A new solvent system containing N,N′-diethyl-N,N′-ditolyl-2,9-diamide-1,10-phenanthroline in 1-(trifluoromethyl)-3-nitrobenzene for highly selective UO22+ extraction

• A new solvent system for highly selective UO22+ extraction was developed.
• The new system provides a highly efficient extraction of UO22+ from HNO3 media.
• The new system shows good practical feasibility by cycling organic phase.
• The new system is potentially to be applied in group separation of An over Ln.

A novel tetradentate ligand combining hard O-donor and soft N-donors in the same molecule, N,N′-diethyl-N,N′-ditolyl-2,9-diamide-1,10-phenanthroline (Et-Tol-DAPhen), was developed in our laboratory aiming at the group separation of actinides from lanthanides. Herein, the solvent extraction of UO22+ by Et-Tol-DAPhen in 1-(trifluoromethyl)-3-nitrobenzene diluent was investigated in detail. The effects of contact time, Et-Tol-DAPhen concentration, acidity, and competing ions on the extraction were discussed, the extracted UO22+ speciation was analysed, and the stripping of UO22+ from organic phase was performed. The results clearly show that Et-Tol-DAPhen/1-(trifluoromethyl)-3-nitrobenzene provides a highly efficient extraction of UO22+ from HNO3 media with a fast extraction kinetics of less than 5 min and a large distribution ratio of more than 300. Moreover, the system shows excellent selectivity toward UO22+ over Ln3+ in a wide acidity range. Stripping experiments indicate that almost a complete back extraction of UO22+ could be achieved via only one stage operation using 5% Na2CO3 solution. Findings of the present work provide new data for assessing the feasibility of Et-Tol-DAPhen, as well as other new ligand with hard–soft donors combined in the same molecule, applied in the group separation of actinides over lanthanides.