Effects of basicity and FeO concentration on the retention of 137Cs and 60Co in slag made from non-metallic radioactive wastes

Abstract

Summary Simulated non-metallic wastes containing 60Co, 137Cs and 152Eu were melted to examine the effects of basicity and FeO concentration on the retention of the radioactive nuclides in a resulting solidified product (Al2O3-CaO-FeO-SiO2 quaternary slag). The retention of 60Co was almost independent of chemical composition of slag. On the other hand, the retention of 137Cs decreased with an increase of the basicity of slag, defined as a ratio of CaO to SiO2 in wt. independent of FeO concentration. Energy dispersive X-ray fluorescence spectroscopic analysis and Mössbauer spectroscopic measurement were also conducted for the solidified product. Mössbauer spectra indicated that Fe2+ ions as well as Ca2+ ions existed as network modifying cations in a silicate network structure of slag. Referring to a structure model of silicate glasses, it is inferred that the retention of 137Cs reflects differences in chemical properties between Ca2+ and Fe2+ in the internetwork region formed by modifying cations and anionic non-bridging oxygen.