Oligomer Formation Effects on the Separation of Trivalent
Lanthanide Fission Products
Posted on 2024-07-10 - 20:43
The assessment of
trivalent lanthanide yields from the fission
of uranium-235 is currently achieved using LN (LaNthanide) resin,
di(2-ethylhexyl)orthophosphoric acid immobilized on a solid support.
However, coelution 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+ in contact
with HDEHP, along with infrared spectroscopy, elemental combustion
analysis, inductively coupled plasma atomic emission spectroscopy
(ICP-AES), and mass spectrometry, was used to indicate that an intermediate
species is responsible for the coelution; where similar Ln3+ centers (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 centers 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 behavior
and cause the problematic bleeding of lighter lanthanides (Sm3+ and Eu3+) into Tb3+ fractions. Resin
luminescence measurements were used to propose that the bleeding of
the organic extractant HDEHP from its solid support causes the formation
of the disruptive oligometallic species.
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Walker, Lauren
E.; Heath, Scott L.; Jiang, Jun; Natrajan, Louise S.; Livens, Francis R. (1753). Oligomer Formation Effects on the Separation of Trivalent
Lanthanide Fission Products. ACS Publications. Collection. https://doi.org/10.1021/acs.inorgchem.4c01272