HYDROTHERMAL SYNTHESIS OF ALKALI CATION HEULANDITE ALUMINOSILICATE MOLECULAR-SIEVES

Heulandite molecular sieves with a Si/Al ratio of 3.2 similar to 3.8 h ave been, synthesized hydrothermally in the presence of the alkali cat ions Li+; Li+, K+; and Na+, K+ at 190 degrees C at autogenous pressure . They have been characterized by X-ray powder diffraction and scannin g electron micrographs. Heulandites can be formed in the Li+ and Na+, K+ cation systems only with similar to 10 wt% seed crystals. But heula ndite can be synthesized in the presence of Li+, K+ cations without se ed crystals. The formation of heulandite-type zeolites occurs over a n arrow crystallization field and depends on the Si/Al ratio, the OH-/Si ratio, and on the presence of seed crystals. Scanning electron microg raphs show a thin-plate topology for the crystals. Heulandite is therm ally unstable for calcination beyond 350 similar to 450 degrees C. (C) Elsevier Science Inc. 1997.