Batch adsorption of 2,4-dichlorophenoxy-acetic acid (2,4-D) from aqueous solution by granular activated carbon

Adsorption equilibrium, kinetics and thermodynamics of 2,4-dichlorophenoxy-acetic acid (2,4-D), one of the most commonly used phenoxy acid herbicides, onto granular activated carbon were studied in aqueous solution in a batch system with respect to pH, temperature and initial 2,4-D concentration. At 600 mg l(-1) initial 2,4-D concentration activated carbon exhibited the highest 2,4-D uptake capacity of 518.0 mg g(-1) at 45degreesC and at an initial pH value of 2.0. Freundlich, Langmuir, Redlich-Peterson and Koble-Corrigan isotherm models were applied to experimental equilibrium data of 2,4-D adsorption depending on temperature. Equilibrium data fitted very well to the Freundlich and Koble-Corrigan equilibrium models in the studied concentration range of 2.4-D at all the temperatures studied. Some simple mass transfer and kinetic models were applied to the experimental data to examine the mechanisms of adsorption and potential rate controlling steps such as external mass transfer, intraparticle diffusion and adsorption process. It was found that both the boundary layer and intraparticle diffusion played important roles in the adsorption mechanisms of 2,4-D, and adsorption kinetics followed a pseudo first-order kinetic model rather than pseudo second-order and saturation type kinetic models for all temperatures studied. The activation energy of adsorption (EA) was determined as 8.46 kJ mol(-1) using the Arrhenius equation. Using the thermodynamic equilibrium coefficients obtained at different temperatures, the thermodynamic constants of adsorption (DeltaGdegrees, DeltaHdegrees and DeltaSdegrees) were also evaluated. (C) 2003 Elsevier B.v. All rights reserved.