CHEMICAL FRACTIONATION OF SOME NATURAL RADIONUCLIDES IN A SOIL CONTAMINATED BY SLAGS

To investigate the chemical fractionation of U-238, Ra-226, Pb-210, an d Ra-228 in soils contaminated by slags from coal firing and from pyri te roasting, a sequential extraction method (modified Tessier procedur e) has been applied. The following fractions were each extracted: I, e asily exchangeable; II, bound to carbonates; III, bound to iron-mangan ese oxides; IV, bound to organic matter; V, persistently bound; VI, re sidual. In addition, the extractants were also analyzed for the insolu ble matrix elements Al and Fe to provide some information on the effec t of each extraction step on the dissolution of the matrix. The result s show that the percentage amounts of these radionuclides in fractions I (<5%) and II (<10%) are quite low for all soil/slag mixtures. Signi ficant differences in the chemical fractionation of the four radionucl ides were however observed for the subsequent fractions III-VI. Redist ribution processes of the radionuclides between the various solid cons tituents of the soil/slag mixture were examined for each extraction st ep by applying sequential extraction a Iso to the uncontaminated soil a nd to the pu re slags. In this way, it was possible to demonstrate t hat in a soil/slag mixture U-238 and Pb-210 released from the slag by the iron-manganese oxide extractant are subsequently reabsorbed rapidl y 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 V I. As a result of such redistribution processes, it will be almost imp ossible to predict quantitatively the chemical fractionation of radion uclides in contaminated soils by investigating pure slags only.