Adsorption of Eu(III) onto Gaomiaozi bentonite corroded by cement waters: Effect of cement solutions on the long-term sorption performance of bentonite in the repository conditions

Abstract : The adsorption of europium (Eu(III)) onto Gaomiaozi (GMZ) bentonite corroded by cement water at different stages was studied by batch experiments considering the in-situ conditions in a high-level radioactive waste (HLW) repository. Before this, the corrosion tests were carried out on compacted GMZ bentonite specimens with two cement solutions (Young Cement Water -YCW and Evolved Cement Water -ECW) simulating the early and late cement degradation waters during the long-term operation of a repository. X-Ray diffractometry (XRD) tests and scanning electron microscope (SEM) tests were performed to identify the characteristics of corroded GMZ bentonite. The results indicate that the adsorption capability of YCW corroded bentonite is similar to that of ECW corroded bentonite, and both of them are higher than that of raw GMZ bentonite. Cement solutions impact the adsorption performance of bentonite mainly by increasing pH of pore water in bentonite and altering its mineralogy (forming secondary minerals). Increasing pH implies increasing the sorption percentage of nuclide ions. Besides, most of the secondary minerals in bentonite have a good adsorption capacity. As a consequence, the cement solutions have positive effect on the long-term adsorption performance of bentonite, suggesting that GMZ bentonite is a good retention material in a high-level radioactive waste (HLW) disposal system.