Adsorptive removal of As(III) from aqueous solution using iron oxide coated cement (IOCC): Evaluation of kinetic, equilibrium and thermodynamic models

Abstract

The ability of iron oxide coated cement (IOCC) to remove As(III) by sorption from solution was assessed. Batch experiments were conducted to characterize the As(III) removal capacity of IOCC. The effects of process parameters such as pH (3.2–12), agitation speed (50–250 rpm), contact time, initial As(III) concentration (0.7–13.5 mg l −1) and background ions (Ca 2+, Mg 2+, Fe 3+, SO 4 2−, PO 4 3−, Cl − and NO 3 −) on As(III) uptake were investigated. The adsorption kinetics study at 303 K revealed that the uptake of As(III) ion was very rapid and most of fixation occurred within the first 20 min of contact and pseudo-second order rate equation was able to provide realistic description of adsorption kinetics. Linear regression analysis showed that the equilibrium data of As(III) adsorption at different initial As(III) concentrations and adsorbent dose of 30 g l −1, obeyed the Langmuir isotherm model with maximum sorption capacities of 0.73, 0.69, 0.67 and 0.66 mg g −1 of As(III) on IOCC at 288, 298, 308 and 318 K, respectively. Non-linear error analysis showed that Freundlich isotherm best-fits the equilibrium data for As(III) adsorption onto IOCC. Evaluation of the thermodynamic parameters Δ H°, Δ S° and Δ G° indicated a spontaneous and exothermic nature of adsorption. The presence of co-existing ions such as Ca 2+, Mg 2+, Fe 3+, SO 4 2−, PO 4 3−, Cl − and NO 3 − had no noticeable effect on As(III) removal showing excellent As(III) sequestering capability of IOCC. The adsorbent was also suitable for repeated use (for three cycles) without noticeable loss of capacity.