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[HRE13-P13] Iron precipitation and associated microbial activities in acid mine drainages of Ainai and Shojin river mine
Keywords:passive treatment, acid mine drainage, ion oxidizing bacteria
Powder X-ray diffraction analysis and electron microscopy observations showed that the precipitates of the Ainai mine drainages were mainly aggregates of iron-hydroxide colloids with ~50 nm diameters with minor components of Zn-containing layered double hydroxides and thin films of Mn-hydroxides. On the other hand, the precipitates at the 1 and 3 pits, which is the main source for the drainages of the Shojin river mine, are mixtures of schwertmannite colloid aggregates, acidophilic diatoms, and microbially-derived carbonaceous materials such as microbes and the biofilms. Schwertmannite aggregates sometimes form filamentous morphology entangled in biofilms, suggesting the microbial enhancement of the iron precipitation. The results of 16SrRNA microbial flora analysis showed that the majority of the flora in the Ainai mine sediments was Proteobacteria and Gallionella, the iron-oxidizing bacteria, accounted for a high proportion (<31%), whereas the flora of the Shojin river mine sediments was dominated by cyanobacteria with the slight contribution of iron-oxidizing bacteria. Previous study indicated the drainage of the Shojin River mine is Fe3+-dominant, which might lead to the inactivity of iron-oxidizing bacteria on the site. These results indicated that iron-oxidizing bacteria promotes iron precipitation (Fe2+→Fe3+) in the near neutral pH range in the mine drainage channel of the Ainai Mine, while photosynthetic microbial activities promote iron precipitation in the mine drainage channel of the Shojin River Mine.