Efficient preconcentration and separation of actinide elements from large soil and sediment samples

Large (approximately 10 g) soil and sediment samples are often required for analysis of low-level man-made actinides for monitoring environmental radioactivity. However, use of large environmental samples often results in significant chemical losses during chemical separations due to matrix interferences. We present a technique based on the ion-exchange resin Diphonix which selectively collects actinides and lanthanides into a common form, which then behaves uniformly and predictably during subsequent separation schemes. Diphonix is attractive for this purpose because it has an extremely high affinity for actinides and a low affinity for most common ions and is resistant to hydrofluoric acid. After being adsorbed onto Diphonix resin in a column mode at a pH approximately 1, actinides are completely eluted with 0.5 M 1-hydroxyethylidene-diphosphonic acid (HEDPA). After destruction of the HEDPA by ozonation or use of Fenton's reagent, Am, Pu, U, and Th are separated from each other and the remaining matrix by use of extraction chromatographic resins. We obtained high and consistent chemical recoveries (mean, 85%), as well as excellent chemical separations, for Am, Pu, U, and Th through the entire procedure for several 10-g soil and sediment samples.