Equilibrium studies for the sorption of chromium and nickel from aqueous solutions using raw rice bran

The capacity of raw rice bran for chromium and nickel removal from aqueous solutions was investigated. The Langmuir and Freundlich adsorption models, which are in common use for describing sorption equilibrium for wastewater-treatment applications, were used to represent the experimental data and equilibrium data fitted well to the Freundlich isotherm model. The negative value of ΔG° for Cr(III) indicates the spontaneous nature of sorption, but positive values were determined for Cr(VI) and Ni(II). Indeed, Cr(VI) and Ni(II) are sorbed due to the strong interactions with the active sites of the sorbent. The kinetics data for chromium and nickel sorption onto rice bran were studied according mass transfer and intraparticle diffusion models in order to increase sorption process understanding. A very good correlation coefficient was obtained using the pseudo-second-order kinetic model, suggesting that chromium and nickel sorption process onto rice bran particles tend to follow second-order kinetics.