Multicomponent adsorption of phenols with activated carbon from aqueous solutions

Abstract

The adsorption of phenols with activated carbon has been studied as a model system for liquid-phase adsorption of organics from aqueous solutions. The design of adsorption equipments and the prediction of performance of equipment require information on the adsorption equilibria and mass transport mechanisms of adsorbates. For multicomponent adsorption systems, the competitive adsorption and the diffusional interaction between adsorbable species should also be considered. Single and two-component adsorption isotherms for phenols on activated carbon were studied experimentally. The Freundlich isotherm was suitable for single component systems. For competitive two-component adsorptions, two different Freundlich-type multicomponent isotherms were tested. An empirical isotherm proposed by Fritz and Schlunder (1974) gave good predictions of the amount adsorbed whereas the isotherm derived by Sheindorf et al. (1981) could be used satisfactorily when each component had a similar affinity for activated carbon. Experimental data of single component systems obtained in batch experiments were analyzed by two diffusion models, the pore diffusion model and the surface diffusion model. Although the amount of each adsorbate adsorbed was predicted properly by both models, the surface diffusion was more proper in describing the intraparticle diffusion than the pore diffusion. The concentration dependence of surface diffusion coefficients, $D_s$, was represented by a simple empirical equation in terms of the amount adsorbed, q, and the surface coverage, $\theta$. For multicomponent systems, it was better to use the dependence of $D_s$ on $\theta$ than that on q, since surface migration of each adsorbate is affected by the surface coverage formed by all species on the surface. The adsorbate having lower affinity for the adsorbent had stronger concentration dependence of $D_s$. The affinities of phenols for activated carbon are in the order: $\mbox{phenol}< \mbox{p-chlorophenol}< \...