Utilization of electrochemical impedance spectroscopy for monitoring pyrite oxidation in the presence and absence of Acidithiobacillus ferrooxidans

In this work, the electrochemical behavior of a pyrite–carbon paste electrode in the presence and absence of Acidithiobacillus ferrooxidans was investigated by electrochemical impedance spectroscopy (EIS) in conjunction with X-ray photoelectron spectroscopy (XPS). The EIS responses varied over time in both inoculated and sterile solution, suggesting the change of kinetic processes at the pyrite-solution interface during the leaching process. The pyrite oxidation rate was initially controlled by iron moiety dissolution in both of the systems with and without bacteria, with the formation of intermediate products such as elemental sulfur and polysulfide at the surface of pyrite. In the presence of bacteria, these intermediate products could further be oxidized to SO 4 2 - . However, the oxidation of S in the sterile solution was undetectable by EIS measurement. These results were also confirmed by XPS measurements, which showed that the presence of microorganisms was able to remove the elemental sulfur from pyrite surface.