Durability of an La2Zr2O7 waste form in water

Hayakawa, Issei; Kamizono, Hiroshi

doi:10.1007/bf00357832

Cited by 20 publications

(6 citation statements)

References 4 publications

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“…4 and 5). When compared to other UO 2 wt% in stoichiometric non -metamict betafite reported in the mineralogical literature (average of 31.19 wt%; Cámara et al, 2004), the studied betafite has a similar value (31.23 wt% UO 2 , (Hayakawa and Kamizono, 1993;Subramanian et al, 1983).…”

Section: Betafitesupporting

confidence: 50%

Role of geochemical alteration on the formation of secondary Zr- and U-bearing minerals in El Atshan trachyte, central Eastern Desert, Egypt

El‐Naby

2009

Journal of Mineralogical and Petrological Sciences

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El Atshan area, situated in the central Eastern Desert of Egypt, is a good location for studying the influence of high -and low -T alterations on the formation of Zr -and U -bearing minerals within a trachyte sill. These minerals are mainly represented by an unidentified secondary Zr -rich silicate mineral, betafite, and liandratite. The unidentified Zr -rich silicate mineral is considered to be an alteration product of the precursor zirconolite during high -T alteration. This is indicated by the changes in the composition marked by an increase in the amount of hydration (H 2 O), Si, and U and a decrease in the amount of Ca, Ti, Nb, and Fe. The morphology of this unidentified mineral is similar to that of zirconolite. For seven oxygen atoms, the calculated formula of the unidentified Zr -rich silicate mineral is (Si . With more extensive alteration, it was found that the unidentified secondary Zr -rich silicate mineral was unstable and it underwent re -equilibration with U -rich fluid, which led to alterations in betafite. The two possible mechanisms responsible for the alteration of the unidentified Zr -rich silicate mineral to betafite are as follows: (1) the dissolution of the unidentified Zr -rich silicate mineral and precipitation of betafite and (2) the ion -exchange between partially to fully amorphized zones and the U -rich fluid. Such alteration is indicated by a marked increase in the amount of U, Ti, and Nb and a decrease in the amount of Zr, Si, Ca, P, Y, and ΣREE.

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Section: Betafitesupporting

confidence: 50%

Role of geochemical alteration on the formation of secondary Zr- and U-bearing minerals in El Atshan trachyte, central Eastern Desert, Egypt

El‐Naby

2009

Journal of Mineralogical and Petrological Sciences

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“…13 Zirconate pyrochlores have been investigated in terms of their slow dissolution kinetics as a function of temperature and pH and with respect to the release of the A component. 14,15 Many dissolution studies of potential nuclear waste forms in the literature have used macroscopic approaches. 16−18 Recently microscopic approaches were applied to gain a deeper understanding about the variability of the dissolution rates and the contribution of different dissolution mechanisms.…”

Section: Introductionmentioning

confidence: 99%

“…During the entire dissolution experiment, no formation of a leached layer was observed, even though a preferential release of Nd compared to Zr is well-known for the acidic pH range. 14,15,19,31 2.5. Statistical Analysis of Surface Topography Data.…”

Section: Introductionmentioning

confidence: 99%

Direct Measurement of Surface Dissolution Rates in Potential Nuclear Waste Forms: The Example of Pyrochlore

Finkeldei

Brandt

Bosbach

et al. 2015

ACS Appl. Mater. Interfaces

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The long-term stability of ceramic materials that are considered as potential nuclear waste forms is governed by heterogeneous surface reactivity. Thus, instead of a mean rate, the identification of one or more dominant contributors to the overall dissolution rate is the key to predict the stability of waste forms quantitatively. Direct surface measurements by vertical scanning interferometry (VSI) and their analysis via material flux maps and resulting dissolution rate spectra provide data about dominant rate contributors and their variability over time. Using pyrochlore (Nd2Zr2O7) pellet dissolution under acidic conditions as an example, we demonstrate the identification and quantification of dissolution rate contributors, based on VSI data and rate spectrum analysis. Heterogeneous surface alteration of pyrochlore varies by a factor of about 5 and additional material loss by chemo-mechanical grain pull-out within the uppermost grain layer. We identified four different rate contributors that are responsible for the observed dissolution rate range of single grains. Our new concept offers the opportunity to increase our mechanistic understanding and to predict quantitatively the alteration of ceramic waste forms.

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“…Incorporation of Zr 4+ , an ion of intermediate size, is known in natural pyrochlore, particularly those from carbonatites (e.g. Hogarth, 1989), where Zr 4+ is assigned to the B site in accordance with synthetic REE-Zr pyrochlores (Hayakawa and Kamizono, 1993;Subramanian et al, 1983). Concentrations of ZrO 2 as high as~10 wt.% have been reported for pyrochlore from the Cape Verde Islands (Hodgson and Le Bas, 1992).…”

Section: Resultsmentioning

confidence: 99%

Non-metamict betafite from Le Carcarelle (Vico volcanic complex, Italy): occurrence and crystal structure

Cámara¹,

Williams²,

Ventura³

et al. 2004

Mineral. mag.

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N o n -m e t a m i c t b e t a f i t e , a p y r o c h l o r e -g r o u p m i n e r a l w i t h g e n e r a l f o r m u l a (O,OH).Compared with other occurrences reported in the mineralogical literature, betafite from Le Carcarelle is extremely enriched in U and depleted in Th. Due to its young age of formation (~150 k.y.), this betafite sample is highly crystalline, thus allowing structure refinement of unheated material. Betafite from Le Carcarelle is cubic Fd3m, with a = 10.2637(13) Å , and V = 1081.21(35) Å 3 , and has a smaller A site (consistent with the higher U content), and a larger and more distorted B site (consistent with the higher Ti content) than calciobetafite from Campi Flegrei, Italy (Mazzi and Munno, 1983). Analysis of the atomic displacement parameters provides evidence for static disorder at the X site.

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Durability of an La2Zr2O7 waste form in water

Cited by 20 publications

References 4 publications

Role of geochemical alteration on the formation of secondary Zr- and U-bearing minerals in El Atshan trachyte, central Eastern Desert, Egypt

Role of geochemical alteration on the formation of secondary Zr- and U-bearing minerals in El Atshan trachyte, central Eastern Desert, Egypt

Direct Measurement of Surface Dissolution Rates in Potential Nuclear Waste Forms: The Example of Pyrochlore

Non-metamict betafite from Le Carcarelle (Vico volcanic complex, Italy): occurrence and crystal structure

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