Perrhenate and Pertechnetate Behavior on Iron and Sulfur-Bearing Compounds

Abstract

AbstractInvestigations on the behavior of the radioactive element technetium frequently use a stable isotope of rhenium as an analogue. This is justified by citing the elements' similar radii, major oxidation states of +7 and +4, and eH-pH diagrams. However, recent studies (e.g.,[1] have shown this analogy to be imperfect. Therefore, one goal of our study is to compare the behavior of these elements with emphasis on the adsorption of perrhenate and pertechnetate (the major forms of Re and Tc in natural waters) on mineral surfaces.Quantum mechanical calculations were performed on the adsorption of these two anions on relaxed clusters of the well-characterized sulfide galena (PbS) and some other Fe and S-bearing materials. With these calculations, we gain insight into differences between the anions' adsorption behavior, including geometry, adsorption energies, and electronic structure. Differences between interactions on terraces and step edges, the effects of co-adsorbates such as Na+ and Cl-, and chloride complexation are also explored. The influence of water was calculated using homogeneous dielectric fluids.As a complement to the calculations, batch sorption tests are in progress involving ReO4-/TcO4- solution in contact with Fe metal, 10% Fe-doped hydroxyapatite, goethite, hematite, magnetite, pyrite, galena, and sphalerite.