11:00 〜 13:00
[HRE13-P13] Iron precipitation and associated microbial activities in acid mine drainages of Ainai and Shojin river mine
キーワード：パッシブトリートメント、酸性鉱山廃水、鉄酸化細菌
In mine development, acid mine drainages generated from mine mouth and accumulation sites can pollute water sources in the surrounding areas. Active treatments have been applied as a classical method to precipitate toxic elements by injecting chemicals into the acid mine drainage. Recently, passive treatments that utilizes the natural remediation system in on-site environment is attracting attention as a low-cost treatment method. However, the practical application is still in progress in Japan and subsequently the knowledge for the applications in project sites, particularly the roles of the microflora to form toxic elements-bearing iron precipitates, is limited. Here, we report influences of microbiological activities on iron precipitation by identifying components of sediments and microbial flora analysis in the mine drainage channels of two sites: the Ainai mine in Kosaka, Akita Prefecture, and the Shojin river mine in Nanae city, Hokkaido Prefecture, showing different pH of the mine drainages (near neutral to acidic) each other.
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.
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.