The treatment of alkaline High-Level Waste (HLW) is an ongoing challenge in remedying the by-products of nuclear weapons production during the Cold War. Two processes - the Actinide Removal Process (ARP) and the Next Generation Caustic-Side Solvent Extraction (NG-CSSX) – are used to separate radioactive isotopes (137Cs (extraction by calixarene; NG-CSSX), 90Sr and actinides from the HLW stream, generating a reduced volume of HLW and leaving the rest as Low Activity Waste. A largely unexplored compound, rhodizonate (Rhod), can form precipitates with trivalent lanthanides (Ln3+) and UO22+ in aqueous solutions while keeping the Ln-Rhod or UO2-Rhod complex in solution in mixed “water/polar organic solvent” systems. This versatility makes rhodizonate separation and immobilization chemistry a new, potentially fruitful area of research for solving problems in processing HLW. Using lanthanides as surrogates for actinides, we have demonstrated that rhodizonate complexes several lanthanides. The solid-state FT-IR spectra of different Ln-Rhod complexes show markedly different absorption bands, particularly in those corresponding to C=O stretches, suggesting different coordination modes of the Rhod in the complexes. UV-Vis titrations of lanthanides by rhodizonate in water/ethanol (1:1) show notable changes confirming complexation. The complex between the various Ln3+ and Rhod is strong (K11 ≈ 105 M-1), suggesting that rhodizonate has the potential to be an effective ligand when it comes to issues of sequestering radioisotopes involved in HLW separations.

Complexation of lanthanides with the rhodizonate anion

2019 Spring National Meeting

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