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Modeling of H+ and Cu2+ Adsorption on Calcium-Montmorillonite

Published online by Cambridge University Press:  28 February 2024

Markus Stadler*
Affiliation:
Institute for Inorganic Chemistry, University of Berne, Freiestrasse-3, CH-3012-Berne, Switzerland
Paul W. Schindler
Affiliation:
Institute for Inorganic Chemistry, University of Berne, Freiestrasse-3, CH-3012-Berne, Switzerland
*
1Author to whom correspondence should be addressed.

Abstract

The interaction of H+- and Cu2+-ions with Ca-montmorillonite was investigated in 0.1 mol/dm3 solutions of Ca(CIO4)2 at 298.2 K by Potentiometrie titrations using both glass electrodes (for H+) and ion specific electrodes (for Cu2+ ). The experimental data were interpreted on the basis of the surface complexation model. The calculations were performed with the least-squares program FITEQL (Westall, 1982) using the constant capacitance approximation. The best fit was obtained with a set of equilibria of the general form

pH++qCu2++≡SOH⇔(H+)p(Cu2+)q(≡SOH)(p+2q)+βp,q(int)s=[HpCuq(≡SOH)(p+2q)][H+]p[Cu2+]q[≡SOH]
and the constants log β1,0(int)S = 8.16 (± 0.04), log β-1,0(int)S = −8.71 (± 0.08), log β0,1(int)S = 5.87 (± 0.06), log β−1,1(int)S = −0.57 (± 0.12), log β−2,1(int)S = −6.76 (± 0.02). An appropriate modeling of the H+ adsorption data requires the introduction of a second surface group ≡ TOH with the acidity constant
≡TOH−H+⇔≡TO−logβ−1,0(int)S=−5.77(±0.07).
In addition, the ion exchange equilibria Ca2+ − Cu2+ and Ca2+ − H+ had to be taken into account. Arguments are presented to identify the groups ≡ SOH and ≡ TOH as surface aluminol groups =Al(OH)(H2O) and surface silanol groups ≡ Si-OH, respectively.

Type
Research Article
Copyright
Copyright © 1993, The Clay Minerals Society

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