Liquid- and Solid-Phase Extraction of Uranium(VI), Thorium(IV), and Rare Earth Elements(III) from Nitric Acid Solutions Using Acid-Type Phosphoryl-Containing Podands

Abstract

A possibility to use acid-type phosphoryl-containing podands with diethylene glycol polyether chain, which differ in substituent at the phosphoryl group, as extractants for the recovery of U(VI), Th(IV), and rare earth elements(III) from nitric acid solutions has been studied. Features of the effect of HNO₃ concentration on U(VI) and Th(IV) extraction with solutions of the phosphoryl-containing podands in dichloroethane has been revealed. Uranium(VI) is extracted as a normal intracomplex salt of dibasic acid UO₂L³ with chelate coordination of both POO⁻ groups to one cation. Thorium(IV) produces a complex as a normal intracomplex salt of composition Th(L³)₂ where two bivalent anions of ligand acid are coordinated via all four POO⁻ groups to Th(IV) cation. Sorption of U(VI), Th(IV), and REE(III) by impregnated sorbent based on LPS-500 polymer with 1,5-bis[2-(oxyethoxyphosphoryl-4-ethyl)phenoxy]-3-oxapentane from 0.052 and 3.52 mol/L HNO₃ has been studied. It has been established that the obtained sorbent shows high selectivity in the separation of U(VI), Th(IV), and REE(III). The separation factor for uranium(VI) and europium(III) (β_U/Eu) has been found to be 202 and ∼55000 upon sorption from 3.52 and 0.052 mol/L HNO₃, respectively, at V/m = 500 mL/g. At thorium(IV) sorption from 3.52 and 0.052 mol/L HNO₃, β_Th/U = 66 and ∼5050, respectively.