The Hanford and Savannah River US DOE sites contain the majority of high-level waste (HLW) in the US, with about 100 MGal in volume and combined activity of over 400 MCi. Several approaches have been adopted to separate the waste into high activity and low activity waste forms, in order to reduce the overall volume and reduce contamination risks by disposing low level waste in cementitious form (grout) and immobilizing remaining low volumes of HLW components in solid form within glass (vitrification).
At Savannah River Site (SRS), the two sequential approaches used are the Actinide Removal Process (ARP) followed by the Caustic Side Solvent Extraction (CSSX). The ARP is a sorption process using monosodium titanate (MST) to remove Sr(II) and actinides. The CSSX process selectively extracts Cs(I) by using a calixarene extractant. Our group is focusing its efforts to CSSX-compatible additives (ligands) for combined extraction of f-elements, together with Cs(I) and Sr(II), thus reducing the amount of MST and contact time needed during the slower ARP process, and thus simplifying overall HLW processing.
We now present N-(5-(tert-butyl)-2-hydroxyphenyl)-5-(dimethylamino)naphthalene-1-sulfonamide (L_D), which is a o-sulfonamidophenol ligand bearing the signaling fluorescent dansyl moiety for the sequestration and in-situ sensing of f-elements in HLW. We observed 92% extraction of Sm(III) (used as an experimental surrogate for actinides) from pH 13.0 into dichloromethane after one extraction/strip cycle. Addition of several Ln(III) to acetonitrile solutions of (L_D) in the presence of organic bases showed notable fluorescence enhancements, while UV-Vis titrations in acetonitrile suggested 1:1 binding stoichiometry, with binding constant of LogK = 5.31 ± 0.33 obtained using the Hypspec program. Though we have established the stability of (L_D) under alkaline conditions, compatibility studies of the ligand in the CSSX solvent are currently underway.

Cristian Gonzalez

Appearances