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Study of Uranium Incorporation Into Zircon: Solubility Limits and Durability of Fixation

Published online by Cambridge University Press:  10 February 2011

S.V. Ioudintsev ,
B.I. Omelianenko  and
M.I. Lapina
S.V. Ioudintsev
Affiliation:
Institute of Geology of Ore Deposits, Staromonetny 35, 109017 Moscow, Russia
B.I. Omelianenko
Affiliation:
Institute of Geology of Ore Deposits, Staromonetny 35, 109017 Moscow, Russia
M.I. Lapina
Affiliation:
Institute of Geology of Ore Deposits, Staromonetny 35, 109017 Moscow, Russia
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Abstract

Research on synthetic zircons fabricated in system ZrO2-UO2-SiO2 at T = 400 - 750° C, PH20 = 100-200 MPa, and Ni-NiO oxygen buffer was made in order to estimate the limits of uranium incorporation into the phase's structure. It was shown that up to 27 wt.% of uranium may locally enter into the synthetic zircons. SEM/EDS study of the samples has showed that the element is uniformly distributed within the zircon crystals. Incorporation of U into zircon increases its unit-cell dimensions up to α = 6.70 A and c = 6.00 A relative to 6.60 and 5.98 A for a pure phase without impurities.

After thermal high temperature treatment of the samples under 1400° C, in air, for 6 hours inhomogeneous distribution of uranium within the zircon grains was revealed. Very small uranium rich spots probably corresponding to a newly formed phase were observed in the zircon crystals. Contents of the element throughout the grains decreased to about 10 wt.%. It is probably caused by destruction of zircon-coffinite solid solution formed at hydrothermal conditions in the course of its re-heating.

Study of interaction of natural zircons with alkaline carbonate solution at 100° C shows that U release from the phase can reach up to 6 % of total uranium in the samples even under relatively short term interaction. Loss of uranium rises with the element content (or amorphisation degree) and run duration, as well as with grain size reduction. Research on uranium distribution in natural zircons picked up from altered and weathered rocks is characterised by strong depletion of U at grain margins relative to the centre of the crystals. These results indicate that zircon may lose some uranium and, probably, the other actinides with time due to its lattice destruction under radioactive decay followed by hot water attack.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 506: Symposium – Scientific Basis for Nuclear Waste Management XXI , 1997 , 185
Copyright
Copyright © Materials Research Society 1998

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References

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