Effect of pulp density on the bioleaching of metals from petroleum refinery spent catalyst.

Bioleaching is one of the well-known methods of metal recovery with Environmental benefits. This process has been extensively used for combating improper waste management issues along with metal reclamation. The aim of this study is to bioleach spent petroleum refinery catalyst at variant pulp densities (PD) (5, 10 and 15%) using microorganisms in acidic pH (1.5-1.6) and mesophilic temperature (30-35 °C). The study includes leaching yields of metals like nickel, molybdenum, copper and aluminum. The three bioleaching experiments with different pulp densities yielded a maximum of more than 90% nickel, 73% copper, 87% molybdenum and 24% aluminum. The results are validated 5, 10, and 15% pulp density and the result is validated with pH, Redox potential, microbial population, sulphate concentration and ferrous iron, concentration. The time saving due to faster nickel dissolution using iron and sulphur oxidizing microorganisms would be economical for the bioleaching process.