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Formation of Natural Silicate Hydrates by the Interaction of Alkaline Seepage and Sediments Derived from Serpentinized Ultramafic Rocks at Narra, Palawan, the Philippines

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Title: Formation of Natural Silicate Hydrates by the Interaction of Alkaline Seepage and Sediments Derived from Serpentinized Ultramafic Rocks at Narra, Palawan, the Philippines
Authors: Shimbashi, Misato Browse this author
Yokoyama, Shingo Browse this author
Watanabe, Yasutaka Browse this author
Sato, Tsutomu Browse this author →KAKEN DB
Otake, Tsubasa Browse this author →KAKEN DB
Kikuchi, Ryosuke Browse this author
Yamakawa, Minoru Browse this author
Fujii, Naoki Browse this author
Keywords: alkaline seepage
ophiolite
silicate hydrate
smectite
tobermorite
Issue Date: Aug-2020
Publisher: MDPI
Journal Title: Minerals
Volume: 10
Issue: 8
Start Page: 719
Publisher DOI: 10.3390/min10080719
Abstract: In radioactive waste disposal facilities, low-permeability engineered barrier materials are important for inhibiting radionuclide migration. However, dissolution-precipitation reactions under alkaline conditions change the permeability of engineered barriers. To understand long-term dissolution-precipitation reactions under alkaline conditions in chemically complex systems, trenches and drill holes were excavated at Narra in Palawan, where alkaline fluids (pH > 11) have been naturally produced, seeping into clastic sediments derived from serpentinized ultramafic rocks and gabbro of Palawan ophiolite. Interaction between the alkaline seepage and clastic sediments, which have been deposited since 15,000 radiocarbon years before present (C-14 yr BP), led to dissolution of minerals and the precipitation of Si-bearing phases which were divided into two main categories: Fe-Mg-Si infillings and Ca-Si infillings. The former category was composed of iron-magnesium-silicate-hydrate (F-M-S-H) and a nontronite-like mineral and was widely recognized in the clastic sediments. The nontronite-like mineral likely formed by interaction between silicates and alkaline seepage mixed with infiltrated seawater, whereas F-M-S-H formed by the reaction of silicates with alkaline seepage in the absence of seawater infiltration. Ca-Si infillings included 14 angstrom tobermorite and were precipitated from alkaline seepage combined with the Ca and Si supplied by the dissolution of calcite and silicates in the clastic sediments.
Rights: © 2020 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/).
http://creativecommons.org/licenses/by/4.0/
Type: article
URI: http://hdl.handle.net/2115/79596
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)

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