDS, XPS, TGA, Laser Particle Size Analyzer, and ICP-OES. The Ni and Co leaching rates both reached around 95% with 2.0 mol/L HSO at 120 °C for 75 min. The impurity of Al in the leachate was removed via solvent extraction with 30% P204 at A/O of 1 and pH of 2.0. The Co and Ni in the raffinate was separated via two stages of counter-current extraction with 20% Cyanex 272 at A/O of 1 and pH of 5.7. The CoSO and NiO products were characterized by XRD, and there are no impurity peaks. We also did DFT calculations, which show the binding energies of Al with extractants are in the order of Al-P204 > Al-P507 > Al-Cyanex 272, and Cyanex 272 exhibits the highest difference in binding energies of Ni and Co. The process of Ni and Co recovery from the alkaline leaching residue of spent HPCs was proposed. Only 8 t CO and 120 kg SO emissions were generated during all the component recovery per ton of the spent HPCs using our proposed process. They are much less than pyro-hydrometallurgical processes.