Chemistry of Solvent Extraction of Nd(NO3)3 and Pr(NO3)3 from Nitrate Solutions with TOMAN–TBP Mixtures in Toluene

Abstract The isomolar series method was used to identify the regions of synergistic extraction of praseodymium and neodymium from low-acid nitrate solutions containing ammonium nitrate as a salting-out agent with isomolar mixtures of tri- n -octyl(methyl)ammonium nitrate and tri- n -butyl phosphate in toluene. The synergistic effect in the praseodymium extraction was detected for a limited range of mixture compositions, while in the case of neodymium extraction, this effect was manifested over the whole range of studied compositions. It was found that the chemistry of synergistic extraction is determined by the formation of a continuous sequence of mixed praseodymium or neodymium complexes, with antiparallel variation of the number of extractant molecules in the complexes and the extractant molar ratio. As the concentration of quaternary ammonium nitrate in the mixture increases, the phosphoryl groups of tri- n -butyl phosphate are replaced by the nitrate ligands of the quaternary salt, up to their complete displacement from the lanthanide coordination sphere.