Kinetic and Thermodynamic Studies of Ion Exchange Process in Removal of Ca2+ and Mg2+ from Cooling Tower Water using Amberlite IR 120 and Amberjet 1200

Abstract

In this study, the thermodynamics and kinetics parameters of the ion exchange process in removing Ca²⁺ and Mg²⁺ from cooling tower water using Amberlite IR1200 and Amberjet were investigated. Thermodynamics and kinetics were studied by varying the amount of contact time (min), adsorbent (mL), temperature (K), concentration (mg/L) and pH of the solutions. The effectiveness of pecentage removal was found to rely on pH, as there was a significant increase of removal percentage Ca²⁺ and Mg²⁺ from pH of 3 to 6. The contact time was reached after 60 min on both resins. The correlation coefficients (R²) of Langmuir, Freundlich and Tempkin isotherms ranged from 0.92 to 1, suggesting that the experimental data best described the models. However, correlation coefficients (R²) for the D-R model range between 0.5 to 0.8, which means that experimental data does not fit the model well. Thermodynamic functions such as entropy (ΔSº), enthalpy (ΔHº) and change of free energy (ΔGº) were obtained from the gradient and intercepts of straight-line graphs. The positive values of ΔGº indicated that the adsorption is not spontaneous. Positive values of ΔHº were found, meaning the endothermic type of adsorption, which indicates the chances of physical adsorption. The correlation coefficient (R²) values of pseudo-first-order, pseudo-second-order and intraparticle models ranged from 0.89 to 1 on both metals. This observation indicates that pseudo-first-order, pseudo-second-order and intraparticle diffusion models best describe the experimental data in removing Ca²⁺ and Mg²⁺ from cooling tower water.