The cold war era reprocessing of nuclear fuel via the PUREX process for plutonium production has led to the generation of large volumes of caustic high-level waste (HLW) stored in underground tanks at the Savannah River Site (SRS) and the Hanford Site (HS) in the US. Current reprocessing at SRS is based on a two-step process, consisting of the Actinide Removal Process (ARP) for 90Sr and actinides (An) by sorption on monosodium titanate followed by the Next-Generation Caustic-Side Solvent Extraction process (NG-CSSX) for 137Cs separation. Actinide chelators compatible with the NG-CSSX process could potentially achieve simultaneous separation of Cs, Sr, and An, by a one-step solvent extraction process, reducing the contact times and amounts of titanate sorbent during the slower ARP process and thus significantly improving the efficiency of overall HLW processing. Recently, we reported effective extraction of Sm(III), used as a surrogate for Am(III), from alkaline aqueous media by o-phenylenediamine-derived aryldisulfonamides. Sm(III) recovery up to 81% at pH 13.0 in chlorinated solvents after just one loading-stripping cycle was demonstrated. Encouraged by these results we extended our work to o-(monosulfonamido)-phenol type ligands and achieved Sm(III) extraction efficiencies of &gt; 90% at pH = 14 in dichloromethane. The use of chlorinated solvents however, represents a major drawback for industrial application. Hence, to facilitate application of these high- performing ligands, we have now developed and present new highly-lipophilic aryl- and alkyl-substituted disulfonamide and o-(monosulfonamido)-phenol derivatives, that can extract Sm(III) efficiently in process solvents, such as n-dodecane, n-dodecane/octanol from up to 2M NaOH. Preliminary experiments with some of these ligands in the actual CSSX solvent and process compatibility issues will also be discussed.

Highly-lipophilic sulfonamide chelators and analogs for actinide separation from caustic high-level waste

ACS Spring 2022

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