Study On Attachment Of Leptospirllum Ferriphilum YSK Grown On Different Energy Sources To Pyrite Surface And Surface Properties

The gram-negative bacteria Leptospirillum ferriphilum is obligate aerobic microorganism, which habits in extremely acidic (pH1.5-1.8) environment and derives energy from the oxidation of ferrous ion. In biological leaching studies, L. ferriphilum has been widely reported and is considered the major iron-oxidizing bacteria. Pyrite is the most common sulfide mineral, and is often associated with various useful components such as copper, molybdenum, gold, silver, cobalt, gallium and other noble metals. In order to discuss the mechanism of bio-leaching of pyrite and improve the efficiency of bio-leaching in industrial practice, L. ferriphilumYSK grown on different energy sources were studied in this paper to investigate their growth characteristics and effect on pyrite bio-leaching; using fluorescence real-time quantitative polymerase chain reaction (PCR) method determined the adsorption quantity on pyrite surface under different conditions; investigate the surface properties after pyrite interaction with bacteria, application of adsorption, infrared spectroscopy, contact angle measurements and surface characterization by atomic force microscopy, and these research results are the basis for revealing the micro-organism and pyrite mechanism.By drawing the growth curves of L. ferriphilum YSK grown on different energy sources (FeSO4·7H2O and pyrite), it can be known that growth cycle of L. ferriphilumYSK grown on pyrite is longer than cells grown in ferrous ion solution. Ferrous ion cultured bacteria entered into period of logarithmic phase faster and the generation time was about 22.1h; however, time of pyrite grown cells into the period of logarithmic phase was about 12 hours and the generation time was about 33.2h, which was 11 hours longer than ferrous ion cultured bacteria. Flask bio-leaching experiments showed that, pyrite bio-leaching is an acid production process with pH value decreased while redox potential was ascend in initial bio-leaching stage and a relatively high potential was benefit for leaching of pyrite. Compared with ferrous ion grown bacteria, pyrite grown L. ferriphilum YSK can adapt to bio-leaching environment earlier and the leaching effect was much higher. In latter stage, solution was accumulated with high concentration of Fe3+ and generating jarosite hindered dissolution of pyrite, which leaded to the decline of slurry potential and low leaching velocity.Application of real-time quantitative PCR to research the adsorption behavior of different energy cultured L. ferriphilumYSK on pyrite surface was proved to be feasible. Results showed that different energy sources grown L. ferriphilum can adsorb onto pyrite surface obviously and reached equilibrium between 30 minutes and 40 minutes, but adsorption quantity of pyrite grown bacteria was higher than soluble ferrous ions grown bacteria. During the attachment process, surface properties of bacteria played a vital role. Due to the changes in pH value of solution, bacterial surface had been changed, which affected the adhesion of cells to mineral surface. Therefore, pH value was identified as the most crucial factor in L. ferriphilumYSK's adsorption into the pyrite surface, and the adsorption amount was relatively high in acidic conditions. Temperature had some impact on the adsorption behavior of leaching bacteria L. ferriphilumYSK in pyrite surface and the optimum growth temperature, the maximum adsorption capacity.Surface properties of bacteria and mineral research suggested that the surface properties of different energy substrates grown L. ferriphilum YSK changed certainly, and pyrite cultured bacteria had bigger contact angle and stronger hydrophobic property than that cultivation in ferrous ion solution. Howerver, they shared a similar change trend of pyrite surface properties after conditioning with these cells. Study of outer membrane protein using transmission electron microscopy showed that solid matrix (pyrite) grown bacteria synthesized more surface protein than grown in soluble ion, which was the reason that solid matrix cultivated bacteria was more hydrophobic. Isoelectric points (IEPs) of pyrite after bacterial treatment moved towards IEPs of pure cells. The surface hydrophilicity of pyrite increased in leaching process for that the metabolization of bacteria made iron in pyrite formed into hydrophilic substances such as Fe2O3, FeOOH and Fe2(SO4)3. Images of atomic force microscopy showed that L. ferriphilum had strong corrosion ability for pyrite leaching.