SYNTHESIS OF NA-ZEOLITES FROM FLY-ASH

The present study focuses on the synthesis of zeolites after fly ash a ctivation, the major objectives being: (a) to study the activation pro cesses; (b) to elucidate the activation conditions for maximum synthes is efficiency; (c) to optimize the conditions for the monomineral synt hesis; and (d) to test synthesis efficiencies for different fly ash ty pes. Fly ash was activated by NaOH and KOH solutions in a closed syste m. The zeolite conversion was studied as a function of temperature (15 0-200 degrees C), reaction time (8-100 h) and solution concentration ( 0.1-1 M). The estimated pressure during activation ranged from 0.48 MP a at 150 degrees C to 1.55 MPa at 200 degrees C. The activation was pe rformed using a sample concentration of 0.055 g mL(-1) The zeolites sy nthesized were NaP1, Nap derivatives (mainly sodalite hydrate), analci me, gmelinite and nepheline hydrate after NaOH activation, and phillip site after KOH activation. Subsequent experiments focused on short rea ction times for high conversion efficiencies and monomineral synthesis of zeolites. High synthesis efficiencies for NaP1 zeolite and analcim e were obtained with the fly ash types studied. The results highlight the importance of the mineralogical composition of the fly ash. Fly as hes with very similar SiO2/Al2O3 ratios show different zeolites synthe sis behaviour under the same activation conditons. These differences c ould be attributed to different SiO2/Al2O3 ratios of the glass matrix inferred from the differences in mineralogy at the same bulk chemical composition. (C) 1997 Elsevier Science Ltd.