Adsorption of ammonium from an aqueous solution by fly ash and sepiolite: Isotherm, kinetic and thermodynamic analysis

Abstract

This study aimed to remove ammonium from paper mill industry (4500 m 3 h −1) wastewater, which is discharged to sea from a plant located in the western Turkey. As adsorbent, fly ash, raw sepiolite and thermal activated sepiolite (TAS) were used. The effect of factors such as; particle size, temperature and pH on adsorption process was investigated. From kinetic studies, equilibrium time was found as 1 h for both adsorbents. From experiments carried out at different pHs, it was observed that pH plays an important role in the ammonium adsorption process, both ionizating the compounds and modifying sorbent surfaces. It was also observed that fly ash is more effective than raw sepiolite and TAS to remove ammonium and in addition, adsorption increases with decreasing particle size. The kinetic data support pseudo-second-order model ( r 2 ⩾ 0.99) but show very poor fit for pseudo-first order model ( r 2 < 0.90). Intra-particle model also shows that there are two separate stages in sorption process, namely, external diffusion and the diffusion of inter-particle. Adsorption isotherms for fly ash and TAS were fitted to Freundlich models more effectively than Langmuire models ( r 2 ⩾ 0.999). Thermodynamics parameters such as; free energy (Δ G 0), enthalpy (Δ H 0) and entropy (Δ S 0) were also calculated. Based on the results, it can be concluded that the sepiolite and fly ash have potential of being used as a sorbent for removal of ammonium in wastewater treatments from Bleached Kraft Mills Effluent (BKME).