Adsorption of As and Pb by Stone Powder/Chitosan/Maghemite Composite Beads (SCM Beads): Kinetics and Column Study

Adsorption kinetics of As and Pb onto composite beads synthesized with stone powder, chitosan, and maghemite (SCM beads) with weight ratio of 1:1:0.5 were investigated in batch mode. Several kinetic models such as pseudo-first order kinetic model (PFOKM), pseudo-second order kinetic model (PSOKM), two compartment first order kinetic model (TCFOKM), and modified two compartment first order kinetic model (MTCFOKM) were utilized to analyze the kinetics. Although the beads had low specific surface area and pore volume, MTCFOKM, one of two compartment models, could predict the most accurately because the As and Pb were adsorbed onto at least two kinds of adsorption sites such as functional groups in chitosan and Fe in maghemite. In MTCFOKM, both the fast adsorption fraction (f(1)') and the fast adsorption constant (k(1)') for Pb were higher than those for As. Therefore, the equilibrium time (t(eq)) for Pb adsorption was shorter than that for As adsorption, indicating that Pb adsorption was more affinitive than As adsorption onto SCM beads (especially maghemite). Column study with a bed column reactor packed with the SCM beads was also conducted. For column study, the effect of flow rate and pore volume on removal efficiency of As and Pb was also investigated. Three models such as the Thomas, Adams-Bohart (A-B), and Yoon-Nelson (Y-N) models were used to fit the column experimental data to analyze the breakthrough curves and the saturation time. Both Thomas and Y-N models were most appropriate. Conclusively, the SCM beads are suitable for adsorption treatment of As and Pb from contaminated groundwater and are particularly effective in Pb removal.