Yan Shan, Yang Dongyan, Chen Shuangqiang, Wen Juan, He Wenhao, Ji Shiyin, Xia Yue, Wang Yinlong, Zhou Liangfu, Li Yuhong
School of Nuclear Science and Technology, Lanzhou University, Lanzhou, 730000, China.
Dalton Trans. 2020 Feb 25;49(8):2578-2588. doi: 10.1039/c9dt04915k.
In this study, Ca4La6-xNdx(SiO4)4(PO4)2O2 (x = 0, 1, 2, 3, 4, 5, and 6) apatites were explored for nuclear waste immobilization, and Nd3+ ions were used as the surrogate of radionuclides (such as Am3+, Cm3+, and Pu3+). The synthesized samples conform to the P63/m (176) symmetry in the hexagonal system according to the characterizations by means of X-ray diffraction, Raman spectra, and Fourier-transform infrared spectra. Rietveld analyses indicate that both Ca2+ and Ln3+ (La, Nd) cations are located at the M4f and M6h sites, which is different from earlier studies. The M6h sites prefer to be occupied by Ln3+ (La, Nd) cations with higher valence. Besides, the content of the impurity phase Ca3(PO4)2 reduces from 2.815 wt% to 0 with the incorporation of Nd3+ ions. These results demonstrate that apatites possess excellent ability to accommodate radionuclides with various valences and radii at the M4f and M6h sites. Moreover, we investigated the thermal expansion behavior by high-temperature X-ray diffraction. There is no phase transformation in the range of 298-1173 K, and the Ca4La6-xNdx(SiO4)4(PO4)2O2 apatites exhibit lower thermal expansion coefficients than other candidates that have been extensively studied. Furthermore, the thermal expansion coefficient gradually decreases with the accommodation of Nd3+ ions. All the results suggest that apatites are promising candidates for nuclear waste immobilization.
在本研究中，探索了Ca4La6-xNdx(SiO4)4(PO4)2O2（x = 0、1、2、3、4、5和6）磷灰石用于固定核废料，并且使用Nd3+离子作为放射性核素（如Am3+、Cm3+和Pu3+）的替代物。通过X射线衍射、拉曼光谱和傅里叶变换红外光谱表征表明，合成的样品符合六方晶系中的P63/m(176)对称性。Rietveld分析表明，Ca2+和Ln3+（La、Nd）阳离子均位于M4f和M6h位点，这与早期研究不同。M6h位点更倾向于被高价的Ln3+（La、Nd）阳离子占据。此外，随着Nd3+离子的掺入，杂质相Ca3(PO4)2的含量从2.815 wt%降至0。这些结果表明，磷灰石在M4f和M6h位点具有容纳各种价态和半径的放射性核素的优异能力。此外，我们通过高温X射线衍射研究了热膨胀行为。在298-1173 K范围内没有相变，并且Ca4La6-xNdx(SiO4)4(PO4)2O2磷灰石的热膨胀系数低于其他已被广泛研究的候选物。此外，热膨胀系数随着Nd3+离子的掺入而逐渐降低。所有结果表明，磷灰石是用于固定核废料的有前景的候选物。
