Comparison of Extraction Capacity for the Systems Based on Mono-2-Ethylhexyl 2-Etylhexylphosphonate and Bis(2,4,4-Trimethylpentyl)Phosphinic Acid in Separation of Rare Earth Elements at the Gd/Tb Line

Extraction of Gd(NO3)3 and Tb(NO3)3 from low-acid nitrate solutions with 1.0 M isomolar mixtures of Cyanex 272 and PC-88a ammonium salts with methyltrioctylammonium nitrate in dodecane has been studied. Using the isomolar series method, it has been found that mixtures of Cyanex 272 ammonium salt with methyltrioctylammonium nitrate exhibit a synergistic effect for terbium in several regions with a maximum of 1.78 for the composition 0.1 M Cyanex 272 ammonium salt–0.9 M methyltrioctylammonium nitrate, while a pronounced antagonistic effect is observed during extraction of Gd(NO3)3 and Tb(NO3)3 with PC-88a ammonium salt with methyltrioctylammonium nitrate. It has been established that synergistic mixtures of Cyanex 272 ammonium salt and methyltrioctylammonium nitrate can be used to separate the medium and heavy group of rare earth elements at the Tb/Gd line, when the total concentration of the components of the aqueous phase increases or a salting-out agent is introduced.