Bacterial Diversity Analysis Of Middle-temperature Bioleaching Environment And Bioleaching Of Marmatite Using Moderately Thermophilic Bacteria

In the paper, Bacterial biodiversities of three moderately thermophilic bioleaching micro floras grown at 50℃on media with pyrite, chalcopyrite, and pure ferrous iron supplemented with sulfur as energy sources were investigated respectively by PCR-RFLP analysis. The structural differences of microfloras enriched by different energy sources were compared. After that, these moderately thermophilic bacteria were inoculated into an industrial simulating bioleaching column which was filled with chalcopyrite. During the running of the bioreactor, microflora structures of different periods in it were investigated. Finally, the process of bioleaching marmatite using moderately thermophilic bacteria has been studied in this research.The species identified from the flasks during bioleaching of pyrite, pure ferrous iron supplemented with sulfur, and chalcopyrite were closely related to Acidithiobacillus caldus, Sulfobacillus thermotolerans, Sulfobacillus thermosulfidooxidans, Leptospirillum ferriphilum, two uncultured forest soil bacterium clones and one uncultured proteobacterium clone. Among these bacteria, Acidithiobacillus caldus, Sulfobacillus thermotolerans and Leptospirillum ferriphilum were the dominant bacterial species. L. ferriphilum was the most dominant species in microfloras enriched in media with pyrite and ferrous iron supplemented with sulfur as energy sources, the abundance were 53．8% and 45．9% respectively. In the culture with chalcopyrite as energy sources, S. thermotolerans had the highest abundance of 70．1%.The results of the PCR-RFLP analysis of the sample collected in the bioleaching column of chalcopyrite during different periods of bioleaching shows that the microflora in the column was composed of L. ferriphilum, S. thermotolerans and A. caldus. And the microflora structure in the bioleaching column was kept on changing. At the initial stage of the bioleaching reaction, L. ferriphilum was the most dominant species (81%), and then its percentage in the column decreased, followed with the rise of the percentages of S. thermotolerans and A. caldus, the abundance were 53．8% and 45．9% respectively at the metaphase. At the telophase of the bioleacing, S. thermotolerans had the highest abundance of 79%.The process of bioleaching marmatite using moderately thermophilic bacteria has been studied in this research by comparing the marmatite leaching performance of mesophiles and moderate thermophiles and valuating the effect of venting capacity as well as pulp density on marmatite leaching performance of moderate thermophiles. The results show that moderate thermophiles have more advantages over mesophiles in bioleaching of marmatite at 45℃with the pulp density of 5 %, and the zinc extraction achieved 93．1 % in 20 d. Aeration agitation can improve the transferring of O₂ and CO₂ in solution and promote the growth of bacteria and therefore, enhance the leaching efficiency. Under the venting levels of 50 mL/min,200 mL/min and 800 mL/min, the zinc extraction by moderate thermophiles were 57．8 %,92．5 % and 96．0 %, respectively. With the increase of pulp density, the total leaching amount of valuable metals increased, however, the percentage of zinc extraction decreased due to many reasons, such as increasing shearing force leads to poorly growth condition for bacteria, etc. The zinc extraction decreased remarkably to 58．9 % while the pulp density mounted up 20 %.