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Open AccessArticle

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

1
Central Research Institute of Electric Power Industry, Chiba 270-1194, Japan
2
Division of Sustainable Resources Engineering, Graduate School of Engineering, Hokkaido University, Hokkaido 060-8628, Japan
3
Division of Sustainable Resources Engineering, Faculty of Engineering, Hokkaido University, Hokkaido 060-8628, Japan
4
Radioactive Waste Management Funding and Research Center, Tokyo 104-0052, Japan
*
Author to whom correspondence should be addressed.
Minerals 2020, 10(8), 719; https://doi.org/10.3390/min10080719
Received: 30 June 2020 / Revised: 8 August 2020 / Accepted: 12 August 2020 / Published: 17 August 2020
(This article belongs to the Special Issue Emerging Insights into Serpentinites)
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 (14C 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 Å 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. View Full-Text
Keywords: alkaline seepage; ophiolite; silicate hydrate; smectite; tobermorite alkaline seepage; ophiolite; silicate hydrate; smectite; tobermorite
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MDPI and ACS Style

Shimbashi, M.; Yokoyama, S.; Watanabe, Y.; Sato, T.; Otake, T.; Kikuchi, R.; Yamakawa, M.; Fujii, N. Formation of Natural Silicate Hydrates by the Interaction of Alkaline Seepage and Sediments Derived from Serpentinized Ultramafic Rocks at Narra, Palawan, the Philippines. Minerals 2020, 10, 719. https://doi.org/10.3390/min10080719

AMA Style

Shimbashi M, Yokoyama S, Watanabe Y, Sato T, Otake T, Kikuchi R, Yamakawa M, Fujii N. Formation of Natural Silicate Hydrates by the Interaction of Alkaline Seepage and Sediments Derived from Serpentinized Ultramafic Rocks at Narra, Palawan, the Philippines. Minerals. 2020; 10(8):719. https://doi.org/10.3390/min10080719

Chicago/Turabian Style

Shimbashi, Misato; Yokoyama, Shingo; Watanabe, Yasutaka; Sato, Tsutomu; Otake, Tsubasa; Kikuchi, Ryosuke; Yamakawa, Minoru; Fujii, Naoki. 2020. "Formation of Natural Silicate Hydrates by the Interaction of Alkaline Seepage and Sediments Derived from Serpentinized Ultramafic Rocks at Narra, Palawan, the Philippines" Minerals 10, no. 8: 719. https://doi.org/10.3390/min10080719

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