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

Dissolution of the zeolites NaA (sodium form of zeolite A), KA (potassium e xchanged zeolite A), and the solids K-as (amorphous aluminosilicate obtaine d by heating zeolite KA at 962 degrees C for 30 min) and kk (mixture of kal silite and kaliophilite obtained by heating zeolite KA at 962 degrees C for 180 min) in 2 M NaOH solution at 70 degrees C was investigated by X-ray di ffractometry, scanning-electron microscopy, single point nitrogen absorptio n, differential thermogravimetry, measurement of particle size distribution , and chemical analysis of both the solid and the liquid phase at various s tages of the dissolution process. While the dissolution of zeolite NaA and the starting dissolution of zeolite KA occurred in accordance with a previo usly 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 tran sformation of the solids K-as and kk into zeolite NaA. The observed differe nces in the dissolution behavior are explained in the terms of structural c haracteristics of the investigated solids.