Selective Extraction of Thorium(IV) from Uranium and Rare Earth Elements Using Tetraphenylethane-1,2-diylbis(phosphoramidate)

Tetraphenylethane-1,2-diylbis(phosphoramidate) is studiedfor the first time to form a 1:2 metal/ligand complex with thorium(IV).In the liquid-liquid extraction of thorium by bis(phosphoramidate)from 2-8 mol L-1 acidic medium, the complexappears as a white insoluble solid in the organic medium of chloroformand room temperature ionic liquid. Such a unique extraction processwill facilitate the separation of thorium from its ore and irradiatedthorium fuel. Tetraphenylethane-1,2-diylbis(phosphoramidate) in conjugationwitha room temperature ionic liquid in chloroform medium is reported forthe first time in the liquid-liquid extraction of thorium (Th).The extracted Th(IV) is collected as a white solid in the organicmedium, thereby facilitating its easy separation. A high distributionratio (D) of (12.4 +/- 0.1) x 10(3) in 2-8mol L-1 acidity range and high decontamination factors(alpha) of Th(IV) from uranium, lanthanides, and a number of transitionelements makes this extraction process versatile and selective. Anumber of experimental investigations in synergism with extended X-rayabsorption fine structure (EXAFS) spectroscopy and density functionaltheory (DFT) studies are interpreted to confirm the structure of thechelated complex. A 1:2 metal/ligand complex in which the two oxygenand two nitrogen atoms of each bis(phosphoramidate) molecule satisfyingthe eight coordination sites of Th(IV) is found to be formed. Theextracted white solid thorium complex is easily converted to ThO2 after washing and heating at 1300 degrees C under O-2 atmosphere. This work is expected to find direct application inthe thorium fuel cycle, especially in the mining process of thoriumfrom its ores and in the separation of fissile U-233 fromfertile Th-232 in irradiated fuel.