Spectroscopic and Theoretical Insights into Surprisingly Effective Sm(III) Extraction from Alkaline Aqueous Media by -Phenylenediamine-Derived Sulfonamides.

Alkaline high-level waste (HLW) generated as a result of years of nuclear weapons production has complicated composition and requires comprehensive treatment methods, which would allow concentrating its most radiotoxic components in a small volume for geological disposal. We have investigated six alkyl-substituted -phenylenediamine-derived sulfonamides for extraction and consecutive stripping of Sm(III) from alkaline aqueous media. Up to 81% of Sm(III) recovery at pH 13.0-13.5 was achieved by disulfonamide () or /EtN in CHCl, measured after contact with organic phases and subsequent stripping with 0.1 M HNO. The use of EtN dramatically enhances Sm(III) extraction at lower pH ranges (10.5-11.5) but decreases extraction at pH 13.0-13.5, while control experiments with EtN and no showed no extraction. Analysis of the extraction equilibria gave a 1:1 sulfonamide-Sm(III) complexation ratio, with the extracted species also presumed to contain coordinated HO or OH, as also shown by DFT calculations. Titration experiments of sulfonamides with Sm(III) in CHCN were consistent with a 1:1 complexation ratio of to Sm(III) with a = 6.6 × 10 M derived from nonlinear regression analysis of the 1:1 binding isotherm. Theoretical DFT calculations determined the structures of possible species formed during extraction and the thermodynamics of extraction processes based on several initial [Sm(OH)(NO)(HO)] species and 1:1 Sm(III)/ complexes formed in the organic phase, in which complexes to Sm(III) in its bis-deprotonated form (denoted below as ). Organization of close ion pairs of type {Na[Sm()(OH)]·2HO} was shown to be thermodynamically favorable for extraction from alkaline aqueous media with pH = 13.0-13.5. Theoretical calculations also demonstrated thermodynamically favorable coordination to Am(III).