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Uranium facilitated transport by water-dispersible colloids in field and soil columns

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Title: Uranium facilitated transport by water-dispersible colloids in field and soil columns
Authors: Crançon, P.1 pierre.crancon@cea.fr, Pili, E.1, Charlet, L.2
Source: Science of the Total Environment. Apr2010, Vol. 408 Issue 9, p2118-2128. 11p.
Subjects: Migration of uranium, Colloids, Surface contamination, Groundwater, Water pollution, Clay soils, Humic acid content of soils
Abstract: Abstract: The transport of uranium through a sandy podzolic soil has been investigated in the field and in column experiments. Field monitoring, numerous years after surface contamination by depleted uranium deposits, revealed a 20cm deep uranium migration in soil. Uranium retention in soil is controlled by the <50µm mixed humic and clayey coatings in the first 40cm i.e. in the E horizon. Column experiments of uranium transport under various conditions were run using isotopic spiking. After 100 pore volumes elution, 60% of the total input uranium is retained in the first 2cm of the column. Retardation factor of uranium on E horizon material ranges from 1300 (column) to 3000 (batch). In parallel to this slow uranium migration, we experimentally observed a fast elution related to humic colloids of about 1–5% of the total-uranium input, transferred at the mean porewater velocity through the soil column. In order to understand the effect of rain events, ionic strength of the input solution was sharply changed. Humic colloids are retarded when ionic strength increases, while a major mobilization of humic colloids and colloid-borne uranium occurs as ionic strength decreases. Isotopic spiking shows that both 238U initially present in the soil column and 233U brought by input solution are desorbed. The mobilization process observed experimentally after a drop of ionic strength may account for a rapid uranium migration in the field after a rainfall event, and for the significant uranium concentrations found in deep soil horizons and in groundwater, 1km downstream from the pollution source. [Copyright &y& Elsevier]
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Abstract:Abstract: The transport of uranium through a sandy podzolic soil has been investigated in the field and in column experiments. Field monitoring, numerous years after surface contamination by depleted uranium deposits, revealed a 20cm deep uranium migration in soil. Uranium retention in soil is controlled by the <50µm mixed humic and clayey coatings in the first 40cm i.e. in the E horizon. Column experiments of uranium transport under various conditions were run using isotopic spiking. After 100 pore volumes elution, 60% of the total input uranium is retained in the first 2cm of the column. Retardation factor of uranium on E horizon material ranges from 1300 (column) to 3000 (batch). In parallel to this slow uranium migration, we experimentally observed a fast elution related to humic colloids of about 1–5% of the total-uranium input, transferred at the mean porewater velocity through the soil column. In order to understand the effect of rain events, ionic strength of the input solution was sharply changed. Humic colloids are retarded when ionic strength increases, while a major mobilization of humic colloids and colloid-borne uranium occurs as ionic strength decreases. Isotopic spiking shows that both 238U initially present in the soil column and 233U brought by input solution are desorbed. The mobilization process observed experimentally after a drop of ionic strength may account for a rapid uranium migration in the field after a rainfall event, and for the significant uranium concentrations found in deep soil horizons and in groundwater, 1km downstream from the pollution source. [Copyright &y& Elsevier]
ISSN:00489697
DOI:10.1016/j.scitotenv.2010.01.061