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Clays and Clay Minerals

, Volume 22, Issue 5–6, pp 435–441 | Cite as

Surface Acidity of Montmorillonites

  • M. Frenkel
Article

Abstract

Surface acidity of almost homoionic montmorillonites was measured by titrating selected Hammett indicators adsorbed on the clay with n-butylamine.

As expected, the acidity is strongly affected by the exchangeable cations and the degree of hydration of the clay. Greater polarizing ability of the interlayer cations increases both the strength and number of acid sites per H0 value. The acidity of ‘activated’ or heated H-montmorillonite does not exceed that of untreated H-montmorillonite. The origin of the negative charge in the montmorillonite appears to affect the acidity of the clay.

It is concluded that the very high acidities reported in the literature (H0 < −5–6) are apparent only and are due to physisorption of the indicator.

Résumé

L’acidité de surface de montmorillonites pratiquement homoioniques a été mesurée en titrant par la n butylamine des indicateurs de Hammett sélectionnés, adsorbés sur l’argile.

Comme on peut s’y attendre, l’acidité est fortement affectée par les cations échangeables et le degré d’hydratation de l’argile.

Un pouvoir polarisant des cations interfeuillets plus élevé augmente à la fois la force et le nombre des sites acides pour une valeur de H0.

L’acidité de la montmorillonite-H “activée” ou chauffée ne dépasse pas celle de la montmorillonite-H non traitée. L’origine de la charge négative de la montmorillonite semble affecter l’acidité de l’argile.

On conclut que les très fortes acidités citées dans la littèrature (H0 inférieur à −5,6) sont seulement apparantes et sont dues à la physisorption de l’indicateur.

Kurzreferat

Die Oberflächenazidität von nahezu homoionischen Montmorilloniten wurde durch Titration von an dem Ton adsorbierten ausgewählten Hammet-Indikatoren mit n-Butylamin gemessen.

Wie erwartet, wird die Azidität stark durch die Art des austauschbaren Kations und den Hydratationsgrad des Tons beeinflußt. Größere Polarisierbarkeit der Zwischenschichtkationen erhöht sowohl die Stärke als auch die Anzahl der sauren Austauschplätz pro H0-Wert. Die Azidität von ‘aktiviertem’ oder erhitztem H-Montmorillonit übersteigt nicht diejenige von unbehandeltem H-Montmorillonit. Die Herkunft der negativen Ladung im Montmorillonit scheint die Azidität des Tons zu beeinflussen.

Es wird geschlossen, daß die sehr hohen Aziditäten, über die in der Literatur berichtet wird H0 < −5,6), nur scheinbaren Charakter haben und die Folge einer physikalischen Adsorption des Indikators sind.

Резюме

Поверхностная кислотность большей части гомоионных монтмориллонитов измерялась титрованием избранных указателей Хаммет адсорбированных на глине и-бутиламином. Как предполагалось, на кислотность сильно влияют обменные катионы и степень гидратации глины. С увеличением поляризационной способности катионов промежуточных слоев увеличиваются как кислотность так и количество кислых участков на величину числа H0.. Кислотность «активированных» или нагретых H-монтмориллонитов не превышает кислотности необработанных. Появление отрицательного заряда монтмориллонита повидимому влияет на кислотность глины. B заключении говорится, что очень высокие числа кислотности, указываемые в литературе (H0<—5,6), являются только кажущимися и зависят от физической сорбции индикатора.

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Copyright information

© Clay Minerals Society 1974

Authors and Affiliations

  • M. Frenkel
    • 1
  1. 1.Department of GeologyThe Hebrew University of JerusalemJerusalemIsrael

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