Adhesion of Paenibacillus polymyxa on chalcopyrite and pyrite: Surface thermodynamics and extended DLVO theory

The adhesion behaviour of Paenibacillus polymyxa bacteria on pyrite and chalcopyrite is examined by the surface thermodynamics and the extended DLVO theory approaches. In addition, the bacteria are adapted to pyrite and chalcopyrite minerals, and the adhesion behaviour of these bacteria is also investigated. The significance of acid-base interactions in adhesion is assessed. The essential parameters needed for the calculations of interaction energy between bacteria and mineral are experimentally determined. The results illustrate that the bacterial surfaces are more energetic than the mineral surfaces and the bacteria acquired acid-base surface energy component during their adaptation to mineral. The extended DLVO approach is found to be more effective in predicting the adhesion behaviour than the expectations from thermodynamic approach. The thermodynamic approach yields no bacterial adhesion on minerals and this discrepancy is the result of inadequate description of electrostatic interactions. The adhesion predictions by the DLVO approach are able to partially explain the bioflotation results of pyrite and chalcopyrite. Extended DLVO shows that on account of high bacterial surface energy, their aggregation is not feasible. But due to the hydrophobicity of pyrite and chalcopyrite, their aggregation is possible.