Sorption of Np, Cs, Co, Pu by different clayey soils - the role of Fe(III) surface coatings

The aim of this work was to study sorption of 237Np(V), 137Cs, 60Co, 238Pu(IV) by different clayey soils and to establish possible role of surface coatings on it. Samples were fractionated granulometrically (0.5 - 0.25 mm; 0.25 - 50 μm; 50 μm - 10 μm and <10 μm). For each fraction specific surface area and porosity were determined. All samples were characterized by scanning (SEM) and transmission electron microscopy (TEM). The sorption of radionuclides was studied by initial clayey soil samples and by samples after extraction of Fe(III) amorphous compounds. The sorption of all studied radionuclides varied both for different fractions and for samples with Fe(III) surface coatings and without them. The highest sorption of actinides (Np and Pu) was established for the largest fraction (0.5 - 0.25 mm) and the finest fraction (<10 μm). These fractions were enriched with Fe(III) amorphous compounds. The extraction of Fe(III) from the samples resulted in a significant decrease of actinide sorption. It was established by sem, that Fe is present both in the form of separate particles of hematite, and in the form of surface coatings. (author)