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Clays and Clay Minerals; February 2003; v. 51; no. 1; p. 65-74; DOI: 10.1346/CCMN.2003.510108
© 2003 Clay Minerals Society
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WETTABILITY OF MONTMORILLONITE CLAYS IN HUMIC ACID SOLUTIONS

Juan de Dios García López-Durán1, Asmae Khaldoun2, Mohamed Larbi Kerkeb2, María del Mar Ramos-Tejada3 and Fernando González-Caballero1,*

1 Department of Applied Physics, Faculty of Sciences, University of Granada, 18071 Granada, Spain
2 Department of Physics, Faculty of Sciences, Abdelmalek Essaadi University, 93000 Tetouan, Morocco
3 Department of Applied Physics, Faculty of Experimental Sciences, University of Jaén, 23071 Jaén, Spain

* E-mail address of corresponding author: fgonzale{at}ugr.es

The effect of humic acid (HA) adsorption on the hydrophilicity of two different montmorillonite samples (Na-montmorillonite, NaMt, and a Na-fluorinated Na-montmorillonite, FNaMt, or ‘Rassoul’) was investigated. The changes in the wettability of clays were discussed in terms of the non-electrostatic free energy of interaction between the clay particles immersed in aqueous humic acid solutions ({Delta}G121), using the van Oss-Chaudhury-Good (vOCG) model. The surface free energy components (both non-polar or Lifshitz-van der Waals, and polar or acid-base) of clays were obtained from contact angle measurements, after adsorption of humic acid, at acid or basic pH, in 10–2 M NaCl solutions. It was found that: (1) at acid pH, a progressive decrease in the hydrophilic character of both clays was observed when the humic acid concentration was increased; (2) at basic pH, the hydrophilic character of both samples studied increased with HA concentration; (3) the effect of humic acid adsorption on the wettability of model edge surfaces of the laminar montmorillonite particles was estimated from a parallel study on silica and alumina surfaces, and only a slight decrease in the hydrophilicity was observed, whatever the pH of the liquid media. The {zeta} potentials of both clays in the absence and presence of humic acid were determined and the linkage between {zeta} potential and the electron-donor character of the materials is discussed.

Key Words: Humic Acid • ‘Rassoul’ • Sodium-montmorillonite • Surface Free Energy • Wettability






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