CRYSTAL STRUCTURE AND RIETVELD REFINEMENT OF ZEOLITE A SYNTHESIZED FROM FINE-GRAINED PERLITE WASTE MATERIALS

Abstract

Synthetic zeolites have been produced from a variety of natural silica-rich rocks including volcanic glasses, such as perlite and pumice. The Zeolite studied in this work has been synthesized from perlite and expanded perlite fines. Detailed powder X-ray diffraction studies determined it as Zeolite A. In early studies the structure of Zeolite-Α was described with a cubic cell with a=12.3 A and space group Pm-3m. However the observation of the (531) reflection indicates that a F lattice with a larger cell of 24.60 A gives a more accurate description. Two end products were studied on the basis of the degree of crystallization of the parent gels to zeolite A . One end product was characterized by total conversion of the incipient gel to zeolite A with high degree of crystallinity, whereas in the second a substantial amount of the original gel did not crystallize out and zeolite A coexisted with amorphous material. The former resulted from gels with S1O2/AI2O3 molar ratio 2:1 and 5 hours reaction time and the latter from gels with SÌO2/AI2O3 molar ratio of 2.5:1 and 3 hours reaction time. The X-ray powder diffraction data recorded from the former sample were used for the analysis of the crystal structure of zeolite A and the final model was refined by the Rietveld method.