Chemical Fractionation of Some Natural Radionuclides in a Soil Contaminated by Slags

To investigate the chemical fractionation of 238 U, 226 Ra, 210 Pb, and 228 Ra in soils contaminated by slags from coal firing and from pyrite roasting, a sequential extraction method (modified Tessier procedure) has been applied. The following fractions were each extracted: I, easily exchangeable; II, bound to carbonates; III, bound to iron−manganese oxides; IV, bound to organic matter; V, persistently bound; VI, residual. In addition, the extractants were also analyzed for the insoluble matrix elements Al and Fe to provide some information on the effect of each extraction step on the dissolution of the matrix. The results show that the percentage amounts of these radionuclides in fractions I (<5%) and II (<10%) are quite low for all soil/slag mixtures. Significant differences in the chemical fractionation of the four radionuclides were however observed for the subsequent fractions III−VI. Redistribution processes of the radionuclides between the various solid constituents of the soil/slag mixture were examined for each extraction step by applying sequential extraction also to the uncontaminated soil and to the pure slags. In this way, it was possible to demonstrate that in a soil/slag mixture 238 U and 210 Pb released from the slag by the iron−manganese oxide extractant are subsequently reabsorbed rapidly to a considerable extent by soil minerals and thus do not appear in the iron−manganese oxide fraction III but rather in fractions IV and VI. As a result of such redistribution processes, it will be almost impos sible to predict quantitatively the chemical fractionation of radionuclides in contaminated soils by investigating pure slags only.