Location of Alkali Ions and their Relevance to Crystallization of Low Silica X Zeolite

A novel method of intermediate addition of alkali ions is proposed to give phase selectivity of zeolite in crystallization stages. Location of alkali metal ions in formed zeolite A, low silica zeolite X (LSX), and their hydrogel prior to the crystallization is investigated with ion exchange isotherms in order to clarify the crystallization mechanism, where the specific alkali metal ion is required for selective growth of the zeolites. The role of potassium ion for the crystallization is found to be important to determine the final phase of crystals. Hydrated potassium ion has a function to assemble aluminosilicate precursors to form LSX by a strong salting-out effect; otherwise, sodium ion assembles the same building units into zeolite A. Intermediate addition of potassium ion into crystallizing media controls the final precipitating crystalline phase kinetically. Here our proposed method enables the building unit for zeolite A to be quenched and deposited into aluminosilicate hydrogel, resulting in the selective formation of LSX in the hydrogel phase.