Removal of Vanadium(IV) from Aqueous Solutions by Adsorption Process with Aluminum-Pillared Bentonite

Abstract

The objective of this research work is to investigate the possibility of using a natural bentonite clay as a precursor to produce aluminum-pillared clay (Al−PILC) for the removal of vanadium(IV) from aqueous solutions. The original bentonite and Al−PILC were characterized with the help of surface area analyzer, X-ray diffraction, scanning electron microscopy, and potentiometric titration. The adsorption of vanadium(IV) onto Al−PILC has been dynamically and thermodynamically investigated. Batch experiments were carried out as a function of solution pH, contact time, vanadium(IV) concentration, adsorbent dose, ionic strength, and temperature. The maximum adsorption capacity was observed in the pH range 4.5−6.0. The maximum adsorption of 99.8 and 88.5% took place at pH 5.0 from an initial concentration of 5 and 10 mg/L, respectively. The external mass-transfer and intraparticular mass-transfer diffusion models were tested to describe the kinetic data. It was shown that the adsorption of vanadium(IV) could be fitted to the intraparticular mass-transfer model. The temperature dependence indicates the endothermic nature of adsorption. The activation energy of sorption was also calculated. The percentage removal of vanadium(IV) decreased with increasing ionic strength. The equilibrium isotherm data were fitted to the Langmuir, Freundlich, and Scatchard isotherm equations to obtain the characteristic parameters of each model. The Freundlich isotherm was found to well represent the measured sorption data. Isotherm experiments conducted at different temperatures allowed the calculation of the isosteric heat of adsorption at different surface loading. The desorption data showed that the spent PILC can be regenerated for further use by 0.1 M HCl.