Oligomer Formation Effects on the Separation of Trivalent Lanthanide Fission Products

Lauren Walker, Scott Heath, Jun Jiang, Louise Natrajan, Francis Livens

Research output: Contribution to journalArticlepeer-review

Abstract

The assessment of trivalent lanthanide yields from the fission of uranium-235 is currently achieved using LN (LaNthanide) resin, di(2-ethylhexyl)orthophosphoric acid (HDEHP) immobilised on a solid support. However, co-elution of lighter lanthanides into terbium (Tb3+) fractions remains a significant problem in recovery of analytically pure fractions. In order to understand how the separation of trivalent lanthanides and yttrium (Ln3+) with LN resin proceeds and how to improve it, their speciation with the organic extractant HDEHP must be fully understood under aqueous conditions. A comprehensive luminescence analysis of aqueous solutions of Ln3+ contacted with HDEHP, alongside infrared spectroscopy, elemental combustion analysis, inductively coupled plasma atomic emission spectroscopy (ICP-AES) and mass spectrometry was used to indicate an intermediate species is responsible for the co-elution; where similar Ln3+ centres (e.g. Eu3+ and Tb3+) are bridged by the O-P -O moiety of deprotonated HDEHP to form large heteronuclear oligomeric structures with the general formula [Ln2(DEHP)6]n. Energy transfer from Tb3+ to Eu3+ in this structure confirms that lanthanide centres are within 10 Å and was used to propose that the oligomeric [Ln2(DEHP)6]n structure is formed rather than a dimeric Ln2(DEHP)6 structure. The effect of this speciation on LN resin column elution is investigated using luminescence spectroscopy, confirming that the oligomeric [Ln2(DEHP)6]n species could disrupt regular elution behaviour and cause the problematic bleeding of lighter lanthanides (Sm3+ and Eu3+) into Tb3+ fractions. Resin luminescence measurements were used to propose that bleeding of the organic extractant HDEHP from its solid support causes the formation of the disruptive oligometallic species.
Original languageEnglish
JournalInorganic Chemistry
Publication statusAccepted/In press - 21 Jun 2024

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