A novel bidentate diamide ligand DODQ for the separation of uranium and rare earth ions in nitric acid medium

Abstract

High efficiency extractants play a necessary role in the selective removal of uranium from rare earth minerals. In this paper, a novel cyclic bidentate diamine extractant, 1, 4-dioctyl-1, 4-dihydroquinoxaline-2, 3-dione (DODQ), was synthesized, and the complexation and extraction of UO₂²⁺ in nitric acid medium were systematically studied. The results indicate that DODQ exhibits a unique combination of properties in removing UO₂²⁺, with an extraction capacity 132 times higher than that of DODPhOA (acyclic structure). Extraction isotherm experiments and slope analyses illustrate the formation of a 1:1 DODQ/UO₂²⁺ regime during the extraction process. Electrospray mass spectrometry, fluorescence spectroscopy, and X-ray crystal diffraction analyses further corroborated its stoichiometric properties. In addition, DODQ can remove UO₂²⁺ from rare earth solutions containing UO₂²⁺ with high selectivity. This study provides an alternative method to separate uranium from the leaching solution of rare earth ore and has a new understanding of the coordination and complexing behavior of UO₂²⁺ with bidentate oxygen-containing ligands.