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BackgroundIn cave disposal environment, surrounding rock is the last barrier to prevent radionuclides from entering the environment, and the colloid of surrounding rock produced in the long-term disposal process increases the risk of radionuclides migration.PurposeThis study aims to explore the adsorption performance of surrounding rock colloid for Sr2+ disposed the repository, and the stability of surrounding rock colloid.MethodsFirst of all, the surrounding rock colloid sample was prepared with approximate mass concentration of 0.03 g·L-1, zeta potential of 21.53 mV and particle size of 205.7 nm. Then, the effects of time, pH value, various ions under different concentrations, and other factors on the adsorption properties, such as the zeta potential and average particle size of the surrounding rock colloids were investigated by experimental measurements. Finally, the adsorption kinetics and adsorption isothermal model were analyzed.ResultsExperimental results show that the colloid adsorption Sr2+ reaches equilibrium at 12 h, and the equilibrium adsorption capacity is 41.79 mg·g-1. In alkaline environment, the adsorption capacity increases with the increase of pH. The adsorption of Sr2+ by colloid of surrounding rock is inhibited by different ions, and the inhibitory effect of cations is greater than that of anions.ConclusionsResults of this study indicate that pH value, temperature and partial ions in the groundwater of the cave disposal facility all have influence on the stability of surrounding rock, and the surrounding rock colloid has good stability in the groundwater environment of the repository. The adsorption of Sr2+ by surrounding rock colloid conforms to the quasi-second-order kinetic model and the Freundlich adsorption isothermal model.

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.

BackgroundCement mortar is an essential building and barrier material for geological disposal repositories of radioactive waste. Therefore, it is of great significance to study the preparation of the cement mortar and its adsorption property and mechanism for radionuclides.PurposeThis study aims to study the preparation of M15 cement mortar and its adsorption property as well as mechanism for Co2+.MethodsA cavern-type low and/or intermediate-level radioactive waste repository under construction in the South China was selected as a real reference for the design and manufacture of M15 cement mortar. Adsorption properties of the M15 cement mortar for Co2+ were determined through the static batch test method combined with the inductively coupled plasma atomic emission spectrometry analysis. Characterization analyses of the M15 cement mortar were performed by X-ray fluorescence spectrometer, X-ray diffractometer, infrared spectrometer and scanning electron microscope.ResultsCompressive strength tests show that the M15 cement mortar with cement:sand:water mass ratio of 1.0∶4.84∶0.84 meets compressive requirements. The characterization analyses reveal that the M15 cement mortar had good crystal structure, large specific surface area, amorphous distribution of particles and surface distributed with a large number of groups, such as OH-, HCO3-, CO32-, SiO42-. Adsorption results from the static batch test show that: (1) the adsorption equilibrium time, adsorption distribution coefficient (Kd) value, adsorption rate and adsorption capacity of the M15 cement mortar are 6 h, 1 453.93 mL∙g-1, 74.14% and 73.37 mg∙g-1, respectively, (2) the Kd value, adsorption rate and adsorption capacity increase with the decrease of particle size, (3) the Kd value is 1 626.02 mL∙g-1 when the solid-liquid ratio is 2 g∙L-1, indicating that the M15 cement mortar has good absorption capability for Co2+, (4) the Kd values rise with the increase of pH values of water phase, and (5) the order of inhibition effects of ions on the Co2+ adsorption is Mg2+>Ca2+>SO42->NO3->Cl->K+. Adsorption mechanism of the M15 cement mortar for Co2+ can be described with the pseudo-second-order kinetic model and Langmuir adsorption isotherm model.ConclusionsThis study provides a useful reference for the preparation of superior performance cement mortar to build disposal repositories of radioactive waste.

For this study, ion-eroded cement was prepared from the cement required for construction of middle- and low-level radioactive waste repositories in caves. The properties for adsorption of 137Cs on cement before and after ion erosion were investigated. XRF, XRD, SEM–EDS and BET were used to analyse various cement materials. The effects of reaction time, solid–liquid ratio, initial radioactivity and different ions on adsorption were studied by static batch experiments. When the initial radioactivity was 1114.5 Bq L−1 and the solid–liquid ratio was 5 g L−1, the adsorption equilibrium time was 12 h. Adsorption of 137Cs on ion-eroded cement was more effective than that on untreated cement. The adsorption process was consistent with the pseudosecond-order kinetic model and the Freundlich isotherm model, and the process involved multilayer chemisorption. This study provides basic research data for construction of a disposal repository. [ABSTRACT FROM AUTHOR]

To the chemical behavior of Pu on backfill material for high-level radioactive waste repository. Adsorption and desorption of Pu on Natural bleaching earth, Na-bentonite, GMZ-bentonite, Ca-bentonite, acid-Ca-bentonite and alk-Ca-bentonite are discussed in this paper. Data analysis shows that adsorption abilities of Ca-bentonite, alk-Ca-bentonite, Ca-bentonite are greater than GMZ-bentonite, Natural bleaching earth, Na-bentonite, and in which Na-bentonite is relatively minimal. Desorption abilities of Na-bentonite, acid-Ca-bentonite are greater than alk-Ca-bentonite, Ca-bentonite, GMZ-bentonite, Natural bleaching earth, and in which GMZ-bentonite and Natural bleaching earth are relatively minimal. When the pH of the water phase is 1 or 13, the adsorption ability of Ca-bentonite is changed obviously. One reason is that the degree of surface complex reaction has been changed. Another reason is that the compositions and structure of Ca-bentonite have been also changed after acidizing or alkalosis by H + or OH − in the water phase. [ABSTRACT FROM AUTHOR]