GEOCHEMICAL BEHAVIOR OF URANIUM IN SOILS .1. INFLUENCE OF PEDOGENETIC PROCESSES ON THE DISTRIBUTION OF URANIUM IN AERATED SOILS

A comparative study of the uranium distribution and that of some major constituents of soils shows a clear relationship between its behavior and the pedogenetic processes. The main types of soils developed on granitic or acidic rocks have been analyzed. A comparison of the U distribution in different aerated systems allows the determination of the specific role of climatic factors on U behavior: U remain in enclosed sytems (fersiallitic, reddish steppic, colluvial brown soils), but is, respectively, slightly and strongly leached from brunified and ferrallitic soils without fixation and accumulation in the soil profiles. By contrast, a clear redistribution of U is observed in profiles of podzolic soils, which is related to the particular organic geochemistry of these soils. Uranium enrichments occur primarily in accumulation horizons (spodic layers), simultaneously with organic compounds and Fe. Chemical extractions allow the determination of two essential constituents of soils (oxyhydroxides and humified organic matter) responsible for U retention and accumulation. Clays alone, appear to be inefficient for U fixation.