Extraction of U(VI) and Th(IV) from HNO3 systems using spirocyclic bis-phosphamide ligands as alternatives to the TBP extractant.
Abstract
Developing structurally robust extractants that remain stable under strongly acidic conditions has always been a critical bottleneck for separation technologies in advanced nuclear fuel cycles. In this study, a set of novel spirocyclic bis-phosphamide ligands featuring rigid spiro skeletons were successfully synthesized and innovatively applied to the selective extraction of U(VI) and Th(IV) from nitric acid solution. Among the synthetic ligands, Bdoa-Trodpo exhibited the most prominent extraction performance, even at a high nitric acid concentration of 6.0 M. Impressively, its distribution ratios toward U(VI) and Th(IV) were 20-fold and 97-fold greater than that of conventional tributyl phosphate (TBP) at 6 M HNO3, the widely used industrial extractant. Slope analysis, high-resolution mass spectrometry (HRMS), Fourier-transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) were fully utilized to clarify the extraction mechanism. The results confirmed that Bdoa-Trodpo differs markedly from TBP, and both phosphoryl (PO) and phospho-oxygen (P-O) functional groups are involved in coordination interactions with actinide metal ions. Such dual-site coordination accounts for its enhanced extraction performance over TBP. The as-established extraction system not only presents superior selectivity for target actinides against common simulated fission products but also has excellent metal loading capability. Furthermore, a near-complete back-extraction efficiency (over 99%) was realized by adopting a hydrolyzed derivative of the original spirocyclic ligand. The experimental findings verify that this novel cyclic bisphosphonate compound is a stable and high-performance extractant. It holds great potential as an alternative to traditional TBP for actinide separation in highly acidic spent fuel reprocessing systems, providing new insight for the development of advanced nuclear separation materials.
Abstract as supplied by the indexing source. © the authors / publisher.