Synthesis of Na- and K-clinoptilolite endmembers

Abstract

We report here the first synthesis of endmembers Na- and K-clinoptilolite. Na, K-clinoptilolites, formed principally in nature by the alteration of siliceous volcanic ash and tuffs deposited in the ocean or in continental saline, alkaline lakes, are the most abundant zeolites occurring as minerals. However, it has been found difficult to delineate in the laboratory the conditions which lead to the crystallization of these minerals at low-temperature and low-pressure conditions. In the reactant systems studied and in a temperature range 120–200 °C at autogenous pressure, Na-clinoptilolite crystallized with the addition of a small amount (1%) of seed crystals, and K-clinoptilolite was synthesized with or without seed. Intermediate Na, K-clinoptilolites also crystallized in the seeded and unseeded systems. Coexisting phases, depending on the reactant composition, included mordenite, phillipsite, gismondine (zeolite P₁) and K-feldspar. An experimental basis has now been established to determine the kinetics and paragenesis of this zeolite occurring in very large amounts in ocean and continental sediments.