Highly efficient recovery of total components from spent hydroprocessing catalysts (HPCs) with minimal CO₂ & SO₂...

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 H₂SO₄ 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_equilibrium 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_equilibrium of 5.7. The CoSO₄ and NiO products were characterized by XRD, and there are no impurity peaks. We also did DFT calculations, which show the binding energies of Al³⁺ with extractants are in the order of Al³⁺-P204 > Al³⁺-P507 > Al³⁺-Cyanex 272, and Cyanex 272 exhibits the highest difference in binding energies of Ni²⁺ and Co²⁺. The process of Ni and Co recovery from the alkaline leaching residue of spent HPCs was proposed. Only 8 t CO₂ and 120 kg SO₂ 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.