Rhenium (Re) As an Analog for Technetium (Tc) in Environmental Sorption Experiments.

Technetium-99 (⁹⁹Tc), a long lived (t_1/2 = 2.13 x 10⁵ yrs) nuclear fission product, represents much of the long-term radioactivity associated with nuclear waste. In partitioning experiments aimed at predicting the fate of ⁹⁹Tc in the environment, rhenium (Re) has been widely used as a non-radiological analogue. Under oxidizing conditions, both Tc and Re are found in the +7 oxidation state as pertechnetate (TcO₄^-) and perrhenate (ReO₄^-), respectively. As anions, both chemical species are assumed to sorb poorly to soil materials and thus remain quite mobile in the soil environment. In the current study, batch and column experiments were conducted using soils and soil minerals (i.e., goethite, kaolinite, etc.) to evaluate the fate and transport of Tc and Re within the highly weather soils of the Southeastern Coastal Plain of the US. While little sorption was observed for surface soil materials (A horizon), both species were significantly retarded in subsoil materials that contain appreciable Fe oxides. Observing similar partitioning behavior under oxidizing conditions does not necessarily confirm that Re is an appropriate chemical surrogate for evaluating Tc behavior under all chemical conditions.