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Minerals 2018, 8(4), 155; https://doi.org/10.3390/min8040155

Formation of Fe- and Mg-Rich Smectite under Hyperalkaline Conditions at Narra in Palawan, the Philippines

1
Graduate School of Engineering, Hokkaido University, N13W8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan
2
Division of Sustainable Resource Engineering, Faculty of Engineering, Hokkaido University, N13W8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan
3
Radioactive Waste Management Funding and Research Center, Akashi-cho 6-4, Chuo-ku, Tokyo 104-0052, Japan
*
Author to whom correspondence should be addressed.
Received: 5 February 2018 / Revised: 30 March 2018 / Accepted: 8 April 2018 / Published: 12 April 2018
(This article belongs to the Special Issue Environmental Mineralogy)
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Abstract

The formation of Fe- and Mg-rich smectite and zeolite under alkaline conditions, as secondary minerals after the alkaline alteration of bentonite in repositories for radioactive waste, is of major concern. It is crucial for safety assessments to know whether smectite is formed as a secondary mineral after the alkaline alteration of bentonite. In the present paper, Fe- and Mg-rich smectite, which interacted with the hyperalkaline groundwater at Narra in Palawan, Philippines, was used. Mineralogical and geochemical investigation was conducted to understand the formation process of the smectite and the factors determining the formation of secondary mineral species. The results suggest that a certain amount of smectite may be generated under hyperalkaline conditions, by alteration from amorphous or poorly crystalline components such as M-S-H and F-S-H. Therefore, the controlling factor determining whether smectite or zeolite will be generated as secondary minerals after alkaline alteration of bentonite could be whether nuclei of M-S-H and/or F-S-H are formed. Whether such formation takes place may be determined by the presence of dissolved Mg2+ and Fe2+ in the environment. The formation process of smectite under alkaline conditions, suggested by the results here, is analogous to the generally accepted model of smectite formation as it may have occurred on early Mars. View Full-Text
Keywords: Fe- and Mg-rich smectite; alkaline; ophiolite; M-S-H; F-S-H; C-S-H; geological disposal; natural analogue; Mars Fe- and Mg-rich smectite; alkaline; ophiolite; M-S-H; F-S-H; C-S-H; geological disposal; natural analogue; Mars
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Shimbashi, M.; Sato, T.; Yamakawa, M.; Fujii, N.; Otake, T. Formation of Fe- and Mg-Rich Smectite under Hyperalkaline Conditions at Narra in Palawan, the Philippines. Minerals 2018, 8, 155.

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