The removal of methyl orange (MO) from aqueous solution by adsorption on cholestyramine resin was
evaluated by batch mode. The experiments were performed as a function of initial dye concentration, stirring rate,
ionic strength, adsorbent dosage, pH and temperature. Adsorption process was attained to the equilibrium within
40 minutes. The adsorption capacity of MO increased with increasing initial dye concentration, stirring rate, and
decreased with increasing ionic strength, pH, adsorbent dosage and temperature. The experimental data were
analyzed by Langmuir and Freundlich isotherm models and fitted well to Langmuir model with a value of
adsorption capacity of (Qo) 200 mg/g of MO. The effect of temperature on removal capacity was examined and
was found to be an exothermic process. Thermodynamic parameters such as change in free energy (∆G), enthalpy
(∆H) and entropy (∆S) were determined. ΔH value was -17.85 kJ/mol confirming that adsorption was mainly
physisorption. The negative values of ΔG reflected the spontaneous nature of adsorption process and the negative
values of entropy change ΔS (-103.2 J/mol) imply an increase of randomness at the solid–solution interface
through the adsorption at low temperatures.