The Structure And Dynamics Of Microbial Community During Bioleaching Under PH Stimulation

pH is an important parameter during bioleaching, which affects the growth, activity of microorganisms and microbial community, as well as the formation of intermediates. Especially during industrial application of bio-heap, a sudden rainfall or sustained drought may lead to significant change of pH in system. In this paper, moderate thermophiles were utilized to leach chalcopyrite under the adjustment of initial and processing pH, combining ecological methods and mineralogical methods, to explore the effect of pH stimulation on the structure and dynamics of microbial community, to clarify synergistic mechanism of microbial leaching and ecological laws and to provide a theoretical basis for the dynamic regulation of microbial populations during bioleaching.The moderate thermophiles utilized in experiments were collected from acid mine drainage in many areas. After repeated domestication, the bioleaching of chalcopyrite could achieve better performances. DGGE technology was used to analyze microbial composition of the enrichment. The results showed it was mainly composed of A. caldus, L. ferriphilum, S. thermosulfidooxidans and the only archaeal F. thermophilum.At initial pH1.0,2.0and3.0, the copper extraction in22days respectively amounted to84.6%(18.41g/L),88.2%(19.2g/L) and77.5%(16.87g/L), and the highest extraction was achieved at initial pH2.0. The initial pH was still2.0, when the mixed culture entered into the late log phase, the processing pH was respectively adjusted to pH1.0and3.0to simulate a sustained drought and sudden rainfall. The results suggested that, the stimulation of processing pH1.0and3.0extended the leaching period from22days to32days, and the leaching rate also decreased significantly. The XRD analysis of ore residues showed that, processing pH1.0stimulation slowed down the formation of jarosite. But contrary for processing pH3.0, which decreased dramatically the content of the oxidant Fe3+and seriously affected the leaching effect.The effect of pH stimulation on microbial community structure during bioleaching of chalcopyrite was investigated by DGGE technology. The results indicated that, L. ferriphilum was more sensitive to the pH stimulation. After the stimulation of processing pH1.0and3.0, L. ferriphilum both decreased, even could not be detected in the system of processing pH3.0. Subsequently, the microbial community at processing pH1.0was gradually back to its original state. But processing pH3.0stimulation dramatically decreased the content of the oxidant Fe3+, promoted the formation of jarosite and irreversibly changed the bioleaching environment, which led to the structure of microbial community not to be recovered.Real-time PCR was used to investigate the effect of pH stimulation on the dynamics of free and attached microbial populations. The results showed that the attached microorganisms and microbial community was more resistant to the stimulation of processing pH, while the structure of free microbial community was easier to be disrupted by pH stimulation.