Adsorption of Tl(I) on Na-montmorillonite and kaolinite from aqueous solutions

Na-montmorillonite (Na-Mt) and kaolinite as low-cost adsorbent were performed to remove thallium( I) from aqueous solutions, and their adsorption behavior toward Tl(I) was evaluated. The adsorption of Tl(I) was strongly ionic strength and pH-dependent. Pseudo-first-order and pseudo-second-order models fitted well with the adsorption kinetic studies for all materials with an equilibrium time of 5 min. Furthermore, the adsorption isotherm were analyzed and fitted best by the Langmuir model. The adsorption capacity of Na-Mt was, 29.3 mg/g, much higher than that of kaolinite under the chosen conditions. The adsorption of Tl(I) on Na-Mt was an endothermic process, but on kaolinite, it was exothermic process. The desorption and regeneration studies demonstrated that Na-Mt and kaolinite, which underwent five consecutive adsorption-desorption processes, still retained high Tl(I) removal efficiency. The possible adsorption mechanisms in view of cation exchange and surface complexation predominated that the Tl(I) adsorption processes were interpreted, and the X-ray diffraction and desorption results also verified the possible mechanisms. This work suggested that Na-Mt and kaolinite may be promising candidates for the removal of Tl(I) ions from aqueous solutions.