Microwave-assisted synthesis of coal fly ash-based zeolites for removal of ammonium from urine

Zeolites synthesized from biomass waste materials offer a great opportunity in the sustainable utilization of the waste. In this work, energy-efficient processes (i.e. microwave and ultrasound irradiation) were used to synthesize pure phase sodalite (zeolite) from coal fly ash obtained from a power plant in South Africa. The pure-phase sodalite was obtained with a comparatively higher surface area (16 m² g^-1) and cation exchange capacity (2.92 meq. g^-1) with 40 min total reaction time. The removal of ammonium from urine was carried out using (i) the coal fly ash-derived sodalite, (ii) raw coal fly ash and (iii) a commercially available natural zeolite (clinoptilolite). The pure phase sodalite exhibited the highest removal efficiency of about 82% and 73% in synthetic and real hydrolyzed urine respectively. The adsorption process followed the pseudo second-order kinetic model and the Freundlich adsorption isotherm, indicating that the adsorption process occurred on a heterogeneous surface.