Iron Oxide-Coated GAC Adsorbents: Diffusion-Controlled Sorption of Selenite

Abstract

Iron oxide-impregnated granular activated carbon has been proven to be successful in removal of selenite (Se(IV)) from aqueous solution. However, the key application component of the mass transfer operations and diffusion coefficient has not been determined. In this study, a modified finite bath diffusion control model with changing initial Se(IV) concentrations was analytically derived, and a constant related to radius of the absorbent particle and the fractional attainment of adsorption was introduced into this model. Batch adsorption studies of Se(IV) onto Fe−GAC were conducted at three different initial concentrations ranged from 0.5 to 2.0 mg/L with loading rate from 0.21 to 0.80 g/L. Results confirmed that the modified model is applicable to both low initial concentration with low fractional attainment and high initial concentration with X̅ > 0.5, while the original model was only applicable for the low initial Se(IV) concentration. The observed sorption kinetics was consistent with the finite bath diffusion, with an average value of 2.9 × 10−4 cm2/s for the product of the distribution coefficient and the effective diffusivity in the adsorption of Se(IV) on the iron oxide-coated granular activated carbon.