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

TL;DR

A new system using diglycolamide and ionic liquid efficiently extracts Sr2+ from waste, improving the purity of 90Sr for medical generators.

Contribution

A novel diglycolamide ligand in an ionic liquid system was developed for efficient Sr2+ extraction.

Findings

The novel ligand DPDBDGA forms a 1:3 complex with Sr2+ in [C4mim][NTf2].

Sr2+ can be fully recovered in two stages using 1 M mineral acid.

The system is compatible with existing separation processes for high-purity 90Sr.

Abstract

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.

Figures