Hydrothermal Dissolution of Perovskite: Implications for Synroc Formulation

Kastrissios, T.; Stephenson, M.; Turner, Peter S.; White, Timothy J.

doi:10.1111/j.1151-2916.1987.tb05689.x

Cited by 35 publications

(9 citation statements)

References 20 publications

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“…From reaction (1), we should expect that the decrease in alkalinity results in increasing the leaching rate of Na from loparite. Note that in experimental systems, cation leaching from perovskite-type compounds occurs in the pH range 4.5-6.0 (Myhra et al, 1984;Kastrissios et al, 1987).…”

Section: Discussionmentioning

confidence: 99%

“…Significantly less information is available on the stability of the Ti-based REE-ACT hosts in various geological environments. There is a very limited number of experimental studies on the behaviour of these phases under hydrothermal conditions (Nesbitt et al, 1981;Myhra et al, 1984;Kastrissios et al, 1987), and mineralogical publications describing primary or secondary alteration of naturally-occurring titanates (Banfield and Veblen, 1992;Lumpkin and Ewing, 1996).…”

Section: Introductionmentioning

confidence: 99%

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Loparite and ‘metaloparite’ from the Burpala alkaline complex, Baikal Alkaline Province (Russia)

et al. 1999

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Loparite-(Ce) is a ubiquitous accessory mineral in modally diverse albite-rich metasomatic rocks of the Burpala alkaline complex, Siberia. Compositionally, the mineral approaches the ideal formula NaREETi206 (REE -Ce > La > Nd > Pr > Sin), and contains minor CaTiO3 (<4.8 omOl.%), SrYiO3 (<4.7 tool.%) and NaNbO3 (<6.4 tool.%), The mineral is pseudocubic lap = 3.8815(3) A], and produces an XRD pattern similar to that of synthetic NaCeTi206 [Pnma, a = 5.4517(4), b = 7.7058(9), c -5.4333(6) A]. The atomic coordinates and isotropic thermal parameters of synthetic NaCeTi206 refined from an XRD powder pattern using the Rietveld method, are given. At Burpala, loparite precipitated from an alkaline REE-rich fluid during the metasomatic alteration of earlier-formed intrusive rocks. In some parageneses, loparite was replaced by 'metaloparite' during the final stages of metasomatism. 'Metaloparite' has the empirical formula REETi;06 x(OH,F)x.nH20, and shows minor enrichment in Ca and depletion in Sr, compared to co-existing loparite. The formation of 'metaloparite' involved cation leaching, hydration and ion-exchange between loparite and a fluid. 'Metaloparite' is metamict at room temperature, but some samples regain the perovskite-type strncture upon heating.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Loparite and ‘metaloparite’ from the Burpala alkaline complex, Baikal Alkaline Province (Russia)

et al. 1999

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“…At temperatures below 100 ~ the major alteration product on the surface of Synroc consists of an amorphous or poorly crystalline Ti-O-H film derived mainly from the dissolution of perovskite (Murakami 1985;Kastrissios et al 1987;Myhra et al 1988bMyhra et al , 1988cSolomah & Matzke 1989;Lumpkin et al 1991Smith et aL 1997a). Some dissolution of Mo-rich intermetallic particles is also observed at this temperature.…”

Section: Polyphase Ceramicsmentioning

confidence: 93%

Geochemical behaviour of host phases for actinides and fission products in crystalline ceramic nuclear waste forms

Lumpkin

Smith

Gieré

et al. 2004

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A number of polyphase or single-phase ceramic waste forms have been considered as options for the disposal of nuclear waste in geological repositories. Of critical concern in the scientific evaluation of these materials is their performance in natural systems over long periods of time (e.g., 103 to 106 years). This paper gives an overview of the aqueous durability of the major titanate host phases for actinides (e.g., Th, U, Np, Pu, Cm) and important fission products (e.g., Sr and Cs) in alternative crystalline ceramic waste forms. These host phases are compared with reference to some basic acceptance criteria, including the long-term behaviour determined from studies of natural samples. The available data indicate that zirconolite and pyrochlore are excellent candidate host phases for actinides. These structures exhibit excellent aqueous durability, crystal chemical flexibility, high waste loadings, and well-known processing conditions. Although both pyrochlore and zirconolite become amorphous due to alphadecay processes, the total volume swelling is only 5-6% and there is no significant effect of radiation damage on aqueous durability. Hollandite also appears to be an excellent candidate host phase for radioactive Cs isotopes. Brannerite and perovskite, on the other hand, are more prone to alteration in aqueous fluids and have a lower degree of chemical flexibility. With the exception of hollandite, many of the properties of these potential host phases have been confirmed through studies of natural samples.

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“…The incorporation of Th 4+ within the more abundant perovskite phase (~14 wt%) would be considered highly undesirable, as the lower durability of perovskite with respect to the target zirconolite phase may negatively impact the overall performance of the wasteform, resulting in accelerated release of Th 4+ (and Pu, by analogy) from the ceramic phase into solution in the disposal environment. 32 Undigested ThO 2 was observed in the microstructure, clearly visible in Figure 11 as relics with bright contrast, with a clear reaction rim surrounding the ThO 2 cores. The composition of these reaction rims was consistent with both XRD and EDS analyses as ThTi 2 O 6 (i.e., thorutite), evidencing that the reactions did not reach equilibrium under the imposed conditions (1300°C dwell temperature maintained for…”

Section: Microstructure Analysismentioning

confidence: 96%

Synthesis, structure, and characterization of the thorium zirconolite CaZr_1‐xTh_xTi₂O₇ system

et al. 2021

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The United Kingdom is in the process of consolidating all civil Pu inventories at the Sellafield site, in an effort to satisfy security and proliferation requirements, presenting a significant decommissioning challenge in terms of materials degradation. 1 The Nuclear Decommissioning Authority (NDA) is liable for the management and disposition of all nuclear wastes under UK safeguards, and has commissioned a credible options analysis to identify technically mature reuse and disposition options, one of which is a strategy of immobilization and disposal. 2 Zirconolite (nominally CaZrTi 2 O 7 ) is the proposed candidate ceramic wasteform for the immobilization of Pu oxides. [3][4][5][6][7] The zirconolite-2M parent structure is derived from the anion-deficient fluorite unit cell, and is closely related to the A 2 B 2 O 7 pyrochlore structure (Fd-3m) by a compression along the (111) direction. Furthermore, a range of polytypical zirconolite structures (e.g., 4M, 3O, 3T) have been reported, the formation of which is controlled by cation substitution and processing conditions. [8][9][10] The zirconolite-2M unit cell is considered the archetype, with observed stability over the compositional range CaZr x Ti 3-x Ti 2 O 7 (0.8 < x < 1.3), with a lamellar unit cell crystallizing in the space group C2/c. 11 The nomenclature "2M" is a

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Hydrothermal Dissolution of Perovskite: Implications for Synroc Formulation

Cited by 35 publications

References 20 publications

Loparite and ‘metaloparite’ from the Burpala alkaline complex, Baikal Alkaline Province (Russia)

Loparite and ‘metaloparite’ from the Burpala alkaline complex, Baikal Alkaline Province (Russia)

Geochemical behaviour of host phases for actinides and fission products in crystalline ceramic nuclear waste forms

Synthesis, structure, and characterization of the thorium zirconolite CaZr_1‐xTh_xTi₂O₇ system

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Hydrothermal Dissolution of Perovskite: Implications for Synroc Formulation

Cited by 35 publications

References 20 publications

Loparite and ‘metaloparite’ from the Burpala alkaline complex, Baikal Alkaline Province (Russia)

Loparite and ‘metaloparite’ from the Burpala alkaline complex, Baikal Alkaline Province (Russia)

Geochemical behaviour of host phases for actinides and fission products in crystalline ceramic nuclear waste forms

Synthesis, structure, and characterization of the thorium zirconolite CaZr1‐xThxTi2O7 system

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Synthesis, structure, and characterization of the thorium zirconolite CaZr_1‐xTh_xTi₂O₇ system