Characterization of different bentonite and its application in the sorption of Cs and Sr from aqueous solution by bentonite-alginate microcapsules

The bentonite materials are frequently designed as buffer/backfill material for engineered barrier in final disposal for spent nuclear fuels (SNFs) or high-level radioactive waste (HLW) repository. The clay minerals showed a favourable environment for sorption of Cs and Sr, bentonite having high sorption toward Cs and Sr were encapsulated in the biopolymer matrices (sodium alginate, NaALG) in this study. The characterization of bentonite-alginate microcapsules (MCs) enclosing different bentonite (Taiwan, China, U.S) was examined and analysed by SEM, and the sorption of Cs and Sr in different bentonite-alginate MCs was investigated by batch methods. Spherical and elastic granules were obtained, and the particle size of microcapsules was about 500 -700 µm. A relatively higher distribution coefficient (K_d) of Cs for bentonite-alginate MCs than Sr. The sorption isotherm of Cs and Sr followed a Langmuir-type equation and it indicated that the sorption capacity of different bentonite-alginate MCs in Cs were ( 233.96 -266.57 mg/g) higher than Sr ( 19.40 - 63.01 mg/g). In fact, the ZH bentonite-alginate MCs has a lowest sorption capacity for Sr due to the ZH bentonite is Ca-type bentonite and the higher Ca²⁺ component and pyrite (FeS) mineral would may have a sorption competition with Sr²⁺ in the solution. In this study, the effect of different concentrations of non-radioactive Cs on the survivability of natural anaerobic bacteria was determined. The impact of Cs on bacteria was examined using molecular-biological methods and transmission electron microscopy techniques. Lower Cs concentrations (0.5 mM) promoted bacteria growth, while higher concentrations (1 mM) limited their growth, and 5 mM was lethal. (author)