Journal of Materials Science, Vol.43, No.1, 190-196, 2008
Study of the influence of the basicity and chromate-chloride anionic composition in the synthesis of the cancrinite-sodalite system
The influence of basicity and anionic composition (CrO42- and Cl-) was studied in the synthesis of chromate-cancrinite and chlorosodalite zeolites. Zeolite X was used as starting material by using different NaOH concentrations (3, 8 and 16 M) and variable weight ratio (NaCl/(NaCl + K2CrO4)) equal to: 0.00, 0.25, 0.50, 0.75, and 1.00 in such a way that the total grams were 1.5 g. The syntheses were carried out at 80 degrees C and autogenous pressure during 40 h. The crystals obtained were characterized by powder X-ray diffraction (XRD), FT-IR spectroscopy, and scanning electron microscopy (SEM) coupled with an energy-disperse X-ray detector (EDX). Depending on the basicity employed and anionic composition (CrO42- and Cl-), the chromate-cancrinite or chlorosodalite zeolite was obtained. Owing to a low 3 M NaOH concentration and 100% Cl--,Cl- chlorosodalite mixed with zeolite X was observed in the XRD pattern. Owing to another Cl--CrO42-proportions, inclusive to 100% CrO42, the starting material were not transformed (3 M NaOH). Pure chromate-cancrinite was produced when 8 and 16 M NaOH and 0% Cl- concentrations were used. Chloride anions showed a strong structure directing effect for sodalite framework structure in comparison with chromate anions which favoring the cancrinite structure. Therefore, we determined pure chlorosodalite, when it was used until 75%Cl- (8 M NaOH) and 25% (16 M NaOH). Results showed that cancrinite or sodalite zeolites are separately formed.