Optimization of hydrothermal synthesis of pure phase zeolite Na-P1 from South African coal fly ashes

This study was aimed at optimizing the synthesis conditions for pure phase zeolite Na-P1 from three coal fly ashes obtained from power stations in the Mpumalanga province of South Africa. Synthesis variables evaluated were: hydrothermal treatment time (12-48 hours), temperature (100-160°C) and varying molar quantities of water during the hydrothermal treatment step (H ₂O:SiO ₂ molar ratio ranged between 0-0.49). The optimum synthesis conditions for preparing pure phase zeolite Na-P1 were achieved when the molar regime was 1 SiO ₂: 0.36 Al ₂O ₃: 0.59 NaOH: 0.49 H ₂O and ageing was done at 47C for 48 hours. The optimum hydrothermal treatment time and temperature was 48 hours and 140°C, respectively. Fly ashes sourced from two coal-fired power plants (A, B) were found to produce nearly same high purity zeolite Na-P1 under identical conditions whereas the third fly ash (C) lead to a low quality zeolite Na-P1 under these conditions. The cation exchange capacity for the high pure phase was found to be 4.11 meq/g. These results highlight the fact that adjustment of reactant composition and presynthesis or synthesis parameters, improved quality of zeolite Na-P1 can be achieved and hence an improved potential for application of zeolites prepared from coal fly ash.