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The synthesis of zeolite from coal fly ash by alkali hydrothemal reaction with NaOH was investigated under various conditions and the physical properties of the products were measured in this study. The reaction rate of cation exchange and substitution ratio of calcium ion were examined with some solutions containing calcium ion. Also, some physical properties of calcium type zeolite were measured. Zeolite P which had large cation exchange capacity (about 500 meq / 100 g as CEC) was synthesized from coal fly ash under the particular synthesis condition; reaction temperature of 393 K, reaction time of 5 hrs, NaOH concentration of 1.5 mol / dm3 and solid-liquid ratio of 200 g / 800 cm3. The crystal type of synthesized zeolite changed from zeolite P to hydroxysodalite with an increase in concentration of NaOH. The reaction rate was obviously increased when the reaction temperature was over boiling point of water. It was confirmed that the cation exchange reaction of zeolite synthesized in this study could be almost reversible between calcium ion and sodium ion. Optimum condition for zeolite synthesis with high CEC and calcium substitution, and some factors affecting zeolite synthesis and cation exchange reaction were discussed.

Alkali Hydrothermal Synthesis of Zeolite from Coal Fly Ash and its Cation Exchange Property.