Investigation of Sr²⁺ Extraction from Aqueous Phase Using Novel Diglycolamide/Ionic Liquid System

Obtaining high-purity ⁹⁰Sr is crucial because it is the parent radionuclide of the ⁹⁰Sr/⁹⁰Y generator. However, ⁹⁰Sr products recovered from high-level liquid waste (HLLW) often fail to meet the stringent purity requirements. This necessitates the development of a novel extraction system that can seamlessly connect with existing separation processes to achieve the required purity level. A novel diglycolamide (DGA) ligand was designed and synthesized. The distribution ratios (D) of several traditional organic diluents and ionic liquids (ILs) as diluents were compared under the same experimental conditions; 1-butyl-3-methylimidazolium bis(trifluoromethanesulphonyl)imide ([C₄mim][NTf₂]) was chosen as the optimal diluent. The HNO₃ concentration, ligand concentration, [C₄mim]⁺ concentration, etc., were assessed. The extraction mechanism was confirmed to ensure that the extraction proceeded mainly via the [C₄mim]⁺ and H⁺ exchange mechanisms. Slope analysis and the ESI-MS results revealed that the novel ligand N,N-diphenyl-N',N'-dibutyl diglycolamide (DPDBDGA, L) in [C₄mim][NTf₂] formed a 1:3 complex with Sr²⁺. The experiments on Sr²⁺ indicated that it can be recovered completely with 1 M mineral acid within two stages. Furthermore, we predicted that the novel DGA ligand would provide a good extraction capacity for Sr²⁺ in dilute nitric acid in the [C₄mim][NTf₂] system. This system can be linked to the separation process of extracting Sr²⁺ from HLLW using N,N,N',N'-tetraoctyl-diglycolamide (TODGA) or crown ethers as extractants. Consequently, high-purity ⁹⁰Sr products can be obtained.