Sequential extraction of radioactive metals in soils from Crucea uranium mine (Romania)
Résumé
ICP and XRF Spectroscopy methods were used to evaluate the metals (ppm) from soils for the mining dumps of Crucea-
Botusana uranium deposit (Bistrita Mountains, Romania). The sequential extraction has emphasized the fact that U is
associated with all the mineral fractions present in the soil samples. A great percentage of U can be found in the
carbonate, organic and oxides fractions. The percentage of U detected in the exchangeable fraction is rather small. The fact
that 21.77% of the total U can be found in the specifically absorbed and carbonate bound fraction, indicated the
important role played by the carbonates in the retention of U; one the other hand this fraction is liable to release U if the pH should happen to change.Th appear in high-enough concentration in the soil is scarcely available because 70.29% is present in residual fraction, and about 21.78% in the organic and oxides fractions. This is certainly due to the fact that this naturally occurring radionuclide can be associated with relatively insoluble mineral phases like alumino-silicates and refractory oxides. Its association with the organic matter suggests that it can form soluble organic complexes that can facilitate its removal by the stream waters. In the case of Sr, the sequential extraction shows that it is very strongly fixed because the residual fraction concentrates the great amount of this element. What is interesting is the percentage of 2.65 % of Sr from the exchangeable fraction because it can be easily released and transported to the surrounding environment. Pb it is present in various relatively soluble pools (17.81% in carbonate boud and 34.85% in organically bound), which appears to be an efficient sink for this element. This fact may indicate a possible link between the biological activity and the Pb cycling into the soil. In addition, only 17.78% is present in the insoluble residual fraction. Although from our research it resulted that the radioactive metals does not concentrate in the exchangeable fraction (Th) or it concentrates very little in it (U and Sr), the isolation of the mineral fraction of soil rich in U, Th and Sr helps us in the future identification of the connections which control the cycle of the radioactive metals. These results have important implications for remediation strategies. The thorium and uranium from Crucea mining area are in labile, not strongly retained, fractions, thus making them amendable for remediation by phytoremediation.