Influence of heavy metals adsorption on the surface-energy properties of fluorinated montmorillonite clays "Rassoul"

We investigate the adsorption strength of some very toxic substances like lead, cadmium and mercury and sodium triphosphate, a highly environmental contaminant, on purified and homogenized fluorinated sodium montmorillonite NaFMt or "Rassoul", and the influence on its electronic and surface-energy properties. The changes in the wettability of this clay due to the adsorbed elements are discussed in terms of the non-electrostatic interaction free-energy between the clay particles (ΔG121), using the van Oss-Chaudhury-Good (vOCG) model. The surface free energy components (both the van der Waals, and the polar acid-base interactions) of clays are obtained from contact angle measurements. We find that the total surface free energy did not depend on the adsorption of any metal ions studied. However, the different contributions to the surface tension show large variations. The changes of the electrokinetic properties of the Rassoul particles after adsorption of the same substances are studied by determination of the particles' zeta potential ζ as a function of metal concentration in solution. We found that the zeta potential of the clay particles is always negative independent of the metal concentration in solution. A sharp decrease in ζ was found when the concentration of divalent ions increased up to ≈10-2 M. Finally, we have studied the effect of the adsorption of Na5P3O10. A significant effect of anion adsorption was observed on the zeta potential: The ζ-potential becomes more negative for increasing concentrations of the sodium triphosphate in solution. © 2006 Elsevier B.V. All rights reserved.