Nuclear waste reprocessing: study of the separation of radioactivecations 137Cs+ and 90Sr2+from high level activity radioactive waste (HLW) by extractantsderivatives of the hydroborates B₁₀H₁₀2and B₁₂H₁₂2

摘要

New extractants [R₁R₂R₃NB₁₀H₉]- and [R₁R₂R₃N-B₁₂H₁₁]- obtained from[B₁₀H₁₀]2- and [B₁₂H₁₂]2- anions respectively were tested in the extractionof radioactive cations Cs+ and Sr2+ from aqueousnitric acid solution. The method used was liquid-liquid extraction basedon the complexation of these cations by anions (extractants) to formneutral compounds that are very soluble in organic solvents and lesssoluble in aqueous medium. After extraction of the organic phase, itstreatment by adding an excess of concentrated nitric acid would permitthe recovery of the radioactive cations. Our products showed a goodstability in very acidic medium and could be classified as goodextractants of Cs+. The best results were obtained withderivatives of [B₁₀H₁₀]2- or [B₁₂H₁₂]2- in which the tertiary amine includestwo benzyl groups that could sequestrate the Cs+ cation. [B₁₂H₁₂]2- is more hydrophobic than [B₁₀H₁₀]2-, its derivatives were moreefficient 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 aqueousphase explaining the very weak D_Sr values obtained. The mostefficient extraction solvent was nitrobenzene. Using hydrochloric orsulfuric acid instead of nitric acid gave similar results in theCs+ extraction