Assessment of individual and mixed alkali activated binders for solidification of a nuclear grade organic resin loaded with 134Cs, 60Co and 152+154Eu radionuclides

• Published in: Journal of hazardous materials 2019-08, Vol.375, p.149-160
• Main Authors: El-Naggar, M.R., El-Masry, E.H., El-Sadek, A.A.
• Format: Article
• Language: English
• Subjects: Direct immobilization; fission/activation products; Geopolymeric microstructures; Leaching; Organic ion-exchangers
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2019.04.063

•Single, binary and ternary binders with at least 8% KY-2 have been well optimized.•Comparative leaching of 134Cs, 60Co and 152+154Eu radionuclides were assessed.•Leachability indexes were high and sometimes be twice the waste acceptance criteria.•The ternary binders were radiation stable while the solidified hot beads were not.•A three-step mechanism of such instability of the solidified hot beads was proposed. Individual metakaolin-based alkali activated binder (AAB) was utilized to optimize binary and ternary ones having feldspar/metakaolin and slag/feldspar+metakaolin ratios of 0.3 and 0.4, respectively. These three AABs had the ability to directly solidify 10.0 (FMK0-10R), 8.0 (FMK3-8R) and 12.0% (S4FMK3-12R) of the nuclear grade KY-2 beads, respectively, recording compressive strength values greater than twice the waste acceptance criteria. Leaching of 134Cs, 60Co and 152+154Eu, whether singularly or multiply loaded, was assessed. The multi-radionuclidic systems recorded greater leached fractions in the order of: 152+154Eu>134Cs>60Co. Among the studied systems, S4FMK3-12R formulations recorded the lowest diffusion coefficient values (D). Gamma-irradiation made a desired influence on all studied leaching systems with inverse relationships with the applied irradiation doses. Irradiating the optimized ternary AAB with 3.0 KGy (S4FMK3-12R-ɣ3) yielded the lowest D value (6.65 × 10−13 cm2/s), when single component-60Co was diffused. The leachability indexes of all irradiated AABs were not only greatly exceeded the value of 6 but also sometimes be twice such value. XRD, FT-IR and SEM examinations of S4FMK3, S4FMK3-12R and S4FMK3-12R-ɣ3 reflected their multi-layered semicrystalline natures and to what extent these AABs and the solidified beads had good and poor radiation stabilities, respectively, with a proposed three-step mechanism of such instability.