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Minerals 2018, 8(9), 362; https://doi.org/10.3390/min8090362

Authigenic Clay Minerals from Interface Reactions of Concrete-Clay Engineered Barriers: A New Perspective on Mg-Clays Formation in Alkaline Environments

1
Department of Geology and Geochemistry, Faculty of Sciences, Autonomous University of Madrid, Cantoblanco, 28049 Madrid, Spain
2
Environmental Applied Geology Unit. CIEMAT. Av. Complutense 40, 28040 Madrid, Spain
*
Author to whom correspondence should be addressed.
Received: 15 July 2018 / Revised: 1 August 2018 / Accepted: 17 August 2018 / Published: 21 August 2018
(This article belongs to the Special Issue Authigenic Clay Minerals: Mineralogy, Geochemistry and Applications)
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Abstract

Artificial and singular geochemical environments are created around the engineered barrier systems (EBS) designed to isolate high level nuclear wastes in deep geological repositories. A concrete-bentonite interface takes place within the EBS and it builds a significant chemical gradient (pH), approximately from pH 8 (bentonite) to pH 12 (low alkali concrete), in a few millimetre thickness. This disequilibrium triggers dissolution and precipitation reactions and form a thin altered region. In this area, poorly ordered authigenic clay minerals, mainly hydrated magnesium silicates, are formed adjacent to hydrated calcium silicates and calcite precipitates adhered to the interface with concrete. This paper presents the development of this authigenic mineral layer comparing 6–18 months to 13 years interfaces. Scanning Electron Microscopy with Energy Dispersive X-ray spectroscopy (SEM-EDX) morphological and chemical characterization with the aid of ternary plots, X-ray diffraction (XRD) and infrared (IR) data show the young to old interface evolution from single brucite layers to stevensite-saponite silicates composition. Geochemical calculations indicate that this layer acts as a pH~11 buffer useful to minimize bentonite alteration and to favour the retention of amphoteric metal ions. View Full-Text
Keywords: concrete-bentonite interaction; nuclear waste; deep geological repository; engineered barrier system; Mg-clays concrete-bentonite interaction; nuclear waste; deep geological repository; engineered barrier system; Mg-clays
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Cuevas, J.; Ruiz, A.I.; Fernández, R.; González-Santamaría, D.; Angulo, M.; Ortega, A.; Torres, E.; Turrero, M.J. Authigenic Clay Minerals from Interface Reactions of Concrete-Clay Engineered Barriers: A New Perspective on Mg-Clays Formation in Alkaline Environments. Minerals 2018, 8, 362.

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