Ammonium ion removal from aqueous solutions using fly ash derived zeolites by alkaline fusion

In this study, fly ash (FA) with different chemical compositions was converted into zeolites by a fusion method, as confirmed by Fourier-transform infrared spectroscopy (FTIR). FA was obtained from three different thermal power plants in Bosnia and Herzegovina: Ugljevik, Stanari and Gacko. In the FA spectrum, a quite wide absorption band was observed at 1097 cm(-1), while in those of the synthesized zeolites, this absorption band is narrowed and elongated and displaced toward 972 cm(-1). These characteristic bands can be attributed to substitution of Si4+ with Al3+ in the tetrahedron, during the formation of alumosilicate and their interaction with Na+ ions. Chemical analysis has shown that the dominant component was SiO2 in the FA Ugljevik (UF) and FA Stanari (SF) with mass fractions of - 36.43 and 48.18 %, respectively and CaO in the FA Gacko (GF) with the mass fraction of 65.89 %. In studies of ammonium ion adsorption equilibrium was achieved after 24 h in zeolites of UF and SF, while for the GF sample it was necessary 48 h to reach the equilibrium. Kinetic studies of have shown that the adsorption process on all zeolites followed the Elovich model with high values of the coefficient of determination. The largest amounts of adsorbed ammonium ions were measured at the pH 8 amounting to 5.98, 6.54 and 4.23 mg NH4+/g zeolite for UF, SF and GF, respectively. Examination of adsorption isotherms have shown the better agreement of the obtained results with the Langmuir model for the SF zeolite sample, and the Tempkin model for the UF and GF zeolite samples. Regenerated zeolites have shown similar adsorption capacities for ammonium ions (for UFr 10.3 mg/g; for SF 12.0 mg/g; for GFr 7.8 mg/g) as initial zeolites (for UF 12.2 mg/g; for SF 12.1 mg/g; for GF 14.3 mg/g). Examination of adsorption isotherms of regenerated samples has also shown the best agreement with the Langmuir model for all regenerated samples. The obtained similar and even higher removal percentages of ammonium ions from a real sample of wastewater by using regenerated zeolites (for UFr 60.7 %; for SFr 55.2%; and for GFr 30.7 %) as compared to the initial ones (for UF 45.1 %; for SF 60.6%; for GF 26.0 %) show potentials of the synthesized zeolites from fly ash for ammonium ion removal from wastewaters.