Zeolites Other than Erionite

Natural zeolites occur in over 40 countries and are mined in 11 of these at a rate of around 250 thousand tonnes per year. Discovery of the characteristic ion-exchange, dehydration and selective-adsorption properties of these zeolites, which are related to their unique honeycomb structure, stimulated the development of severa1 processes for the manufacture of synthetic zeolites. These synthetic zeolites share and improve upon these properties of natural zeolites. So far, nearly 100 structural types of synthetic and natural zeolites have been reported (Meier et aL., 1996; Roland & Kleinschmit, 1996); within these types, a large number of chemically diverse synthetic zeolites and 40 natural zeolites are now known (Roskil Information Services Ltd, 1988). Among the natural zeolites, erionite was previously evaluated as a human carcinogen (IARC, 1987) and is not included in this monograph.