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 long-lived radionuclide of significant environmental concerns. 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 (TcO₄⁻) 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. However, the product is not sufficiently stable over the long term in the presence of O₂. The third chapter discusses the potential interference of selected coexisting species on TcO₄⁻ sulfide immobilization reaction under both aerobic and anaerobic environments. Results showed that none of them had significant effect on the immobilization process to yield Tc₂S₇ within typical concentrations found in the vadose zone. The fourth chapter examines the immobilization of TcO₄⁻ in aqueous solution under anaerobic environments by synthetic iron sulfide. This amorphous FeS was found to effectively reduce TcO₄⁻ to TcO₂ with high capacity (867 mg Tc (VII) / g FeS) and fast kinetics. The long-term stability assessment showed potential for the in situ immobilization of TcO₄⁻ 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.