Adsorption kinetics modeling of benzene from aqueous solution onto rice husk activated carbon prepared by H3PO4 activation

Abstract

Biochemistry Department, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Kingdom of Saudi Arabia Hot Laboratories Centre, Atomic Energy Authority, Cairo 13759, Egypt E-mail : [email protected] Fax : 966-14675932 Manuscript received online 10 March 2014, revised 27 April 2014, accepted 27 April 2014 Benzene is one of the most hazardous organic pollutants in groundwater. The removal of benzene from water is very important from health point of view and for environmental protection. Activated carbon from rice husk (RHC) with H₃PO₄ activation was used to study batch aqueous benzene remediation kinetics. The adsorption profile showed an initial rapid uptake of benzene which decreased and became almost constant after 40 min of contact at which up to 80% benzene was removed from water. Different rate-based and diffusion-based kinetic models were adopted to understand the benzene adsorption mechanism on RHC. Three typical kinetic models namely, pseudo-first order, pseudo-second order and Elovich equations, were applied to interpret the kinetic data. The rate constants have been determined and the correlation coefficients have been calculated in order to assess which model provides the best fit predicted data with experimental results. The pseudo-second order models were well fitted to the kinetic data (R² = 0.98), thereby indicating that chemisorption. To investigate the rate determining step, the intra-particle diffusion and Boyed model was applied on the experimental data. External mass transport with intra-particle diffusion phenomena governed the rate limiting process, which has been confirmed from the Boyd poor non-linear kinetic plots. A comparative study on the benzene adsorption revealed that the RHC had better benzene adsorption capacity (365 mg/g) as compared to CNTs and other granular activated carbon. This suggests that the RHC are efficient benzene adsorbents and that they possess good potential for benzene removal in wastewater treatment.