Film-pore diffusion model for the fixed-bed sorption of copper and cadmiumions onto bone char

The sorption of copper and cadmium ions onto bone char in single component systems has been studied using fixed-bed column adsorbers. The effects of s olution flowrate, initial metal ion concentration and bone char particle si ze have been studied. A film-pore diffusion model has been developed to pre dict the fixed-bed breakthrough curves for the two metal ions. A sensitivit y analysis has been carried out to investigate the influence of the externa l mass transfer coefficient (film resistance), the effective diffusion coef ficient (pore diffusion) and the solid phase loading capacity. It is round that under the experimental conditions employed in the study, film diffusio nal resistance was tow and the Biot numbers were relatively high. Furthermo re. a constant effective pore diffusivity was not sufficient to correlate t he breakthrough curves accurately and a variable dependent effective diffus ivity was required; suggesting a possible contribution front surface diffus ion. Since the metal ion-bone char systems take a long time to reach equili brium. the solid phase loading capacity as predicted by the "best-fit" equi librium isotherm. was not Suitable for use in the diffusional mass transpor t model and the mass balance solid phase loading was utilised instead. (C) 2001 Elsevier Science Ltd. All rights reserved.