Adsorption properties of Cs⁺for composite adsorbents and their irradiation stabilities

Novel composite adsorbents using impregnation-precipitation methods have been developed; these fine crystals are loaded in the macropores of porous silica gels and zeolites, considering the stable granulation of these adsorbents and cost efficiency in the separation processes. The present study deals with the preparation of composite adsorbents, their characterization, breakthrough properties of Cs⁺ and irradiation stability. The composite adsorbents (KCoFC-NM (NM: natural mordenite, 0.4∼1.0 mm), KCoFC-SG (SG: porous silica gel, NH and Q-10)) were prepared by impregnation-precipitation methods. The breakthrough properties of Cs⁺ were examined by varying the kind of matrix (SG and NM), particle size (0.2∼1.3 mm φ), flow rate (0.1, 0.2 cm³/min) and component system (single and mixed solutions). The breakthrough profile for the single solution (200 ppm Cs⁺- 400 g/L NaNO₃- 4.3 g/L Na₂SO₄) was considerably affected by the particle size and the KCoFC-SG (Q-10, 0.6∼1.0 mm φ) had an excellent S-shaped profile (Fig. 1) and relatively large breakthrough capacity (0.038 mmol/g) of Cs⁺. The breakthrough capacity for the mixed solution was almost similar to that for the single solution. The breakthrough property of KCoFC-NM column was similar to that of KCoFC-SG (Q-10, 0.6∼7.0 mm φ). The flow rate in the range of 0.1∼0.2 cm ³/min had no effect on the breakthrough property. The ⁶⁰Co-irradiation stability of KCoFC-NM in the presence of 400 g/L NaNO₃ was compared with that of KCoFC loaded resin (T-KCFC). The distribution coefficient and saturation capacity of Cs⁺ for KCoFC-NM were almost constant even after irradiation up to 2.72 MGy, while those for T-KCFC resin were lowered after irradiation above 0.52 MGy and many cracks were observed on the surface. The KCoFC-SG and KCoFC-NM composites are thus effective for the selective separation of ¹³⁷Cs in LLW containing highly concentrated sodium nitrate.