Interaction of phenol and chlorophenols with activated carbon and synthetic zeolites in aqueous media

The adsorption of phenol and the three chlorophenol (CP) isomers from aqueous solutions (in the concentration range 0.6-48 mmol dm(-3)) at 293 +/- 3 K has been studied in an agitated batch system using activated carbon and Na-Y and Ni/Na-Y zeolites as adsorbents. While equilibrium uptake on activated carbon was achieved within the first 2 to 4 h, extended treatment times were required to ensure an attainment of the maximum uptake on the zeolite samples; the latter observation is attributed to diffusion limitations. Uptake of CP on Na-Y was characterized by cyclical behavior indicative of a reversibly and irreversibly adsorbed component. The experimental adsorption isotherms were regressed using standard Langmuir and Freundlich treatments. Uptake on both activated carbon and Na-Y adhered to the Langmuir model, which, however, provided a poor fit to the Ni/Na-Y data; the latter were better represented by a Freundlich model. Adsorption is discussed in terms of the affinity factors that are extracted from the model isotherms and the variation of solution pH with uptake is illustrated. The three sorbents are assessed in terms of solute removal efficiencies, rates of adsorption, and sorbent capacities and the nature of sorbate/sorbent interactions are discussed. The heat evolved during adsorption was measured by calorimetry and the values/trends are compared with the model isotherm affinity parameters. (C) 2000 Academic Press.