Insights into the Complexation Mechanism of a Promising Lipophilic PyTri Ligand for Actinide Partitioning from Spent Nuclear Fuel

Abstract

The challenging issue of spent nuclear fuel (SNF) management is being tackled by developing advanced technologies that point to reduce environmental footprint, long-term radiotoxicity, volumes and residual heat of the final waste, and to increase the proliferation resistance. The advanced recycling strategy provides several promising processes for a safer reprocessing of SNF. Advanced hydrometallurgical processes can extract minor actinides directly from Plutonium and Uranium Reduction Extraction raffinate by using selective hydrophilic and lipophilic ligands. This research is focused on a recently developed N-heterocyclic selective lipophilic ligand for actinides separation to be exploited in advanced Selective ActiNide EXtraction (SANEX)-like processes: 2,6-bis(1-(2-ethylhexyl)-1H-1,2,3-triazol-4-yl)pyridine (PyTri-Ethyl-Hexyl-PTEH). The formation and stability of metal–ligand complexes have been investigated by different techniques. Preliminary studies carried out by electrospray ionization mass spectrometry (ESI–MS) analysis enabled to qualitatively explore the PTEH complexes with La(III) and Eu(III) ions as representatives of lanthanides. Time-resolved laser fluorescence spectroscopy (TRLFS) experiments have been carried out to determine the ligand stability constants with Cm(III) and Eu(III) and to better investigate the ligand complexes involved in the extraction process. The contribution of a 1:3 M/L complex, barely identified by ESI–MS analyses, was confirmed as the dominant species by TRLFS experiments. To shed light on ligand selectivity toward actinides over lanthanides, NMR investigations have been performed on PTEH complexes with Lu(III) and Am(III) ions, thereby showing significant differences in chemical shifts of the coordinating nitrogen atoms providing proof of a different bond nature between actinides and lanthanides. These scientific achievements encourage consideration of this PyTri ligand for a potential large-scale implementation.

The fate of reverse micellar aggregation in irradiated diglycolamide inn-dodecane solution

“…The third phase was dissolved by adding 1 M nitric acid pre-equilibrated organic phase and the LOC and LAS were determined in the organic phase immediately after the dissolution of the third phase. 37,38 bNT – no third phase formation.…”

“…The LOC and CAC of nitric acid were determined by acid-base titration. 29,37,38 2.5 Dynamic light scattering 2.5.1 Theory of dynamic light scattering. The underlying principle of the dynamic light scattering technique is based on Brownian motion, where the reverse micellar aggregates present in the organic phase undergo a constant random motion due to collision with the solvent molecules present in the sample.…”

“…Therefore, LAS is the limiting aggregate size of the organic phase for third phase formation. 37,38 Fig. 4 Average aggregate size of the nitric acid equilibrated organic phase (0.1 M TODGA/n-DD) irradiated to various absorbed gamma dose levels.…”

Interactions of CyMe4‐BTBP ligand with lanthanides and actinides: Insights from ESI‐MS and DFT calculations

“…19 By contrast, ESI-MS reveals the complexes or protonated ligand directly, and it has been validated as an appropriate technique for characterizing the complexes in solution. 20 The advantage of this technique is that it can quickly, directly, and accurately determine the complex species in solution and investigate their stability in the gas phase. 21 Several recent studies have shown that the complexes between the liquid-phase and gas-phase have good consistency.…”

“…The hydrolytic and radiolytic degradation products of CyMe 4 ‐BTBP have also been reported 19 . By contrast, ESI‐MS reveals the complexes or protonated ligand directly, and it has been validated as an appropriate technique for characterizing the complexes in solution 20 . The advantage of this technique is that it can quickly, directly, and accurately determine the complex species in solution and investigate their stability in the gas phase 21 .…”