Adsorptive Selenite Removal Using Iron-Coated GAC: Modeling Selenite Breakthrough with the Pore Surface Diffusion Model

Abstract

Iron-coated granular activated carbon (Fe-GAC) was proven to be effective for removing selenite from aqueous solution in batch studies. Design and use of the adsorbent in column settings requires understanding the key mass transfer characteristics for full-scale applications. In this study, rapid small-scale column tests (RSSCTs) were conducted at various empty bed contact times (EBCTs). A pore and surface diffusion model (PSDM) was introduced to predict selenite breakthrough curves of continuous flow packed columns containing Fe-GAC. Effluent Se(IV) breakthrough occurred immediately in the experiment with 0.055-min EBCT. The column reactor was found to treat approximately 780 bed volumes of water containing 1.0 mg/L Se(IV) when EBCT was increased to 0.447 min before breakthrough occurred. The adsorption capacity was estimated to be 3.06 mg/g. The adsorption results showed that the PSDM could provide satisfactory predictions for the column performance with the external mass transport coefficient (kf) of 8.55×10−3 cm/s. Full-scale column design criteria, such as hydraulic loading rate (HLR), carbon usage rate (CUR), and degree of column utilization (DoCU) were calculated and recommended.