Study of the adsorption of 2,4-dichlorophenoxyacetic acid from the aqueous solution onto activated carbon

Abstract

In this work, batch adsorption experiments were carried out for the removal of 2,4-dichlorophenoxyacetic acid (2,4-D) from the aqueous solution using activated carbon (AC) in the concentration range from 52.248 to 205.672 mgL-1. Adsorption isotherm of 2,4-D onto the AC was determined at 283, 293, 303 and 313 K. Adsorption equilibrium data were fitted to the Langmuir, Freundlich and Temkin isotherm models in the range of experimental concentrations and isotherm constants were determined. The equilibrium data were best represented by the Freundlich model. The adsorption data were analyzed using pseudo–first-order, pseudo-second-order and Weber-Morris kinetic models. It was found that the pseudo-second-order kinetic model was the most appropriate model for describing the adsorption kinetics and apparent equilibrium was reached within 40 min. Weber-Morris kinetics results included three linear portions within 1 to 120 minutes, indicating that there were at least three adsorption stages, including: film diffusion, intra-particle diffusion and mass action, but mainly governed by intra-particle diffusion. The adsorption of 2,4-D onto AC was a spontaneous and exothermic process with characteristics of physical adsorption, based on the observed thermodynamic conditions. Therefore, the increase in temperature, as predicted, hindered the adsorption and the rate of 2,4-D removal from solution by AC.