Gamma Radiolysis of TODGA and CyMe₄BTPhen in the Ionic Liquid Tri-n-Octylmethylammonium Nitrate

ABSTRACT

Radiolytic stability of the extractants N,N,N’,N’-tetraoctyl diglycolamide (TODGA) and 2,9-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-1,10-phenanthroline (CyMe₄BTPhen) in the ionic liquid tri-n-octylmethylammonium nitrate ([N₁₈₈₈][NO₃]) was studied via the combination of a steady-state irradiation by cobalt-60 gamma-radiation, followed by solvent extraction and identification of radiolysis products by High-Performance Liquid Chromatography coupled to Electro Spray Ionisation Mass Spectrometry (HPLC-ESI-MS). The observed trend for the distribution ratios of trivalent minor actinides and Eu(III) showed a decrease as a function of absorbed dose in the case of the TODGA solvent. The gamma irradiations were conducted in the presence or absence of an acidic aqueous phase. The determined dose constants for TODGA under neutral or acidic conditions were up to four times lower than the values reported in aliphatic diluents under comparable conditions. The degradation patterns were similar to those found by former studies on TODGA diluted in n-dodecane; only de-alkylation and bond ruptures within the diglycolamide core were observed. The presence of an acidic aqueous phase during irradiation resulted in a different relative abundance of certain radiolysis products of both the diluent and TODGA and a higher dose constant compared to the neutral irradiation conditions. A quantification of CyMe₄BTPhen in irradiated samples with the [N₁₈₈₈][NO₃] diluent was not possible, but the effect on its extraction properties was evaluated. The distribution ratios slightly increased under the effect of absorbed dose, indicating the formation of radiolysis products that are efficient extractants as well.

KEYWORDS:

• Solvent extraction
• TODGA
• CyMe₄BTPhen
• gamma radiolysis
• ionic liquids
• HPLC-ESI-MS

Acknowledgments

The authors would like to thank Andrei Goussarov, Steven Van Loven and Kris Thys from the BEX unit for performing the γ- irradiations. P. Z. acknowledges the SCK•CEN Academy for providing funding for a PhD fellowship and the FOD Economie for providing additional support via the Energietransitiefonds. The authors would like to thank Magda Ooms for the help with the alpha spectrometry measurements and Prisca Verheyen for the help with the ICP-MS measurements.

Supplementary material

Supplemental data for this article can be accessed here.