Preparation of Alkali‐Activated Slag‐Fly Ash‐Metakaolin Hydroceramics for Immobilizing Simulated Sodium‐Bearing Waste

The radioactive sodium-bearing waste (SBW), which is mainly generated from spent nuclear fuel reprocessing activities, requires to be stabilized into a solid form for geological disposal. In this study, the alkali-activated slag–fly ash–metakaolin hydroceramic (ASFMH) waste form for solidifying simulated SBW (S-SBW) was prepared by hydrothermal process. The mineralogy, morphology, composition, compressive strength, and chemical durability of ASFMH waste form were investigated. It is shown that crystalline analcime phase was formed in the hydration products of ASFMH waste form after alkaline activation and hydrothermal process. The introducing of S-SBW not only contributed to forming crystalline zeolite phase but also reduced the temperature and time for forming zeolite phase. Importantly, the cations including simulated radionuclides Sr2+ and Cs+ in S-SBW could be immobilized as cationic components in the channels or voids of zeolitic structure during the formation of analcime phase. Moreover, when the loading content of S-SBW in ASFMH waste form was 37.5 wt%, ASFMH waste form still exhibited superior mechanical strength, which was higher than 24 MPa. The product consistency test leaching results showed that ASFMH waste form possessed superior chemical durability after leaching test carried out for 7 d. It is suggested that ASFMH waste form is a promising candidate for application in immobilizing SBW.