Geochemical analyses on long-term performance of engineered barrier

为了提高放射性废物处置的安全性评价水平，安装具有高吸附能力的IO_3~-材料是非常重要的。类水滑石被认为是一种潜在的吸附IO_3~-的粘土矿物，其夹层中含有CO_3~(2-)、NO_3~(2-)或Cl~(2-)等。为了了解IO_3^-在不同类型水滑石上的吸附机理，我们研究了IO_3^-在含有CO_3^-作为层间阴离子的CO_3^-水滑石(HTCO_3)和含NO_3^-水滑石(HTNO_3)的层间阴离子中的吸附行为。结果表明，HTCO_3达到吸附平衡的时间比HTNO_3短，HTCO_3的吸附等温线由两个朗缪尔型吸附过程组成，而HTNO_3的吸附等温线只有一个，解吸行为有很大不同。这些结果表明，IO_3^-在HTCO_3外表面上的吸附很弱，包括两种吸附机制。另一方面，IO_3~-在HTNO_3层间的吸附是通过阴离子交换反应进行的。此外，还用DTA/TG和粉末X射线衍射法探讨了IO_3~-在HTCO_3和HTNO_3上的吸附机理。

For the improvement of safety assessment of radioactive waste disposal, it is important to install the material that has high capacity to sorb IO_3^-. Hydrotalcite-like compound, of which CO_3^<2->, NO_3^- or Cl^- etc. is contained in its interlayer, is considered to be a potential clay mineral for sorbing IO_3^-. In the present study, we studied the sorption behavior of IO_3^- to CO_3^<2->-hydrotalcite (HTCO_3) that contains CO_3^- as interlayer anion and NO_3^--hydrotalcite (HTNO_3) that contains NO_3^- as interlayer anion in order to understand the difference of the sorption mechanism of IO_3^- to the different type of hydrotalcite. It was found that the time to reach sorption equilibrium was shorter for HTCO_3 than that for HTNO_3, that the sorption isotherm for HTCO_3 consisted of two Langmiur type sorption processes but that for HTNO_3 consisted of one, and that the desorption behavior was quite different each other. These results suggest that the sorption of IO_3^- is occurred weakly on the external surface of HTCO_3 and includes two mechanisms of sorption. On the other hand, the sorption of IO_3^- to HTNO_3 is occurred in its interlayer by the anion exchange reaction. Furthermore, the sorption mechanisms of IO_3^- to HTCO_3 and HTNO_3 were also discussed from DTA/TG and Powder-XRD measurement.