Behavior of uranium and thorium isotopes in soils of the Boréon area, Mercantour Massif (S.E. France): Leaching and weathering rate modeling

S. Rezzoug; F. Fernex; H. Michel; G. Barci-Funel; V. Barci

doi:10.1007/s10967-008-7341-1

Journal of Radioanalytical and Nuclear Chemistry

Volume/Issue:: Volume 279: Issue 3

Behavior of uranium and thorium isotopes in soils of the Boréon area, Mercantour Massif (S.E. France): Leaching and weathering rate modeling

Authors:

S. Rezzoug

S. Rezzoug Sciences Analytiques et Environnement Laboratoire de Radiochimie 28 Avenue Valrose 06108 Nice Cedex 2 France

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F. Fernex

F. Fernex University of Nice-Sophia Antipolis Département des Sciences de la Terre 28 Avenue Valrose 06108 Nice Cedex 2 France

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H. Michel

H. Michel Sciences Analytiques et Environnement Laboratoire de Radiochimie 28 Avenue Valrose 06108 Nice Cedex 2 France

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G. Barci-Funel

G. Barci-Funel Sciences Analytiques et Environnement Laboratoire de Radiochimie 28 Avenue Valrose 06108 Nice Cedex 2 France

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, and

V. Barci

V. Barci Sciences Analytiques et Environnement Laboratoire de Radiochimie 28 Avenue Valrose 06108 Nice Cedex 2 France

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Pages:: 801–809

Online Publication Date:: 07 Mar 2009

Publication Date:: 01 Mar 2009

Article Category:: Research Article

DOI:: https://doi.org/10.1007/s10967-008-7341-1

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Abstract

Four cores were collected in weathered rocks and soils in the Boréon forest area (1765 m, Mercantour Massif, France). The samples were analyzed for the isotopes ²³⁰Th, ²³²Th, ²³⁴U and ²³⁸U. The activity and isotopic ratio profiles suggest that uranium was mobilized (leaching and precipitation) during the weathering process, as well as thorium but in a much less proportion. A model was drawn up to evaluate the U leaching rate and the time that some levels of the weathered rocks have been subjected to weathering. It utilizes LATHAM and SCHWARCZ’s two equations,¹⁵ expressed as ²³⁴U/²³⁸U and ²³⁰Th/²³⁸U activity ratios, which assume that the alpha recoil effect allows easier leaching for ²³⁴U than ²³⁸U and no Th mobility. But this last assumption does not correspond to the observations made in the Boréon area, since it appears that in some soil deeper layers ²³⁰Th and ²²⁸Th are in radioactive deficit relatively to their parents. As there are four unknown quantities (the time, the leaching rates of ²³⁸U, ²³⁴U, ²³⁰Th), the problem to be solved requires two more equations; these can be obtained utilizing the U activity ratio in water, and taking into account the ²³²Th behavior. In some sites the ²³⁸U leaching rate is high in deeper soil levels (near the fresh rocks); this would correspond to a loss of half the U amount in less than 24 000 years.

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Journal of Radioanalytical and Nuclear Chemistry

Print ISSN:: 0236-5731

Online ISSN:: 1588-2780

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Journal of Radionalytical and Nuclear Chemistry
Language	English
Size	A4
Year of Foundation	1968
Volumes per Year	1
Issues per Year	12
Founder	Akadémiai Kiadó
Founder's Address	H-1117 Budapest, Hungary 1516 Budapest, PO Box 245.
Publisher	Akadémiai Kiadó Springer Nature Switzerland AG
Publisher's Address	H-1117 Budapest, Hungary 1516 Budapest, PO Box 245. CH-6330 Cham, Switzerland Gewerbestrasse 11.
Responsible Publisher	Chief Executive Officer, Akadémiai Kiadó
ISSN	0236-5731 (Print)
ISSN	1588-2780 (Online)