Generation behavior of extracellular polymeric substances and its correlation with extraction efficiency of valuable metals and change of process parameters during bioleaching of spent petroleum catalyst

The vital functions of extracellular polymeric substances (EPS) have been well recognized in bioleaching of sulfide ores. However, no report is available about the role of EPS in bioleaching of spent catalyst. To completely and deeply understand the functions of EPS in bioleaching of spent catalyst, the generation behavior of EPS at various pulp densities during bioleaching was characterized by three-dimensional excitation-emission matrix (3DEEM), and its relevance with bioleaching performance and process parameters were analyzed using mathematical means. The results showed that the EPS contain humus-like substances as main component (>70%) and protein-like substances as minor component (<30%). Both total EPS and humus-like substances mainly keep growing over the whole duration of bioleaching at low pulp density of 5.0% or lower; whereas total EPS and humus-like fraction keep declining at high pulp density of 7.5% or higher. Among the total EPS and its components, humus-like substances only have a positive significant correlation with bioleaching efficiencies of both Co and Mo and affect bioleaching process more greatly due to greater correlation coefficient. Biofilm appears at the spent catalyst surface under 2.5% of pulp density mediated by EPS while no biofilm occurs at 10% of pulp density due to shortage of EPS, accounting for the great difference in bioleaching efficiencies between high and low pulp densities which are 48.3% for Mo and 50.0% for Co at 10% of pulp density as well as 75.9% for Mo and 78.8% for Co at 2.5% of pulp density, respectively.