Elucidation of complexation of tetra and hexavalent actinides towards an amide ligand in polar and non-polar diluents: Combined experimental and theoretical approach

Mechanism unravelling for highly efficient and selective 99TcO4 - sequestration utilising crown ether based solvent system from nuclear liquid waste: experimental and computational investigations

Selective and efficient separation of pertechnetate (TcO4 -) from nuclear waste is desirable for the safe and secure management of radioactive waste. Here, we have projected dibenzo-18-crown-6 ether (DB18C6) in a highly polar nitrobenzene medium for enhancing the removal efficiency of 99Tc from reprocessing plant low level waste (LLW). An effort was made to determine the stoichiometry of metal-ligand complex by slope ratio method, revealing that one ligand (DB18C6) binds with one TcO4 - moiety. Optimum ligand concentration for 99Tc extraction was evaluated. Relevant interference of the anions was studied systematically. The effect of solution pH was analysed on the extraction efficiency of 99Tc. A kinetic study was carried out for maximum extraction of metal ions. A quantitative stripping study was also achieved for metal ions with a suitable stripping solution. After evaluation of all essential parameters, selectivity and feasibility studies were finally carried out with actual low level reprocessing plant waste to demonstrate a laboratory scale process for effective separation of TcO4 - ions. Density functional theory (DFT) calculations were carried out to understand the nature of the complexation of TcO4 - ion with DB18C6 in different solvents systems and to elucidate the key aspect behind ionic selectivity and enhanced the 99Tc extraction efficiency of DB18C6 in the studied diluent systems. The ΔE and ΔG values for different modeled complexation reactions were evaluated systematically. From the calculated free energy of complexation of TcO4 - with DB18C6, it was observed that the consideration of explicit solvent plays a vital role in predicting the experimental selectivity.

Complexation of thorium with pyridine monocarboxylate-N-oxides: Thermodynamic and computational studies

The feed wastes and waste water treatment plants are the major sources for the entry of N-oxides into the soils then to aquatic life. The complexation of actinides with potentially stable anthropogenic ligands facilitate the transportation and migration of the actinides from the source confinement. The present study describes the determination of thermodynamic parameters for the complexation of Th(IV) with the three isomeric pyridine monocarboxylates (PCNO) namely picolinic acid-N-oxide (PANO), nicotinic acid-N-oxide (NANO) and isonicotinic acid-N-oxide (IANO). The potentiometric and isothermal calorimetric titrations were carried out to determine the stability and enthalpy of the formations for all the Th(IV)-PCNO complexes. Th-PANO complexes are more stable than Th-NANO and Th-IANO complexes which can be attributed to chelate formation in the former complexes. Formation of all the Th-PCNO complexes are endothermic and are entropy driven. The geometries for all the predicted complexes are optimized the energies, bond distances and charges on individual atoms are obtained using TURBOMOLE software. The theoretical calculation corroborated the experimental determinations.