MOLECULAR SIMULATIONS OF ZN-MONTMORILLONITE

Molecular simulations using the Cerius(2) modelling environment have b een used to investigate the structure of montmorillonite (MMT) interca lated with Zn cations. Basal spacing and bonding of Zn2+ cations in th e interlayer have been investigated with regard to their dependence on the water content. In the first part of the work, Zn cations in the i nterlayer are coordined by six water molecules and the energy of the s ystem is discussed. The energy discussion is focused on the influence of the different starting orientations of the Zn octahedron, and diffe rent positions of Mg atoms in the octahedral sheet. An energy scan at fixed d-spacing was carried out. Later the hydration simulation giving the hydration curve (i.e. the dependence of d-spacing on the number o f water molecules in the interlayer) was also carried out. Two differe nt hydration states were found - for certain humidity ranges there is almost constant d-spacing and between these intervals there is a sharp edge. Finally the structure of totally dehydrated Zn-MMT was simulate d.