Bioleaching of refinery hydroprocessing Ni-Mo catalyst by heterotrophic fungi

Abstract

Spent NiMo catalyst was physically and chemically characterized, and subjected to 1-step and 2-step bioleaching processes using Aspergillus niger and Penicilium simplicissium. SEM-EDX analysis of the decoked spent catalyst revealed a change in the metal distribution within the catalyst during the decoking process. This paved a way to explain the metal leaching kinetics during bioleaching. In general, A. niger showed a higher metal leaching efficiency than P. sp. The highest Mo (87.3%) and Al (17.20%) leaching efficiencies were obtained (at the end of 43 days) from decoked grounded (<45B5m) spent catalyst whereas the highest Ni leaching efficiency (94%) was achieved from the as-received spent catalyst in 2-step bioleaching of A. niger. Fungal growth was not observed in 1-step bioleaching (for A. niger and P. sp), indicating metal toxicity to the fungal spores on direct contact with the catalyst.