| This paper mainly focuses on the investigation on the interactions between Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans or Leptospirillum ferrooxidans and chalcopyrite. The topographically and chemically various surfaces of these bacteria and mineral were detected and analysed. The interactions between bacteria with or without EPS and mineral were measured by Atomic Force Microscope (AFM) and calculated by Extended-DLVO theory. The results disclosed the mechanism of bacteria adhering onto the surface of chalcopyrite. Furthermore, the effects of the initial absorption forces, which were applied by bacteria on the chalcopyrite, on the attachment and bioleaching efficiency were discussed by the bioleaching data obtained, such as the quantities of bacteria adhering on the mineral within2hours, thereby developing the interacting mechanism for bacteria-mineral interfacial system.The measurements for the surface characteristics demonstrated the following points. First, the chalcopyrite has high hydrophobicity and is negatively charged in the iron-free9K medium while the three bacteria mentioned above all exhibit weak hydrophobicability, positively charged. In addition, when energy source is different, the surface properties of bacteria vary in terms of hydrophobicity, electric quantity and smoothness. More importantly, the absence of EPS results in obvious changes in the bacterial surface; therefore, the bacterial surface properties are heavily associated with EPS.Some findings were also obtained by using the Extended-DLVO theory. The total free energy for bacteria and chalcopyrite is always negative regardless of whether the EPS is removed or not. This behavior indicates that the adhesion of microbe with or without EPS on the mineral will proceed. The Acidithiobacillus ferrooxidans-chalcopyrite Acidithiobacillus thiooxidans-chalcopyrite and Leptospirillum ferrooxidans-chalcopyrite interfacial free energies are-5.81mJ/m2,-5.22mJ/m2and-7.80mJ/m, respectively and the counterparts are-1.94mJ/m2,-1.22mJ/m2and-3.06mJ/m2while in the absence of EPS. The calculated results through employing the Extended-DLVO theory are verified by the experimental data measured by AFM, which illustrates that the Extended-DLVO theory is capable of predicting the initial attachment behavior of microbe. The AFM measurements indicate that the initial adhesion lies on the surface properties of microbe, i.e., the electric quantity, the hydrophobicability and the roughness. Besides, the large decrease of attractive force between bacteria and mineral delivers that the EPS is crucial to the mediation of bacteria onto the surface of mineral.The research results of the adhesion and the bioleaching efficiency indicate that in the first2hours the amount of bacteria initially attaching to the chalcopyrite was propotional to the initial adhesion force and so was the irrecoverable attaching amount to the bioleaching efficiency. After21-day bioleaching, most Acidithiobacillus ferrooxidans adhered to the mineral surface, with the highest bioleaching efficiency and the strongest corrosion to the mineral while the Acidithiobacillus thiooxidans behaved oppositely. However, it cannot be concluded that the permanent adhesion of bacterial onto mineral was controlled by the initial attractive force because the adhering amount of each bacterium changed after21days. Consequently, the initial attractive force between bacteria and mineral determined the initial absorption rate while the permanent adhesion of bacteria on mineral rested on bacteria themselves (i.e., the bacterial preference to energy source). And the permanent adhesion of bacteria on mineral was relevant to the bioleaching efficiency. Moreover, EPS has an important role in the adhesion amount and efficiency of bacteria. The absence of EPS, for example, reduced the attaching amount of microbe greatly. |
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