AVS 46th International Symposium
    Surface Science Division Tuesday Sessions
       Session SS-TuP

Paper SS-TuP23
X-ray Photoemission and Near Edge Absorption Studies of Rhenium (VII) Sorption onto Fe-bearing Materials

Tuesday, October 26, 1999, 5:30 pm, Room 4C

Session: Poster Session
Presenter: P. Liu, Lawrence Berkeley National Laboratory
Authors: P. Liu, Lawrence Berkeley National Laboratory
W.W. Lukens, Jr., Lawrence Berkeley National Laboratory
E.J. Moler, Lawrence Berkeley National Laboratory
D.K. Shuh, Lawrence Berkeley National Laboratory
Correspondent: Click to Email
Technetium (@sup 99@Tc) is a radioactive byproduct of nuclear fission, and its concentration may set the regulatory limit for disposal of nuclear wastes. Therefore, the high solubility and mobility of TcO@sub 4@@sup -@ needs to be addressed. A solution is to reduce Tc@sup 7+@ to Tc@sup 4+@, which is much less soluble and mobile. One method is by adsorbing Tc@sup 7+@ onto surfaces of reducing agents. While previous experiments demonstrated that Tc@sup 7+@ ions were sorbed on and reduced by some materials, the products and the mechanism of sorption and reduction are not fully characterized or understood. Rhenium (Re) has similar redox properties as Tc, and can be treated as a surrogate for Tc in selected systems. Since Re is non-radioactive, experiments are more efficiently performed. A class of possible reductants are Fe, Fe oxides, and sulfides. Sorption samples were prepared by immersing powders of Fe metal, FeO, FeS, and FeS@sub 2@, respectively, in 0.010M Re(VII) solution for 24 hours or longer, during which time the powder and the solution were constantly mixed. The reacted powders were extracted after the mixtures were centrifuged and the solutions decanted. The photoemission of Re 4d and 4f core levels, and NEXAFS of Re N@sub III@ experiments were carried out at the Advanced Light Source. The results reveal that the amount of absorbed Re decreases from Fe metal, through FeO, FeS, to FeS@sub 2@; and that different species of Re are sorbed on surfaces of different Fe-bearing materials, with more oxidized species tending to dominate on the less sorbed surfaces. Together with the pH measurements of the residual solutions, the results suggest that the sorption and reduction of Re on the surfaces of Fe-bearing materials are partially controlled by the final pH of the solution-particle mixture.