Nuclear waste reprocessing: study of the separation of radioactive cations 137Cs+ and 90Sr2+ from high level activity radioactive waste (HLW) by extractants derivatives of the hydroborates [B10H1

New extractants [R₁R₂R₃NB₁₀ H₉]^- and [R₁R₂R₃ N-B₁₂H₁₁]^- obtained from [B₁₀H₁₀]^2- and [B₁₂H₁₂ ]^2- anions respectively were tested in the extraction of radioactive cations Cs⁺ and Sr²⁺ from aqueous nitric acid solution. The method used was liquid-liquid extraction based on the complexation of these cations by anions (extractants) to form neutral compounds that are very soluble in organic solvents and less soluble in aqueous medium. After extraction of the organic phase, its treatment by adding an excess of concentrated nitric acid would permit the recovery of the radioactive cations. Our products showed a good stability in very acidic medium and could be classified as good extractants of Cs⁺. The best results were obtained with derivatives of [B₁₀H₁₀]^2- or [B₁₂ H₁₂]^2- in which the tertiary amine includes two benzyl groups that could sequestrate the Cs⁺ cation. [B ₁₂H₁₂]^2- is more hydrophobic than [B ₁₀H₁₀]^2-, its derivatives were more efficient in the Cs⁺ extraction. The Sr²⁺ extraction was less efficient because the 2+ charge of Sr²⁺ favoured its solvation and prevented its extraction from the aqueous phase explaining the very weak D_Sr values obtained. The most efficient extraction solvent was nitrobenzene. Using hydrochloric or sulfuric acid instead of nitric acid gave similar results in the Cs⁺ extraction