M. Trautmannsheimer et al., CHEMICAL FRACTIONATION OF SOME NATURAL RADIONUCLIDES IN A SOIL CONTAMINATED BY SLAGS, Environmental science & technology, 32(2), 1998, pp. 238-243
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.