Dissolution of the zeolites NaA, potassium exchanged zeolite (KA) and the amorphous and crystalline phases obtained by thermal treatment of zeolite KA in hot alkaline solution

Abstract

Dissolution of the zeolites NaA (sodium form of zeolite A), KA (potassium exchanged zeolite A), and the solids K-as (amorphous aluminosilicate obtained by heating zeolite KA at 962°C for 30 min) and kk (mixture of kalsilite and kaliophilite obtained by heating zeolite KA at 962°C for 180 min) in 2 M NaOH solution at 70°C was investigated by X-ray diffractometry, scanning-electron microscopy, single point nitrogen absorption, differential thermogravimetry, measurement of particle size distribution, and chemical analysis of both the solid and the liquid phase at various stages of the dissolution process. While the dissolution of zeolite NaA and the starting dissolution of zeolite KA occurred in accordance with a previously developed model of dissolution, the dissolution of the solids K-as and kk occurred in two stages: rapid dissolution of a thin (sub)surface layer and slower dissolution of bulk particles followed by solution mediated transformation of the solids K-as and kk into zeolite NaA. The observed differences in the dissolution behavior are explained in the terms of structural characteristics of the investigated solids.