Synthesis of zeolites Na-A and Na-X from tablet compressed and calcinated coal fly ash

Abstract

Zeolites Na-A and Na-X are important synthetic zeolites widely used for separation and adsorption in industry. It is of great significance to develop energy-efficient routines that can synthesize zeolites Na-A and Na-X from low-cost raw materials. Coal fly ash (CFA) is the major residue from the combustion of coal and biomass containing more than 85% SiO 2 and Al 2 O 3 , which can readily replace the conventionally used sodium silicate and aluminate for zeolite synthesis. We used Na 2 CO 3 to replace the expensive NaOH used for the calcination of CFA and showed that tablet compression can enhance the contact with Na 2 CO 3 for the activation of CFA through calcination for the synthesis of zeolites Na-A and Na-X under mild conditions. We optimized the control variables for zeolite synthesis and showed that phase-pure zeolite Na-A can be synthesized with CFA at reactant molar ratio, hydrothermal reaction temperature and reaction time of 1.3Na 2 O: 0.6Al 2 O 3 : 1SiO 2 : 38H 2 O at 80°C for 6 h, respectively, while phase-pure zeolite Na-X can be synthesized at 2.2Na 2 O: 0.2Al 2 O 3 : 1SiO 2 : 88H 2 O at 100°C for 8 h, respectively. The composition, morphology, specific surface area, vibration spectrum and thermogravimetry of synthesized Na-A and Na-X were further characterized.