Collectable adsorbent based on the adsorption characteristics of sodium citrate-pretreated vermiculite for cesium ion in an aquatic environment

This study aimed to develop a collectable adsorbent for Cs using clay mineral and alginate gel. The adsorption capacity of vermiculite (Verm) for Cs increased from 97.1 mg/g to 119 mg/g after sodium citric treatment. The Verm used in this study has a partial chlorite structure, and the existence of interlayer material was considered. The adsorption sites of Verm for Cs increased because the interlayer material in the partly chlorite structure was removed via sodium citric treatment. The Langmuir adsorption isotherm described this adsorption phenomenon well, indicating that the adsorption of Cs by Verm after sodium citric treatment (Verm-Cit) is monolayer adsorption. Since a typical phenomenon was also observed in which the basal spacing became approximately 1.0 nm when Cs was adsorbed by the interlayer of vermiculite, the interlayer of Verm-Cit functioned as an adsorption site. Verm-Cit was encapsulated in alginate gel beads (AG-Verm-Cit) for accessible collection after adsorption. Although the equilibrium adsorption time of AG-Verm-Cit was extended from 10 min without encapsulation (Verm-Cit) to over 360 min, an adsorption capacity of 60.5 mg/g was obtained even after 30 min. The developed adsorbent requires time to reach equilibrium; however, the adsorption capacity was similar to or higher than reported in previous studies, even with a relatively shorter contact time. Additionally, the weight and volume of the adsorbent encapsulated in alginate gel beads can be decreased by air drying without heat. These properties can contribute to removing Cs from the aquatic environment and to the stable management of adsorbents with radionuclides.