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

This study aimed to remove ammonium from paper mill industry (4500 m3 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 (r2 ⩾ 0.99) but show very poor fit for pseudo-first order model (r2 < 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 (r2 ⩾ 0.999). Thermodynamics parameters such as; free energy (ΔG0), enthalpy (ΔH0) and entropy (ΔS0) 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).

SEM micrographs of TAS (a) and intra-particle diffusion model for both adsorbents (b).Figure optionsDownload as PowerPoint slideResearch highlights
► In the present study, it was aimed to study the removal of ammonium from BKME by various sorbents, namely, fly ash, raw sepiolite and TAS, which are low-cost and abundantly available materials.
► In addition, the adsorption mechanism through various adsorption kinetics models was investigated.
► There is no study reported in the literature related to the use of fly ash and sepiolite as an adsorbent to remove ammonium from BKME discharged from the plant, which produces wastewater of 4500 m3 per hour.