Author:
Helean K. B.,Burakov B. E.,Anderson E. B.,Strykanova E. E.,Ushakov S. V.,Ewing R. C.
Abstract
ABSTRACT“Gel-zircon”, an unusual Zr-silicate phase from the Manibay uranium mine,
northern Kazakhstan, was studied using X-ray diffraction (XRD), electron
microprobe energy dispersive X-ray spectroscopy (EDS) and high resolution
transmission electron microscopy (HRTEM). XRD results indicate that
gel-zircon is mostly amorphous and occurs with numerous impurity phases.
Microprobe EDS results indicate a UO2 content up to 9.14 wt. %.
HRTEM images revealed that the microtexture of gel-zircon consists of
nanocry stal lites of zircon, 2–10 nm in size, in a dominantly amorphous
matrix. Despite the U-Pb age of 420±25 my and the lack of significant
crystallinity, the gel-zircon is an apparently chemically durable phase.
Leaching of uranium ores which contain gel-zircon as the major U-bearing
phase is impossible using existing uranium plant technologies. The
alpha-decay dose, 2.64 displacements per atom (dpa), corresponding to the
age of gel-zircon is much higher than that (0.5 dpa) required to cause
metamictization of crystalline zircon. However, the morphology of gel-zircon
which occurs as veins up to 5 mm thick and tens of mm long does not indicate
initial crystallinity. Initially crystalline natural zircons often preserve
their crystal morphology after metamictization. This amorphous phase is
analogous to the highly damaged state characteristic of zircon proposed as a
waste form for the disposition of excess weapons plutonium.
Publisher
Springer Science and Business Media LLC
Cited by
3 articles.
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