Bioflotation: Bacteria-Mineral Interaction for Eco-friendly and Sustainable Mineral Processing

In the current study, the action of two bacteria capable of producing biosurfactants and oxidizing iron (Fe) and sulfur (S), namely Bacillus pumilus SKC-2 and Alicyclobacillus ferrooxydans SKC/SAA-2, was investigated with respect to their ability in possessing dual-function as either bio-collector or depressant for the development of sulfide bioflotation processes. Both bacterial strains were able to produce high amounts of biosurfactants interacted with pyrite that had an important role in their adhesion on the surface of pyrite as well as the change of pyrite surface properties. Over the course of the experiments, the pH of the solutions gradually decreased to ～3, indicating the active oxidation of pyrite minerals by bacteria. The growth of both bacterial strains resulted in the generation of biosurfactants as represented by the decrease of the surface tension of the solutions and the increase of the contact angle of the pyrite surfaces as a function of time. However, the contact angle of pyrite surfaces gradually decreased after 5 days of incubation until the experiments terminated on 30 days. Scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM-EDS) and Fourier transform Infrared (FTIR) analyses also confirmed the role of both bacterial strains in changing the pyrite surface properties to be more hydrophobic or more hydrophilic depending on the time of incubation. These results indicate that the changes of pyrite surface properties are clearly as the results of bacterial action, likely serving as both bio-collector or bio-frother and depressant that would be very applicable for flotation processes. These results increase our knowledge on the interactions in pyrite-bacteria complexes and could potentially be a very useful result with real exploitable value for those working on sulfide bioflotation processes.