Thermally activated boiling of hydrothermal Ca-Na-zeolites

Boiling of natural zeolites at high temperatures is the major peculiarity b y which they are recognized and From which they derived their name. The mic romechanism of this process was studied by IR spectroscopy. It has been est ablished that the source of the gas phase in the process is not the initial "zeolite water", as supposed earlier, but the product of its high-temperat ure evolution, which passes through three stages: 1) dissociation of the "z eolite water" (released during partial dehydration of the zeolite) under th e action of the electrostatic field of the coordinatively unsaturated polyv alent cations; 2) hydroxylation of the aluminosilicate framework; 3) dehydr oxylation of the latter with release of gas H2O. This gas phase causes boil ing of natural zeolites at high temperatures as they reach a pyroplastic st are. Small polyvalent cations, such as Ca2+, Mg2+ etc., play an important r ole in high-temperature hydroxylation of zeolites and, correspondingly, in their boiling, as they have a high charge density and, hence, a high polari zation capacity.