Abstract
High-uranium natural zircon with signs of hydrothermal (up to 300°C) treatment is studied via transmission electron microscopy, Raman spectroscopy, electron probe microanalysis, and local energy-dispersive analysis performed in situ with a transmission electron microscope. Uranium-based phases are not found in the regions with uranium concentrations of up to 10 wt % that exceed considerably the limit of solubility in synthetic zirconium silicate. Uranium is dissolved in a heterogeneous matrix that is formed as a result of the decomposition of radiation-damaged (a dose of 1017 α-decays/mg) zircon under hydrothermal influence. The matrix incorporates amorphous partially hydrated silicon oxide and nanocrystalline cubic (Zr,Hf)1-y MeyO2 stabilized with metal Me impurities (Y, Ca, Al, Fe; y ≈ 0.04). Cubic zirconium oxide is regarded as the preferred phase for uranium localization, while the total impurity concentration is ~0.13.
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