Preparation of Na-P1 zeolite with high cation exchange capacity from coal fly ash

Abstract

Na-P1 zeolite having a high cation exchange capacity (CEC) was synthesized from coal fly ash using a modified conversion method into the zeolite by alkali fusion prior to conventional alkali hydrothermal reaction. For comparison, alkali hydrothermal and alkali fusion methods were studied at different conditions using NaOH as an alkali source; the CEC for NH4+ ions was measured with the products under each reaction condition. The results are discussed in terms of the crystal structure of the products. The coal fly ash was converted into the zeolite by an alkali hydrothermal reaction, through the course of Na-P1 --> hydroxy-sodalite with increasing NaOH concentration. The coal fly ash was mainly converted into sodium aluminum silicate by the alkali fusion method, without formation of any zeolite crystals. The products of the alkali hydrothermal reaction showed higher CEC values than did those obtained by fusion reactions because of crystal formation of Na-P1 zeolite. The coal fly ash was effectively converted into Na-P1 zeolite with high crystal purity and high conversion efficiency when using the modified method; it had a high CEC value of 221 meq/100 g.