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Precipitation of Magnesium Silicate Hydrates in Natural Alkaline Surface Environments

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Title: Precipitation of Magnesium Silicate Hydrates in Natural Alkaline Surface Environments
Authors: Nishiki, Yuto Browse this author
Sato, Tsutomu Browse this author →KAKEN DB
Katoh, Takayuki Browse this author
Otake, Tsubasa Browse this author →KAKEN DB
Kikuchi, Ryosuke Browse this author →KAKEN DB
Keywords: alkaline condition
carbon dioxide capture and storage
magnesium silicate hydrate (M–S–H)
mineral–water interaction
radioactive waste disposal
natural analogue
Issue Date: 30-Jun-2020
Publisher: The Clay Science Society of Japan
Journal Title: Clay Science
Volume: 24
Issue: 1
Start Page: 1
End Page: 13
Publisher DOI: 10.11362/jcssjclayscience.24.1_1
Abstract: Magnesium silicate hydrate (M–S–H) has been considered to play a significant role in different fields of engineering geology including radioactive waste disposal and geological storage of CO₂. However, M–S–H has been discussed only with synthetic samples in most previous studies. To confirm and characterize M–S–H precipitated in natural surface environments, and to assess the formation conditions and processes of the M–S–H, we investigated present-day precipitation of M–S–H at an ultramafic body in the Kamuikotan tectonic belt, Hokkaido, Japan. We collected seepage, surface water, and surface sediments on the ultramafic rock mass. Seepage and surface water showed alkaline pH and Mg²+–HCO₃- type water. Although bulk XRD analysis of the sediments did not clearly identify peaks of M–S–H due to its low crystallinity, microscopic observation showed that the sediments contained solid phases that are precipitated interstitially around the detrital serpentine particles. A TEM analysis identified the phases as M–S–H that may be mineralogically considered as a low-crystalline chrysotile with nano-tubular morphology. Thermodynamic calculations for the collected liquid samples suggest that mixed solution of seepage and surface water having high Si activity can induce the formation of M–S–H. The precipitation of M–S–H is likely to be a commonly occurring phenomenon in natural Mg–Si–H₂O systems where geochemical environments contain alkaline fluid that shows high Si activity and meets the thermodynamic conditions for M–S–H formation. In addition to the precipitation of M–S–H in Mg–Si–H₂O systems, we also observed that M–S–H is precipitated even under conditions including Ca and CO₂ species (i.e., Mg–Ca–Si–CO₂–H₂O systems), with a simultaneous precipitation of aragonite. This study supports an understanding of the precipitation of M–S–H by mineral–water interactions in natural surface/subsurface environments for various engineering geology fields.
Type: article
Appears in Collections:工学院・工学研究院 (Graduate School of Engineering / Faculty of Engineering) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 佐藤 努

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