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Experimental Study of the Stability and Phase Relations of Clays at High Temperature in a Thermal Gradient

Published online by Cambridge University Press:  01 January 2024

O. Vidal ,
A. Baldeyrou ,
D. Beaufort ,
B. Fritz ,
N. Geoffroy  and
B. Lanson
O. Vidal*
Affiliation:
CNRS, Université Joseph Fourier, Grenoble, Isterre, 1381 rue de la piscine, BP 53, 38041 Grenoble Cedex, France
A. Baldeyrou
Affiliation:
CNRS, Université de Strasbourg/EOST, LHYGES, 1 rue Blessig, 67084 Strasbourg Cedex, France
D. Beaufort
Affiliation:
CNRS, Université Poitiers, Hydrasa, 40 avenue du recteur Pineau, 86022 Poitiers Cedex, France
B. Fritz
Affiliation:
CNRS, Université de Strasbourg/EOST, LHYGES, 1 rue Blessig, 67084 Strasbourg Cedex, France
N. Geoffroy
Affiliation:
CNRS, Université Joseph Fourier, Grenoble, Isterre, 1381 rue de la piscine, BP 53, 38041 Grenoble Cedex, France
B. Lanson
Affiliation:
CNRS, Université Joseph Fourier, Grenoble, Isterre, 1381 rue de la piscine, BP 53, 38041 Grenoble Cedex, France
*
*E-mail address of corresponding author: olivier.vidal@ujf-grenoble.fr
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Abstract

Clays are involved in a variety of natural and managed processes, and calculation of their stability conditions is important. Such calculations are still fraught with large uncertainties owing to the lack of experimental constraints on the thermodynamic properties of clays, and bracketing of equilibrium reactions at low temperature is barely possible. Experiments aimed at studying the thermal stabilities of, and composition-temperature relations among, smectite, illite, kaolinite, pyrophyllite, mica, and chlorite at different levels of SiO2, K2O, MgO, and Al2O3 species in solution were conducted under a strong thermal gradient in the simple K2O-Al2O3-SiO2-H2O (KASH), MgO-Al2O3-SiO2-H2O (MASH), and KMASH systems. The crystallization series observed in the different experiments match to some degree those observed in active geothermal systems where clay minerals precipitate from oversaturated solutions. Smectite and/or ordered mixed-layer materials, smectite-donbassite, or possibly pyrophyllite-donbassite were observed to crystallize in both KASH and MASH experiments. Similar crystallization sequences and clay composition variations with temperature were observed in most cases when the relative positions of the starting solids were switched. The experimental results were used to refine the thermodynamic properties of K- and Mg-smectite. Stability diagrams calculated by energy minimization and activityactivity diagrams are consistent with the experimental mineral variations, suggesting that smectite is thermodynamically stable at temperatures as high as 300°C in the presence of diluted water and quartz and K-feldspar-free systems.

Keywords

Experimental StudyPhase RelationsSmectiteThermodynamic

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Type
Article
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Clays and Clay Minerals , Volume 60 , Issue 2 , April 2012 , pp. 200 - 225
Copyright
Copyright © Clay Minerals Society 2012

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