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Clays and Clay Minerals

, Volume 41, Issue 3, pp 288–296 | Cite as

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

  • Markus Stadler
  • Paul W. Schindler
Article

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
$$\begin{array}{c}pH^{+}+qCu^{2+}+\equiv{SOH}\Leftrightarrow(H^{+})_p(Cu^{2+})_q(\equiv{SOH})^{(p+2q)+}\\ \beta_{p,q(int)}^s=\frac{\text[H_pCu_q(\equiv{SOH})^{(p+2q)}]}{\text[H^+]^{p}[Cu^{2+}]^q[\equiv{SOH}]}\end{array}$$
and the constants logβ 1,0(int) S = 8.16 (± 0.04), logβ-1,0(int)S = −8.71 (± 0.08), logβ0,1(int)S = 5.87 (± 0.06), logβ−1,1(int)S = −0.57 (± 0.12), logβ−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
$$\equiv{TOH}-H^+\Leftrightarrow{\equiv}{TO}^-log\beta_{-1,0(int)}^S=-5.77(\pm0.07).$$
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.

Key Words

Adsorption Copper Modeling Montmorillonite 

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Copyright information

© The Clay Minerals Society 1993

Authors and Affiliations

  • Markus Stadler
    • 1
  • Paul W. Schindler
    • 1
  1. 1.Institute for Inorganic ChemistryUniversity of BerneBerneSwitzerland

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