Molten-salt method for the synthesis of zeolitic materials II. Characterization of zeolitic materials

Characterization of zeolitic materials synthesized by the newly developed m olten-salt method was carried out. Their physicochemical properties were in vestigated and compared to those of zeolitic materials prepared by the conv entional hydrothermal method. The molten-salt method exhibited much less el emental loss during the zeolitization process. The product yield based on t he reaction weight was about twice as high in the molten-salt method as in the hydrothermal method. The molten-salt method resulted in zeolitic materi als with higher purity, larger contents of alkali metals, lower pH values, and lower cation exchange capacity (higher Si/Al ratio). Salt occlusion als o took place in the cavities of the resulting zeolites during the zeolitiza tion of fly ash by the molten-salt method. It seems, therefore, apparent th at the high temperature and dry conditions in the molten-salt method lead t o zeolitic materials which are somewhat different from hydrothermally synth esized zeolitic materials. (C) 2000 Elsevier Science B.V. All rights reserv ed.