Cement serves as an essential cementitious material required for the construction of repositories for radioactive waste. Over the operational lifespan of such repositories, environmental CO₂ infiltrates the cement, leading to its carbonization and alteration of its physicochemical properties. This, in turn, affects its efficacy in blocking radionuclides.

This study aims to assess the long-term safety implications of cement carbonization on radioactive waste repositories.

The carbonization patterns of cement and its adsorption capabilities regarding the fission nuclide ¹³⁷Cs was taken as investigating object. Characterization techniques, such as X-ray fluorescence spectrometer (XRF), X-ray diffractometer (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), etc., were employed to analyze the changes in physicochemical properties of cement before and after carbonization. Furthermore, batch adsorption experiments were conducted to examine the adsorption behavior of ¹³⁷Cs in carbonized cement, elucidating the impact of carbonization on cement's adsorption performance.

Analysis results reveal that the carbonization process in cement primarily involves the conversion of hydration products such as Ca(OH)₂ and hydrated calcium silicate into CaCO₃, resulting in an increase in the specific surface area of cement with higher degrees of carbonization, hence significantly enhance the adsorption capacity for ¹³⁷Cs due to carbonization. Interestingly, the adsorption capacity exhibits an initial increase followed by a subsequent decline with increasing degrees of carbonization, surpassing that of non-carbonized cement.

Results of this study implicate that cement's adsorption of ¹³⁷Cs operates via chemical single-layer adsorption, and the mechanism remains unchanged by carbonization.