MOLECULAR SIMULATIONS OF MONTMORILLONITE INTERCALATED WITH ALUMINUM COMPLEX CATIONS - PART I - INTERCALATION WITH [AL13O4(OH)(24-X)]((7-X)+)(X)(H2O)(12)

The structure of montmorillonite intercalated with [Al13O4(OH)(24+x)(H 2O)(12-x)]((7-x)+) cations (Al-13((7-x)+) for short), where x = 0, 2 a nd 4, has been studied using the Cerius(2) modeling environment. The C rystal Packer module used in the present study takes into account only the nonbonded interactions between the silicate layer and the Keggin cations. Minimization of the total sublimation energy led to the follo wing conclusions: the structure of the interlayer (that is, the orient ation of Keggin cations and the basal spacing) depends on the charge o f cations (that is, on the degree of hydrolysis, x). The values of bas al spacings in the range 19.38-20.27 Angstrom have been obtained, depe nding on the charge and arrangement of cations in the interlayer. The dominating contribution to the total sublimation energy comes from the electrostatic interactions. Translations of Al-13((7-x)+) cations alo ng the 2:1 layers give only small fluctuations of the total sublimatio n energy and basal spacings. No preference for the position of Al-13(( 7-x)+) cations in the interlayer of montmorillonite was found during t ranslation along the 2:1 layers. This result confirmed the inhomogeneo us distribution of cations in the interlayer and turbostratic stacking of layers.