Chromatographic separation of Cs in simulated high-level liquid wastes

摘要

Spherical and elastic AWP-CaALG microcapsules (～700 μm 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_(d,Cs) value was almost constant over 10~3 cm~3/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) H2O->1 M HNO3->5 M HNO3->3 M NH4NO3->5 M NH4NO3 (25°C), (2) H2O->3 M NH4NO3 (25°C), (3) H2O->1 M NH4NO3->5 M NH4NO3 (25°C), (4) H2O->1 M NH4NO3-> 5 M NH4NO3 (40°C), (5) H2O->1 M NH4NO3->5 M NH4CI (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.