Bioleaching of spent fluid catalytic cracking catalyst using Aspergillus niger

The use of the fungus Aspergillus niger for the bioleaching of heavy metals from spent catalyst was investigated, with fluid catalytic cracking (FCC) catalyst as a model. Bioleaching was examined in batch cultures with the spent catalysts at various pulp densities (1-12%). Chemical leaching was also performed using mineral acids (sulphuric and nitric acids) and organic acids (citric, oxalic and gluconic acids), as well as a mixture of organic acids at the same concentrations as that biogenically produced. It was shown that bioleaching realised higher metal extraction than chemical leaching, with A. niger mobilizing Ni (9%), Fe (23%), Al (30%), V (36%) and Sb (64%) at 1% pulp density. Extraction efficiency generally decreased with increased pulp density. Compared with abiotic controls, bioleaching gave rise to higher metal extractions than leaching using fresh medium and cell-free spent medium. pH decreased during bioleaching, but remained relatively constant in both leaching using fresh medium and cell-free spent medium, thus indicating that the fungus played a role in effecting metal extraction from the spent catalyst.