Phillipsite synthesis from fly ash prepared by hydrothermal treatment with microwave heating

Coal fly ash was treated hydrothermally with NaOH aqueous solution at 373 K using microwave heating and conventional heating. X-ray diffraction and energy dispersive X-ray fluorescence measurements indicated that the crystal structure and chemical composition of the product powder do not depend on the heating method. However, microwave heating reduces the particle size of synthesized phillipsite. Moreover, microwave heating makes the waiting time for the beginning of crystallization much shorter than conventional heating, although it reduces the crystal growth rate slightly. It was also found that microwave heating promotes the rate of increase of the adsorption capacity of the product powder. Changes in the ion concentrations in NaOH aqueous solution and the peak intensity and adsorption capacity of the product powder suggest that microwave heating mainly has effects on nucleation and crystal growth of phillipsite. We proposed a new heating procedure, ‘partial microwave heating’, which has the advantages of both microwave heating and conventional heating. This heating procedure can develop the crystallinity and adsorption capacity of the product without reducing the crystal growth rate.