Kinetics and Mechanism of Cr(VI) Sorption from Aqueous Solution on a Modified Lignocellulosic Material

Abstract

Abstract Kinetic aspects of sorption of Cr(VI) on modified lignocellulosic material rice straw (RS-AE) in a neutral water solution has been studied through batch sorption experiments and test of experimental data with pseudo-first and -second order rate models, Elovich's equation and a diffusion model. Results showed pseudo-second order rate expression provided the best fit kinetic model for all of the Cr(VI)–RS-AE system studied. Activation energy (Ea=24.53 kJ/mol) suggested that the sorption of Cr(VI) is an endothermic chemical sorption process. It was found that film diffusion governed the rate-limiting process under most experimental conditions except for the dilute Cr(VI) solution (0.15 mM). The removal mechanism of Cr(VI) was also investigated in this work, and it found that Cr(VI) was removed mainly through ion exchange with chlorine on RS-AE under neutral pH conditions. Appearance of Cr(III) both in a solution and in RS-AE indicated that reduction of Cr(VI) was included in the removal mechanism.