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.
Among radioactive by-products generated by nuclear technologies, solid organic waste is drawing attention because of difficult management and incompatibility with the disposal strategies traditionally adopted. Recently, geopolymers have been proposed as valid and green alternatives to cement-based matrices. In this work, novel geopolymeric formulations have been studied at laboratory scale to encapsulate ashes from incineration of surrogate solid organic waste and to further pursue sustainability and circular economy goals. Indeed, the most widely used precursor of literature geopolymers, calcined kaolin, has been totally replaced by natural raw materials and recycled industrial by-products. In addition, a highly zeolitized volcanic tuff has been chosen to further improve the intrinsic cation-exchange capacity of the geopolymer, hence enhancing waste-matrix interaction. The alkaline activation of the precursors, achieved without silicates of any metal, resulted in a promisingly durable geopolymeric matrix, whose chemical composition has been optimised to provide compressive strength above 10 MPa after 28 days of curing. A water-saturated sealed chamber provided the optimal curing condition to limit the efflorescence and improve the mechanical properties. At least 20 wt% loading of treated surrogate waste was achieved, without compromising workability, setting time, and compressive strength, the latter remaining within acceptable values. In order to demonstrate matrix durability, leaching behaviour and thermal stability were preliminarily assessed by immersion tests and thermogravimetric analyses, respectively. The leachability indices of constituent elements resulted far above 6, which is the generally agreed requirement for cement-based matrices. Moreover, the mechanical resistance was not worsened by the water immersion. The preliminarily obtained results confirm the promising properties of the new matrix for the immobilization of nuclear waste.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.