Quantum Chemical Studies of Localisation and Hydration of Ca2+ and Mg2+ Cations in the Clinoptilolite 8- and 10-member Rings

Abstract

To study the energetic and structural characteristics of the systems involved in the Ca2+ ↔ Mg2+ ion exchange at clinoptilolite, the quantum chemical modelling was performed of several clusters representing the portion of the heulandite lattice which involve one 10-member (10M) ring containing the isomorphic substitution, one 8-member (8M) ring also containing the isomorphic substitution, and adjacent 4- and 5-member rings. It was shown that, while for dehydrated systems the localisation of Mg2+ ion in the 10M ring and Ca2+ ion in the 8M ring is preferable, for the partially hydrated systems the localisation of Ca2+ ion in the 10M ring and Mg2+ ion in the 8M ring is favourable, with the energetic yield of corresponding ion exchange reaction of the order of 100 kJ/mol.