Adsorption kinetics, isotherms and thermodynamic studies of methyl blue in textile dye effluent on natural clay adsorbent

The study aimed to evaluate the adsorption efficiency for removing methylene blue (MB) from synthetic textile dye effluents on natural clay, sodium bentonite. The optimized parameters of the adsorption process were adsorbent dose, shaking speed, temperature, initial concentration of synthetic dye effluent (MB), contact time, and pH. The equilibrium isotherm and adsorption kinetics of Na-bentonite were studied using the Langmuir and Freundlich models, and pseudo-1st and 2nd order kinetics equations. The adsorption efficiency of Na-bentonite for removing methyl blue (MB) from textile dye effluents was more than 90% at the optimum conditions (120 rpm agitation speed, 60 min contact time, 4 gL⁻¹ adsorbent dose and 30 °C). The Langmuir equation showed a good agreement in correlation value than the Freundlich equation. The calculated value of qe (25.19 mg g⁻¹) for the pseudo-2nd-order equation was found to be in noble covenant with those of experimental value (24.99 mg g⁻¹). The calculated value of ΔH, ΔS and ΔG were found to be − 9.134 (kJ mol⁻¹), 25.062 (Jmol⁻¹ K⁻¹) and (− 17.02, − 15.84, − 22.03, − 15.88 and − 14.19 kJ mol⁻¹), respectively. The thermodynamic study illustrated that the adsorption process was exothermic and spontaneous. The study observed that the natural clay, Na-bentonite could be a potential adsorbent for removing methylene blue (MB) from textile dye effluents.