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Mineralogical and Microtextural Characterization of “Gel-Zircon” from the Manibay Uranium Mine, Kazakhstan

Published online by Cambridge University Press:  03 September 2012

K. B. Helean ,
B. E. Burakov ,
E. B. Anderson ,
E. E. Strykanova ,
S. V. Ushakov  and
R. C. Ewing
K. B. Helean
Affiliation:
Department of Earth & Planetary Sciences, University of New Mexico, Albuquerque, NM 87131
B. E. Burakov
Affiliation:
V.G. Khlopin Radium Institute, St. Petersburg, Russia
E. B. Anderson
Affiliation:
V.G. Khlopin Radium Institute, St. Petersburg, Russia
E. E. Strykanova
Affiliation:
V.G. Khlopin Radium Institute, St. Petersburg, Russia
S. V. Ushakov
Affiliation:
V.G. Khlopin Radium Institute, St. Petersburg, Russia
R. C. Ewing
Affiliation:
Department of Earth & Planetary Sciences, University of New Mexico, Albuquerque, NM 87131
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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.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 465: Symposium II – Scienfific Basis for Nuclear Waste Management XX , 1996 , 1219
Copyright
Copyright © Materials Research Society 1997

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