Fundamental study on the solidification of radionuclides with hydrous TiIV oxide modified with either Si or Zr

The potentiality of hydrous TiIV-Si oxide (TS) and hydrous TiIV-Zr oxide (TZ) for the selective sorption and immobilization of radioactive Co2+, Eu3+, Th4+ and UO22+ ions has been studied experimentally: the distribution coefficients and sorption capacity for these ions at various conditions in solutions, the structure and the composition of the exchangers in relevant ionic forms at high temperatures, and the leaching rates form the calcined exchangers into water and 0.01M HNO3 solution at room temperature. These results were discussed together with the results previously obtained for Cs+ and Sr2+, in order to evaluate the performance of TS and Tz as solidification media for radioactive liquid waste. TS takes up these cations more than TZ does in acidic solutions due to the higher acidity of the exchange site. In TZ, transition metal ions show high affinity despite the small distribution coefficients for representative metal ions. The dissolution of Co2+, Eu3+, and Th4+ is very slow from both calcined exchangers due to the crystallization of titanates of these cations. The leaching rates of Cs+, Sr2+ and UO22+ from calcined Ts are much slower than those from TZ, indicating the formation of titanium silicate containing these cations. Based on these results, TS is considered to be superior to TZ in the sorption capacity and fixation capability of various kinds of radionuclides and is considered as a promising material for the solidification of radwaste