Solid phase separation and ICP-OES/ICP-MS determination of rare earth impurities in nuclear grade uranium oxide

Determination of rare earth elements in uranium materials by ICP-MS and ICP-OES after matrix separation by solvent extraction with TEHP

A simple analytical procedure has been developed for the determination of trace rare earth elements (REEs) in uranium materials by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP-OES), after selective extraction of uranium matrix using tri(2-ethylhexyl)phosphate (TEHP). The separation method reduces uranium concentration in the raffinate to less than 10 mg L^-1 (from initial value of ~40,000 mg L^-1), thus, eliminating severe matrix interferences from uranium, such as isobaric and polyatomic interferences in ICP-MS, and spectral interferences in ICP-OES. The raffinate is directly used for the analysis of REEs, without any pretreatment. The proposed method was validated by applying it to the ICP-MS determination of REEs in uranium dioxide (UO₂) samples, by spiking with standard reference REE solutions and performing the recovery tests. The recoveries ranged from 94.0 to 105.5%. The validation was also performed similarly for ICP-OES measurements on U₃O₈ as well as UO₂ samples, which provided recoveries in the ranges of 96-105.8% and 99.2-101.6%, respectively. The method offers a fast, simple and effective method with low detection limit, and is suggested for the determination of REEs in uranium-based nuclear grade materials such as uranyl nitrate hexahydrate, uranium hexafluoride and uranium trioxide.