Adsorption Performance and Mechanism in Binding of Azo Dye by Raw Bentonite

The adsorption behavior of methyl orange (MO) from aqueous solution onto raw bentonite (RB) sample was investigated as a function of parameters such as pH, inorganic anion, contact time, and temperature. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms. Langmuir adsorption capacity was found to be 34.34 mg/g at pH 4.0. The pseudo‐first‐order, pseudo‐second‐order kinetic, and the intra‐particle diffusion models were used to describe the kinetic data. The values of the energy ( E a ), enthalpy (Δ H ≠ ), and entropy of activation (Δ S ≠ ) were calculated as 38.62 kJ/mol, 36.04 kJ/mol, and −150.05 J/mol K, respectively, at pH 4.0.