CEA, DAM, DIF, F-91297 Arpajon, France.
Sci Total Environ. 2010 Apr 1;408(9):2118-28. doi: 10.1016/j.scitotenv.2010.01.061. Epub 2010 Feb 23.
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 20 cm deep uranium migration in soil. Uranium retention in soil is controlled by the <50 microm mixed humic and clayey coatings in the first 40 cm 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 2 cm 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 (238)U initially present in the soil column and (233)U 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, 1 km downstream from the pollution source.
已在野外和柱实验中研究了铀通过沙质灰壤的传输。铀贫化沉积物表面污染后多年的现场监测揭示了土壤中铀的 20 厘米深迁移。土壤中铀的保留受<50 微米混合腐殖质和粘土层的控制，这些层位于前 40 厘米处，即 E 层。使用同位素标记进行了各种条件下铀传输的柱实验。在洗脱 100 个孔隙体积后，总输入铀的 60%保留在柱的前 2 厘米处。E 层物质上铀的阻滞因子范围为 1300（柱）至 3000（批）。在这种缓慢的铀迁移的同时，我们还实验观察到与腐殖质胶体相关的快速洗脱，约占总铀输入的 1-5%，通过土壤柱以平均孔隙水速度转移。为了了解雨事件的影响，输入溶液的离子强度急剧变化。当离子强度增加时，腐殖质胶体被阻滞，而当离子强度降低时，腐殖质胶体和胶体携带的铀会发生大量迁移。同位素标记表明，初始存在于土壤柱中的(238)U 和由输入溶液带来的(233)U 都被解吸。离子强度降低后实验中观察到的迁移过程可能解释了雨事件后野外铀的快速迁移，以及在污染源下游 1 公里处深土壤层和地下水中发现的大量铀浓度。
