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Study of Natural Zircon-Xenotime Assemblages for Estimation of the Actinide Waste Forms Stability

Published online by Cambridge University Press:  10 February 2011

M. I. Lapina  and
S. V. Yudintsev
M. I. Lapina
Affiliation:
IGEM RAS, Staromonetny 35, Moscow 109017, Russia, mil@igem.msk.su
S. V. Yudintsev
Affiliation:
IGEM RAS, Staromonetny 35, Moscow 109017, Russia, mil@igem.msk.su
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Abstract

In order to estimate compositions and structural stability of YPO4-ZrSiO4-USiO4- ThSiO4 solid solution, natural specimens of (U,Th)-enriched zircon-xenotime assemblages were studied. The samples were picked from granitic pegmatites of North Karelia of about 1,850 Ma age. TEM data show that amorphization of the zircon structure is not complete. Xenotime has typical crystal structure. ASEM and EPMA results indicate that zircon and xenotime are micro-heterogeneous in there compositions. Numerous micro-inclusions (<5 μm in diameter) of xenotime and uranium oxide were found within the zircon grains. Xenotime is free from inclusions. The results give rise to the conclusions that xenotime-zircon solid solution is restricted due to high difference in ionic radii (y3+ vs. Zr4+ and p5+ vs. Si4+). Data on high amounts of rare earth elements and phosphorus in natural zircons are result from REE-phosphate inclusions in analyzed zircons. Content of U in the zircon allowed the estimation of the solubility of coffinite end member to be no less than 5 mol.% "USiO4".

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 556: Symposium QQ – Scientific Basis for Nuclear Waste Management XXII , 1999 , 785
Copyright
Copyright © Materials Research Society 1999

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References

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