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.