Transport of radioselenium oxyanions by diffusion in unsaturated soils

Abstract

There is a lack of data on the diffusion of longlived radionuclides in soils, especially of those originated from the leaching of radioactive waste in waste disposal facilities. Here, the simultaneous diffusion of two radioselenium species, which were postulated to be radioselenite and radioselenate, was examined for the first time in four soils at laboratory level by applying the planarsource method. The Gaussian-shaped experimental diffusion profile was deconvoluted into two Gaussian functions, and then the apparent diffusion coefficients ( a ) were quantified for each species. Radioselenate a values ranged from 1.4 × 10 −11 to 1.5 × 10 −10 m 2 s −1 , while those of radioselenite were two orders of magnitude lower (from 5.2 × 10 −13 to 2.7 × 10 −12 m 2 s −1 ) for all samples and conditions tested. The radioselenite distribution coefficient values derived from a correlated to soil properties, such as pH and Al/Fe mineral content, and thus were consistent with the factors controlling the sorption of selenium species in soils.