Iron-Modified Sepiolite for Ni2+ Sorption from Aqueous Solution: An Equilibrium, Kinetic, and Thermodynamic Study

Sepiolite was used for the synthesis of the sepiolite−iron oxide system to obtain a sorbent suitable for the removal of Ni 2+ from aqueous solution. The modified material, Fe-sepiolite, was characterized by X-ray diffraction analysis, Fourier transform infrared spectroscopy, differential thermal/thermogravimetric analysis, and point of zero charge (pH pzc ) determination. The sorption experiments were performed as a function of the initial metal concentration, equilibration time, and temperature using the batch method. The Fe-sepiolite had a higher sorption capacity than the natural sepiolite sample due to a higher specific sorption and a higher ion exchange with Mg 2+ ions from the sepiolite surface. Thermodynamic parameters, such as enthalpy, Gibbs energy, and entropy, were calculated from the temperature-dependent sorption isotherms, and these values showed that the sorption of Ni 2+ onto sepiolites was endothermic. Pseudo-second-order kinetic models provide the best correlation of the experimental kinetic data.