Synthesis of zeolites A and X from fly ashes and their ion-exchange behavior with cobalt ions

A modified fusion process was studied to synthesize zeolites A and X from f ly ash. It was found that the addition of aluminum hydroxide to the fused f ly ash solution followed by hydrothermal treatment at 60 degreesC produced single-phase zeolite A or a mixture of zeolites A and X depending on the so urce-of the as-received fly ash. The result confirms that the quantity of d issolved AZ species is critical for the type of zeolite formed in precursor solutions prepared from fused fly ashes. The ion-exchange behaviors of tre ated fly ashes containing zeolites A and X were tested with Co2+ ions. It w as found that the ion-exchange capability (IEC) of treated fly ash with Co2 + ions was much larger than that with Cs+ ions. In addition, the Co2+ ion-e xchange rate of zeolite X was faster than that of zeolite A. This is probab ly related to the bigger pore channels in zeolite X. The Co2+ IEC Of treate d fly ash containing zeolite A reached 67.6% of commercial zeolite A and th at containing zeolite X 83.1% of commercial zeolite X. Our study demonstrat ed that fly ashes can be converted to zeolites A and X, and these treated f ly ashes have great potential for removing heavy metals.