Removal of NH₃-N from wastewater by novel zeolite X: adsorption behavior and removal mechanism

Abstract

This study utilized a straightforward method to fabricate zeolite X, demonstrating high adsorption performance for the removal of NH₃-N from wastewater. The adsorption behavior of zeolite X towards NH₃-N was investigated through various methods including adsorption kinetics, isothermal adsorption, and thermodynamic models. The mechanism of zeolite X for removing NH₃-N were analyzed using techniques such as SEM, EDS, XRD, BET, and XPS. The results indicated that when <i>t</i> = 30 min, pH = 6, zeolite dosage was 20 g/L and initial NH₃-N concentration was 100 mg/L, the removal efficiency of NH₃-N could reach 95.5%. The adsorption process followed Freundlich model and were endothermic. The enthalpy change (Δ<i>H</i>), entropy change (ΔS) and Gibbs function (ΔG(308.15 K)) were 10.66 kJ/mol, 28.81 J/(mol･K), and 1.78 kJ/mol, respectively. SEM and XRD analysis show that the crystal shape of zeolite X is octahedral, which is a typical morphology of FAU-type zeolite. The specific surface area of zeolite X was as high as 643 m²/g. The results of XPS analysis show that after Na⁺ exchange with NH₄⁺, hydrogen bonds were formed between ammonia nitrogen and oxygen in zeolite X. This study introduces a novel adsorbent, offering a fresh approach to tackling ammonia nitrogen pollution in wastewater.