Pertechnetate immobilization with sulfide in aqueous media under anaerobic and aerobic environments

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Technetium-99 (Tc-99) is a high yield radionuclide produced from thermal neutron fission. As a consequence of the development of nuclear weapons over the past 50 years, the Hanford Site of the Department of Energy has inherited significant contamination from a variety of radionuclides including Tc-99. The chemistry and nuclear properties of Tc-99 make clean-up of this site an important issue. The scope of this dissertation is to improve the understanding of Tc-99 chemistry important for potential environmental remediation. The second chapter describes the reaction between pertechnetate (TcO[subscript 4][superscript -]) and sulfide in both anaerobic and aerobic environments, including kinetics and stoichiometry studies. Pertechnetate can be effectively immobilized by sulfide to generated Tc2S7 in high yield under anaerobic environments. The reaction is first order with regard to both TcO[subscript 4][superscript -] - and sulfide. However, the product is not sufficiently stable over the long term in the presence of O[subscript 2]. The third chapter discusses the potential interference of coexisting species on the TcO[subscript 4][superscript -] -sulfide immobilization reaction under both aerobic and anaerobic environments. The selected species (inorganic anions, chelating agents, low molecular weight organic acids, and non-reducing minerals) had no significant effect on the immobilization process to yield Tc[subscript 2]S[subscript 7] within typical concentrations found in the vadose zone. The fourth chapter examines the immobilization of TcO[subscript 4][superscript -} - in aqueous solution under anaerobic environments by synthetic iron sulfide. This amorphous FeS was found to effectively reduce TcO[subscript 4][superscript -] - to TcO[subscript 2] with high capacity (867 mg Tc (VII) / g FeS) and fast kinetics. The TcO[subscript 4][superscript -] - -FeS reaction is a surface mediated reaction with pH dependence. The long-term stability assessment showed potential for the in situ immobilization of TcO[subscript 4][superscript -] - under both aerobic and anaerobic environments. The fifth chapter draws the conclusions of this dissertation. The sixth chapter proposes some interesting thoughts for future studies.