Research on the carbonization law of cement and its adsorption of 137Cs

BackgroundCement 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.PurposeThis study aims to assess the long-term safety implications of cement carbonization on radioactive waste repositories.MethodsThe 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.ResultsAnalysis 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.ConclusionResults of this study implicate that cement's adsorption of 137Cs operates via chemical single-layer adsorption, and the mechanism remains unchanged by carbonization.