Estimating the radionuclide available fraction in mineral soils using an extraction technique

Abstract

An extraction technique was used to estimate the radionuclide available fraction in two mineral soils, with loam-sandy and loamy textures, which had been contaminated by an aerosol containing ⁸⁵Sr and ¹³⁴Cs. A set of extractant solutions, including monovalent and divalent cations, and the experimental conditions (extraction time, ratio of volume of extractant solution to mass of soil, single or successive extractions, use of an ionic adsorbent) were tested. When applying single extractions, radiostrontium was less sensitive to changes in the extractant solutions. For radiocaesium, the desorption yields were higher with monovalent cations, although successive extractions suggested a potential collapsing effect of monovalent cations in the loam-sandy soil, since the divalent cation led to a higher desorption yield. In general, the higher the solution/soil ratios and time of extraction, the higher were the desorption yields, although a dependence on the type of radioactive contamination (aerosol and soluble) was noticed for radiostrontium. It was difficult to choose a common procedure to quantify the available fraction for all the radionuclides, but overnight extraction with a monovalent cation is suggested. Predictions of radionuclide mobility based on the available fraction alone depended on whether single or successive extractions were taken into account, and also on whether divalent or monovalent cations were considered. The comparison with vertical migration data suggested that an overnight extraction with a monovalent cation could also be chosen for prediction purposes.