Bioleaching of nickel from equilibrium fluid catalytic cracking catalysts

This study investigates the possibility of reusing metal-contaminated equilibrium fluid catalytic cracking (FCC) catalyst after bioleaching. Leaching with Aspergillus niger culture was found to be more effective in the mobilization of nickel from the catalyst particles compared to chemical leaching with citric acid. Bioleaching achieved 32% nickel removal whereas chemical leaching achieved only 21% nickel removal from catalyst particles. The enhanced nickel removal from the catalysts in the presence of A. niger culture was attributed to the biosorption ability of the fungal mycelium and to the higher local concentration of citric acid on the catalyst surface. It was found that 9% of solubilized nickel in the liquid medium was biosorbed to fungal biomass. After nickel leaching with A. niger culture, the hydrogen-to-methane molar ratio and coke yield, which are the measures of dehydrogenation reactions catalysed by nickel during cracking reactions, decreased significantly.