Sorption characteristics and mechanisms of ammonium by coal by-products: slag, honeycomb-cinder and coal gangue

The adsorption behaviors of ammonium from aqueous solutions were investigated for three solid coal wastes, slag, honeycomb-cinder and coal gangue. The ammonium sorption processes were well modeled by the pseudo second-order model (R ² > 0.99). The experimental data were fitted to both the Langmuir model and the Freundlich model, with the Langmuir model better representing the data. The maximum ammonium sorption capacities calculated from the Langmuir model were 3.1, 5.0 and 6.0 mg/g for the slag, honeycomb-cinder and coal gangue samples, respectively. The pH value of the solution affected the ammonium removal, and the higher uptakes found in either neutral or alkaline conditions for the three materials. The thermodynamic parameters, ΔH, were calculated to be 29.75, 25.21 and 17.91 kJ/mol for the SL, HC and CG samples, respectively, with the positive values indicating that the ammonium sorption processes were endothermic. Based on the results, it can be concluded that coal gangue may have more potential for being used as a sorbent for the ammonium removal from wastewater among the three coal by-products.