The synthesis and chemical durability of Nd-doped single-phase zirconolite solid solutions

Cai, Xin; Teng, Yan; Wu, Lei; Zhang, Kuibao; Huang, Yi

doi:10.1016/j.jnucmat.2016.07.042

Cited by 24 publications

(7 citation statements)

References 32 publications

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“…Zirconolite structured materials have been widely studied for the immobilization of actinide-rich radioactive waste streams, due to excellent chemical alteration resistance and radiation tolerance. − This includes use as a major constituent of the various SYNROC assemblages for the disposition of high-level actinide-rich wastes derived from nuclear fuel reprocessing. , The CaZrTi 2 O 7 parent structure has been shown to accommodate U, Pu, Np, and Cm and is therefore a suitable host matrix for minor actinide (MA) species such as Am. − Natural analogue specimens have also been shown to retain ∼20 wt % U/Th over geological timescales . The parent structure ABC 2 O 7 is derivative of the anion deficient fluorite structure type and is closely related to the pyrochlore A 2 B 2 O 7 family of minerals.…”

Section: Introductionmentioning

confidence: 99%

Phase Evolution in the CaZrTi₂O₇–Dy₂Ti₂O₇ System: A Potential Host Phase for Minor Actinide Immobilization

et al. 2022

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Zirconolite is considered to be a suitable wasteform material for the immobilization of Pu and other minor actinide species produced through advanced nuclear separations. Here, we present a comprehensive investigation of Dy 3+ incorporation within the self-charge balancing zirconolite Ca 1– x Zr 1– x Dy 2 x Ti 2 O 7 solid solution, with the view to simulate trivalent minor actinide immobilization. Compositions in the substitution range 0.10 ≤ x ≤ 1.00 (Δ x = 0.10) were fabricated by a conventional mixed oxide synthesis, with a two-step sintering regime at 1400 °C in air for 48 h. Three distinct coexisting phase fields were identified, with single-phase zirconolite-2M identified only for x = 0.10. A structural transformation from zirconolite-2M to zirconolite-4M occurred in the range 0.20 ≤ x ≤ 0.30, while a mixed-phase assemblage of zirconolite-4M and cubic pyrochlore was evident at Dy concentrations 0.40 ≤ x ≤ 0.50. Compositions for which x ≥ 0.60 were consistent with single-phase pyrochlore. The formation of zirconolite-4M and pyrochlore polytype phases, with increasing Dy content, was confirmed by high-resolution transmission electron microscopy, coupled with selected area electron diffraction. Analysis of the Dy L 3 -edge XANES region confirmed that Dy was present uniformly as Dy 3+ , remaining analogous to Am 3+ . Fitting of the EXAFS region was consistent with Dy 3+ cations distributed across both Ca 2+ and Zr 4+ sites in both zirconolite-2M and 4M, in agreement with the targeted self-compensating substitution scheme, whereas Dy 3+ was 8-fold coordinated in the pyrochlore structure. The observed phase fields were contextualized within the existing literature, demonstrating that phase transitions in CaZrTi 2 O 7 –REE 3+ Ti 2 O 7 binary solid solutions are fundamentally controlled by the ratio of ionic radius of REE 3+ cations.

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Section: Introductionmentioning

confidence: 99%

Phase Evolution in the CaZrTi₂O₇–Dy₂Ti₂O₇ System: A Potential Host Phase for Minor Actinide Immobilization

et al. 2022

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“…Anyhow, the leaching rates of Ca, Cu, and Hf are lower than or comparable to borosilicate glass (about 10 -2 g·m -2 ·d -1 , 90 ℃) [40,41]. Compared with zirconolite and pyrochlore based waste forms prepared by CS, hot pressing (HP), and hot isostatic pressing (HIP) [22,[42][43][44][45], the leaching rates of Ca and Cu in this research are much higher. Nevertheless, the Hf-bearing zirconolite-rich composite waste form is a durable waste form and the combustion synthesis is a rapid route for nuclear waste disposal.…”

Section: Chemical Stability Of the Cu-hf-06 Samplementioning

confidence: 67%

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

Zhang

Yin

et al. 2019

J Adv Ceram

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Zirconolite is recognized as one of the most durable waste matrices for the disposal of high-level radioactive wastes (HLWs). In this study, HfO 2 was employed as the surrogate of tetravalent actinides. Hf-bearing zirconolite-based composite waste forms (CaZr 1-x Hf x Ti 2 O 7 ) were rapidly prepared by combustion synthesis (CS) using CuO as the oxidant, where quick pressing (QP) was introduced to obtain densified samples. Similar as solid state reaction process, the Zr site of zirconolite can be totally occupied by Hf (x = 1.0) under the CS reaction. The original 2M zirconolite structure was maintained and a small amount of perovskite impurity phase was generated in the final products. The aqueous durability of representative sample (Cu-Hf-0.6) was tested, where the 42-day normalized leaching rates (LR i ) of Ca, Cu, and Hf are 0.25, 3.10×10 -2 , and 1.11×10 -8 g·m -2 ·d -1 .glasses is generally recognized as the first generation waste management method. 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]. Due to that the Ti 4+ and Zr 4+ ions can be mutually occupied, the zirconolite J Adv Ceram 2019, 8(3): 448-455 449 www.springer.com/journal/40145

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“…In contrast to the deionized water, weakly alkaline leaching agents will also promote the dissolution of the ceramic waste form, 50 which can lead to a slight enhancement of the normalized leaching rate of Nd. The leaching resistance of zirconia/garnet multi-phase ceramics waste forms with other ceramic waste forms was further compared, including widely studied single-phase ceramics 9,11,[50][51][52] and some multiple-phase ceramics, 17,19 the specific data are shown in Figure 8. The results showed that zirconia/garnet multi-phase ceramics exhibited superior chemical stability.…”

Section: Leaching Experimentsmentioning

confidence: 99%

Zirconia/garnet multiphase ceramics with high immobilization capacity for Nd confers better physical and chemical stability

Ge,

Xu,

Liao

et al. 2023

J Am Ceram Soc.

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Multiphase ceramics have a high application potential in the field of nuclear waste immobilization because of the efficient synergy between the individual phases. In this work, zirconia/garnet multiphase ceramics with high efficient and effective immobilization capacity of trivalent actinides were successfully prepared using conventional solid‐phase sintering. ZrO2 doping increases the lattice site available for nuclide substitution and advance the immobilization capacity of the ceramic substrate for nuclide. At the same time, the phase change of zirconia is used to tougher and improve the physical properties of the ceramic waste form. The feasibility of using multiphase ceramics for the efficient immobilization of trivalent actinides was assessed by studying the phase evolution, microstructure, Vickers hardness, and chemical stability of the multi‐phase ceramics. Zr1‐xNdxO2‐x/2/Ca3‐yNdyZr3‐yFey‐1Fe3O12 multiphase ceramics exhibited superior physical or chemical properties compared to most of the multiphase ceramics as well as the previously prepared single‐phase calcium garnet ceramic waste forms. The Vickers hardness of all the multiphase ceramic samples ranged between 685 and 730 HV0.5. Under the condition of using simulate Bei Shan groundwater as leaching agent, the normalized leaching rates of Nd is approximately 10−6 g·m−2·day−1, showing good chemical stability and achieving efficient and effective immobilization of trivalent actinides. The excellent chemical, as well as physical properties of Zr1‐xNdxO2‐x/2/Ca3‐yNdyZr3‐yFey‐1Fe3O12 multiphase ceramics are expected to make them one of the substrates for more efficient and effective immobilizing of trivalent actinides.

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The synthesis and chemical durability of Nd-doped single-phase zirconolite solid solutions

Cited by 24 publications

References 32 publications

Phase Evolution in the CaZrTi₂O₇–Dy₂Ti₂O₇ System: A Potential Host Phase for Minor Actinide Immobilization

Phase Evolution in the CaZrTi₂O₇–Dy₂Ti₂O₇ System: A Potential Host Phase for Minor Actinide Immobilization

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

Zirconia/garnet multiphase ceramics with high immobilization capacity for Nd confers better physical and chemical stability

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The synthesis and chemical durability of Nd-doped single-phase zirconolite solid solutions

Cited by 24 publications

References 32 publications

Phase Evolution in the CaZrTi2O7–Dy2Ti2O7 System: A Potential Host Phase for Minor Actinide Immobilization

Phase Evolution in the CaZrTi2O7–Dy2Ti2O7 System: A Potential Host Phase for Minor Actinide Immobilization

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

Zirconia/garnet multiphase ceramics with high immobilization capacity for Nd confers better physical and chemical stability

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Phase Evolution in the CaZrTi₂O₇–Dy₂Ti₂O₇ System: A Potential Host Phase for Minor Actinide Immobilization

Phase Evolution in the CaZrTi₂O₇–Dy₂Ti₂O₇ System: A Potential Host Phase for Minor Actinide Immobilization