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A Modelling Study on the Fractionation of Uranium Among Minerals During Rock Weathering

  • Toshihiko Ohnuki (a1), Takashi Murakami (a1) and Nobuyuki Yanase (a1)

Abstract

A modelling study has been carried out to understand the effect of rock alteration on the fractionation of uranium among coexisting minerals (chlorite, vermiculite, kaolinite, amorphous and crystalline iron minerals) at the Koongarra ore deposit, Australia. The model considers the chlorite weathering process, its mechanism and rate, and assumes the presence of reversible and irreversible sorption sites in the secondary minerals. The calculated uranium concentrations at the two different sites in the minerals were compared with the results of sequential extraction experiments. Good agreement between the calculated and observed uranium concentrations was obtained only when an appropriate fraction of uranium is fixed to the irreversible sorption sites of the altered clay minerals. However, a conventional Kd model gave inconsistent uranium concentrations. The calculated results show that the crystalline iron minerals sorb uranium during all stages of weathering, and that the uranium fractionation among the minerals varies with time until the end of the weathering.

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[1] Snelling, A. A., in Uranium in the Pine Creek Geosyncline, edited by Forguson, J. and Goleby, A. B. (IAEA, Vienna 1980) pp. 487498
[2] Murakami, T., Isobe, H. and Edis, R., in Scientific Basis for Nuclear Management XIV, edited by Abrajano, T. A. Jr., and Johnson, L. H. (The Mater. Res. Soc. Proc. 212, Pittsburg, PA, USA, 1991) p741.
[3] Yanase, N., Nightingale, T., Payne, T. and Duerden, P., Radiochimica Acta, 52/53, 387393(1991).
[4] Murakami, T., Ohnuki, T. and Sato, T., Kinetic analysis of chlorite alteration, Abstr. Fall Meeting of the Mineral. Soc. Japan (with English abstract), Sendai, Japan (1991).
[5] Ueno, private communication, Japan Atomic Energy Research Institute, Tokai, Ibaraki, Japan.
[6] Ohnuki, T., Yanase, N., Sekine, K., Murakami, T., in preparation for publication.
[7] Payne, T., in Alligator Rivers Analogue Project 1st Annual Report, edited by Duerden, P., (Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2232, Australia, 1990) p 119.
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A Modelling Study on the Fractionation of Uranium Among Minerals During Rock Weathering

  • Toshihiko Ohnuki (a1), Takashi Murakami (a1) and Nobuyuki Yanase (a1)

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