An Optimized Integrated Process for the Bioleaching of a Spent Refinery Processing Catalysts

Bioleaching of spent refinery processing catalysts using adapted indigenous strains of Acidithiobacillus ferrooxidans to recover Ni and Mo, and the separation of Ni from bioleaching liquor using iron magnetic nanoparticles were optimized in this study. Bioleaching optimization was performed using central composite design (CCD) method to optimize temperature (32 to 38oC), initial pH 1.5 to 2), particle size (-30 to -190μm sieve fraction) and pulp density (0.1 to 0.5%). The maximum values for Mo and Ni extraction were determined to be 62.72 and 92.34%, respectively, at 34 ºC, -90.38μm sieve fraction, 0.22 % pulp density and initial pH of 1.8 under controlled pH condition. The results of bioleaching study suggest the shaking bioreactor as a suitable tool to optimize pulp density at low values for scale up purposes. The optimum pH value for Ni adsorption from synthetically made Ni solutions was found to be 8. The Ni adsorption increased with increasing temperature and the mass of the adsorbent. The percentage of Ni adsorption from a bioleaching liquor contained 30 ppm Ni and 5g/l magnetic nanoparticles was determined to be 97% after 1 hour at 34oC and pH 8. An integrated process for bioleaching of Ni and Mo from spent catalysts and adsorption of Ni using magnetic nanoparticles has been proposed in this study.