Self-propagating synthesis of Y2−xNdxTi2O7 pyrochlore and its aqueous durability as nuclear waste form

Synchrotron x‐ray spectroscopy investigation of the Ca1−xLnxZrTi2−x(Al, Fe)xO7 zirconolite ceramics (Ln = La, Nd, Gd, Ho, Yb)

“…Monoclinic‐ZrO 2 and ZrSiO 4 are typical pure ZrO 7 and ZrO 8 coordination, respectively and employed as reference compounds in many researches . The reason for only using these two coordination environments is that there are only seven‐ and eight‐ coordinated sites for Zr in the zirconolite‐2M structure . According to the results shown in Figure D and the studies to differentiate ZrO 7 and ZrO 8 environments in the literature, it is concluded that the Zr has a major sevenfold oxygen environment with a trace of 8‐coordinated environment.…”

“…[49][50][51][52][53] The reason for only using these two coordination environments is that there are only seven-and eight-coordinated sites for Zr in the zirconolite-2M structure. 10,11 According to the results shown in Figure 10D and the studies to differentiate ZrO 7 and ZrO 8 environments in the literature, 49,[51][52][53] it is concluded that the Zr has a major sevenfold oxygen environment with a trace of 8-coordinated environment. This conclusion is consistent with those reported by Rossell who used Rietveld structural XRD to study the cations occupancy in zirconolite-2M structure and revealed that 2-7.5% of Ca 2+ sites (in forms of CaO 8 ) was replaced by Zr 4+ in zirconolite-2M structure.…”

“…After decades of research, the SYNROC, glass-ceramic, and single-phase ceramic minerals (zirconolite, pyrochlore, monazite and so on) have been employed to immobilize HLW which contains considerable minor actinides due to their advantages in physicalchemical properties and high solubility of actinides. 1,3,[6][7][8][9][10][11][12][13][14][15][16] As one of the advanced ceramic waste forms, zirconolite has excellent properties in radiation resistance, mechanical stability, high waste loading, high thermal conductivity, and low leach rate and has been considered to be a potential candidate for the disposal of HLW. 9 As a promising matrix of HLW ceramic waste forms, zirconolite has several polymorphs.…”

Rapid Synthesis and Chemical Durability of Gd2- x Nd x Zr2O7 (0.0 ≤ x ≤ 2.0) Sub-Micron Ceramics as Nuclear Waste Forms

“…Then, there is a slight uctuation between the 7th and 42nd days. For short-term leaching tests, uctuations in LR i values on the same order of magnitude is a common phenomenon [41] . The leaching values of Nd and Zr on the 42nd day are 1.1 × 10 − 6 g•m − 2 •d − 1 and 2.5 × 10 − 7 g•m − 2 •d − 1 , respectively.…”

Combustion synthesis of Hf-doped zirconolite-rich composite waste forms and the aqueous durability

“…In recent decades, highly durable ceramic materials have been proposed as an alternative medium for HLW immobilization [4][5][6]. The naturally existed zirconolite and pyrochlore are important actinide-bearing ceramic materials, which exhibit excellent chemical and physical durability over geological time scales [7][8][9][10][11][12]. Zirconolite (ideally CaZrTi 2 O 7 ) was also developed as a crystalline phase to sequester Pu from surplus nuclear weapons, which makes it receive great attention as a potential waste form [13].Zirconolite is formed by the stacking layers of edge shared Ti-O polyhedra (TiO 5 and TiO 6 ) and layers of Ca 2+ and Zr 4+ cations [14].…”