(374l) Selective Removal of Cs+ in Acidic Nuclear Water Waste Using Epoxy Resins

The sequestration of Cs⁺ from aqueous media via adsorption had been the focus of many studies in the past few years because it complements the waste vitrification step before concentrated radioactive wastes are sent for long-term storage. Meanwhile, most studies have dealt with the treatment of contaminated surface waters and very few have reported on the adsorptive sequestration of Cs⁺ from nuclear fuel processing wastes or high level liquid wastes (HLLW). HLLW contains a variety of interfering metal ions which undermines the selective sequestration of Cs⁺. Also, HLLW contains high concentrations of oxidizing acid (~3 M HNO₃) which adversely affects the sequestration capacity of most adsorbents. As such, very few adsorbents have been employed successfully at removing Cs⁺ from HLLW, and so far these sorbents have been prepared only with calixarenes or its derivatives via impregnation in macroporous silica or polymeric resin, or by grafting onto mesoporous carbon.

In this work, a new class of adsorbents for the sequestration of Cs⁺ in HLLW is presented. Three types of low molecular weight oxygen- and sulfur-bearing bis-epoxides (BE) as binding sites for Cs⁺ were reacted with aliphatic diamine curing agents to obtain highly crosslinked epoxy resins as Cs⁺ adsorbents. The effects of diamine linker length, BE structure, and complexing atoms were navigated and correlated with the adsorption performance of the epoxy resins, particularly in terms of their capacity and selectivity for Cs⁺ in simulated HLLW.

Results reveal that the most Cs⁺-selective epoxy resin is prepared from a bis-epoxide bearing a benzene moiety having oxygen and sulfur donor atoms in ortho position and cured with diaminopropane (resin BE2-Ep). BE2-Ep is a yellow glassy resin that is thermally stable and mechanically tough in acidic medium. It has the right dimension of channel spaces which permit Cs⁺ permeation through its matrix. BE2-Ep registers a maximum capacity of 1.004 mmol g^-1 (133.5 mg g^-1) which is higher than that of other known Cs⁺ sorbents used in highly acidic media. BE2-Ep is most selective towards Cs⁺, rejecting other competing metal ions in simulated HLLW. This is the first report on epoxy resins with innate selectivity and capacity for Cs⁺.

This study was supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Science and ICT (2020R1A2C1003560, 2021R1A2C2093746, and 2021R1H1A2008284), Basic Science Research Program through the Ministry of Education (2020R1A6A1A03038817).