Challenging conventional f-element separation chemistry – reversing uranyl(vi)/lanthanide(iii) solvent extraction selectivity

Abstract

The water soluble tetradentate Schiff base, N,N 0 -bis(5-sulfonatosalicylidene)-diaminoethane (H 2 salen-SO 3 ), will readily coordinate to the uranyl(VI) cation, but not to the same extent to trivalent lanthanide cations. This allows for the reversal of conventional solvent extraction properties and opens the possibility for novel separation processes.

Water-soluble Schiff base-actinyl complexes and their effect on the solvent extraction of f-elements

“…21 Considering that the present data were acquired in the absence of U(VI), the difference in these results indicate that there was competition between the metal ions for complexation/extraction by HDEHP in the previous study, where the formal HDEHP concentration was 50-fold greater than the combined Eu(III) and U(VI) concentrations. We postulate that the activity of the extracting form of the ligand ( i.e., DEHP·HDEHP dimer) 34 at the organic-aqueous interface may be significantly reduced at this relatively high pH.…”

“…Preliminary results related to Eu(III) and U(VI) extraction by bis (2-ethylhexyl)phosphoric acid (HDEHP) suggest that a significant increase in Ln(III)/An(VI) selectivity could be achieved by addition of a water-soluble Schiff base that preferentially binds to U(VI) under appropriate conditions. 21 The chemistry of the extraction of U(VI) and Eu(III) by HDEHP in toluene is well known, both being readily extractable from mildly acidic aqueous solution. 22 In our previous work we showed that the introduction of a water soluble Schiff base (N,N'-bis(5-sulfonatosalicylidene)-ethylenediamine -H2salenSO3) to the aqueous phase led to a reversal in the extraction order of U(VI) and Eu(III).…”

“…22 In our previous work we showed that the introduction of a water soluble Schiff base (N,N'-bis(5-sulfonatosalicylidene)-ethylenediamine -H2salenSO3) to the aqueous phase led to a reversal in the extraction order of U(VI) and Eu(III). 21 In this paper, we report an extended study into the chemistry of disodium H2salenSO3, in the context of actinyl coordination and solvent extraction chemistry. Firstly, our previous report indicated that this Schiff base ligand will at least partially decompose in aqueous solution and we have thus investigated the extent of hydrolytic decomposition in order to quantify the stability of the U(VI) complex with this complexant.…”

“…Firstly, our previous report indicated that this Schiff base ligand will at least partially decompose in aqueous solution and we have thus investigated the extent of hydrolytic decomposition in order to quantify the stability of the U(VI) complex with this complexant. 21 Finally, the chemical equilibrium basis for the trends observed in metal ion extraction were studied by various spectroscopic techniques.…”

Phosphorous‐Based Pillar[5]arenes for Uranyl Extraction

“…[16] Therefore, separation and recovery of uranium in the form of the uranyl(VI) dication 2 2 (UO ) ＋ , the most stable species in solution, [17] are of great scientific and practical significance. Particularly, efficient extraction process calls for design of novel extractants and understanding of structural factors that dominate the efficacy and selectivity of separation.…”