Ammonium removal from landfill leachate using natural zeolite: kinetic, equilibrium, and thermodynamic studies

Abstract

The scope of this study is to research the removal of NH₄-N from landfill leachate using natural Turkish zeolite by adsorption process. The effects of pH (2–8), contact time (5–1,440 min), adsorbent dosage (30–150 g L⁻¹), agitation speed (100–300 rpm), initial concentration (263.2–1,363.6 mg L⁻¹), and particle size (10–65 mesh) were examined on the adsorption process. The optimum conditions in the adsorption process were established as follows: pH (its pH value of leachate), 60 min of contact time, 100 g L⁻¹ of adsorbent dosage, 200 rpm of agitation speed, 263.2 mg L⁻¹ of initial concentration, and −20 + 35 mesh of particle size. The adsorption kinetics and isotherms were tested to understand the adsorption mechanism using three kinetic models, i.e. Elovich, intraparticle diffusion, the pseudo-second-order reaction kinetic models, and four isotherm models, i.e. Dubinin–Radushkevich, Langmuir, Tempkin, and Freundlich isotherm models. Correlation coefficients, kinetic, and isotherm parameters were calculated. It was shown that the best conformity kinetic model was the pseudo-second-order reaction kinetic model (R² > 0.99) for the present study. According to the results obtained from isotherms experiments, the adsorption equilibrium was defined well by the Langmuir and Tempkin isotherm model for NH₄-N adsorption onto zeolite. The thermodynamic parameters were also detected. The values of Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy of activation (ΔS°) were 5.7113–6.5018 kJ mol⁻¹, −8.5415, and 8.8209 J mol⁻¹ K⁻¹, respectively. They were showed that the NH₄-N adsorption process onto zeolite was an exothermic physical adsorption process, randomness, and non spontaneous in the temperature range studied (25–60°C). Results indicate that zeolite is the most efficient cation exchanger for NH₄-N removal from landfill leachate.