The thermal behavior of k-exchanged forms of natrolite

A series of K-exchanged forms of natrolite are easily obtained by treatment with KCl solution at room temperature for 1-62 days. The maximum degree of exchange of K is 91.94%. The thermal behavior of the exchanged forms is studied by DTA-TG and high temperature X-ray powder diffraction. The DTA curve of the exchanged form of the 91.94% sample exhibits a single large endotherm at 150°C due to a one-step dehydration, showing the remarkable decrease in dehydration temperature compared with natrolite. The dehydrated phase of natrolite collapses at about 800°C, while destruction of the dehydrated K-form occurs above 1000°C. It is well recognized that the thermal stability of natrolite is increased by Na-K exchange.