Japan Geoscience Union Meeting 2014

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Symbol U (Union) » Union

[U-05_30PM2] Interrelation between Life, Water, Mineral, and Atmosphere

Wed. Apr 30, 2014 4:15 PM - 5:45 PM 419 (4F)

Convener:*Tsubasa Otake(Division of Sustainable Resources Engineering, Faculty of Engineering, Hokkaido University), Yohey Suzuki(Graduate School of Science, The University of Tokyo), Fumito Shiraishi(Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University), Ken Takai(Extremobiosphere Research Center, Japan Agency for Marine-Earth Science & Technology), Yuichiro Ueno(Department of Earth and Planetary Sciences, Tokyo Institute of Technology), Takeshi Naganuma(Graduate School of Biosphere Science), Takeshi Kakegawa(Graduate School of Science, Tohoku University), Tadashi Yokoyama(Department of Earth and Space Science, Graduate School of Science, Osaka University), Kentaro Nakamura(Precambrian Ecosystem Laboratory (PEL), Japan Agency for Marine-Earth Science and Technology (JAMSTEC)), Chair:Yohey Suzuki(Graduate School of Science, The University of Tokyo), Takeshi Naganuma(Graduate School of Biosphere Science)

5:15 PM - 5:30 PM

[U05-P17_PG] Anion adsorption and post-adsorption behavior of metastable iron hydroxides

3-min talk in an oral session

*Ritsu KODAMA1, Haruko OKAHASHI1, Takato YAMAMOTO1, Tsutomu SATO1, Tsubasa OTAKE1, Tetsuro YONEDA1 (1.Laboratory of Environmental Geology, Hokkaido university, Graduate School of Engineering, Hokkaido U)

Pollution by dissolved anions has been a pertinent environmental concern in many areas around the world. For example, acid mine drainage from abandoned mines and contaminated waters resulting from the Fukushima nuclear power plant accident emphasize the importance of predicting the behavior of the dissolved trace elements on Earth’s surface environments. Iron minerals may play a potentially important role in the control of dissolved trace elements in the environment. In particular, poorly crystalline iron minerals exhibit excellent adsorption capacities for toxic anions due to their high specific surface areas and reactivity. In order to evaluate the potential of poorly crystalline iron minerals as stable sinks of dissolved hazardous ions, it is necessary to investigate the adsorption mechanism on these minerals and their post-adsorption behaviors. Adsorption experiments using arsenate, phosphate, chromate, sulfate, selenate, fluoride, and chloride were performed to investigate the selectivity of Schwertmannite and Ferrihydrite for various anions. Adsorption selectivity decreases in the following order: H2AsO4-›H2PO4-›HCrO4-›SeO42-≒SO42-≫F-≒Cl- . Schwertmannite and Ferrihydrite didn’t have an ability to adsorb F- and Cl-.The adsorption mechanism of these anions was investigated using zeta potential measurements. The results indicated that H2AsO4-, H2PO4- and HCrO4- formed inner-sphere complexes while SeO42- and SO42- formed outer-sphere complexes. The adsorption mechanism of these anions to both Scwertmannite and Ferrihydrite is generally similar, except in the case of HCrO4-. Accelerated alteration experiments were performed to observe post-adsorption behaviors of Schwertmannite and Ferrihydrite. Oriented specimens loaded with varying amounts of adsorbed anions were aged under saturated water vapor pressure conditions at 50℃ for 30 days and analyzed by XRD. Results show that larger amounts of adsorbed anions delay the transformation of Schwertmannite and Ferrihydrite into more stable phases, indicating that adsorption of anions, particularly as inner-sphere complexes, stabilizes poorly crystalline iron minerals. These results show that poorly crystalline iron minerals are capable of taking up a range of toxic anions from contaminated waters and that the stability of these minerals will be affected by the amount of anions sorbed on the surface. These suggest that poorly crystalline iron minerals may serve as stable, long-term sinks for toxic anions.