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Water sorption on Ca-saturated clays: I. Multilayer sorption and microporosity in some illites

Published online by Cambridge University Press:  09 July 2018

Kathy Branson
Affiliation:
Rothamsted Experimental Station, Harpenden, Herts. AL5 2JQ, UK
A. C. D. Newman
Affiliation:
Rothamsted Experimental Station, Harpenden, Herts. AL5 2JQ, UK

Abstract

Measurements of water desorption and sorption on four Ca-saturated illitic clays show that the shapes of the isotherms are very similar to those for other oxide surfaces, indicating that the formation of water multilayers is quantitatively similar. This enables graphs of multilayer thickness against mass sorbed to be drawn and used to assess microporosity. Hysteresis occurs and this is attributed to loss of external surface as drying brings platy particles in close face-to-face contact. Mixed-layer mica-smectites, however, exhibit no microporosity by this test and behave as if all surfaces are freely accessible to multilayer formation. The reason for this is not at present understood.

Resume

Resume

Des mesures d'adsorption et de désorption d'eau sur 4 argiles de type illite saturée en Ca montrent que les formes des isothermes sont très semblables à celles rencontrées pour d'autres surfaces d'oxyde; la formation des multicouches d'eau est donc quantitativement semblable. On peut ainsi représenter l'épaisseur de la multicouche par rapport à la quantité adsorbée et utiliser ces courbes pour déterminer la microporosité. On constate une hystérèse que l'on attribue à la perte de surface externe lors du séchage qui favorise le contact des particules planes. Par contre les interstratifiés mica-smectites ne présentent aucune microporosité au moyen de ce test et se comportent comme si toutes les surfaces éaient librement accessibles à la formation de multicouches. Aucune explication ne peut être avancée.

Kurzreferat

Kurzreferat

Die Messungen der Wasser-Desorption und -Sorption an vier Cagesättigten illitischen Tonen zeigen, daß die Form der Isothermen sehr ähnlich der anderer oxidischer Oberflächen ist, die Bildung der Wasser-Mehrfachschichten also quantitativ ähnlich verläuft. Das erlaubt es, eine Beziehung zwischen der Schichtdicke und der Masse des sorbierten Wassers aufzustellen und zur Abschätzung der Mikroporosität zu benutzen. Bei diesem Sorptionsvorgang tritt Hysteresis auf, da beim Trocknen plättchenförmige Partikel flach aneinander gelagert werden und sich daher die äußere Oberfläche vermindert. Wechselgelagerte Glimmer-Smectite zeigen jedoch bei diesem Verfahren keine Mikroporosität und verhalten sich so, als ob alle Oberflächen vollständig frei für die Mehrschiehtenadsorption zur Verfügung stünden. Ein Grund hierfür konnte nicht gefunden werden.

Resumen

Resumen

Las medidas de adsorción y desorción de agua en cuatro arcillas iliticas saturadas con calcio indiean que la forma de las isotermas es muy similare a las obtenidas para otros óxidos indicando que la formación de multicapas de agua es cuantitativamente similar. Este hecho permite representar gráficamente el espesor de la multicapa en funcion de la masa de agua adsorbida y a partir de esta gráfica calcular la microporosidad. El proceso de histeresis que se observa se atribuye a la pérdida de superficie externa como consecuencia del seeado, lo que provoca el apilamiento de las particulas. Los minerales interestratificados tipo micaesmectita, sin embargo, no presentan microporosidad según este test, comportándose como si todas las superficies fueran accesibles libremente a la formación de la multicapa. No se tiene hasta ahora una explicación para este comportamiento.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1983

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