Extraction of U(VI), Th(IV), Sc(III), and Rare‐Earth Elements from Nitric Acid Solutions by Selected Bifunctional Neutral Organophosphorus Compounds

Abstract

The extraction of microquantities of U, Th, Sc, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y from HNO₃ solutions by bifunctional neutral organophosphorus compounds R₂P(O)CH₂P(O)Ph(OBu), R = Ph (II), R = Oct (IV), R = p‐Tol (V), R = p‐CH₃OC₆H₄ (VI) in organic diluents has been studied. The effect of HNO₃ concentration in the aqueous phase and that of the extractant concentration in the organic phase on the extraction of metal ions is considered. The stoichiometry of the extracted complexes has been determined and the extraction constants calculated. The replacement of phenyl radicals in the Ph₂P(O)CH₂‐fragment of compound II by p‐tolyl or p‐methoxy‐phenyl ones leads to an increase of metal ions extraction. The introduction of octyl substituents at the same part of molecule II instead of phenyl ones favors the extraction of Th(IV), Sc(III), and heavier Ln(III) ions. However, the extraction of La–Eu from HNO₃ solutions decreases when octyl‐substituted compound IV is used as an extractant. All effects of substituent replacements were studied with 1,2‐dichloroethane as diluent. The extractive efficiency of compounds II, IV, V, and VI is compared with that of tetraphenylmethylene‐diphosphine dioxide (I) and dibutyl(diphenylphosphinylmethyl)phosphonate (III).

Keywords:

• Rare‐earth elements
• Extractant
• Organophosphorus compounds
• Nitric acid solution

Acknowledgments

We are grateful to T. A. Orlova and A. E. Lezhnev for the assistance in the ICP‐MS measurements.