Abstract

Excessive release of ammonium (NH4+) into aquatic ecosystems can promote eutrophication. In this study, the natural adsorbents, coal (C) prepared from Hawthorn (Acacia caven) and coal fly ash obtained from C, were used to remove NH4+ from aqueous systems through batch adsorption-desorption studies. Both adsorbents were physically and chemically characterized, while Fourier-transform infrared spectroscopy and zeta potential were used to understand the surface functional groups and surface charge characteristics. CFA showed a higher pH, BET specific surface area, electrical conductivity and higher % values for CaO and MgO than C. Kinetic studies of NH4+ adsorption at pH = 4.5 for both materials fitted the pseudo-second-order model giving the r(2) of 0.970-0.983 and the chi(2) of 0.008-0.005 and at pH = 6.5 only for C with the r(2) of 0.986 and the chi(2) of 0.013. Meanwhile, the adsorption isotherm data at pH = 4.5 for both materials and 6.5 for CFA complied with the Freundlich model (r(2) > 0.965 and chi(2) < 0.012), suggesting that NH4+ adsorption onto both adsorbents at those pH values occurred through the formation of a multilayer adsorption on heterogeneous surfaces. This indicates that the dominant adsorption of both adsorbents was physisorption with no site-specific interaction. Based on these results, CFA is proposed as a promising and economical material for the removal of NH4+ from aqueous systems.