SELECTIVE EXTRACTION OF EXTRAFRAMEWORK ALUMINUM FROM USY ZEOLITE

The extraction of extraframework aluminum from USY zeolite prepared by a hydrothermal treatment at 780 degrees C was investigated. A series of extracted samples was prepared by the addition of concentrated hydr ochloric acid to the suspension of the zeolite in a solution of NH4NO3 . X-ray data and chemical analysis were used for the characterization of the samples. Results showed that the presence of competitive NH4+ c ations to the H+ ions in the solution increased the stability of frame work aluminum toward acid. The removal of extraframework Al species wa s very selective at pH as low as 0.85. The discrepancy observed betwee n the pH and the selectivity of the extraction indicated that the pH i s not the decisive factor influencing the dealumination of the zeolite framework in this reaction system. It was found that the degree of fr amework dealumination depends on the equivalent fraction of protons S- H(+) in the solution, and to obtain the high process selectivity, the extraction had to be carried out at as low S-H(+) as possible. Results also showed that the supplementary dealumination of the hydrothermall y treated zeolite framework during the extraframework aluminum extract ion led to the decrease of the crystallinity of the USY zeolite sample .