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The Alteration of Uraninite to Clarkeite

Published online by Cambridge University Press:  01 January 1992

Robert J. Finch  and
Rodney C. Ewing
Robert J. Finch
Affiliation:
Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, U.S.A.87131
Rodney C. Ewing
Affiliation:
Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, U.S.A.87131
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Abstract

The oxidative alteration of uraninite by alkali-bearing, hydrothermal (200-400° C) solutions in granitic rocks produces the rare mineral clarkeite. The general formula for Na-clarkeite is

{(Na,K)6-y-z(M2+PM3+qM4+r)y(□1+z-xPbx)}[UO2)7-xOt0]·nH2O. z ≈ p+2q+3r.

The terms in square brackets designate the sheet structure; the other elements and vacancies (0) occur in interlayer sites. Clarkeite can accommodate Ca, Sr, Ba, Y, Th, and lanthanides. Thus, clarkeite is a potential actinide and fission product host. The replacement of uraninite by clarkeite occurs in the solid state and results in the loss of one-half of the uranium from uraninite. As U decays to Pb, the radiogenic Pb enters interlayer vacancies in clarkeite. This destabilizes the structure and clarkeite eventually decomposes to wölsendorfite, (Pb,Ca)2U2O7·2H2O, or curite, Pb3U8O27·3H2O.

Clarkeite from Spruce Pine, North Carolina is zoned compositionally, with a K-rich core (atomic ratio K:Na:Ca = 1.0 : 0.11 : 0.12) surrounded by Na-clarkeite (Na:K:Ca = 1.0 : 0.03 : 0.03), rimmed and veined by Ca-clarkeite (Ca:Na:K = 1.0 : 1.25 : 0.05). Volumetrically, Na-clarkeite is the most important constituent. The chemical zoning reflects the disparate chemistries of K+, Na+, and Ca2+. Na-clarkeite and Ca-clarkeite are structurally similar, but have different sheet structures. The solubility of K in Na-clarkeite is less than five mole percent and is due to the different sizes of Na+ and K+ ions. The K-phase may not be related structurally to clarkeite.

Exposed to ground water at low temperatures, clarkeite alters to the uranyl silicates, uranophane and kasolite. The alkalis are leached by ground water. The fate of Th, Y, and lanthanides from clarkeite is uncertain.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 294: Symposium V – Scientific Basis for Nuclear Waste Management XVI , 1992 , 513
Copyright
Copyright © Materials Research Society 1993

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References

REFERENCES

1. Finch, R.J. and Ewing, R.C., SKB Technical Report 91-15 (1991).Google Scholar
2. Finch, R.J. and Ewing, R.C., Radiochimica Acta 53/54 (1991) 391.Google Scholar
3. Finch, R.J., Miller, M.L. and Ewing, R.C., Radiochimica Acta (in press).Google Scholar
4. Finch, R.J. and Ewing, R.C., in Scientific Basis for Nuclear Waste Management XVI, edited by Sombret, C. (Materials Research Society, Pittsburgh, 1992) pp. 465–472 Google Scholar
5. Janeczek, J. and Ewing, R.C., in Scientific Basis for Nuclear Waste Management XVI, edited by Sombret, C. (Materials Research Society, Pittsburgh, 1992) pp. 497–504 Google Scholar
6. Murphy, W.M. and Pearcy, E.C., in Scientific Basis for Nuclear Waste Management XVI, edited by Sombret, C. (Materials Research Society, Pittsburgh, 1992) pp. 521–528 Google Scholar
7. Murakami, T., Isobe, H., Nagano, T., Nakashima, S. in Scientific Basis for Nuclear Waste Management XVI, edited by Sombret, C. (Materials Research Society, Pittsburgh, 1992) pp. 473–480 Google Scholar
8. Hemond, C., Menet, C. and Meneger, M.T., in Scientific Basis for Nuclear Waste Management XVI, edited by Sombret, C. (Materials Research Society, Pittsburgh, 1992) pp. 489–496 Google Scholar
9. Chapman, N., McInley, I., Shea, M., Smellie, J., SKB Technical Report 90-24 (1991).Google Scholar
10. Ross, C.S., Henderson, E.P. and Posnjak, E., American Mineralogist 16 (1931) 213.Google Scholar
11. Gruner, J., American Mineralogist 39 (1954) 836.Google Scholar
12. Frondel, C. and Meyrowitz, R., American Mineralogist 41 (1957) 127.Google Scholar
13. Frondel, C., U.S. GEOLOGICAL, Society Bulletin 1064 (1958).Google Scholar
14. Toussaint, C.J. and Avogadro, A., Journal of Inorganic and Nuclear Chemistry 36 (1974) 781.Google Scholar
15. Wamser, C.A., Belle, J., Bemsohn, E., Williamson, B., Journal, American Chemical Society 74 (1952) 1020.Google Scholar
16. Loopstra, B. O. and Rietveld, H.M., Acta Crystallographica B25 (1969) 787.Google Scholar
17. Fonteneau, G., L'Helgoualch, H. and Lucas, J., Revue de Chimie Mindrale 12 (1975) 382.Google Scholar
18. Bobo, J.-C., Revue de Chimie Mindrale 1 (1964) 3.Google Scholar
19. Brisi, C. and Appendino, M.M., Annali di Chimica (Rome) 59 (1969) 400.Google Scholar
20. Cejka, J., Collection'Czechoslovakia Communications 34 (1969) 1635.Google Scholar
21. Rogova, V.P., Belova, L.N., Kiziyrov, G.P., Kuznetsova, N.N., Zap. Vses. Miner. Obshch. 103 (1974) 108.Google Scholar
22. Finch, R.J. and Ewing, R.C., Journal of Nuclear Materials 190 (1992) 133.Google Scholar