Evaluation of a sequential extraction method for determining actinide fractionation in soils and sediments

A sequential chemical extraction method for the determination of the geochemical fractionation of Am, Pu, and U was evaluated rigorously on a single marine sediment standard (IAEA-135). Partitioning of actinides was operationally defined for five reagent fractions and stable element analyses (Al, Ca, Fe, Mn, Ti, etc.) were performed to assist in establishing the phase specificity of the extractions. The method produces, in general, results that agree to within a one standard deviation interval for replicate measurements for each fraction. Actinide readsorption, examined by a double-spiking technique, was found to be significant in some cases. Ethylenediamine-tetraacetic acid (EDTA) was examined as a hold-back reagent to lessen the effect of readsorption but seriously compromised the phase selectivity of the extractants. In addition, the use of NaOCl for the destruction of organic matter was found to dissolve carbonates out of sequence and is not recommended for carbonate-bearing materials.