Adsorption properties of surrounding rock for 137Cs in a cavern-type low and intermediate radioactive waste repository

BackgroundAt present, radioactive waste is treated by deep geological treatment. Caves-type repository as a geological repository near the ground, are more and more international and domestic concern due to its nuclear safety, low environmental pollution and good economy. A cavern-type low and intermediate radioactive waste repository is being constructed in Yangjiang area of Guangdong province, China, the surrounding rock of the waste repository will be the main dispose material of nuclide 137Cs.PurposeThis study aims to investigate the adsorption performance of the surrounding rock of this cavern-type low and intermediate radioactive waste repository for 137Cs.MethodsFirst of all, series of characterization analysis, such as X-ray Fluorescence (XRF), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), Brunauer-Emmett-Teller (BET), Barret-Joyner-Halenda (BJH) were employed to observe crystal structure and content of the surrounding rock of the waste repository. Irregular sheet-like structures stacked, the sheets in a compacted state, and the surface groups such as -OH, Si-O-Si, Si-O-Al, Si-O, etc. were shown to have good crystal structure and the highest SiO2 composite content. Then, the effects of time, pH value, solid-liquid ratio, initial radioactive activity concentration, and ions on the adsorption were investigated through static adsorption experiments. Finally, the adsorption kinetics and adsorption isotherm models were analyzed.ResultsThe results show that when the solid-liquid ratio is 5 g∙L-1, the initial radioactivity is 1 114.5 Bq∙L-1, the adsorption equilibrium time is 12 h, the equilibrium adsorption rate is 40.41%, and the equilibrium adsorption capacity is 90.07 Bq∙g-1. The adsorption rate increases with the increase of the solid-liquid ratio, and decreases with the increase of the initial radioactivity. The adsorption is inhibited under acidic conditions, but has little effect under neutral and alkaline conditions. Different ions inhibit the adsorption of 137Cs on the surrounding rock of the repository, and K+ has the greatest inhibition.ConclusionsThe adsorption of 137Cs by the surrounding rock is more in line with the pseudo-second-order kinetic model and the Freundlich adsorption isotherm model, providing the basic data for nuclear waste geological disposal engineering.