Fundamental study on the separation and solidification of radwaste with hydrous titanium(IV) oxides modified with either silicon or zirconium

无机离子交换剂对放射性物质具有较高的吸附能力，并且可以通过简单的热处理转化为稳定的废物形式，是一组很有前途的放射性废液固化材料。实验研究了放射性Cs^+、Sr^<2+>、Co^<2+>、Eu^<3+>、Th^<4+>和UO_2^<2+>离子在水合Ti^<IV>-Si氧化物（TS）和水合Ti^<IV>-Zr氧化物（TZ）中的选择性去除和固定化潜力。研究了这些离子在不同条件下在溶液中的分布系数和吸附量，交换剂在高温下相应离子形态的结构和组成，以及煅烧后的交换剂在室温下对水和0.1 m HNO_3溶液的浸出率。TS对这些阳离子的吸收比TZ多，但对Cs^+和Sr^<2+>中Th^<4+>和UO_2^<2+>的分离在TZ上比TS更彻底。Sr^<2+>、Co^<2+>、Eu^<3+>和Th^<4+>在（]SY.gtoreq）煅烧的TS和TZ交换剂中溶解。[)900 .由于Co^<2+>, Eu^<3+>和Th^<4+>的钛酸锶硅酸盐或钛酸盐结晶速度很慢。随着热处理温度的升高，TS中Cs^+和UO_2^<2+>的浸出率显著降低，而TZ中由于可溶的Cs_2O和α - u_3o_8的形成而没有这种影响。在Cs^+和UO_2^<2+>形式的TS交换剂中，大部分强烈的x射线衍射峰不能归属于已知的化合物，表明形成了晶体学上未知的硅酸钛铯和硅酸钛铀。综上所示，TS对各种放射性核素的吸附和固定能力均优于TZ，是一种很有前途的放射性废物固化材料。

Inorganic ion-exchangers are a group of promising materials for the solidification of radioactive liquid waste, since they have high sorption capacity for radioactive species, and can be converted into stable waste forms suitable for disposal by simple thermal treatment. The potentiality of the selective removal and immobilizatin of radioactive Cs^+, Sr^<2+>, Co^<2+>, Eu^<3+>, Th^<4+>, and UO_2^<2+> ions in hydrous Ti^<IV>-Si oxide (TS) and hydrous Ti^<IV>-Zr oxide (TZ) has been studied experimentally : The distribution coefficient 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 rate from calcined exchangers into water and a 0,01M HNO_3 solution at room temperature.TS uptakes these cations much more than TZ does, but the separation of Th^<4+> and UO_2^<2+> from Cs^+ and Sr^<2+> is performed more completely on TZ than TS.The dissolutions of Sr^<2+>, Co^<2+>, Eu^<3+> and Th^<4+> from calcined TS and TZ exchangers at (〕SY.gtoreq.〔)900ﾟC are very slow due to crystallization of strontium titanium silicate or titanates of Co^<2+>, Eu^<3+> and Th^<4+>. The leaching rate of Cs^+ and UO_2^<2+> from TS significantly decreases with increasing temperature for thermal treatment, while such effect is not observed in TZ due to the formation of soluble Cs_2O and alpha-U_3O_8. In calcined TS exchangers in the Cs^+ and UO_2^<2+> forms, most of the intense X-ray diffraction peaks cannot be assigned to known compounds, indicating the formation of crystallographycally unknown caesium titanium silicate and uranium titanium silicate.Based on these results, TS is superior to TZ in the sorption capacity and fixation capability of various kinds of radionuclides and considered as a promising material for the solidification of radwaste.