CHELATE LIGANDS AS MINERALIZING AGENTS IN HYDROTHERMAL SYNTHESIS OF FAUJASITE-TYPE ZEOLITES - A KINETIC-STUDY

The faujasite zeolites NaX and NaY are suitable model systems to study the role of mineralizing agents in the processes of nucleation and cr ystal growth. In a preceding paper, the influence of NaF addition was investigated. The present contribution deals with the chelate ligands acetylacetonate, citrate, oxalate, nitrilotriacetate, EDTA, HEDTA, DTP A, and CyDTA. Their presence accelerates both crystal growth and nucle ation. The well known ''nucleation suppressor'' triethanolamine turns out to accelerate crystal growth, too, if the nucleation is done by se eding. Unlike hydroxide, none of the mineralizers drastically decrease s the framework Si/Al molar ratio of the crystalline product. Aluminat e incorporation seems to be the rate-determining factor of NaY crystal lization. The presence of chelate ligands influences the equilibrium o f gel dissolution, providing additional aluminate species. Kinetic con siderations give some evidence that some of these intermediates are mi xed hydroxo complexes that are incorporated in the same way as tetrahy droxoaluminate.