Thermodynamic Study of Adsorption Process of Direct Red 16 Pollutant by LECA/Zirconia Adsorbent

Document Type : Original Article

Authors

1 Department of Applied Chemistry, Faculty of Basic Sciences, Malayer University, Malayer, Iran

2 Department of Physical Chemistry, Islamic Azad University of Tabriz, Tabriz, Iran

Abstract

This study investigates the effect of temperature and consequently the thermodynamic study of the adsorption process of Direct Red 16 dye as a target pollutant in an aqueous environment using fixed LECA/Zirconia adsorbent substrates. For this purpose, a mineral compound called LECA (as a stable substrate) and zirconia nanoparticles (as adsorbent) were prepared separately in the laboratory. Zirconia nanoparticles were coated onto LECA substrate surfaces to form fixed LECA/Zirconia adsorbent substrates. The successful fabrication of the substrates was confirmed by examining transmission and scanning electron microscopy images. To perform the adsorption process, the substrates were fixed on the inner walls of a double-walled hexagonal container. The effect of ambient temperature on the adsorption process was investigated by conducting several experiments at pH 2.7 in the temperature range of 5°C–40°C on solutions with an initial concentration of 30 mg/L of the target pollutant. The results show that temperature has a dual effect on pollutant removal efficiency in the initial and final stages of the adsorption process. In the second minute, increasing the temperature from 5°C to 40°C increased the removal efficiency from 44.1% to 55.7%. In the 30th minute, increasing the temperature from 5°C to 40°C decreased the removal efficiency from 93.2% to 89.3%. Thermodynamic studies showed that the negative values obtained for enthalpy (ΔH° = -18.51 (kJ/mol)), entropy (ΔS° = -0.049 (kJ/mol.K)), and Gibbs free energy (ΔG° < 0 (kJ/mol)) changes indicate exothermic physical adsorption, disorder reduction, and spontaneity of the adsorption process, respectively. The activation energy of the process was obtained by examining the effect of temperature on the second-order rate constants of the process based on the Arrhenius linear relationship, which is equal to 16.09 (kJ/mol).

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