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Understanding the Thermodynamics, Kinetics/Mechanism, and Coordination Modes

Understanding the Thermodynamics, Kinetics/Mechanism, and Coordination Modes at the Molecular Level. Linfeng Rao Chemical Sciences Division Lawrence Berkeley National Laboratory, USA. Open-chain diamidoxime. Cyclic imide dioxime. Astheimer et al. SST 1983. Why Important?.

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Understanding the Thermodynamics, Kinetics/Mechanism, and Coordination Modes

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  1. Understanding the Thermodynamics, Kinetics/Mechanism, and Coordination Modes at the Molecular Level Linfeng Rao Chemical Sciences Division Lawrence Berkeley National Laboratory, USA

  2. Open-chain diamidoxime Cyclic imide dioxime Astheimer et al. SST 1983 Why Important? • Different configurations of AO could form in grafting + chemical reaction, such as I and II • II was believed to bind U(VI) more strongly – tridentate, but less stable against acid washing • The decrease in sorption efficiency was believed to be related to the instability of II under strongly acidic conditions

  3. What to study/measure? • Discover the conditions that favor a specific configuration • Measure the stability constants of U(VI) complexes with each configuration • Measure the enthalpy of complexation • Study the stability under acid/basic conditions • Identify the molecular structure of the U(VI) complexes Tian & Rao, unpublished data Witte et al. Inorg. Chim. Acta (1984)

  4. Higher U loading • More repetitions • Higher efficiency • Higher selectivity Cost Reduction Tamada, 2009 What help to provide • Guidance for generating the preferred (more efficient) configuration in high yield • Guidance for increasing the stability of the preferred configuration against acid washing • Understanding and making better use of the temperature effect • Guidance for designing new ligands with high selectivity

  5. UO2(CO3)34- is a very stable species at seawater pH. Efforts on developing extraction process using sorbents directly for anionic UO2(CO3)34- species? The selectivity for U over transition metals could be higher with such process (carbonato complexes of transition metals may not be as strong as U)?

  6. Criteria • Simple and robust (stable in marine environments) • Easy and inexpensive to make on a large scale • Strong binding with U(VI) (high basicity?) • Fast in sorption rate • Easy to elute U A balance between these properties and the selectivity must be achieved. Developing specific ligands to improve selectivity

  7. R&D in Japan: Marine Experiments The Stack Collection System Tamada 2009

  8. R&D in Japan: Marine Experiments Effect of Temperature? R = 0.68

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