Abstract: The formation and cation exchange capacity (CEC) of zeolite synthesized after alkaline activation of a Chinese fly ash, as a function of temperature, liquid/solid ratio, NaOH concentration
and reaction time in closed systems were investigated. Temperature affected mainly the crystallinity of zeolite formed, liquid/solid ratio
affected mainly the type of zeolite, and while NaOH concentration and reaction time influenced both of them. The CEC value of synthesized products
increased greatly as a function of temperature, liquid/solid ratio and reaction time until the temperature of 110℃, the ratio of 2.5,
and the time of 16h were reached, and then approached to a constant value. The CEC value of synthesized zeolite increased initially with the increase
in NaOH concentration, reached its maximum value at a concentration of 2mol·L^-1, and then decreased sharply above the concentration.
The results show that from the economic point of view, the optimal conditions are as follows: a temperature of 110～120℃, a reaction time of 8～16h,
a liquid/solid ratio of 2.5, and a NaOH concentration of 2mol·L^-1.

Key words: zeolite, synthesis condition, fly ash, cation exchange capacity