Studies on the adsorption behavior of methyl orange from dye wastewater onto activated clay

In this study, activated clay was used as adsorbent for the removal of methyl orange (MO) from aqueous solution in a batch system. Experiments were carried out as a function of contact time, initial concentrations of solution, adsorbent dosage, solution pH, and temperature, and consequently, optimum condition of adsorption was obtained. The equilibrium adsorption data of MO on activated clay were analyzed by Langmuir, Freundlich and Temkin isotherm models, the results indicate that Langmuir and Temkin models provide better correlation of the experimental data. The pseudo-first-order, pseudo-second-order and Elovich kinetics models were used to analyze the kinetics data obtained at different concentrations. Among the kinetics models studied, the pseudo-second-order model was the best applicable model to describe the adsorption of MO onto activated clay. The values of Gibbs free energy of adsorption (ΔG°) were found to be −7.462 kJ mol−1, the negative value indicated the spontaneity of the adsorption process of MO onto activated clay. The values of ΔH° and ΔS° were found to be −12.289 kJ mol−1 and −16.474 J mol−1 K−1, respectively. The negative value of ΔH° reveals the adsorption is exothermic, and the negative value of ΔS° suggests that the confusion degree of adsorption process is decreasing.