Extraction of Uranyl Ion Using 2-Thenoyltrifluoro Acetone (HTTA) in Room Temperature Ionic Liquids

Abstract

The extraction of UO 2 2+ ion was studied using six different solvent systems containing 2-thenoyltrifluoroacetone (HTTA) in room temperature ionic liquids such as [C n mim][X] (where, n = 4, 6 or 8 and X -= PF 6 -or NTf 2 -) from low to moderate pH solutions for the first time. The extraction kinetics studies indicated rather slow attainment of equilibrium which in some cases improved if the solutions were pre-equilibrated with the aqueous phase prior to the actual experiments. The D U values were found to increase with increasing pH and leading to a plateau like profile at higher pH values. The D values were quite high as compared to that obtained with molecular diluents. The nature of the extracted species was ascertained by slope analysis method which suggested species of the type: (UO 2 TTA) + IL , (UO 2 2+ )(TTA -) 2,IL and (UO 2 2+ )(TTA -) 2 (HTTA) in different ionic liquid based solvents. Temperature variation studies on UO 2 2+ ion extraction were also carried out and the thermodynamic parameters were calculated which indicated high endothermic reactions with large positive entropy values.

Advancing Understanding of the +4 Metal Extractant Thenoyltrifluoroacetonate (TTA–); Synthesis and Structure of MIVTTA4(MIV= Zr, Hf, Ce, Th, U, Np, Pu) and MIII(TTA)4–(MIII= Ce, Nd, Sm, Yb)

“…For experiments with these +3 metals, addition of NH 4 OH created a murky solution. However, over the course of 2 to 3 d, the solution cleared, and crystals of (NH 4 )M III (TTA) 4 emerged leaving behind the dissolved NH 4 Cl byproducts. In our laboratory, crystallizations with tetraphenyl phosphonium (PPh 4 + ), tetrabutyl ammonium (NBu 4 + ), and tetramethylammonium (NMe 4 + ) cations were unsuccessful suggesting that the 28 In comparison to many studies that have compared reactivity across the lanthanide series, the syntheses of the M III (TTA) 4 − were somewhat unique.…”

“…Advances in actinide separations science have had an impact in virtually every technologically relevant area associated with the f-elements. This spans from isotope production to advanced nuclear fuel cycle development, plutonium sustainment, and the national nuclear security administration’s (NNSA) missions in nuclear science. − Among numerous actinide separations relevant to these operational efforts, those associated with separating Pu, Np, and U are particularly important. For instance, being able to cleanly isolate trace amounts of Np and Pu from bulk U matrices is critical for quantifying actinide mobility and abundances in the environment .…”

“…Of the many approaches for separating Pu, Np, and U, ,,,, one particularly effective operational procedure involves an extraction step with thenoyltrifluoroacetone (HTTA), Figure . ,− This method involves an oxidation state adjustment of the metal to +4 in acidic media (e.g., HCl, 1 M), followed by HTTA extraction into an aromatic solvent (e.g., o- xylene, toluene, benzene, etc.). The process selectively extracts +4 metals into the organic phase, while leaving behind metal ions (including actinides and lanthanides) in other oxidation states, such as +3, +5, and +6 .…”

“…Despite widespread use of the HTTA extraction procedure for actinide processing in analytical chemistry and significant efforts to characterize the parameters for conducting successful HTTA extractions (separation factors, distribution coefficients, etc. ,− ), little is understood about the interworking of the separation. Although it has been proposed that the +4 metals react with HTTA to form the M­(TTA) 4 extracted complex, the identities of the extracted species have not been characterized, and the driving force for the selectivity is mysterious.…”

“…In all of the fits, optimized Debye−Waller factors were in a normal range, spanning from 0.0031(8) to 0.0084(8) Å 2 . For the control samples, coordination numbers were fixed based on the solid-state single-crystal X-ray diffraction measurements, and S 0 2 values were allowed to converge to 0.93(5) for Np IV (TTA) 4 and 0.97 (6) for Pu IV (TTA) 4 .…”