Study on Leaching Behaviors of Pyrochlore-rich Synroc Under Simulated Disposal Conditions

The leaching behavior of pyrochlore-rich synroc incorporated with 46.8% simulated actinides is studied under the following five simulated geological disposal conditions: bentonite, granite, granite+ferroferric oxide, granite+cement, and bentonite+ferroferric oxide. The mass loss rate reaches 1×10~(-7) g·cm~(-2)·d~(-1) after 182 d. That suggests that the mass loss rate of pyrochlore-rich synroc loaded with 46.8% actinide waste is very low. The surfaces of the leached specimens are analyzed by XRD, SEM/EDS. The experimental results show that two new phases form on the specimen surface of pyrochlore-rich synroc, that contains bentonite and cement, after leaching at 90 ℃ for 728 d. The bentonite and cement can retard leaching of elements from the specimen, while ferroferric oxide can speed the leaching process. Except Ti ions being depleted on the specimen, the other ions, such as U, Zr, Al, and Ca, are in a steady state, whereas Ba ions are enriched during the leaching process. These facts indicate that the simulated geological medium possesses good retarding ability for element leaching.