Effects of Synthesis Conditions on the Formation and Quality of Zeolite During the Hydrothermal Zeolitization Processes of Fly Ash

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.