Colloids existing in soils and groundwater aquifers can facilitate the transport of environmental contaminants including radionuclides as well as hydrophobic organic compounds. The mobility of colloids depends strongly on dispersion and aggregation of the particles. Therefore, the environmental fate and stability of colloidal bentonite particles under various conditions are crucial for assessing the safety of radioactive waste repository. In China, bentonite from Gaomiaozi region (Inner Mongolia, China) has drawn widely concerns as a buffer material in high-level radioactive waste repository. Erosion of the back-filled bentonite blocks by flowing in-situ groundwater is expected to produce bentonite colloids easily.
In present work, aggregation of bentonite colloids were investigated by the photon correlation spectroscopy (PCS), effects of colloids concentration, pH, background electrolytes (including Eu3+, Ba2+, Sr2+, Ca2+, Mg2+ and Na+) and humic substance on colloidal aggregation were discussed in detail, and the DLVO model were employed to demonstrate the aggregation process. Results showed that the stability of GMZ Na-bentonite colloids was dependent significantly on cations concentrations and pH values, while slightly on colloids concentrations and anions concentrations, aggregation was getting obvious and kinetically fast when increasing either salinity or acidity. The presence of humic acid enhanced colloidal stability and thus acted as an unstable role in repository terrains. The results in present work can provide a fundamental understanding on environmental behavior of bentonite colloids as well as a vital reference for safety assessment of high-level radioactive waste repository.