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Surface Potentials Derived from Co-Ion Exclusion Measurements on Homoionic Montmorillonite and Illite

Published online by Cambridge University Press:  02 April 2024

D. Y. C. Chan ,
I. R. M. Pashley  and
J. P. Quirk
D. Y. C. Chan
Affiliation:
Department of Applied Mathematics, Research School of Physical Sciences, Australian National University, Canberra, Australia
I. R. M. Pashley
Affiliation:
Department of Applied Mathematics, Research School of Physical Sciences, Australian National University, Canberra, Australia
J. P. Quirk
Affiliation:
Waite Agricultural Research Institute, Glen Osmond, South Australia 5064, Australia
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Abstract

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Simple equations are presented which allow double-layer potentials of clays to be derived from co-ion exclusion measurements in monovalent and divalent electrolyte solutions. These equations have been used to re-interpret earlier results for illite and montmorillonite. The potentials derived follow the lyotropic series for the various homoionic modification of each clay. We have demonstrated that the Schofield equation, which assumes high double-layer potentials, cannot be applied to co-ion exclusion in clay systems. Re-analysis of earlier measurements has shown that for a given homoionic clay the potentials are almost independent of concentration over the range 0.3 to 0.003 molar. Thus, clay surfaces appear to behave more like constant-potential than constant-charge surfaces.

Резюме

Резюме

Представлены простые уравнения, при помощи которых можно получить величины потенциалов двойного слоя для глин из измерений, исключая ионы одинакового знака в одно-и двувалентных электролитических растворах. Эти уравнения использовались для ре-интерпретации ранних результатов для иллита и монтмориллонита. Полученные потенциалы следуют лиотропные серии для разных одноионных модификации каждой глины. Показано, что уравнение Шефельда, которое принимает высобкие потенциалы двойного слоя, не может применятся к исключениям ионов одинакового знака в системах глин. Уточнения ранних измерений показали, что для данной одноионной глины потенциалы почти независят от концентрации в диапазоне 0,3 до 0,003 моля. Таким образом представляется, что поверхности глин ведут себя скорее как поверхности постоянного потенциала, чем постоянного заряда. [E.G.]

Resümee

Resümee

Es wurden einfache Gleichungen angegeben, mit deren Hilfe man die Doppelschichtpotentiale von Tonen aus “Co-ion exclusion measurements” in ein- und zweiwertigen Elektrolytlösungen ableiten kann. Diese Gleichungen wurden benutzt, um frühere Ergebnisse für Illit und Montmorillonit neu zu interpretieren. Die abgeleiteten Potentiale folgten der lyotropen Serie für verschiedene homoionische Modifikationen jedes einzelnen Tons. Es wurde gezeigt, daß die Schofield-Gleichung, die hohe Doppelschichtpotentiale voraussetzt, bei der “Co-ion exclusion” in Tonsystemen nicht angewandt werden kann. Eine erneute Analyse früherer Messungen hat gezeigt, daß die Potentiale für einen bestimmten homoionischen Ton über den Bereich von 0,3 bis 0,003 molar nahezu unabhängig von der Konzentration sind. Das heißt, daß Tonoberflächen sich eher wie Oberflächen mit konstantem Potential zu verhalten scheinen und weniger wie Oberflächen mit konstanter Ladung. [U.W.]

Résumé

Résumé

On presente de simples équations qui permettent de dériver des potentiels à couches doubles d'argiles à partir de mesures d'exclusion de co-ions dans des solutions electrolytes monovalentes et divalentes. Ces équations ont été utilisées pour ré-interpréter des résultats précédants pour l'illite et la montmorillonite. Les potentiels dérivés suivent la série lyotropique pour les modifications homoioniques variées de chaque argile. On a démontré que l’équation de Schofield, qui suppose des potentials élevés à couches doubles, ne peut être appliquée à l'exclusion de co-ions dans des systèmes argileux. La ré-analyse de measures précédantes a montré que pour une argile homoionique donnée, les potentiels sont pres-qu'indépendants de la concentration sur l’étendue 0,3 à 0,003 molaire. Les surfaces d'argiles semblent ainsi se comporter plus comme des surfaces à potential constant que comme surfaces à charge constante. [D.J.]

Keywords

Co-ion exclusionDouble-layer potentialIlliteMontmorilloniteSurface charge
Type
Research Article
Information
Clays and Clay Minerals , Volume 32 , Issue 2 , April 1984 , pp. 131 - 138
Copyright
Copyright © 1984, The Clay Minerals Society

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