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 (5-1,440min), adsorbent dosage (30-150gL(-1)), agitation speed (100-300rpm), initial concentration (263.2-1,363.6mg 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), 60min of contact time, 100g L-1 of adsorbent dosage, 200rpm of agitation speed, 263.2mg 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 (R-2>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 (G degrees), enthalpy (H degrees), and entropy of activation (S degrees) were 5.7113-6.5018kJmol(-1), -8.5415, and 8.8209Jmol(-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 degrees C). Results indicate that zeolite is the most efficient cation exchanger for NH4-N removal from landfill leachate.