Hydrothermal Synthesis of Zeolite from Coal Fly Ash by Using NaOH/Na2Co3 Solution

Zeolites have been synthesized through hydrothermal reaction of coal fly ash with alkaline solutions in order to facilitate effective use of the fly ash generated from the coal power stations. The properties of synthesized zeolite were examined by X-ray diffraction, and characterized by cation exchange capacity (CEC) and specific surface area. Each of NaOH solution or Na2CO3 solution was applied to test the effects of alkali type on hydrothermal reaction. The reaction conditions established in the present work ware the ratio of solid and liquid, 1 : 4 and reaction temperature, 393 K for the favored synthesis of zeolite in only few hours without any pretreatment. Only zeolite P was synthesized when 0.5 ～ 3.0 mol/dm3 NaOH was used, whereas both zeolite P and hydroxysodalite were produced in the case of NaOH solution of 4.0 mol/dm3. CEC value of 350 meq/100 g of the zeolite P synthesized with 2.0 mol/dm3 NaOH was sufficient for a cation exchanger. SEM photographs showed the growth of zeolite on the surface of the undissolved fly ash, resulting texture of amorphous fly ash covered with the crystallized zeolite. Sodium carbonate solution of 1.0 mol/dm3 alone failed the synthesis reaction of zeolite, whereas addition of more than 15% of NaOH proceeded the reaction. The thickness of zeolite layer depended on the amount of NaOH