Determination of affecting parameters on removal of methylene blue dyestuff from aqueous solutions using natural clay: Isotherm, kinetic, and thermodynamic studies

Abstract

In this study, the removal of methylene blue dye, which is widely used in the textile industry, from aqueous solutions prepared synthetically using natural clay was investigated. The effects of initial pH, initial dye concentration, adsorbent concentration, particle size, stirring speed and temperature on the adsorption efficiency were examined and the suitability of the adsorption data to the adsorption models of Langmuir, Freundlich, BET and Temkin was investigated. The highest removal efficiency was obtained as 94.69% in the experiments using 0.3 g L−1 adsorbent concentration and 20 mg L−1 dye concentration. Experimental data were consistent with the Langmuir isotherm model. As a result of the kinetic study, methylene blue adsorption was found to be suitable for pseudo first order at low adsorbent doses and pseudo second order rate kinetics at high adsorbent dosages. The reaction enthalpy was determined as ∆Ho = -14.915 kJ mol−1 and the reaction entropy as ∆So = -23.196 J mol−1. Since the activation energy of adsorption is Ea = 35.08 kJ mol−1, it has been determined that the reaction is an exothermic reaction and takes place physically.