Investigations on the adsorption efficiency of iron oxide coated cement (IOCC) towards As(V) - kinetics, equilibrium and thermodynamic studies

The potential of using iron oxide coated cement (IOCC) as a new material for the adsorption of As(V) from aqueous solution was investigated. The iron content of the adsorbent was 22.5 mg g(-1) and the pH of the point of zero charge (PZC), pH(pZc) = 11.1. Laboratory experiments were carried out as a function of pH, contact time, initial As(V) concentration and temperature to study the removal of As(V) on IOCC in a batch system. The IOCC showed a maximum removal for As(V) at pH similar to 8. The kinetics of adsorption of As(V) by IOCC, at room temperature and at various initial concentrations, was found to be fast, and reached equilibrium within 2 h and best described by the pseudo-second order model. With an adsorbent dose of 3 g l(-1) and contact time of 2 h, removal ranged from 98.7 to 88% at room temperature for initial As(V) concentrations ranging from 0.5 to 10 mg l(-1), respectively, at an initial solution pH similar to 7. The adsorption data fitted well with the Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms at 288, 298 and 308 K. The mean free energy values calculated from the D-R adsorption isotherm indicated a physical nature of adsorption. The thermodynamic parameters, such as Delta H degrees, Delta S degrees and Delta G degrees, were calculated from the slope and intercept of linear plot of In K-D against 1/T. Evaluation of the thermodynamic parameters depicts a spontaneous and endothermic nature of adsorption. The results indicate that IOCC is an effective adsorbent for removing As(V) from the aqueous environment. (c) 2005 Elsevier B.V. All rights reserved.