Abstract
The adsorption isotherm, the adsorption kinetics, and the thermodynamic parameters of ammonium removal from aqueous solution by using clinoptilolite in aqueous solution was investigated in this study. Experimental data obtained from batch equilibrium tests have been analyzed by four two-parameter (Freundlich, Langmuir, Tempkin and Dubinin-Radushkevich (D-R)) and four three-parameter (Redlich-Peterson (R-P), Sips, Toth and Khan) isotherm models. D-R and R-P isotherms were the models that best fitted to experimental data over the other two- and three-parameter models applied. The adsorption energy (E) from the D-R isotherm was found to be approximately 7 kJ/mol for the ammonium-clinoptilolite system, thereby indicating that ammonium is adsorbed on clinoptilolite by physisorption. Kinetic parameters were determined by analyzing the nth-order kinetic model, the modified second-order model and the double exponential model, and each model resulted in a coefficient of determination (R2) of above 0.989 with an average relative error lower than 5%. A Double Exponential Model (DEM) showed that the adsorption process develops in two stages as rapid and slow phase. Changes in standard free energy (∆G°), enthalpy (∆H°) and entropy (∆S°) of ammonium-clinoptilolite system were estimated by using the thermodynamic equilibrium coefficients.
Highlights
Discharging of wastewater streams containing high ammonium concentrations into the receiving body causes serious problems in the natural nutrient cycle between the living world and the soil, water, and atmosphere [1]
The main objective of the present study is to examine ammonium removal by clinoptilolite, which was initially pretreated with aqueous sodium chloride solution, and to analyze the equilibrium modeling by two- and three-parameter adsorption isotherms, the kinetic modeling by nth-order reaction, modified second-order and double exponential model, and the thermodynamic parameters of the ammonium removal
The adsorption of ammonium on clinoptilolite was evaluated as a function of two- and threeparameter isotherms, adsorption kinetics and thermodynamic aspect
Summary
Discharging of wastewater streams containing high ammonium concentrations into the receiving body causes serious problems in the natural nutrient cycle between the living world and the soil, water, and atmosphere [1]. Ramos et al [10] studied the effects of temperature and solution pH on ammonium ion exchange capacity of clinoptilolite obtained from mineral deposits located in San Luis Potosi and Sonora, Mexico. Besides these studies carried out to remove ammonium from the existing environment, zeolites have been examined in a variety of applications such as reducing the potential health risks of carcinogens caused by smoking [11], increasing the compost quality by trapping ammonium and reducing nitrogen losses from the compost [12]
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