A comparative study of the extraction of metals from the spent fluid catalytic cracking catalyst using chemical leaching and bioleaching by Aspergillus niger

The present study evaluates biopotential of Aspergillus niger and chemical potency of strong organic and inorganic acids to leach out Al, Fe, Ti, Ni, V from spent fluid catalytic cracking catalyst (SFCCC). One-step bioleaching (OSBp) and spent medium bioleaching (SMB) of metals at 1%, 3% and 5% pulp densities by Aspergillus niger was investigated. Leaching efficiency was found to be maximum at 1% pulp density and decreased as the pulp density increased to 5%, this is perhaps due to the inhibitory effect of some metals existing in SFCCC. The maximum amount of Al, Fe, Ti, Ni, and V leached from SFCCC are 1388 mg/L, 28 mg/L, 6 mg/L, 2 mg/L and 8 mg/L of leaching medium respectively. Biologically produced leaching agents other than citric, gluconic and oxalic acids produced by Aspergillus niger solely contributed to 50%, 32%, and 42% of Al, Ti and V leaching efficiencies respectively. The acidic pH in OSBp suggests acidolysis as the leading leaching mechanism. The citric acid is the chief leaching agent produced by Aspergillus niger in the presence of SFCCC while gluconic acid dominated in SMB (in the absence of SFCCC). OSBp yielded higher leaching efficiencies of all the metals compared to SMB. OSBp dominated Al, Ti, and V leaching compared to all organic and inorganic acid leaching. While OSBp of Fe was comparable to inorganic acid leaching and oxalic acid leaching is suggested for Ni leaching. The competitive Al, Ti, V and Fe leaching and being environmentally friendly, OSBp of metals from SFCCC by Aspergillus niger is recommended.