Research On Bioleaching Three Sulfide Minerals By Mixed Bacteria And The Microbial Diversity In The Bioleaching Process

The acid mine drainage (AMD) samples from Yunfu Sulfide mine were studied by a PCR-based cloning approach. The samples were cultivated with different sulfldes and the changes of microbial communities of the cultured AMD samples were analyzed by Denatured Gradient Gel Electrophoresis (DGGE) technology. In addition, the pH values, bacterial amount and metal ions concentrations of the solutions were determined for the bioleaching of three sulfide minerals with mixed bacteria. The microbial diversity in the bioleaching process was studied with DGGE method. The surface morphological, chemical composition and element content of mineral samples and bioleached residues were also analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX).A total of 15 operational taxonomic units (OTUs) were obtained from the AMD samples of Yunfu sulfide mine. The phylogenetic analysis revealed that the bacterium in the two samples fell into four putative divisions, which were Alphaproteobacteria, Betaproteobacteria, Gamma-proteobacteria and Nitrospira four families. Organisms of genera Acidithiobacillus and Gallionella, which were in Gamma-proteobacteria family and Betaproteobacteria family, respectively, were dominant in the samples. The microbial communities of samples were much different while they were cultivated with different sulfides (chalcopyrite and Ni-Cu Sulfide). When taking chalcopyrite as energy sources, Acidithiobacillus of Gammaproteobacteria is all through the main microorganism, Leptospirillum of Nitrospira became dominative in latter phase. While taking Ni-Cu Sulfide as energy sources, Leptospirillum ferriphilum of Nitrospira is the dominant bacteria, and there are a little amount of Acidithiobacillus of Gammaproteobacteria existed.The phenomenas in the bio-oxidation course of pyrite and marmatite were quit different. Results show that marmatite can be more easily dissolved and leached than pyrite at initial pH value of 2.0. The solution pH indicates a downward trend and no precipitation is visible because of the lower pH value during bio-oxidation of pyrite. While in the bioleaching of marmatite and chalcopyrite, the pH value rose in the initial and then fell gradually. In addition, the precipitation of jarosite and sulfur S~0 appeared. The SEM images show that the adherence of the bacteria to mineral surfaces existed and a number of erosion pits appeared during pyrite bioleaching. These erosion pits are similar to the bacterium in shape and length. The bacteria attached on the surface of marmatite particles and formed bio-films were observed, but no erosion pits appeared. The key reasons on the difference of two sulfide minerals bioleaching process could be the effects of the crystal characters of minerals and the solution pH values.The microbial compositions were quit different during bioleaching of pyrite, marmatite and chalcopyrite with mixed bacteria. When bioleaching pyrite, in the early time, A. ferrooxidans and A. thiooxidans were the dominant bacteria, but in latter phase A. ferrooxidans beccame the only dominant microorganism, even though a small portion of L. ferrooxidans exist. While in the bio-oxidation process of chalcopyrite, only A. thiooxidans was the main microorganism. When bioleaching marmatite, the main microorganisms were A. ferrooxidans and A. thiooxidans in the initial phase, and then A. ferrooxidans and A. caldus were dominative in the latter phase, small portion of S. thermosulfidooxidans existed.