Chromatographic separation of Cs in simulated high-level liquid wastes

Spherical and elastic AWP-CaALG microcapsules (∼700 m in diameter) were obtained and fine crystals of AWP were uniformly immobilized in alginate matrices. The uptake of Cs⁺, Rb⁺ and Ag⁺ in 2 M HNO₃ for AWP-CaALG was examined by batch method. The uptake of Cs⁺ was fairly fast in the initial stage and the uptake equilibrium attained within 5 h. The decreasing order of K_d was Cs⁺ > Rb⁺ > Ag⁺, and the separation factors of Cs/Rb and Cs/Ag were estimated to be over 10, suggesting the selective separation of Cs⁺. The K_dCs value was almost constant over 10 ³ cm³/g in the wide concentration range of HNO₃ up to 5 M. The uptake (%) of Cs⁺ in simulated HLLW (SHLLW, 28 components solution, SW-11E, JAEA) was estimated to be 97%, and the distribution of Cs⁺ into AWP phase and Zr/Ru to alginate phase were observed by EDS analysis. The stepwise chromatographic separation of Cs⁺ in SHLLW was examined under different eluting conditions using the columns packed with AWP-CaALG xerogels. The stepwise elution conditions were as follows; (1) H ₂O→1 M HNO₃→5 M HNO₃→3 M NH ₄NO₃→5 M NH₄NO₃ (25°C), (2) H₂O→3 M NH₄NO₃ (25°C), (3) H ₂O→1 M NH₄NO₃→5 M NH ₄NO₃ (25°C), (4) H₂O→1 M NH ₄NO₃→ 5 M NH₄NO₃ (40°C), (5) H₂O→1 M NH₄NO₃→5 M NH ₄Cl (25°C). Most effective separation of Cs⁺ was accomplished under the condition of (3); most of the Rb⁺ and Ag ⁺ ions over 90% were eluted by 1 M NH₄NO₃, and Cs+ ions eluted by 5 M NH₄NO₃. The recovery ratio was estimated to be 73.4%. The AWP-CaALG xerogel column is thus effective for the selective separation and recovery of Cs⁺ from SHLLW.