Study Of Effect Of Eps On Adhesion Of A.ferrooxidans On Chalcopyrite And Pyrite Mineral Surface

The interaction between mineral and microorganism, which has been one of the latest field in study of bioleaching mechanism, involves a series of the biochemistry, surface chemical and electrochemical processes. Bacteria are entrapped in the extracellular polymeric substances (EPS) layer of their own, which mediates the contact between the bacterial cell and the sulfidic energy source. EPS plays a pivotal role in organic film formation and bacterium-substratum interaction. The study on effect of EPS of Acidithiobacillus.ferrooxidans is very important to explain the theory of contact-leaching mechanism. Now, "EPS-contact-leaching mechanism" is extensively accepted by researchers. However, the research of EPS-related leaching mechanism has been basically focused on pyrite so far, and the exact role of bacterial extracellular polymers (EPS) in the process of mineral extraction has still been unknown, while the study of EPS on chalcopyrite remained in observation phase. The research on the relationship of ferrous and ferric irons in EPS and the passivation of minerals is fewly.Extracellular polymeric substances (EPS) were extracted from A.ferrooxidans through sonication method associated with centrifugation, which was evaluated with 2-keto-3-deoxyoctonic acid (KDO) as the indicator of EPS by spectrophotometry tentatively. Then the effect of EPS of A.ferrooxidans on the adhesion on chalcopyrite and pyrite surface was studied through a series of comparative experiments. The untreated cells and EPS-free cells of A.ferrooxidans were mixed with EPS suspension, Fe+ or Fe3+ respectively. The planktonic cells were monitored in 2h during bioleaching. The results indicated that the presence of EPS on the cell is an important factor for the attachment to chalcopyrite and pyrite. A decrease of attachment of A.ferrooxidans to minerals was produced by the deficiency of EPS, which can recover mostly when the EPS was re-added into the EPS-free cells. The restore extent is more obvious in pyrite than chalcopyrite. The extent of cell adhesion to chalcopyrite increased when EPS and Fe3+ added, and decreased when the Fe2+ added, which imply the electrostatic interactions maybe play a main role in initial adhesion between bacteria and minerals and it is a drive force for bacteria to produce EPS probably as a result of regaining their attachment ability to copper sulphides.