Geochemical behavior of uranium in soils, part II. Distribution of uranium in hydromorphic soils and soil sequences. Applications for surficial prospecting

Abstract

The vertical distribution of U in hydromorphic soils is not related to climatic conditions and weathering rates but it depends essentially on local factors, i.e. water-table characteristics and topography. While topography may permit the transfer of uranyl species on a large scale, the water table induces specific conditions of redox potential involving two major processes for U fixation: retention with organic components in reduced layers and fixation on amorphous oxyhydroxides in oxidized layers. The analysis of four soil sequences of the temperate zone (France) show that the topography modifies the typical distribution pattern of U. Thus, depletion of U is limited in aerated soils situated on a slope, compared to their analogues located in plains, and enrichment of U is observed in hydromorphic soils, located down this slope. From this study, it is clear that U distribution in soils is related to pedogenetic processes and that soil analysis for U may be successful in evaluating the U content of underlying rock. Therefore some applications for the geochemical prospecting of U from soils are developed.