SYNTHESIS OF ZEOLITE A IN THE NA/K SYSTEM AND THE EFFECT OF SEEDING

Crystallizations were carried out with a standard zeolite A batch composition, but using pure Na, pure K, or mixtures of Na and K with a constant total cation concentration. Larger zeolite A crystals were formed in the presence of K ions; however, other zeolite phases coprecipitated with zeolite A in increasing amounts as the K ion content increased. No zeolite A was formed in the pure K ion system; however, zeolites K-F and K-G did coprecipitate. Using zeolite A seeds in these preparations is shown to promote the formations of new populations of zeolite A, even in the presence of pure K ion systems. Adding smaller amounts of seeds is shown to reduce the crystallization time of the co-precipitated phases in the pure K ion system, even though new zeolite A crystals do not nucleate.