Leaching of nickel and vanadium from the spent fluid catalytic cracking catalyst by reconnoitering the potential of Aspergillus niger associating with chemical leaching

The current study evaluates the bio-potential of Aspergillus niger to leach out Nickel, Vanadium from spent fluid catalytic cracking catalyst (SFCCC) and is compared with chemical leaching by organic and inorganic acids. Bioleaching efficiency of Nickel at 1, 3 and 5% pulp densities were 16.5, 13 and 8% respectively. The percentage Vanadium leaching at same pulp densities was found to be 55, 37 and 27% respectively. Leaching efficiency decreased with increase in pulp density which may be due to the toxic effects of metals present in the SFCCC. The spent medium bioleaching resulted in 4.7% Nickel and 18% Vanadium leaching, which is far less than one step bioleaching (OSB). This may be attributed to high citric acid production (100 mM) in OSB which perhaps be triggered by key metals of SFCCC. The acidic pH of the medium suggests acidolysis as the principal leaching mechanism. Oxalic acid was found to be the dominant leaching agent for Nickel, while for Vanadium, OSB took over. The leaching of Nickel was found to be only due to predominant acids produced by Aspergillus niger. Biogenically produced leaching agents apart from predominant acids accounted for 40% of Vanadium leaching. It is evident that removal of volatile carbonaceous material from SFCCC improved Nickel leaching by three folds.