Native and Magnetic Oxide Nanoparticles (Fe₃O₄) Impregnated Bentonite Clays as Economic Adsorbents for Cr(III) Removal

The present investigation describes the adsorption capability of native and magnetic oxide (Fe₃O₄) impregnated bentonite clays for the adsorption of Cr(III) from aqueous solutions. The characterization of native bentonite as well as the impregnated bentonite was performed by PZC, SEM, BET, XRD and FTIR spectroscopy. The results proved that magnetized bentonite with high specific surface area provides high affinity and fast kinetics for the uptake of Cr(III). In the case of lower metal ion concentration in working solutions, the adsorption efficiency of the impregnated form was better than the native form. The effects of pH, contact time, temperature and initial metal ion concentration on overall adsorption efficiency were determined in detail. The equilibrium data was interpreted by linear forms of Langmuir, Fruendlich and Dubinin–Radushkevich isotherm models. Maximum adsorption capacity (Xm) for Cr(III) uptake was obtained as 1.25 and 1.28 mmol·g⁻¹ for native and impregnated bentonite respectively. The apparent mean free energy of adsorption (E) determined from the DRK model was less than 8 kJ·mole⁻¹ indicating that the Cr(III) adsorption on both adsorbents was physisorption in nature. Two different kinetic models, pseudo first and pseudo second order models were subjected to evaluate the kinetic data and reaction mechanism.