Recovery of cerium(IV) in acidic nitrate solutions by solvent extraction with a novel extractant tris(2-ethylhexyl)phosphine oxide

The extraction of cerium(IV) (Ce(IV)) from a nitric acid (HNO 3 ) system using a novel extractant, tris(2-ethylhexyl)phosphine oxide (TEHPO), was studied. The separation factors of Ce(IV)/Th(IV) and Ce(IV)/Ln(III) (La 3+ , Gd 3+ and Lu 3+ ) were found to be in the range of 60–127 and 121–827, respectively, in the HNO 3 concentration range of 0.5–5.0 mol/L, showing high selectivity with TEHPO. The experimental results showed that TEHPO can effectively extract Ce(IV) from a HNO 3 system quantitatively in a 2:1 form (molar ratio of TEHPO: Ce(IV)), which is unrelated to the experimental conditions, that is, factors such as HNO 3 concentration, extractant concentration, and temperature. The loaded Th(IV) could be stripped efficiently using H 2 O, but Ce(IV) should be stripped using H 2 O 2 . The extraction mechanisms of HNO 3 and Ce(IV) with TEHPO were determined through the slope analysis method, infrared spectroscopy (FT-IR), and electrospray ionization mass spectrometry (ESI-MS), and the extracted complexes were found to be HNO 3 ·TEHPO and Ce(NO 3 ) 4 ·2TEHPO. Comparison of their extraction performances revealed that TEHPO shows a better interfacial phenomenon and higher extraction ability and saturation loading capacity than those of Cyanex923.