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Ca-K Exchange Reaction and Interstratification in Montmorillonite

Published online by Cambridge University Press:  01 July 2024

Atsuyuki Inoue  and
Hideo Minato
Atsuyuki Inoue
Affiliation:
Department of Earth Science and Astronomy, College of General Education University of Tokyo, Komaba, Meguro-ku, Tokyo 153, Japan
Hideo Minato
Affiliation:
Department of Earth Science and Astronomy, College of General Education University of Tokyo, Komaba, Meguro-ku, Tokyo 153, Japan
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Abstract

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Cation-exchange equilibrium for Ca-K-montmorillonite was studied at 35°, 50°, and 90°C and at three total normalities of the equilibrium solution (0.1, 0.05, and 0.01 N). Changes of the standard free energy for the exchange from K-montmorillonite to Ca-montmorillonite were determined to be −53, −270, and −393 cal/eq at 35°, 50°, and 90°C, respectively. Changes of the standard enthalpy and entropy were 1.7 kcal/eq and 5.6 cal/eq/degree at 35°C, respectively. The sign of the change of the standard free energy was found to be determined mainly by the entropy change, in particular, by the hydration entropy of the cations.

The calculation of the excess functions indicates that the mixing model of Ca-K-montmorillonite approximates that of a regular solution. Montmorillonite having potassium equivalent ion fraction of 0.1 to 0.7 consists of a random interstratification of Ca-montmorillonite (15.6 Å) and K-montmorillonite (12.6 Å).

Резюме

Резюме

Изучалось катионно-обменное равновесие для Са-К-монтмориллонита при температурах 35°, 50°, и 90°С и при трех полных нормальностях равновесного раствора (0,1, 0,05, и 0,01 N). Изменения стандартной свободной энергии для обмена от К-монтмориллонита до Са-монтморилло-нита были определены как −53, −270, и −393 кал/эк при 35°, 50°, и 90°С соответственно. Изменения стандартной энтальпии и этропии были соответственно 1,7 ккал/эк и 5,6 кал/эк/градус при 35°С. Было установлено, что знак изменения стандартной свободной энергии определяется в основном изменением энтропии, в особенности гидрационной энтропии катионов.

Подсчет остаточных функций показывает, что модель смешивания Са-К-монтмориллонита апроксимирует модель обыкновенного раствора. Монтмориллонит, имеющий калиевую эквивалентную ионную фракцию от 0,1 до 0,7, характеризуется нерегулярным переслаиванием Са-монт-мориллонита (15,6 Å) и К-монтмориллонита (12,6 Å).

Resümee

Resümee

Das Kationenaustausch-Gleichgewicht für Ca-K-Montmorillonit wurde bei 35°, 50°, und 90°C und bei 3 Gesamtnormalitäten der Gleichgewichtslösung (0,1, 0,05, und 0,01 N) untersucht. Die Änderungen der freien Energie beim Austausch von K-Montmorillonit zu Ca-Montmorillonit ergaben Werte von −53, −270, und −399 cal/Äqu bei 35°, 50°, 90°C und bzw. Die Änderungen der Standard-Enthalpie und -Entropie betrugen 1,7 kcal/Äqu bzw. 5,6 cal/Äqu/Grad bei 35°C. Es zeigte sich, daß die Änderung der freien Energie vor allem von der Änderung der Entropie abhängt, insbesondere von der Hydratations-Entropie der Kationen.

Die Berechnung der Überschußenergien läßt erkennen, daß das Mischungsmodell für Ca-K-Montmorillonit dem einer regulären Lösung nahekommt. Montmorillonit mit einem Kalium-Ionenanteil von 0,1 bis 0,7 bestehen aus einer ungeordneten Wechsellagerung von Ca-Montmorillonit (15,6 Å) und K-Montmorillonit (12,6 Å).

Résumé

Résumé

L’équilibre d’échange de cations pour la montmorillonite Ca-K a été étudié à 35°, 50°, et 90°C et à trois normes totales de la solution d’équilibre (0,1, 0,05, et 0,01 N). Les changements d’énergie libre standard pour l’échange de montmorillonite-K à la montmorillonite-Ca ont été déterminés à −53, −270, et −393 cal/eq à 35°, 50°, et 90°C, respectivement. Les changements de l'enthalpie et de l'entropie standards étaient de 1,7 kcal/eq et 5,6 cal/eq/degré à 35°C, respectivement. On a trouvé que le signe du changement de l’énergie libre standard était déterminé principalement par le changement d'entropie, en particulier, par l'entropie d'hydratation des cations.

Le calcul des fonctions en excès indique que le modèle de mélange de montmorillonite-Ca-K est proche de celui d'une solution régulière. La montmorillonite ayant une fraction d'ion d’équivalent de potassium de 0,1 à 0,7 consiste en une interstratification au hasard de montmorillonite-Ca (15,6 Å) et de montmorillonite-K (12,6 Å).

Keywords

EnthalpyEntropyFree energyInterstratificationIon exchangeMontmorillonite
Type
Research Article
Information
Clays and Clay Minerals , Volume 27 , Issue 6 , December 1979 , pp. 393 - 401
Copyright
Copyright © 1979, The Clay Minerals Society

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