Adsorption of arsenic(V) on bone char: batch, column and modeling studies

Bone char has been used as a low-cost adsorbent for the removal of As(V) from waste water. The batch experiments show that the Langmuir isotherm describes well the adsorption behavior. The adsorption process follows a pseudo-second-order kinetic model. The column experiments were conducted at pH = 4 and 10 mg/L an initial concentration of As(V). The breakthrough curves were investigated for various conditions, such as different flow rates, column bed heights, adsorption cycles, coexisting cations and anions such as Mn2+, Al3+, PO4 (3-), SO4 (2-) and SiO3 (2-). The convection-diffusion equation was used to model the experimental transport data of As(V) for these conditions. It has been found that the coexisting cations can enhance As(V) immobilization and increase retardation factor (R (f)), and coexisting anions significantly decrease the diffusion coefficient (D (L)) of As(V). The secondary adsorption phenomena were observed in the breakthrough curves of column studies of As(V) with cations, especially Mn2+. The regeneration experiments using distilled water and 0.1 mol/L NaOH solution were done to evaluate the desorption degree. The total desorbed amounts from whole column for three experiments decreased from 8.98 to 7.67 mg and the desorption degrees increased from 0.51 to 0.71 unexpectedly, which indicates that the regeneration operation is feasible. Finally, the chemical analysis of column effluents and infrared spectroscopic analysis of absorbent both revealed that the ligand exchange and electrostatic interaction are the main removal mechanisms.