Extraction of U(VI), Th(IV), Pu(IV), Am(III), and rare-earth elements from nitric acid solutions with diphenyl(dialkylcarbamoylmethyl)phosphine oxides substituted in the methylene bridge

Abstract

The extractive power and selectivity of diphenyl(dialkylcarbamoylmethyl)phosphine oxides in extraction of U(VI), Th(IV), Pu(IV), Am(III), and rare-earth elements from nitric acid solutions was studied, as influenced by substitution of one or two hydrogen atoms in the methylene bridge with alkyl, cycloalkyl, CH 2 P(O)Ph 2 , and CH 2 C(O)NBu 2 groups. Diaryl(dialkylcarbamoylmethyl)phosphine oxides (CMPOs) are powerful extractants of transplutonium (TPE) and rare-earth (REE) elements from nitric acid solutions. The relationship between the structure and extractive power of these reagents was extensively studied [1312]. It was found that extraction of Am(III) from nitric acid solutions substantially increased on replacement of alkyl substituents at the P atom by aryl groups [2,3,9]. Possible causes of this effect were discussed in numerous papers [13317]. Replacement of alkyl groups by phenyl groups at the N atom, on the contrary, results in decreased extraction of Am(III) [10]. The structure of alkyl substituents at the N atom in CMPO molecules affects the distribution factors of U(VI), Pu(IV), and Am(III) weakly but differently, which results in different separation factors. The reagents with long or branched substituents are the most selective [12]. Introduction of an alkyl substituent into the methylene bridge of a CMPO molecule increases the solubility of the reagent in organic solvents and its extraction capacity [8], enhances the selectivity of extraction of U(VI) and Pu(IV) relative to Am(III), but does not affect the separation factor of Am(III) and Eu(III) [7].The majority of these studies were made with 1,2-dichloroethane as organic diluent. At the same time, with more polar diluents, extraction of Am(III) with a series of CMPOs increases [18]. For example, fluorinated nitroaromatic compounds such as m-nitrobenzotrifluoride (Fluoropol) ensure both high solubility of CMPOs and their extractable complexes with metal ions in the organic phase and the higher distribution factors, compared to other known diluents [18]. It was of interest to examine the effect of substituents in the methylene bridge of the CMPO molecule on the extractive power and selectivity of reagents in systems with highly polar diluents. For this purpose, we examined in this work some trends in the distribution of U(VI), Th(IV), Pu(IV), Am(III), and REEs between nitric acid solutions and solutions of CMPOs of various structures in Fluoropol. We studied diphenyl(dialkylcarbamoylmethyl)phosphine oxides Ia and Ib with butyl and isobutyl substituents at the N atom and their derivatives substituted in the methylene bridge: IIa!IId (alkyl substituents) and IIIa!IIIc (cyclic derivatives). We also prepared and studied CMPOs IV and V containing additional complexing sites in the same molecule. We compared the extractive powers of CMPO V and its closest diphosphoryl analogs containing no carbamoyl group: tetraphenylethylenediphosphine dioxide VI and 1,2-bis(diphenylphosphinyl)octane VII.

Plutonium (IV) Quantification in Technologically Relevant Media Using Potentiometric Sensor Array

“…These sensors are based on diphosphine dioxide (S3) and carbamoyl phosphine oxides (S8 and S14). These ligands are well known as powerful extracting agents for tetravalent actinides [27][28][29]. The sensors based on diamides of pyridine-2,6-dicarboxylic acid (S1, S5, S9, S11, S13) also demonstrate considerable sensitivity to plutonium, which is in agreement with the liquid extraction behavior of these ligands [30].…”