Modeling of lead (II) biosorption by residue of allspice in a fixed-bed column

Residue of allspice (Pimenta dioica L. Merrill) obtained as a by-product from the essential oil supercritical extraction process, has been evaluated as a biosorbent for removing lead (II) from aqueous solutions in batch studies, but not in a practical system like a fixed bed column [12], [13]. In this paper, the effects of flow rate (20 and 40 mL/min), bed depth (8 and 15 cm) and influent lead concentration (15 and 25 mg/L) on the adsorption capacity of the residue of allspice in a fixed-bed column were investigated. The highest adsorption capacity (99.2%) on a 15 mg/L Pb(II) solution was achieved within a flow rate of 20 mL/min and a bed depth of 15 cm. The experimental data obtained from the adsorption process was successfully correlated with the Thomas, Adams-Bohart, Yoon-Nelson, Bed Depth Service Time (BDST), and Dose Response models. A rigorous model based on the differential balance mass transfer was also used to describe the adsorption process in the column. The results of the parameters zone mass transfer, diffusion and mass transfer coefficients obtained with modeling the continuous process could be applied to scale up the process to an actual industrial column.