Nano Adsorbent Materials for U, Tc and I Remediation: Capacity, Molecular Mechanism, and Application

U, Tc and I are three of the four risk drivers at Department of Energy sites. New technologies are needed for remediation of U, Tc and I from contaminated groundwater or separation from liquid nuclear wastes. U species display limited adsorption onto sediment minerals and synthetic sorbents in pH 4 or pH > 8 groundwater. In Li's work, magnetic mesoporous silica nanoparticles (MMSNs) with magnetite nanoparticle cores were functionalized with various organic molecules using post-synthetic methods. The functionalized MMSNs were effective for U removal from pH 3.5 and 9.6 artificial groundwater (AGW), with the adsorption capacity as high as 38 mg/g and 133 mg/g from pH 3.5 and 9.6 AGW, respectively. These functionalized MMSNs are also effective for U extraction from seawater with adsorption capacity of 54 mg/g. In addition, new organoclays and activated carbon are developed and evaluated for removing anionic TcO₄^-, IO₃^- and I^- contaminants from groundwater. These inexpensive sorbent materials are demonstrated to have exceptionally high capacity for removal of the difficult anionic contaminants and have been deployed in the field to evaluate their effectiveness for Tc and I remediation. Furthermore, U and Tc chemical speciation and molecular binding onto the nano sorbent materials are studied using U L₃-edge or Tc K-edge XANES and EXAFS spectroscopy. Such molecular mechanistic studies will further guide the future selection of organic ligands for developing more robust nano sorbent materials that are more efficient and cost-effective for U and Tc extraction from environmental aqueous systems.