Adsorption of vanadium (V) on natural kaolinite and montmorillonite: Characteristics and mechanism

Knowledge on adsorption behaviour of vanadium (V) on natural clay minerals is critical to understand V mobility in soil and aqueous systems. In this study, the characteristics and mechanisms of V(V) adsorption on two abundant soil clay minerals, namely, natural kaolinite and montmorillonite, as well as the effects of solution pH and ionic strength on the adsorption process were investigated. The results showed that the kinetics of V(V) adsorption on kaolinite and montmorillonite conformed to pseudo second-order, and reached equilibrium within 240 min and 360 min respectively. The adsorption isotherms of V(V) on kaolinite were better fit with the Freundlich model, while the Langmuir model was a better fit for montmorillonite. The Langmuir model indicated that natural montmorillonite and kaolinite have low affinity for V(V) anions with maximum adsorption capacity of 0.98 mg.g(-1) and 0.78 mg.g(-1), respectively. The higher capacity was found at pH 4-10 due to the mass formation of deprotonated hydroxyl groups for V adsorption. The V adsorption capacity on montmorillonite increased with the increasing ionic strength of NaNO3. The results of pH and ionic-strength effect showed that surface complexation and electrostatic interaction may be the V(V) adsorption mechanisms.